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eHam Forums => Mobile Ham => Topic started by: KD0NFY on July 07, 2011, 10:26:13 AM



Title: mini screwdriver or 8.5' whip
Post by: KD0NFY on July 07, 2011, 10:26:13 AM
First let me preface this by saying I know that I should really be using a 25 foot long bug catcher and I'm not a real ham unless my mobile antenna is bigger than the vehicle it's installed on.  Please spare me a lecture on how either of these antennas are no where near the performance I'd get from a real antenna.  I agree with you.  It's just not an option. 

Okay with that out of the way, I'm looking for advice on what would give me better performance in a mobile station.  I have a tiny little car, a Toyota Matrix.  I'm just getting started on planning a mobile station.  If I can get decent performance on 20 meters and up I'll be satisfied.  Here's the plan so far:

mini screwdriver like a Little Tarheel II or an 8.5' whip (SG-237 tuner if using the whip)
Breedlove ball mount on driver's side rear fender
Yaesu 857D  (I want it all in one box, I don't have a lot of room inside)

40 meters and lower would be a bonus, but I know efficiency will be horrible. 

Has anyone done both, and how did it work? 

Thanks!


Title: RE: mini screwdriver or 8.5' whip
Post by: AC4RD on July 07, 2011, 12:27:17 PM
I've got an itty-bitty tiny econobox of a car (2006 xB) and park in a garage with low clearance, so I've been playing with the same issues.   The K0BG website is the best resource I know of for new mobilers--you definitely will benefit from spending some time there.

My own belief is that there isn't much *efficiency* difference between a screwdriver and any other type of mobile antenna, given similar lengths.  But there IS a pretty significant difference between shorter and longer antennas.  That is, the longer you can make your antenna setup, the better your performance will be.

Another completely personal opinion:  You can have PLENTY of mobile fun with a Hamstick <TM> or similar.   Buying a couple of Hamsticks, or a Hustler system, is pretty inexpensive (especially compared to screwdrivers!) and will let you have fun and see if you like HF mobiling.

The system I'm using now is 3/8x24 mounts, aluminum masts from DX Engineering (though I'm looking forward to trying to roll my own using K5LXP's website page), Hustler resonators, and whips with capacity hats.   This is fairly inexpensive, and I'm reasonably pleased with the performance.  AND it fits in my 9-foot-clearance parking garage at work.  :-)

You'll get lots of advice, I'm sure.   This is always a popular topic.   GOOD LUCK!


Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 07, 2011, 03:01:19 PM
Two things really matter. One is effective electrical length, and the other is the current distribution over that length. Base loaded antennas, like the coupler/whip combination, will have about 1/2 the efficiency of a center loaded antenna of the same length. This is true because center loading raises the current distribution within the length of the antenna. THis does not take into account any losses within the coupler, which may be significant especially on 40 meters, and down.

Add a cap hat, and you further change the current distribution. If the cap hat is big enough, and mounted correctly (at the top of the antenna, not the top of the coil), you can increase efficiency by nearly 4 times!

And, since radiation resistance is also a factor of length, increasing the length from 8 to 12 feet increases the efficiency by nearly double! Do all of these things, and you have a winner. Anything less is less.

Short, stubby antennas are a mixed bag of tricks.You can't call them base loaded, and you can't quite call them center loaded, especially if you use a long whip. Do the calculations, and you'll discover that increasing the length of a short, stubby antenna's whip length beyond about 6 feet or so, actually reduces efficiency albeit slightly. Again, it all has to do with factors in the first paragraph.

Every mobile operator has to establish his or hers level of performance. If you're willing to squeak by, fine. I'm not!


