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eHam Forums => Mobile Ham => Topic started by: KF7NUA on November 13, 2012, 02:55:11 PM



Title: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on November 13, 2012, 02:55:11 PM
Is there that much difference that I could be missing?
I feel I have a better than avg mobile setup and I am wondering if I can still be missing quite a bit of TX and RX.
To give you an idea, I usually have no problem reaching any area of the US and Canada.
I have also reached Europe, Africa, Japan, So America, Australia and New Zealand when the other operator was on a big station with a strong signal and the pileup is small, it may take a while and if I get lucky I connect with them for the contact.
I am located in So. Arizona and I do this with Hamsticks, sure I know when the propagation is right anyone should be able to do it with a wet noodle.

I also have a Hi-Q 4/80 sitting in the garage that I cannot seem to find a good spot to mount on my truck without severely compromising it because of the oversize Aluminum Security cap/container mounted in the bed that is just over 8ft tall from the ground.

After looking for an alternative screwdriver, I am sure I can mount a Tarheel 40 or Tarheel 75 without any problems but will I gain any performance over the hamsticks I have been using? This is a costly move if it is a lateral move, but if it is a better move up in performance I may do it. I am usually on 20m, 40m and sometimes on 75m.

Any thoughts on this? 


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 13, 2012, 06:08:12 PM
The Tarheel 40A (I have one) does not do 75 meters, so that option is out unless you do what I'm planning to do. And that is to mount a loading coil at the top of the 40A when I want to work 80 meters. I'll have it built in a week or two. It consists of a 10" long 2" PVC pipe close wound with #14 stranded THHN wire.

I've analyzed the Hamsticks (I have those too) and on 40 meters in my installation the performance advantage of the Tarheel 40A over the Hamstick is 5-6 dB based on impedance measurements and simulations.

The 40A with the additional loading coil for 75 meters will exhibit an even greater improvement over a Hamstick.

My simulations show the 40A being about 2 dB better on 40 meters than the 75A. So if you want 3 or 4 dB over the Hamstick on 40 meters the 75A is the way to go. If you want 5 or 6 dB get the 40A.

If you want to see my path to the 40A read the Little Tarheel II thread down the page.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: AC4RD on November 14, 2012, 09:19:44 AM
I think the hamsticks and similar are best on 20m and higher frequencies.  For 40 and lower, a good screwdriver can have higher efficiency than a 'stick.   Me, since 14mHz is the lowest frequency I use in the car (15m is my favorite band and 12m is a close second when conditions are good), I used hamsticks for several years.  These days I'm using a homebrew/Hustler system that works pretty well and is a bit better than the hamsticks IMO.

But yeah, if you're interested in 40 and 75, my understanding is that you definitely might be better off with a screwdriver type antenna.  GL!


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 15, 2012, 06:46:53 AM
Something interesting about the Tarheel 40A, 75A, and the Hamsticks is that only the 40A requires a shunt inductor for matching. That tells us that the 75A and Hamstick are rather lossy. I'm talking about 40 meters here.

The measured base resistance of my 40A is 16 ohms. The Hamstick is close to 50 ohms and the 75A would probably be 35 ohms or more or they would include a matching inductor. In my installation the radiation resistance of each antenna on 40 meters is roughly 4 ohms. Based on the 16, 35, and 50 ohm base impedances of the three antennas the radiation efficiencies work out to be 25%, 11%. and 8% for the 40A, 75A, and Hamstick respectively.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on November 15, 2012, 08:23:23 AM
I would doubt that a 40A is 16 ohms. You have at least 6 to 8 ohms of ground loss on 40 meters. The whole antenna is just 8 feet long, fully extended, so the Rr is about 1.3 ohms. That would mean the coil loss would need to be no more than 5.5 ohms. It is more like about 12 or 14. I'd believe about 25 ohms perhaps.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 15, 2012, 11:47:29 AM
Alan,

the 40A is 7.5' on 40 meters. It is mounted on the top of a 5.5' vehicle. My "antenna" is a ~12' vertical dipole consisting of the vehicle and the 40A. If you prefer to view my antenna as a ground mounted vertical it is a ~12' vertical.

That is where the roughly 4 ohm Rr comes from, the 12' antenna length. I measured the feedpoint to be 16 ohms. I will run a NEC simulation this weekend to get a more true-to-life Rr. Four ohms is a back-of-the-envelope calculation.

In each of the three cases cited - 40A, 75A, and Hamstick - the Rr is a small fraction of the measured input impedance. Therefore the relative efficiencies based on base impedance measurements (and implied base impedance of the 75A) are valid.

The 40A is 5-6 dB more efficient than the Hamstick. Is this what you would expect in this installation?  






    


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on November 15, 2012, 02:23:26 PM
David, I've heard you spout that conjecture before, and it has the same merit your antenna patents have.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 15, 2012, 07:15:28 PM
Alan,

what I stated is not a conjecture, it is a hypothesis. To credibly refute my hypothesis you must use mathematics and/or simulation. Not hand waving, not sophistry, but true engineering/scientific analysis. You are invited to provide an alternative hypothesis that you must prove mathematically and/or by simulation.





Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: ZENKI on November 16, 2012, 12:37:07 AM
A hamstick with a hamstick radial seems to be doing well in the antenna shootouts on 40 meters. Why not give it try and report back. I will be trying  this configuration next summer.

If you can get within a 0.5db of a Scorpion antenna without all the heavy mounting and engineering you are doing well.  Big heavy screwdrivers are not practical for most people and nor do most people
require the performance if they just chatting within their own country.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on November 16, 2012, 04:58:49 AM
A hamstick with a hamstick radial seems to be doing well in the antenna shootouts on 40 meters. Why not give it try and report back. I will be trying  this configuration next summer.

If you can get within a 0.5db of a Scorpion antenna without all the heavy mounting and engineering you are doing well.  Big heavy screwdrivers are not practical for most people and nor do most people
require the performance if they just chatting within their own country.



Yes you are right, a hamstick is a simple antenna compared to a screwdriver and I do well well with them but the problem is everyone I meet usually says that I am missing much much more signal without the screwdriver, this is why I asked.

