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Author Topic: Hamstick, Hi-Q or Tarheel 40 or 75  (Read 18850 times)
K0BG
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« Reply #15 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.

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WX7G
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Posts: 5982




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« Reply #16 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.


« Last Edit: November 17, 2012, 05:54:45 PM by WX7G » Logged
ZENKI
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Posts: 921




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« Reply #17 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?Huh??
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WX7G
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« Reply #18 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.



« Last Edit: November 18, 2012, 11:01:22 AM by WX7G » Logged
WX7G
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« Reply #19 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.
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WX7G
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« Reply #20 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.

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WX7G
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« Reply #21 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.



« Last Edit: November 20, 2012, 04:06:07 PM by WX7G » Logged
WX7G
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Posts: 5982




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« Reply #22 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.
« Last Edit: November 25, 2012, 06:37:01 PM by WX7G » Logged
W5WSS
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Posts: 1694




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« Reply #23 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.
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WX7G
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« Reply #24 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.

« Last Edit: December 05, 2012, 09:00:10 AM by WX7G » Logged
K0BG
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« Reply #25 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.
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W5WSS
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« Reply #26 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.
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M6GOM
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« Reply #27 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. Roll Eyes
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WX7G
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« Reply #28 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.
« Last Edit: December 05, 2012, 06:01:36 PM by WX7G » Logged
W5WSS
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« Reply #29 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.

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