Title: RE: mini screwdriver or 8.5' whip
Post by: WD5GWY on July 07, 2011, 07:07:05 PM
I have used a 102" whip and an LDG Z-11 PRO autotuner in both my pickup and
big diesel rig. (2007 Kenworth) That setup was fair on 40 meters and pretty decent
from 20 meters to 10 meters. Switched to an Alpine Screwdriver antenna and it was
like night and day. (this was the pickup setup) Much better performance. I did a lot
of bonding and that really helped.
I then moved the whip & auto tuner combo to my big truck. Again, it worked Ok on 40
and decent on 20 and up. I got a good deal on a used Little Tarheel II antenna and removed
the whip & tuner combo  and installed the Tarheel. (again did a lot of bonding,,,,,,,but had other
issues with RFI from the electronic fuel injectors.......) The Little Tarheel II works pretty good on
40 - 10 meters. I feel that it is better than the whip & auto tuner setup.......but, not by a whole
lot. As Alan mentioned , the whip is short (32") and that does make a difference. I recently bought
a 56" whip from Tarheel that I plan to replace the 32" with. I'm hoping that that will improve things
even more.
   Overall, the Little Tarheel II antenna is better than the whip & tuner combo, but, not as good as
a full sized screwdriver antenna. It is almost as expensive (new) as it's larger siblings. If you can get
a good deal on a used one, then I would suggest that route. And as has been mentioned read Alan's
website. He has a lot of useful information there.
  Oh, and one good thing about the Tarheel antennas(and a few other screwdriver antennas), you can get an auto controller that will interface with your radio (Turbo Tuner) and make retuning/band switching much safer if you need to change bands while driving.
  james
 


Title: RE: mini screwdriver or 8.5' whip
Post by: WA8FOZ on July 07, 2011, 08:34:19 PM
"Breedlove ball mount on driver's side rear fender."

YES!!! And optimize your image ('ground") plane. Ground the shield to your chassis by as short and fat a strap as possible, and ground the door, hatch and hood to the chassis. This may also help reduce ignition noise. These things are even more important than your choice of antenna, among the options you propose.

 "Overall, the Little Tarheel II antenna is better than the whip & tuner combo, but, not as good as
a full sized screwdriver antenna. It is almost as expensive (new) as it's larger siblings. If you can get
a good deal on a used one, then I would suggest that route."
This makes sense.

 "And as has been mentioned read Alan's website. He has a lot of useful information there."
If anything, an understatement!

I like my bugcatcher. You can see it on k0bg,com (thanks, Alan). It's big, but I can take all or parts of it down very quickly, since the base and the whip are equipped with quick-disconnects. To do this, or to change bands, I must stop and get out of the car. This doesn't bother me; the combination of cheapness, light weight, simplicity, and efficiency are worth it to me.  If it's important to stay in your car, screwdriver + Turbo Tuner makes sense. Hey, whatever floats your boat - it's all fun.


Title: RE: mini screwdriver or 8.5' whip
Post by: M6GOM on July 08, 2011, 02:10:06 AM
I'm for the Little Tarheel II however with the following caveat. Take the supplied whip and throw it in the bin. Replace it with a 72" CB whip. You'll lose the ability to use 6m but on every other band it will be a massive improvement over the original. In my experience it was at least 6dB on 20m - a fourfold improvement. A received S7 went to S9+ and its reciprocal with TX.

Also don't use magmounts or stupid lip mounts but drill a hole in the roof. When I used mine on a triple magmount, on the 80m band if I tried to put more than 50W through it, the common mode currents were so bad due to the poor grounding that it rebooted the radio. Mine is mounted via a 3/8 mount drilled in the middle of the roof. With the 72" whip on, its still fine doing 80MPH fully extended on 80m into a 50MPH headwind.

I regularly work the USA from east coast England on 100W on phone on 20m and had no problem getting hold of CO6LC the other night at 10pm - a distance of 4500 miles.


Title: RE: mini screwdriver or 8.5' whip
Post by: WA2LLN on July 08, 2011, 06:34:13 AM
I'm using a 102-inch whip and SGC-237 with an IC-7000 in my minivan. The whip is on a Breedlove mount on the rear driver-side pillar, about as high as I could get it and still have the tuner close to the mount and inside the pillar.

I'm really impressed with the Breedlove mount. I feel like you could almost pick up the car with it.

The SGC 237 tuner is OK. There are times it seems to take forever to find a coupling solution, particularly on 20m. And sometimes it never seems to converge. When that happens, if I turn the rig off and back on and re-tune, it works OK.

As far as performance, well, its OK. No, I'm not able to reach the Australian stations I can hear sometimes early in the day on 40m, and I'm not busting big pileups for the rare stuff on 18m, but I have been able to talk to stations all over the globe under the right conditions.