By the way what is a hamstick radial??????


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on November 16, 2012, 05:03:30 AM
Dave - thank you for the tech info and yes I have read your other thread, that is one reason I had chosen the Tarheel as a possibile alternative.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on November 16, 2012, 06:08:54 AM
If it were true, then the input to my mobile antenna would easily be over 50 ohms. While there is current flowing through the body of the vehicle it is no different than the current flowing through a radial system. The only difference is the losses in vehicle radial systems are somewhat greater. But that fact does not mean the vertical is electrically longer as a result.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 16, 2012, 07:56:55 AM
Alan,

as you know the reason a symmetrical, horizontal radial system does not contribute to the radiation resistance of a monopole is because it does not radiate. The magnetic field of opposing radials cancels.

Now picture the same monopole but having radials that slope downward at a 45 degree angle. This configuration is used to increase the radiation resistance of the antenna. The increased radiation resistance comes from the downward sloping radials radiating. While the horizontal magnetic field component of opposing downward sloping radials cancels, the vertical component does not. This antenna is referred to as a monopole but is actually a dipole.

A vehicle with a monopole mounted on top acts like the monopole having downward sloping radials. The current flowing vertically along the vehicle body leads to radiation and contributes to the radiation resistance of the antenna; the antenna consists of the vehicle and the monopole. As with the monopole having downward sloping radials it is referred to as a monopole is is actually a dipole.

A NEC simulation of this is enlightening. Set the vehicle/monopole over perfect ground and measure the resonant frequency and input impedance. Now set the vehicle/monopole in free space and measure the resonant frequency and input impedance. The change in both parameters is relatively small and one can say that the vehicle/monopole forms a largely ground-independent antenna. And as with a vertical dipole the vehicle vertical dipole incurs additional loss when placed close to lossy ground.

Where the monopole is placed on the top of the vehicle matters. When placed in the center of the roof the current flow vertically along the vehicle body is lower than when the monopole is placed at the edge of the roof. In my installation the monopole is placed close to a rear corner of the SUV. This is the best location for radiation resistance.

Working the numbers for my installation with paper-and-pencil the 16 ohm input impedance is composed of:

 3 ohms loading coil (500 ohm reactance, Q =167)
 4 ohms lossless feedpoint resistance
 9 ohms other losses (ground)
16 ohms total

What if the antenna lossless input resistance is in error? Given that it is a relatively small amount of the total input resistance the relative difference between the 40A and the Hamstick is still valid. And that is what the goal of all of this was - to improve my mobile signal on 7 MHz.  

I am able to perform calibrated field strength measurements comparing the Tarheel 40A and the Hamstick and will do this if I write an article on all of this. I expect to measure a 3-6 dB difference in my installation.

Is this what you would expect, a 3-6 dB difference at 7 MHz?

 




Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on November 16, 2012, 10:56:36 AM
The body of the vehicle is coupled to the surface under it. The standing waves between them is what causes the losses in the first place. And that surface is indeed horizontal. While there is radiation from the body of the vehicle, it contributes very little far field radiation.

Higher placement lowers the amount of ground loss because more of the return current flows through the body, rather than the lossier surface under it. Again, that doesn't increase the electrical length of the radiator. The electrical length, and the way the current flow through that length, determines the radiation resistance. The ground loss effects that current and its pattern, but it doesn't increase the electrical length of the radiator. To assume otherwise is a gross error.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 16, 2012, 02:54:48 PM
The far-field E-field (and H-field) produced by a wire carrying RF current is proportional to the current integrated along the length of the wire. This is called "current-area."

1. A mobile whip has RF current along its vertical length. The current-area is equal to the current integrated along the length of the wire. It produces an E-field.  

2. A vehicle body has RF current along its vertical length. The current-area is equal to the current integrated along the vertical length of the vehicle. It produces an E-field.

This is the most fundamental thing to understand about HF mobile antennas. It allows one to quantify how antenna placement affects radiation resistance.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on November 16, 2012, 03:28:06 PM
What you're forgetting is, one element of the "antenna" (the body in this case) is coupled to the surface under the vehicle. We don't after all, live in free space! While there is some body radiation due to ground loss, it is insignificant unless the ground loss is sky rocket high. Even then, the overall field strength reduces in all parts of the antenna system.

By the way, the E and H fields are not the issue.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 17, 2012, 05:39:14 PM
The first EZNEC simulation of my vehicle and 40A is done.

The input impedance of the 40A mounted by itself on perfect GND is 1.2 ohms.
The input impedance of the 40A + vehicle over perfect GND is 3.7 ohms. My earlier paper calculation was "roughly 4 ohms."

The 40A is 7' long and the vehicle is 5' tall (bottom of frame to top of vehicle). The 40A is mounted on the top edge near the rear of the vehicle creating an antenna having a vertical dimension of 12 ft.

The current-area of the 40A by itself is 3.5 A-ft and gives a Rr of 1.2 ohms.
The current-area of the 40A + vehicle is 6.0 A-ft and should give an Rr of (6.0/3.5)^2 x 1.2 ohms = 3.5 ohms. The simulation shows 3.7 ohms.

Replacing the vehicle with a 5.0' wire (same length as the vehicle vertical dimension) yields an Rr = 3.6 ohms.

Conclusions:

1. The vehicle body vertical length acts as a wire having the same vertical length.
2. The vehicle body accounts for 2.5/6.0 x 100% = 42% of the total radiation

---------------------------------------------------------------------------------------------------
"Real" ground model
The vehicle/40A is placed over average S/N GND. The 40A loading coil is assigned a Q of 200. The simulated input impedance is 17 ohms. The measured input impedance is 16 ohms.




Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: ZENKI on November 17, 2012, 07:13:42 PM
Its just a hamstick vertical with a hamstick antenna  as a horizontal radial. Its basically a asymmetrical dipole.

You can read about it on this link. It seems to have held up well over the last 2 years in the shootouts.

http://www.3905ccn.com/newsite/antenna-shootout.htm



A hamstick with a hamstick radial seems to be doing well in the antenna shootouts on 40 meters. Why not give it try and report back. I will be trying  this configuration next summer.

