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Author Topic: Icom AH-4  (Read 1284 times)
N4UCU
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Posts: 22




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« on: July 11, 2003, 08:34:06 AM »

Has any one had any experience using the ICOM AH-4 in a mobile environment? Any comments needed. tnx 73
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K0BG
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« Reply #1 on: July 11, 2003, 09:19:45 AM »

I wrote a several articles here on eham.net about my own mobile installation using an AH-4. The URLs are:

http://www.eham.net/articles/4407
http://www.eham.net/articles/4424
http://www.eham.net/articles/4425
http://www.eham.net/articles/4624

The AH-4 can and does work well if you do a good install. The most important items are: keep the length of the feed from the AH-4 to the antenna as short as possible (18" is too long); never use coax from the AH-4 to the antenna; and keep the whip away from the body as far as possible (mount it high in other words).

Hope the articles help.

Alan
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AA4PB
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« Reply #2 on: July 12, 2003, 02:29:48 PM »

The SGC SG-237 is another good mobile tuner. It will let you get on 6M and 75M with the mobile whip as well. It will also continue to work without modification if you should someday decide to use a mobile rig other than Icom. It may be worth consideration if you haven't purchased anything yet.
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K0BG
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« Reply #3 on: July 13, 2003, 09:53:05 AM »

I agree with Bob, but if you do purchase an SGC unit, make sure you buy the correct model. And this goes for the LDG units too.

Autotuners come in both coax and high-voltage output configurations. Those designed for coax typically do not have the matching range for autotuner/whip applications.

Alan, KØBG
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N4UCU
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Posts: 22




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« Reply #4 on: July 13, 2003, 10:45:10 AM »

Tnx for the comments guys. I have a lot to think about and to learn which has been made apparent by the well informed comments I have received. I am new to HF mobile and it seems I have found the place for all my questions.

I'll be back.    73, Gary

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KG4NEL
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Posts: 400




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« Reply #5 on: July 13, 2003, 01:18:50 PM »

I just got through installing an AH-4 into my van, along with a 102" whip - the install went perfectly, and it works really well with my IC-706MKIIG - on SWL, anyways.

The AH-4/102" whip combination is a great setup, but it does have limits. You could probably load the whip on 75 meters, but don't expect to talk to anyone that you can't see - it's really inefficient down there. 40-6 should be fine, though.

For a relatively cheap system (<$200 if you shop around), bandswitching in seconds, and a pretty low profile, the AH-4/102" whip setup is tough to beat.

73,

Jim
KG4NEL
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AA4PB
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« Reply #6 on: July 13, 2003, 08:27:16 PM »

I read lots of comments about a tuner and 102-inch whip being a "dummy load" on 75 meters. Granted it is not a bug catcher and it may not match a screwdriver antenna but I'll bet it is as good as a 75 meter Hamstick. It's sure better than a dummy load and it'll get out well beyond line of sight.

Now the AH-4 may not be good with the whip on 75 meters - Icom only specs it down to 40M with a whip. Others like the SGC are designed to load a short whip on 75 meters.
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K3MOV
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« Reply #7 on: July 13, 2003, 11:54:00 PM »

Alan, I have been trying to pull up the sites you mention so I can store them in my "Favorites".  No problem with the first three, but the last one just won't come up.  Any suggestions?
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AC2RC
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Posts: 112




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« Reply #8 on: July 14, 2003, 07:44:17 AM »

I just purchased a 75m hamstick to replace an 8' whip for use with my AH-4.I did this after listening to an A/B test - the 102" was worthless on 75m, the hamstick was much better. So if you want to use the AH-4 on 75m get the hamstick. It will also improve the signal on higher frequencies.
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AA4PB
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« Reply #9 on: July 14, 2003, 10:11:32 AM »

Well, the AH-4 is not designed to match a 102-inch whip on 75M so it's not surprising that it works better when you present it with a 75M Hamstick that that has a much more reasonable load impedance. It is quite possible that a tuner (some of the SGCs for example) designed to match a short whip on 75M will perform much better than the AH-4 with a 102-inch whip on 75M.

I have a hard time understanding why a 75M Hamstick would improve efficiency on 20, 15, or 10M however. Hamsticks aren't exactly "low loss" antennas. Who knows what all that inductance and shunt capacitance will do on the higher bands.
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N4UCU
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« Reply #10 on: July 14, 2003, 09:22:48 PM »

I have not used either, however I wonder would it be possible or practicle to use some type of loading coil such as the Hamstick Inducti-Match to improve performance on 80/75 meters when using AH-4/102" whip combo.      Gary
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N4UCU
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Posts: 22




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« Reply #11 on: July 14, 2003, 09:56:12 PM »

another thought for the previous thought.
What about using a 54" Hustler mast, Hamstick Inducti-Match for center loading, topped off with a let's say 48" cb whip.
Just putting it out there for comments.

Gary
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AA4PB
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« Reply #12 on: July 14, 2003, 10:47:53 PM »

I believe the problem on 75M is that the AH-4 is not designed to match a short whip on 75M efficiently. It just doesn't have the tuning range. When you use a 75M Hamstick, the Hamstick is working just as it would if you didn't have the tuner at all - it's using its own built in loading coil. The Hamstick impedance is somewhere between 25 and 50 ohms which is easy for the AH-4 to match efficiently. Any antenna with a built-in loading coil to make it resonant on 75M will work about the same.

Other tuners, like some of the SGC models, have a wider matching range and are designed to load a short whip on 75M. Tests with my SG-237 show no difference between a 75M Hamstick and a Radio Shack 102-inch whip on 75 meters.
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KA9ZIM
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Posts: 63




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« Reply #13 on: July 20, 2003, 04:48:33 PM »

I'm planning to give the tuner and 102" whip combo a shot.  Just wondering if the tuner hunts if the Radio Shack 102" whip is bouncing around as you drive?
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WE8Q
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Posts: 17




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« Reply #14 on: July 22, 2003, 11:31:17 AM »

No, the tuner does not hunt around while you drive as the 102" antenna whips around.  I have the 102" CB antenna and AH-4 combo on my 2002 Silverado.  The AH-4 is mounted underneath the truck all the way at the rear of the truck.  The AH-4 gets hit with everything from the road...water, snow, salt, mud, etc.  I have had it on the truck for two years now without a single failure.  75 meters is OK for listening, but not seriously trying to work anyone.  40-6 meters work great.
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