I am considering switching to a screwdriver, mostly because I want better performance on 40m and I don't want to compromise automatic band switching. I'm pretty sure that even with the Breedlove mount, I'll need some additional support for a large screwdriver.

--
Art


Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 08, 2011, 06:35:23 AM
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.



Title: RE: mini screwdriver or 8.5' whip
Post by: HS0ZIB on July 08, 2011, 06:58:57 AM
Quote
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.

Ah OK... I'll replace my mobile ax with a dummy load and wait for some good band conditions for my next QSO... :)

Simon


Title: RE: mini screwdriver or 8.5' whip
Post by: KD0NFY on July 08, 2011, 07:08:12 AM
I think what Alan's getting at is unless you have a beam on your car, atmospheric conditions are what is doing all the work. 

Thanks everyone for your help.


Title: RE: mini screwdriver or 8.5' whip
Post by: AA4PB on July 08, 2011, 07:27:06 AM
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.

The band conditions have a whole lot to do with it, but a more efficient antenna is certainly going to improve your odds of making the contact. I expect that on 20M and up, there is not all that much difference between a properly installed Hamstick and a full sized screwdriver.

The bottom line is that one cannot use a few DX contacts as proof that any antenna is a particularly great performer. Propagation can have a lot more effect than antenna efficiency differences on the higher bands.


Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 08, 2011, 01:25:55 PM
One thing is for sure, you can tell who uses DX contacts as a justification.

You can indeed work DX on a dummy load. Under the right circumstances, you can circle the globe with just a few microwatts of ERP. Most cheap dummy loads leak more than that!

I further suspect, if most amateurs really found out what their ERP was, they wouldn't believe how low it is.


Title: RE: mini screwdriver or 8.5' whip
Post by: W9PMZ on July 08, 2011, 02:30:07 PM
sometimes listening to 20m i can't believe how high some amateurs ERP could be...


Title: RE: mini screwdriver or 8.5' whip
Post by: N6AJR on July 08, 2011, 05:00:03 PM
In my car, I use an ft 857 d with an ATAS antenna.  it is small and will work ok vfom 2m/440 up to 40 meters.  I tie a piece of fishing line to the tip to bend it over when pulling in the garage. ( it hangs up on the metal garage door.  I have an electric tilt over mount for it, but am just to lazy to install it,  the fishing line works.  in my truck I have a DK 3 and it does 6m to 80 m. and i rund a 2/440/6m fm whip for those bands.  bothe are compromises, but what the hay.  and the ATAS is designed to autotune with the ft 857.  works for me.   a big antenna works better but the ATAS 120 fits in the garage.


Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 09, 2011, 04:26:13 AM
Carl, when you put legal limit (or more) into 6 over 6 over 6 with the top antenna at 200 feet, you might be surprised just how loud some folks are!


Title: RE: mini screwdriver or 8.5' whip
Post by: N5MOA on July 11, 2011, 01:54:38 PM

Every mobile operator has to establish his or hers level of performance. If you're willing to squeak by, fine. I'm not!

I'll agree with this statement. Different strokes.  However, it appears to me to be at odds with your following statement:

The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.



If it is ALL band conditions, what is the point in trying for the most efficient setup?

If it is all band conditions, wouldn't it be a lot easier, and just as good, to slap a hamstick on a mag mount on the roof, and be done?

You make it sound like all antennas are created equal. You've said yourself they aren't, which makes the "has nothing to do with the antenna in use" comment even more surprising, coming from you.

The antenna in use doesn't make much difference when signals are strong, at least on the higher bands.

When signals are weak is when the antenna, and that last db squeezed out of the setup, can make the difference between a qso or not.

Especially on 40m, 80m or 160m.



One thing is for sure, you can tell who uses DX contacts as a justification.



Yep. It's easy. And it's just as valid a justification as "can't really be measured, but must be".

 Get two vehicles, put your favorite antenna for today on one, something else on the other. Mount each as properly as possible. Park them 50 ft apart, get a couple of 50 ft jumpers, a coax switch and a radio.