If you can get within a 0.5db of a Scorpion antenna without all the heavy mounting and engineering you are doing well.  Big heavy screwdrivers are not practical for most people and nor do most people
require the performance if they just chatting within their own country.



Yes you are right, a hamstick is a simple antenna compared to a screwdriver and I do well well with them but the problem is everyone I meet usually says that I am missing much much more signal without the screwdriver, this is why I asked.

By the way what is a hamstick radial??????


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 18, 2012, 10:46:57 AM
Vertical dipole near ground

Using image theory we can explore the affect of ground on vertical and horizontal dipoles.

A horizontal dipole above a conductive plane has its image an equal distance beneath the plane. The image antenna is driven 180 degrees out-of-phase and the radiation from the antennas tends to cancel. As the dipole is moved closer to the plane there is more cancellation of radiation and the radiation resistance of the antenna decreases.

A vertical dipole above a conductive plane has its image an equal distance beneath the plane. The image antenna is driven in-phase and the radiation from the antennas tends to add. As the dipole is moved closer to the plane the radiation resistance of the antenna increases.

Having an HF mobile antenna system (vertical dipole) close to ground increases rather than decreases the radiation resistance (as some sources incorrectly state). For a physically vertical dipole the radiation resistance is doubled over the free-space case.





Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 18, 2012, 02:26:06 PM
The last sentence should read "For a physically small dipole the radiation resistance is doubled over the free-space case."

This is shown when simulating an HF mobile antenna in free space then near perfect ground. The resistive part of the antenna input impedance doubles.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 19, 2012, 06:00:02 AM
As per standard engineering analysis simplified cases are used to gain a basic understanding. The mobile antenna system in free space and near perfect ground have been explored. These things have been shown:

1. The current-area of an HF mobile antenna system, with the antenna mounted on top, is identical to that of an equal length vertical dipole.

2.The vehicle body radiates as does a wire having the same vertical dimension.

3. The the radiation resistance of an HF vehicle antenna system can double between free space and near ground.

These three things have been quantified with a rational explanation for each. Image theory, current-area, and NEC simulation produce the same answers. We can design and predict the performance of a mobile HF antenna system either in free space or over perfect ground.

The next step is to analyze and quantify an HF mobile antenna system on real ground.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 20, 2012, 03:51:30 PM
Alan,

I took a few minutes to look at a few IEEE papers on vehicle HF antennas. I have more to read but "Radiation of a Whip Antenna on the Car Body" written by Zdenek Novacek is particularly interesting. Some notable quotes:

Part 1.  "... the radiation is often analyzed considering the vertical dipole radiation."

Part 4.  "the currents flowing on the car body contribute significantly to the radiation of the antenna system..."

Two other papers go through the analysis of HF NVIS vehicle antennas. These are shown with and without the vehicle body being used as part of the loop antenna.





Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on November 25, 2012, 06:28:20 PM
Alan,

the new Tarheel 40A-HP got a good test this weekend in the CQWW DX (CW) contest. I parked on the road leading across the Great Salt Lake of Utah to Stansbury Island. I had a salt water shot in all directions. Running 200 watts I worked 500 stations in 18 hours. And it worked quite well on 40 meters, which was the primary goal for the new antenna. On that band I worked 16 Europeans.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 05, 2012, 07:56:38 AM
When 1 radial is intentionally applied to replace or also being driven by the shield the vehicle as relative to a driven by the coaxial shield the car body is considered a semi conductor hump coupled to earth surface below and out a bit from center. and the single loaded horizontal radial is asymmetrical....this actually increases loss.

I have already experimented with these questions and found that a mono band quarter wave vertical elevated above the car body  up about 1/8 wave to the base feed point while Not driving the car body with the shielding but rather replacing the car body with 4 symmetrical sloped radials produced maximum Field strength far exceeding a quarter wave using the carbody as the counterpoise.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 05, 2012, 08:39:13 AM
Good data. Is this on 6 meters? Even on 10 meters an antenna with the top 3/8 of a wavelength above the top of the vehicle is not street legal.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on December 05, 2012, 03:50:09 PM
David, a log book entry is an inane reference to any antenna measurement. Under the right conditions, 1 milliwatt will garner you DX contacts all over the globe. You can radiate that much power using a Heathkit dummy load.

What you don't understand, or cannot accept, is the basic fact the body is coupled to the surface under it. Yes, the body does radiate to some degree because the body is an inefficient ground plane (i.e.: there are ground losses present). Depending on how and where you mount the antenna, the amount of radiation from the body can be a few percent, perhaps a bit more. However, most of the radiation from the body of a vehicle is fairly low in angle. It may well indeed help make contacts on the lower bands out to a few miles, but it does nothing for DX contacts where the AOR needs to be between about 15° and 25°.

If you would just take the time to model a decent vehicle (it takes about 200 segments to do so), you wouldn't propagate the myth you are.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 05, 2012, 04:30:27 PM
I do not know if Dave is referring to my comment but yes that is true it certainly would not be street legal on HF following my findings.

The quarter wave vertical base height about 1/8 wave above my carbody was installed on a non conductive pole above about the center of the car roof and used on a hilltop where the wire sloping radials were anchored into the earth surface.

A photo can be seen at my callsign here on eham.

The resultant antenna seen is a fullsize 20m antenna and Was part of the experimental empirical work I conducted about 4 yrs ago.

Removing the car body in exchange for the sloped radials exceeded my expectations when comparing the vertical radiator while including the car body being driven with the shielding.

Actually the hilltop mobile antenna became a center fed vertical dipole monoband antenna capable of smoking the quarter wave and carbody alone.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: M6GOM on December 05, 2012, 05:18:54 PM

Removing the car body in exchange for the sloped radials exceeded my expectations when comparing the vertical radiator while including the car body being driven with the shielding.


Of course there would be a big difference. I can't believe you actually would expect to see something different. ::)


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 05, 2012, 05:51:59 PM
Alan, can you supply some real numbers? Simulations or calculations to back up your theory would be most helpful. You really need to perform a real engineering analysis and present your findings to support your theory.

