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Author Topic: Need smarts about mobile Antennas for HF  (Read 475 times)
BEAST
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« on: May 07, 2001, 01:57:28 PM »

I have my written for General out of the way, and am approaching the time when I will pass my 5 WPM.  I have decided that my lifestyle as such dictates that for the vast majority of my HF work to come would be done from the car.  I would like to know what antennas (currently available on the market) would be good performers for me.  Plaease base your reccommendations on the following info:

Car = Ford Focus ZX3 (Hatchback)
HF Rig = Looking at the ICOM IC706MKIIG or the Yaesu FT-100D
Both radios above are 160M-6M/2M/70cm 100W-HF/ ~40W-2M/ ~20W-440MHz

I do not want to need an antenna tuner, so any good antenna that would not require would be preferable.  Besides, the less equipment ($$$) I have in the car, the better I will feel about leaving it alone.

Thanks all,

73 DE KB9WYZ
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K3MOV
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« Reply #1 on: May 07, 2001, 02:43:02 PM »

What bands do you intend to work primarily? Tom
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WB2WIK
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« Reply #2 on: May 07, 2001, 03:07:16 PM »

VHF antennas (50-146-440 MHz) as commercially made and sold are all 50 Ohm antennas that work fine and require no tuning; however they don't cover the HF bands.  As such, it is generally best to use one antenna, either a "Screwdriver" type which has a tuning mechanism built-in to adjust resonance between 3.5 and 52 MHz (thus covering 80-6m), or an "Outbacker" type which has band "taps" adjustable for 80-10m, or a type with replaceable tuned elements for the various bands (Hustler, Ham Stick, Pro-Am, Spider, etc.), for HF and totally different antennas for VHF.

Any of the commercially made and sold HF mobile antennas can be tuned to look like 50 Ohms, and thus require no antenna tuner, at some frequency in each band.  The problem is bandwidth.  With the exception of the motorized "Screwdriver" type antennas (High Sierra, Big DK3, et al.), the other band-tap or interchangeable element antennas will need to be re-tuned as you change your operating frequency within the band.  Usually this problem is most severe on the lower frequencies (80m - 40m) and much less severe on the higher frequencies (10m - 12m), but it does occur and must be dealt with.

It would be very unusual -- or perhaps impossible -- for an 80m mobile whip to "cover the band."  Typically, a whip tuned for 3800 kHz might resonate and work reasonably well from 3780 to 3820 kHz or so, and that's about it.  Below, and above, those frequencies, its SWR will rise to something very unfavorable, and it won't even work well on receive.

This is one reason that the "Screwdriver" antenna designs have become so popular.  It's not that they work so much better than other designs...the real thing is, they can be tuned for resonance from the driver's seat, without getting out of the car and resorting to tools.  Most convenient!

Of course, all that convenience comes with a cost: The Screwdriver antennas cost more than $200, then must be installed by someone quite proficient at this, on a very strong mounting system.  Most people use a welded or very secure bolt-on attachment for such a large antenna -- nothing less will hold it on, especially at freeway speeds.

73 es have fun mobiling!

Steve WB2WIK/6
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AG4DG
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« Reply #3 on: May 07, 2001, 04:55:54 PM »

The original DK3 Screwdriver from W6AAQ (Don Johnson) himself sells for $160 and is designed for 10m through 80m.  (The knock-offs cost more.)  Even after you add the antenna whip and do the work to add the SO-239, it's still under $200.  You would pay at least this much for a set of Hamsticks to cover 10m through 80m, and Hamsticks aren't as efficient (especially on the lower bands).

If you want the most performance in a mobile antenna, try the Texas Bugcatcher, as it has had the best results in mobile antenna shootouts.  However, the Screwdriver is almost as good, and it is cheaper than the Bugcatcher.  (Henry Allen's Texas Bugcatcher costs over $300.  Texas Radio Products sells a Bugcatcher for $150, but I don't know how good this version is.)
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KM5LO
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« Reply #4 on: May 07, 2001, 05:17:58 PM »

I drive a 97 Escort Wagon, and run an IC 706.  The antenna I use is a Diamond HMVA, I believe it is called a MV3A now (has a fold over base now).  It covers 2M 6M 10M (20M optional) there are several other bands you can work with the optional elements.  I have worked quite a bit of DX sitting in traffic in Dallas.  I like this antenna because it is light, it doesn't draw alot of attention to itself, it handles highway speeds (NOT GUYED) with no problems, and if I need to get into a parking garage, it only takes a minute to unscrew it from the MFJ hatch back mount.  I don't use it for 2M anymore, instead of buying a Duplexer for $50 or more, I bought a 2M whip, ($15 at a ham fest) and have it mounted by the hood.  In your purchases, I might suggest getting the separation kit, they work great!  Good luck with your tests!  73, John KM5LO
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N6TGK
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« Reply #5 on: May 09, 2001, 02:29:41 PM »

I've played around with a few different antennas in my quest to go mobile HF and have a few comments.  As already mentioned, the screwdriver antennas are probably the most practical from the convienence standpoint and they work really well.  However, after reading your requirements and the type of vehicle you have, I doubt that the typical screwdriver antenna is what you're looking for.  There is one you should consider, espeically if you purchase the FT-100D, and that would be the ATAS-100.  I've used the antenna and it works fairly well and mates quite nicely with the FT-100.  It will also work with the 706 with the optional tuner control circuit availble from one of the advertisers on this site.  When I had my ATAS-100, I was able to tune any frequency between 40 meters and 10 meters.  The antenna is supposed to work on 6 meters as well but didn't in my case.  While this antenna is probably not as efficient as the larger screwdriver antennas, it may suit your needs.  If you go with this antenna I would recommend getting a second antenna for VHF/UHF as the ATAS has no gain on 2m/70cm.  The downside to this antenna, and why I got rid of it but may not be a problem for you, is that I go off road quite a bit and the ATAS-100 doesn't take well to a lot of abuse.  I now use an Outbacker Perth Plus and so far like it quite a bit.  It's not too big and seems to work fairly well.  I haven't had a big opportunity to try it out completely yet though.  Yes, it's kind of an inconvienence to get out and move the tap when I change bands or change the whip for 6 meters, but for the most part I just decide what band I want to work while driving to and from work and set the antenna up.  If on a long drive I'll probably set it for 20 meters and try that out for a while.  When I stop for gas I'll check the other bands then and change to the one that has the most activity.
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