Tune each for 40m. Now, tune around, see what you hear. Or what one can't. Find a weak station and establish a qso with whichever antenna will allow you to do that. Compare the two, if you can even have a qso with both.

Now, try it on 80m. 160m leaves a lot of antennas out, so go with whatever has the best results on 80m.

I don't have a degree in anything, or test equipment to check which antenna is more efficient than the another, so that's how I did it for myself. Real time, real world A/B checking.

I like to catch dx, not just chase it.  I chose to try and have the most efficient setup I could, because, in addition to having some propagation, the ability to work a dx station CAN depend on the antenna in use.




Title: RE: mini screwdriver or 8.5' whip
Post by: M6GOM on July 11, 2011, 05:11:43 PM
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.


Yeah because the fact I can do it every day of the week, every week of the year is quite irrelevant apparently as is the fact that I couldn't when I used the stock whip.

It has everything to do with BOTH. Neither is sufficient on its own. Sometimes when you post drivel like that, similar to your "every cars stock wiring without exception is insufficient to power a HF transceiver" rubbish I wonder if you've been on the moonshine when you posted it.


Title: RE: mini screwdriver or 8.5' whip
Post by: N2RRA on July 12, 2011, 06:36:36 AM
The ability to work a DX station has nothing to do with the antenna in use. It has to do with band conditions. Nothing more, nothing less.


Yeah because the fact I can do it every day of the week, every week of the year is quite irrelevant apparently as is the fact that I couldn't when I used the stock whip.

It has everything to do with BOTH. Neither is sufficient on its own. Sometimes when you post drivel like that, similar to your "every cars stock wiring without exception is insufficient to power a HF transceiver" rubbish I wonder if you've been on the moonshine when you posted it.

LMAO! quite true! LOL!


Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 12, 2011, 12:52:09 PM
You do it every week because of where you live. Most amateurs don't realize it is further from LA to NY, than it is from NY to London. Again, the ability to work DX means nothing. A low SWR, a high Q coil, extra whip length, big cap hat, and low ground losses, are no guarantee to working DX. The only thing that counts, is band conditions between the two points. Nothing more, nothing less.

Think about this too. If I draw a 1,000 mile radius on my QTH, I can work about 50 DX entities. An amateur living in Berlin, using the same 1,000 mile radius, could work well over 200. So what's the point?


Title: RE: mini screwdriver or 8.5' whip
Post by: N5MOA on July 12, 2011, 01:33:50 PM
A low SWR, a high Q coil, extra whip length, big cap hat, and low ground losses, are no guarantee to working DX.


I don't recall anyone posting in this thread that it was a guarantee. But it do help.



The only thing that counts, is band conditions between the two points. Nothing more, nothing less.



Again, if it is only band conditions, why go to the trouble of working toward the most efficient mobile setup?

Why even worry about antenna efficiency at all?

Anything will work as an antenna, it's all the band conditions, right?

If you believe that, you wasted a lot of time and effort on your own install.


There has to be propagation. That is a given. Taking as much advantage of said propagation as possible is where the install, and antenna, can make a difference between a qso or not.

You know as well as I do, some antennas are more efficient than others. Some radiate better than others. It is called ERP.

 Sometimes, 1000w gets through when 500w won't. Sometimes, 200w does it, 100w won't. Or 100w vs 50w. 50w vs 5w. The band conditions haven't changed, the ERP has.

It isn't "only" band conditions. The antenna can also make a difference.



Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 13, 2011, 06:52:14 AM
This horse is probably long since beat to death, but...

Using your analogy, why not just use dipoles, and forget about a beam? The reasoning should be obvious.


Title: RE: mini screwdriver or 8.5' whip
Post by: N5MOA on July 13, 2011, 07:33:53 AM
This horse is probably long since beat to death, but...

Using your analogy, why not just use dipoles, and forget about a beam? The reasoning should be obvious.

My analogy was questioning your "The only thing that counts is band conditions between two points. Nothing more, nothing less" statement.

Of course the reasoning is obvious. One gives a greater ERP than the other, among other advantages.  It is not "only" band conditions. Most people understand that.

But I thought we were discussing mobile antennas.