I have run my calculations and simulations to back up my theory. My NEC model has 255 segments. I have taken impedance and VSWR bandwidth measurements that back up my theory. I have cited an IEEE paper that backs up my theory. My theory is not new, it is known in the world non-ham HF antennas. I suspect the "car is a non-radiating ground plane" idea got started in QST decades ago. It looks like I'll have to write an article on this subject.

As to my log entries, I have worked 575 DX stations since installing the antenna exactly one month ago. I have worked Europe on long path and short path on 40 meters with 22 QSO's total. That is the real test of the antenna as Utah-to-Europe is the most difficult path. The antenna system was designed for maximum 40 meter performance. I think my long entries say the antenna is working better than a dummy load and that I am not relying on freak propagation for results.

And please try to be respectful. I have been an engineer for 30 years, am presently a senior engineer, a former Micron Fellow, have published 50 articles (30 are about antenna designs) in engineering and amateur magazines, hold 27 patents (with more pending), and Analog/EMI/SI/RF/Power Electronics is what I do every day.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 06, 2012, 11:12:11 AM
M6gom....Not very many amateurs have actually done what I am suggesting.

No surprise when everything is done properly. I did it right.

The question of asymmetry vs symmetry is the real issue.

Some not all assume that the carbody presents adequate symmetrical completion by which an mostly middle to upper HF quarter wave can reach maximum potential of field strength somewhere in the pattern.

 The performance of a 20m quarter wave mobile antenna that has been optimized pushing against an automobile body works well but is the sum of a straight vertical working with a handicap second half. This is viewed from the perspective that when we have included one half of a dipole (relative to center feeding) that is a weird carbody  shape the straight vertical represents a half minus the maximum symmetry by the car body.....yes we know it works but asymmetry is the normal product whereas symmetry (desirable) can not be assumed but can be carefully sought.

Anyone can slap a quarter wave on a automobile and assume that everything is ok.

Not so fast my friend.

 After I finished mine about 1 years worth of empirical work (very enjoyable and gratifying) it exceeded my expectations,and I know the difference.



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 06, 2012, 04:28:39 PM
W5WSS, what difference (in dB) did you measurement between the two antennas?


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 04:01:33 AM
Hello Dave, The test site is a 20 square acre grassy Pasteur that happens to be a hill top in Oklahoma. I held the range constant as I measured the Field strength using an industry brand Field strength meter calibrator and  reliable.

A meter that I used repetitively to stage antenna sites for clients.

The measurements were plotted to form a 360 degree circle limited to 6ft above flat topography every three degrees!

The methodology was carefully followed and readings were recorded to reflect a series of 360 cross sections forming a circle down range and attenuation was observed as normal. The technique was repeated in succession three times.

The methodology was held constant as the two antenna systems were compared.

The first system was an Aluminum tube tapered using two smaller sections nested forming a 20m quarter wave radon and mounted on an insulator made of Teflon centrally located above the carbody and driven by the center conductor.

The counterpoise was bonded via 6 1/4-20 bolts starwashers and nuts, through an Aluminum mounting plate and the carbody rooftop low resistance bonding (Stripped of paint leaving bare metal outer and inner) throughout was assured and driven by the coaxial shielding.This methodology was intended to exceed normal installation practices.

The mobile quarter wave system was tuned matched and considered optimal and Field strength measurements as previously described were painstakingly conducted.

Asymmetry nor symmetry was assumed.

The results were consistent.

The second system can be seen here at Eham see my picture at my callsign.

The feedline was transfer ed to normalise the test controls.
The base height was selected andheld atop a non conductive pole. the feed point isolated electrically speaking.
The equipment was isolated and powered with a yellow top battery NOT connected to the vehicle.
Radials 4 #14 copper wire and insulated were selected and isolated from ground using non conductive anchors.
Slope angle was set at 45 degrees.
radial placement was set at 0,90,180,360. at feedpoint location and transferred down to anchors where transfer ed means again 0 90 180 and 360.

The quantitative findings are debateable and can be argued.I will not post them here.

The upward bump in strengths measured were seen downrange and attributable to the radials slope angle as a contributor vs the carbody.

Symmetry vs asymmetry and mutual coupling relative to Earth conductivity was held as a constant.

The second system reaches to exceed my expectations with a simple exchange between sloped elevated isolated symmetrical radials and the relative carbody used for the common structure.

The carbody can be expressed as a raised hump of semi conductive material underneath the antenna system number 2..but not for number 1 antenna system.

The difference can be rechecked and was using antenna modeling.

73











Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 04:09:31 AM
Fwiw my extrapolated dbd findings were 2-3dbd favoring the radial exchange everything else held constant.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 07, 2012, 04:53:55 AM
Wow, that is an excellent experiment with lots of work involved. At what distance did you take FS measurements?

Using EZNEC and the model of my vehicle with your antenna setup the difference in E-field at 200' in the Y direction and 6' above ground is 2.1 dB.

Next I removed the vehicle and replaced it with a vertical wire having the same length as the vehicle height. The difference in E-field at the same measurement point is 1.5 dB.





Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 07:30:16 AM
I neglected to mention that in order to add the radials @45 degrees the base height was raised so there is a difference (unavoidable) with height so Try looking with the base height at 13ft. as opposed to the mobile system being 5ft


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 07:33:05 AM
Your are modeling an inverted quadrant center fed L different than my antenna experiments.
But sounds interesting.
I built the antenna that you are modeling and found that one can rotate the horizontal leg and effect changes in FS at point b


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 09:11:24 AM
I had to review the notes for the distances from the two 20m antennas being analysed. following from closest to furthest 33ft 1/2 wave 66ft 1 wave and 700ft10 wavelengths respectively. done in three complete radius's measurements taken every 10 degrees or so.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 07, 2012, 10:22:04 AM
For the mobile system I placed a 17' wire on the top edge of the 5.75' tall vehicle.

For the modified system I placed a 17' wire with the base at 13.75' and four 17' radials sloping downward at 45 deg.

For the wire in place of the vehicle the vehicle was removed and a 5' vertical wire placed in its spot.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 10:33:22 AM
OK fb sounds good now look out at 10 lambda@6ft height and look to see a bump up in signal strength that is indicating a difference that seems to preclude surface wave attenuationinvolved with the closer readings measured when closer to the antenna.

Another words a reinforcement suggesting :sloped radials that are contributing to real radiation increase strength.out in the far field vertically.

I did not sound the area for more and less strength as I was doing allot of walking.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 07, 2012, 11:51:01 AM
OK I will simulate at 10 wavelengths.

The 45 deg sloping radials have 0.7X the current-area that the vertical radiator does and will contribute 0.7/(1.0+0.7)(100%) = 41% of the far-field E-field strength.

A 6' tall vehicle has as much as 0.25X the current-area that the vertical radiator does and will contribute as much as 0.25/(1.0+0.25)(100%) = 20% of the far-field E-field strength. The reason I say "as much as" is because some of the displacement current from the radiator to the vehicle terminates on the horizontal top of the vehicle thereby reducing the current along the vertical length of the vehicle. Because of this the radiation from a vehicle will be less than a vertical wire of equal vertical length. This can be quantified using a NEC simulation.

The current along the 17' radiator is close to a sinusoid and the current area is 0.7 x 17' x 1 amp = 12 A-ft. The current along the 6' vehicle is triangular and the current area is 0.5 x 6' x 1 amp = 3 amp-ft.





Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 07, 2012, 01:44:49 PM
OK Dave, yeah and this common mode as I see it from my perspective as I evaluate your modeling compares quite similarly to what I saw.

The average mobile system suffers from asymmetry to a more or lessor degree as a function of off central positioning of the radon etc. as a consequence common mode develops to the degree that is relative to the size of the vehicle vs frequency applied.and position of the antenna relative to the vehicle etc.

What you have demonstrated in your modeling exercise confirms this revelation to those whom assume any positioning on an HF mobile works properly.

Not the case and further investigation suggests that yes asymmetry increases loss and skews (undesirable) the desired omni directional pattern and field strength that would but does not fully develop.

The problem is accentuated as we move lower in frequency such as 40m and down where the vehicle becomes by %x smaller and smaller.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 07, 2012, 04:54:22 PM
I will revisit this in my modeling. So far, modeling has convinced me that asymmetrical placement of a mobile antenna results in greater current-area and higher radiation resistance compared to symmetrical placement of the antenna.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 08, 2012, 06:10:49 AM
Robert,
I played with my antenna model again and moved the antenna from the edge to the center of the roof. The antenna is a 7.5' base loaded whip at 7.0 MHz. For this simulation the loading coil loss is set to zero.

The feedpoint impedance is 3.74 ohms for both cases. The Average Gain over medium ground is -8.24 dB for the center of the roof and -8.52 dB for the edge of the roof. The Average Gain test accounts for all losses including those in the far-far field. Because of this it cannot be used to assign a radiation efficiency number but it can be used to compare the relative radiation efficiency of two antennas. The result is that at the center of the roof the antenna has 0.28 dB more total radiated power.

The azimuth pattern is skewed by the edge of the roof mounting. The front-to-back ratio, if I may use that term, is 2 dB.

Dave



Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 08, 2012, 01:12:13 PM
Hello Dave, Your contribution to our quest to better understand RF radiation is appreciated.

I had a end fed 1/2 wave vertical positioned on a Dakota truck located inside the truck bed (right rear corner) the antenna uses a matching base coil tapped and is an excellent candidate for which placement about the vehicle can be done.

I experimented with 4 fat Aluminium tubes serving as radials but did NOT drive them with the shielding. I simply set them in positionaround the semi circle of the antenna symmetrically and observed mutual coupling,while these tubes originated directly at the base feed point they were not tightly connected via a dc connection but rather loosely coupled around the antenna mounting bracket.The tubes were 1-1/4" diameter and 4ft in length.
An upward slope angle of 45 degrees yes upward produced increased field strength.
The tubes held their position and were shorter and quite feasible for your 40m endeavor.







Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 08, 2012, 02:46:08 PM
Again neglected to mention that the base height was 12ft above Earth surface and the antenna was upon a non conductive pole.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: K0BG on December 09, 2012, 03:11:00 PM
David, I do my best to be respectful. You tell me you're an engineer, so I guess I'm supposed to believe that you do. I am too, but I'm not an electrical engineer, or a mechanical engineer. I'm a civil engineer, and I have a license to prove it. But I keep getting statements made by you that just don't add up, and I've begin to wonder. For example, your antenna-related, quantitative analyses referencing the number of DX stations worked. That's not all. What's more, I'm still trying to get my head around your boast of a couple of years ago about the patents you hold. In any case, I'm skeptical.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 09, 2012, 04:45:38 PM
Alan,

I had wondered what your background was. It is obvious you've studied the subject of antennas but I suspected you had not taken an Electromagnetics course.

I'm always exploring antennas (as a hobby) and looking at them in different ways. I welcome my ideas being challenged. It helps me to see things from different angles and refine or even change my ideas. I'm presently working toward writing an article on HF mobile antenna theory and simulation.
  
Dave WX7G, NARTE Certified EMC Engineer

   Remove the adjectives and the real substance of a technical presentation is revealed.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: N0JY on December 10, 2012, 09:39:47 PM
Hi Nick,
I used a borrowed 20 meter hamstick style antenna on a triple magnet mount set atop my Buick Rendezvous for a trip from Texas to Illinois in the spring of 2012.  My rig was my FT-817 with a Heil headset/mic.  With 5 watts then, I worked Canary Island, Honduras and around the U.S.  It was not set up to be a DX dream nor did I QSO the entire trip.  I threw it in the car to try it out and see how I liked HF mobile.
So my results are subjective, and I have nothing to compare to.  It worked well for me, I was happy.  I liked it enough to buy an FT-857D which I will use in my car and boat as well.  I too am considering which antenna type to use now, and the Rendezvous has drawbacks for anything mounted on the bumper, the antenna being right next to the body for much of the antenna length.  I was going to just buy some hamsticks or hamstick style antennas since they worked well enough and could be interchanged from car to boat and given what I have read so far on several sites, I don't see a reason not to do that.  It's also at least $300 cheaper than a screwdriver antenna, and since I won't be mobile forever I don't see an immediate need to change bands on the fly.  Rest/pit stops serves well enough to swap out a hamstick.
That's my current leanings anyway, but still looking at the info because I won't be mobiling for a month or two at best.  This thread did leave me with the impression that there was a lot of discussion but not many answers to your question, so I thought I'd toss in my subjective review.  "The best antenna is the one that works for you" or something like that!   :)
73
Jerry