Mobile antenna "A" setup, 70% efficient, is going to put whatever band conditions there are to better use than mobile antenna "B" setup that is only 30% efficient. The reasoning should be obvious.


Title: RE: mini screwdriver or 8.5' whip
Post by: W5DXP on July 13, 2011, 08:17:28 AM
If I can get decent performance on 20 meters and up I'll be satisfied. 

Since 20m is a wavelength, "20m and up" would be lower in frequency. :) (The devil made me do it.)

I have done both and couldn't tell a lot of difference between an auto-tuner driven whip and a screwdriver on 20m-10m. As you suggest, the big difference happens on 40m and especially on 80m where the screwdriver was ~12dB better than the whip plus autotuner.

http://www.w5dxp.com/shootout.htm


Title: RE: mini screwdriver or 8.5' whip
Post by: N6AJR on July 13, 2011, 11:20:18 AM
Heck, IU can do the switch test easily here in the shack.  I have 4 different antennas that work on 20 meters, a 3 ele steppirat 33 feet, a sloper at 33 feet, a gap voyager and a hustler 5btv.

I can switch between antennas with the click of a switch. Most of the time the steppir has the best recieve and  transmit. next is usually the gap voyager, then the alpha-delts sloper, and then the hustler 5btv. Notice I said Usually, some times the 5btv has the best results, I think it is due to take offf angle. most of the time th sloper and the gap are about even, but some times the gap hears better than the  steppir. Again I think it is either take off angle or polorization.  Perhaps it is also dependent on capture area, which is very important on mobile antenna. 

So yes they antenna makes a big difference, along with the take off angle, propagation, capture area, size and local ground conditions ( on a beach near the ocean, on a peak of a 6,000 foot mountain, or in the middle of a big city.  most every thing has a bearing.


Title: RE: mini screwdriver or 8.5' whip
Post by: W4FID on July 14, 2011, 03:37:04 AM
First accept that propagation -- not the antenna -- will be the primary determining factor. Some days great propagation allows nice QSOs with a poor antenna. Some days with poor propagation a great antenna is still not effective. That's beyond your control -- so set your expectatins realistically and enjoy who you work when you work them.

I believe the single most important thing you can do is a great "ground". Mechanical mount to as much as good as you can to the car's metal. Straps between as many "sections" of the car as possible. A car has sections that have rubber shock mounts between them for noise and vibration reduction -- but that means electrically your car is a bunch of smaller metal parts and you want as much mass/area as you can. The metal in your car is a capacitor plate that couples to the earth for your RF ground. Bigger plate closer to the pavement is a beter capacitor -- hense everyone's advice to have the car's chassis or floor pan well connected to the "ground" side of the antenna mount. A mag mount is not in the same league.

I had a screwdriver and it was fine. But it still has most of the length and the high current part of the radiator in a coil at the base. So do "hamsticks" (various manufacturers with their own names). So the effectiveness is about the same. But a few hamsticks on quick disconnects is WAY less cost and less mechanical stress due to less weight and diameter. Also you could debate the safety of adjusting the screwdrivew while driving. That's why I said I had one -- but don't now. Scared myself a few times. And if you tune it while stopped why not just swap sticks? I pick a band I think I'll enjoy when I leave based on expected band conditions and nets I like etc. After a while I stop to pee or get a coffee or gas and maybe swap bands. Works well. I have sticks for 40 -20 -15 -10 which cover the entire general class portions of the SSB sections at under 2:1 SWR at about 20% of the cost of a screwdriver. Also CHECK IT OUT -- the mount for some screwdrivers is NOT a 3/8-24 like most ball mounts are (you mentioned a ball) so check first and buy second.



Title: RE: mini screwdriver or 8.5' whip
Post by: K0BG on July 14, 2011, 06:40:12 AM
Well, that's why automatic antenna controllers are such neat devices. Push the tune button on the microphone, and let electronics do the rest.


Title: RE: mini screwdriver or 8.5' whip
Post by: N6AJR on July 14, 2011, 01:24:09 PM
yup and several of the Yaesu's come with a built in controller for the ATAS antennas. I think the 857, the 897 for sure and perhaps the 847 . change bands or freq's and pushh the tune button. done.