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: AC4RD on December 11, 2012, 03:59:24 AM
It worked well for me, I was happy. ...  I was going to just buy some hamsticks or hamstick style antennas since they worked well enough and could be interchanged from car to boat and given what I have read so far on several sites, I don't see a reason not to do that.  It's also at least $300 cheaper than a screwdriver antenna, and since I won't be mobile forever I don't see an immediate need to change bands on the fly.  Rest/pit stops serves well enough to swap out a hamstick.

Jerry, I'm in the minority on this, but I often tell people that hamsticks or similar are a great way to get started.  They're cheap and convenient, they work well for 20 and up, and you can always sell them once you are ready for a different antenna system.  I used 'sticks for years; even now I'm using a homebrewed single-band system with Hustler resonators and homebrewed cap hats.  This works great for me, and the "no changing bands on the fly" isn't a problem in my book.   I'd say your leanings are sound--and even if you change your mind later, it's a great way to get started.  73 GL!


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: W5WSS on December 11, 2012, 06:45:37 AM
Dave, For an elevated 4-slope radial symmetrical series fed 1/4 wave antenna 12-13ft above average ground isolated and above a carbody by about 5ft such as yours and fed with 100 watts looking back through my notes a ballpark objective goal for surface wave Field strength downrange would be 285mv/m at 1km.@100watts input.

That quantitative objective is obviously very optimistic.

This is sooo debateable but anyhow, what I was looking for in the measurements was a bump upwards that opposed the estimated distance attenuation this bump is a strong indication of the radials contribution+the semi conductive hump of carbody and the coupling to earth surface below averaged,(.IF) the measurement is consistent about  the semi circle downrange.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: M6GOM on December 11, 2012, 07:41:40 AM

Jerry, I'm in the minority on this, but I often tell people that hamsticks or similar are a great way to get started.  They're cheap and convenient, they work well for 20 and up, and you can always sell them once you are ready for a different antenna system. 

With them using a 3/8 mount, if you do a proper job of the installation with the bonding etc etc then upgrading to such as the Little Tarheel II or 75 is simply a matter of screwing it to where the Hamstick sat and running the motor control leads.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: AC4RD on December 11, 2012, 09:14:54 AM
With (hamsticks) using a 3/8 mount, if you do a proper job of the installation with the bonding etc etc then upgrading to such as the Little Tarheel II or 75 is simply a matter of screwing ...

You know, I *do* use 3/8x24 for HF and VHF/UHF on the car; it's really convenient to be able to switch any antenna to any mount.  (I've got three mounts on my car right now.)   But I don't *want* a screwdriver of any kind--it's just not for me.  Expensive and complicated is not what I want, and I'm only on 20-10 plus 6, 2, and 440 from the car, so I don't need the supposed increase in efficiency of a screwdriver on lower bands.  My system ( http://people.duke.edu/~kuzen001/ac4rdmobile.htm ) works well, and experimenting with changes is easy and cheap.   A lot of people don't seem to understand me, but this setup suits my needs perfectly. [shrug]


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: N0JY on December 11, 2012, 10:02:19 AM
Hi Ken,

I appreciate the input and I just checked your website too, I like that.  More options to think about!  The back of the Rendezvous is similar to the back of yours.  Thanks!

Jerry


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on December 13, 2012, 05:40:47 PM
Hi Nick,
I used a borrowed 20 meter hamstick style antenna on a triple magnet mount set atop my Buick Rendezvous for a trip from Texas to Illinois in the spring of 2012.  My rig was my FT-817 with a Heil headset/mic.  With 5 watts then, I worked Canary Island, Honduras and around the U.S.  It was not set up to be a DX dream nor did I QSO the entire trip.  I threw it in the car to try it out and see how I liked HF mobile.
So my results are subjective, and I have nothing to compare to.  It worked well for me, I was happy.  I liked it enough to buy an FT-857D which I will use in my car and boat as well.  I too am considering which antenna type to use now, and the Rendezvous has drawbacks for anything mounted on the bumper, the antenna being right next to the body for much of the antenna length.  I was going to just buy some hamsticks or hamstick style antennas since they worked well enough and could be interchanged from car to boat and given what I have read so far on several sites, I don't see a reason not to do that.  It's also at least $300 cheaper than a screwdriver antenna, and since I won't be mobile forever I don't see an immediate need to change bands on the fly.  Rest/pit stops serves well enough to swap out a hamstick.
That's my current leanings anyway, but still looking at the info because I won't be mobiling for a month or two at best.  This thread did leave me with the impression that there was a lot of discussion but not many answers to your question, so I thought I'd toss in my subjective review.  "The best antenna is the one that works for you" or something like that!   :)
73
Jerry

Hi jerry - yep I still monitor this thread as a daily read so your imput is wellcomed as with the rest of the posters.
I know Dave and Alan have been chewing at each others throat but there has been some info I did pick up from it!


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 14, 2012, 11:37:24 AM
KF7NUA,
you are right about the friction around here. I'm an electrical engineer and of course I work with many other electrical engineers. As such I work with open minded people who must quantify their statements. Feelings about circuits/antennas/etc. and hand waving are simply not part of the environment. Every design and every statement made must be backed up mathematically and proven to a dozen other engineers. We deal in numbers and not adjectives. So, to argue antennas with antenna amateurs (in every sense of the word) who do not have even a rudimentary grasp of antenna fundamentals, yet think they do - and who are close minded - is the real challenge. My time is better spent writing articles about antennas to educate those who are open to learning.   


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KH6AQ on December 14, 2012, 01:15:22 PM
The sticking point here is lossy ground. In the world of amateur radio "ground" in imbued with magical (bad) properties that cannot be known by mere mortals. But it need not be viewed as a magical medium that defies quantitative analysis. It is a lossy dielectric and lossy dielectrics are well understood. They are analyzed as part of transmission lines and antennas on a daily basis. Lossy dielectrics can be analyzed mathematically and modeled using several different 3-D field solvers such as NEC and SONNET. So to quantify the performance of an antenna near the lossy dielectric we call earth is a simple matter.







Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on December 14, 2012, 10:10:53 PM
KF7NUA,
you are right about the friction around here. I'm an electrical engineer and of course I work with many other electrical engineers. As such I work with open minded people who must quantify their statements. Feelings about circuits/antennas/etc. and hand waving are simply not part of the environment. Every design and every statement made must be backed up mathematically and proven to a dozen other engineers. We deal in numbers and not adjectives. So, to argue antennas with antenna amateurs (in every sense of the word) who do not have even a rudimentary grasp of antenna fundamentals, yet think they do - and who are close minded - is the real challenge. My time is better spent writing articles about antennas to educate those who are open to learning.   


No need to explain, I am almost to the point of selling my Hi-Q and going to a Tarheel 40A HP because of a few of the points you made!


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: WN2C on December 15, 2012, 06:54:07 PM
Go with a Scorpion and you won't look back.  Best built screwdriver on the market. I got one in late October, got it mounted on my truck.  I get guys on 40 that ask me how much power I am running and they are surprised to hear... barefoot.  They work very well but you do need a very stout mount.  Do your homework and look around at them all.  If you don't want to be replacing the screwdriver in a few years or replacing parts, then go with the one that has a lifetime warranty.  Oh and by the way, I ran into a guy locally that bought one in 07' and the owner of Scorpion is replacing parts (an upgrade actually) that were not on the ones he sold in 07 - he says for free.  So...there you go.

Yea, I may sound a little prejudiced, but its not that....I am impressed with it.

de wn2c  Rick


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KT0DD on December 16, 2012, 11:05:37 AM
Aside from all the engineering discussions...which I respect... I look at things from a simple point of view. I have always had good luck with Hi-Q although the bigger ones get a little pricey. A larger coil should have better Q and Charlie describes this on his website. He uses top of the line test equipment to check his findings. The military buys alot from him.The best thing I like about the Hi-Q is the physical length doesn't change with band changes since the coil is shorted internally, not externally. I've had reasonably good performance from my Hi-Q's in the past.

I have no experience with the Scorpion, but I hear they're good. However, they too are shorted externally and change length with tuning. It's just something I don't like.

73, Todd-KT0DD


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on December 16, 2012, 11:17:33 AM
Aside from all the engineering discussions...which I respect... I look at things from a simple point of view. I have always had good luck with Hi-Q although the bigger ones get a little pricey. A larger coil should have better Q and Charlie describes this on his website. He uses top of the line test equipment to check his findings. The military buys alot from him.The best thing I like about the Hi-Q is the physical length doesn't change with band changes since the coil is shorted internally, not externally. I've had reasonably good performance from my Hi-Q's in the past.

I have no experience with the Scorpion, but I hear they're good. However, they too are shorted externally and change length with tuning. It's just something I don't like.

73, Todd-KT0DD

I do agree with you on the physical length not changing but my problem is not "not liking the Hi-Q", but not being able to mount the Hi-Q. I have had numerous emails back and forth with Woody at Hi-Q and he even says that trying to mount my Hi-Q antenna on my truck is not going to be easy and it will be a very compromised antenna at best. And as far as a Scorpion, it would be more of a challenge to mount it compared to a Hi-Q.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: WD5GWY on December 16, 2012, 04:54:58 PM
  What kind of truck are you trying to mount the Hi-Q on?
All of these posts have gone astray from what I believe is
the main issue, how to mount your screwdriver antenna!
  I have seen screwdriver antennas mounted in some very
interesting and unusual ways. Going to hamfests can be educational
at times! I'm sure some are compromises, but, sometimes, that
is what you have to do, in order to use what you have and get
on the air.
  I am betting there is a way to mount the Hi-Q and make it useful
for you without you having to get rid of it and use something else
that you may not like.
  So, again, what kind of truck are we talking about here? I use a
Tarheel 100a HP on my 1997 Dodge 2500 pickup. I have it mounted
in the left rear corner of the bed, against one of the stake pockets.
It doesn't hardly move at all.  I also have a Little Tarheel II mounted
on the driver's side mirror on a 2007 Kenworth diesel rig. Not the best
setup in the world, but, it works pretty good in my opinion.
 So, I'm certain there has to be some way to get your antenna mounted
so you can use it.
james
WD5GWY


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on December 17, 2012, 07:06:26 PM
Just to give you an idea on what the truck is it is a 2003 Dodge but the problem is I have an all aluminum security box that is just over 8ft high.
Woody at Hi-Q says that because the coil if mounted correctly above the top of the truck would make the antenna and top hat portion way to high. His suggestion is I would need to mount it at least 12" away from the body and that cant happen. A Scorpion antenna would be even worse. I am confident I could mount a smaller Tarheel on a mount that can be placed on the top of a rear door so the coil would at least be above the cabin portion of the truck.
Here is the picture of my truck.

http://i70.photobucket.com/albums/i115/71GTXD21/Truck800.jpg (http://i70.photobucket.com/albums/i115/71GTXD21/Truck800.jpg)


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: WN2C on December 17, 2012, 08:43:43 PM
Nicolo, have you gone to Scorpion's web site (or others for that matter) and looked at the install photos?  Those will give you some Ideas on how you can install the Scorpion or Hi-Q. Maybe the Scorpion 680s (S=shorty) would be a better than the 680. It's Length retracted: 28”, Extended: 36” 3”, much shorter than the 680.  There is a photo of a guy's SUV w/ the shorty on top.  And one on top of a Hummer.  These should give you some ideas.  You don't need to run a 6 foot stinger.  A shorter one will work or even better w/ a cap hat.  There is a way to mount it.  You just need to find it.
Good luck.

de wn2c  Rick


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KD8RDA on December 18, 2012, 05:06:55 PM
I have my Scorpion 680S mounted inside my aluminum truck cap and the performance is impressive to say the least.
I had it mounted out in the open through the summer and wanted to try it through the cap for the winter season. There is no doubt in my mind that the signal from my Icom 7000 travels further with the through the cap set-up. I've had many surprised contacts when they learn I'm operating from a truck. My antenna controller is a Better RF 7000 - works well for mobile use and I have a 48" rigid mast with a cap-hat.
Alan Applegate has posted three pictures of my truck on his site - http://www.k0bg.com/gallery2/main.php


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: KF7NUA on December 20, 2012, 05:23:28 AM
Nicolo, have you gone to Scorpion's web site (or others for that matter) and looked at the install photos?  Those will give you some Ideas on how you can install the Scorpion or Hi-Q. Maybe the Scorpion 680s (S=shorty) would be a better than the 680. It's Length retracted: 28”, Extended: 36” 3”, much shorter than the 680.  There is a photo of a guy's SUV w/ the shorty on top.  And one on top of a Hummer.  These should give you some ideas.  You don't need to run a 6 foot stinger.  A shorter one will work or even better w/ a cap hat.  There is a way to mount it.  You just need to find it.
Good luck.

de wn2c  Rick

I have my Scorpion 680S mounted inside my aluminum truck cap and the performance is impressive to say the least.
I had it mounted out in the open through the summer and wanted to try it through the cap for the winter season. There is no doubt in my mind that the signal from my Icom 7000 travels further with the through the cap set-up. I've had many surprised contacts when they learn I'm operating from a truck. My antenna controller is a Better RF 7000 - works well for mobile use and I have a 48" rigid mast with a cap-hat.
Alan Applegate has posted three pictures of my truck on his site - http://www.k0bg.com/gallery2/main.php

Yes I have been to the Scorpion website and I also met up with Ron the owner of Scorpion last year at a Hamfest and we discussed possibilities, none which were great. The problem is the Aluminum box that is just over 8ft tall from the ground, getting a coil over it would put the overall height the the antenna in the danger zone. If I could, I would install a large screwdriver be it a Hi-Q (which I have already) or a  Scorpion but it looks like if I want to move away from hamsticks the small Tarheel antennas might be my only choice.

Rick I will check on the Scorpion 680s Shorty and give Ron a call and see what he thinks.


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: M6GOM on December 20, 2012, 06:50:24 AM
The short Tarheels aren't that bad although if you get the Little Tarheel II sacrifice 6m and replace the whip with a 60-72" one. Makes a marked improvement in performance. When propogation is in your favour you can work the world with them. I've done Australia from the UK on 20m with just 100W. I can work the USA daily with the same. Mine has been on the car hitting trees twice daily and doing up to 80MPH into headwind gales for over 2 years without any issue/


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: WD5GWY on December 20, 2012, 04:53:03 PM
Just to give you an idea on what the truck is it is a 2003 Dodge but the problem is I have an all aluminum security box that is just over 8ft high.
Woody at Hi-Q says that because the coil if mounted correctly above the top of the truck would make the antenna and top hat portion way to high. His suggestion is I would need to mount it at least 12" away from the body and that cant happen. A Scorpion antenna would be even worse. I am confident I could mount a smaller Tarheel on a mount that can be placed on the top of a rear door so the coil would at least be above the cabin portion of the truck.
Here is the picture of my truck.

http://i70.photobucket.com/albums/i115/71GTXD21/Truck800.jpg (http://i70.photobucket.com/albums/i115/71GTXD21/Truck800.jpg)
I can see where mounting a large antenna such as the Hi-Q could be a problem!
As mentioned, the Little Tarheel II might be the better solution. (or something
similar) The one I use on the 2007 Kenworth is mounted on the driver's side mirrror
and works pretty good 40-10 meters. And that is with the 32" whip that is supplied
with the antenna. If you get their 54" whip, it will tune as low as 80 meters. But, is
very narrow (bandwidth) on 80. Performance 40-10 meters is better. And as M6GOM
stated, you will loose 6 meters with the longer whip. Their 54" whip (I have one too)
is much more flexible than a 102" whip. And gives better when it strikes overhead
objects. (and it WILL strike overheard objects!)
 Too bad you cannot easily install the Hi-Q as it would be much better than the Little Tarheel II,
or something similar. I did meet one ham that works on a drilling rig that had a Hi-Q mounted
on his Dodge pickup on the front bumper! Looks kind of weird, but, it does work. And he mounted
it in such a way that it was not really that much in his line of vision while driving.
I've seen a couple of truckers with them mounted on the front bumper like that too. But, building
a mount that will swivel the antenna with the hood when it is pulled over for servicing (conventional cab trucks) would be a pain.
james
WD5GWY
 


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: WN2C on December 20, 2012, 09:50:13 PM
Nicolo, I saw a pic of a guy's install of his screwdriver inside of a fiberglass cap. not sure if it would work in an aluminum cap.  He mounted a stinger in top of the cap and fed it with a short wire from the top of the coil.  I think it was a Hi-Q but not sure.  What I remember about it was the coil did not lengthen outward when changing bands (just like a HI-Q)

Rick  wn2c


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: G8YMW on December 21, 2012, 01:54:33 AM
Wont work, fibreglass is RF transparent (dependant on the "paint"), ally isnt


Title: RE: Hamstick, Hi-Q or Tarheel 40 or 75
Post by: M6GOM on December 21, 2012, 08:35:08 AM
Nicolo, I saw a pic of a guy's install of his screwdriver inside of a fiberglass cap. not sure if it would work in an aluminum cap.  He mounted a stinger in top of the cap and fed it with a short wire from the top of the coil.  I think it was a Hi-Q but not sure.  What I remember about it was the coil did not lengthen outward when changing bands (just like a HI-Q)

Rick  wn2c

As long as the coil is clear of the cap then it'll work fine. The Scorpion website shows a picture of a 680 in both retracted and extended position so it does lengthen outwards. If you think about their design, it is the only way any screwdriver antenna can work.