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Author Topic: AH-4 & Whip vs. Small Screwdriver  (Read 916 times)
AJ3U
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« on: November 14, 2005, 06:54:05 PM »

I currently operate HF mobile with a 706MKIIG, AH-4 coupler and 102" whip.  Performance on the upper bands is great, and 40 meters is acceptable.  The AH-4 will match the antenna for 75 meters, but performance is extremely poor which really is not surprising.  Unfortunately, I like to mostly operate on 40 and 75.

I am considering a change to a screwdriver type antenna, however I'm only willing to go for a smaller version such as the Little Tarheel II for aesthetic reasons.

Do you think this change would be worth the investment?  

Thanks!

A.J. Farmer, AJ3U
http://www.aj3u.com
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K0BG
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« Reply #1 on: November 14, 2005, 07:07:42 PM »

You have to be careful, but you can load the whip to make 75 and 40 more efficient. The problem is that voltages can exceed 10 KV even at low power. The coil will have to be spaced quite wide. Ordinary, run of the mill antenna coils won't do the job.

You can also lengthen the antenna. Increasing its length by 50% will nearly double its efficiency.

One of the reasons 40, and certainly 75 meters, isn't very good is the extra ground losses on these bands; perhaps as high as 15 ohms on 75. Proper bonding will help, but not eliminate these losses.

I have a lot of information on my web site about auto couplers, and other items of interest for the mobile operator.

Alan, KØBG
www.k0bg.com
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AJ3U
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« Reply #2 on: November 14, 2005, 08:30:19 PM »

Thanks for the reply, Alan.  Do you have a source for a longer whip?  I did some Internet searches for CB whips and military antennas but I'm coming up empty so far.

Thanks!

A.J. Farmer, AJ3U
http://www.aj3u.com
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AC2RC
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« Reply #3 on: November 15, 2005, 02:13:06 AM »

My solution is to carry a hamstick when I want to go on 80m. The AH-4 will tune within the band and the signal strength is significantly better compared to the 102" whip. Alan must live in an area of no trees or overpasses !!The interstate highway limit is 13 1/2'.The 102" whip mounted on the rail of my F150 + QD mount is about 12 1/2 '.
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N0FPE
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« Reply #4 on: November 15, 2005, 04:19:42 AM »

Im also use the AH-4 and a 108 inch whip. BUT for 75/80 I also carry the 80 meter valor whip. I use this with the 706mk2G of course!
I like this set up as it allows me complete band coverage with minor changes. I tried the screwdriver route and found it to work VERY well but for ease and compact size the whips are the way for me. the screwdriver now sits in the garage waiting installation on the camper. As for grounding. I used 3/4inch premade grounding straps and bonded EVERY body panel together as well as the frame and the exhaust system. The AH-4 has 2 of these straps bonding it to the truck body. All the work with the grounds made a HUGE difference! Oh and dont forget a few clampon torriods on the control lines!!!

73  Dan
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N3ZKP
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« Reply #5 on: November 15, 2005, 11:30:39 AM »

If you are serious about operating 75/80m forget the whip and the baby motorized antennas - get a full-sized motorized and properly mount/install it. You'll be a lot happier with the results.

I run 100w into a High Sierra 1800Pro and work up and down the East coast with no problem, as well as into the mid West on the various MARS frequencies on either side of 75/80m.

Do it right the first time. Smiley

Lon
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AJ3U
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« Reply #6 on: November 16, 2005, 07:21:27 PM »

Well, I took a page from AC2RC's book and tried a 75m hamstick for working 75 meters.  For the price, I figured what did I have to lose.  Well, it did the trick!  I tried checking into the Marconi net on 3.892 tonight with the 102" whip and nobody could hear me at all.  I switched to the 75m hamstick and checked in easily.  I let the guys on the net know what I was up to so they did a round of signal reports for me and I got 55's to 59's all around.  With the 102" whip I was down in the noise.  

Thanks for all the ideas, everyone!  I'm glad I asked here before dropping $350 on a little Tarheel.  I'm sure it's a great antenna, but this was a better solution to my problem.

Alan, your website has a wealth of information.  I always assumed that all the parts of the vehicle were already bonded.  It's metal to metal, right?  I know better now.  I'll be bonding everything at the first opportunity.

Thanks!

A.J. Farmer, AJ3U
http://www.aj3u.com
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AA4PB
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« Reply #7 on: November 17, 2005, 08:09:44 AM »

First off, I don't believe the AH-4 is specified to load an 8-foot whip on 75M even though I read about people doing it.

I ran some A/B tests using an SGC-237 which is specified to load an 8-foot whip on 75M. I found no difference between using it to load a 75M hamstick on 75M and a 102-inch whip on 75M. Granted, neither is very efficient on 75M but I found no difference between the two. Some have found a difference but I suspect that is dependent on how you have the tuner and whip mounted. Mine is high and clear of surrounding metal with the tuner right at the base of the whip. No feed line and minimized capacitance to metal vehicle parts.

I would second the though that if you are really serious about 75M then you need to go with a bigger antenna. A large screwdriver or better yet a bug catcher with a big capacity hat. Hamsticks and 102-inch whips are for those of us who are satisfied with just making a few contacts around the state on 75M.

Also consider carrying one of the long (12-foot I believe) MFJ telescoping whips for 75M use with the AH-4. You can't drive around with one attached but they will certainly improve 75M performance while parked.
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AJ3U
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« Reply #8 on: November 17, 2005, 08:50:28 AM »

I'm not looking for a "full time" mobile setup.  I just need it for occasional contacts so this works for me.  Most of my operating is from home, not from the truck.

As I said before, I'm unwilling to go with a full size "screwdriver" or "bugcatcher" antenna due to the size and looks.  I'm willing to sacrifice the peformance for something with a lower profile.  That's just my preference.

Thanks again for all the input.

A.J. Farmer, AJ3U
http://www.aj3u.com
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WB4M
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« Reply #9 on: November 27, 2005, 08:09:29 AM »

A.J,
I also ran an Icom 706 mobile with the AH-4 and a stainless steel 102-inch whip.  The AH-4 would tune the whip almost instantly!  I made a lot of 40-meter moble contacts with it, but mostly found mobilers on the 17-meter band.   Band changing is quicker with the whip and you are not going to destroy or damage a whip by striking a low limb or whatever.  I think the AH4/whip is the better of the two antennas.  Plus, if you ever do any camping or remote operating, you can toss a wire over a limb, atttach it to the whip and operate that way with even better results.
73 have fun!
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N1LYC
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« Reply #10 on: December 03, 2005, 06:42:54 AM »

Hello all...   I use a Yaesu FC-40 tuner with my 857 and what I do is use a 5/8'ths wave 10 meter antenna and that will tune from 6 meters to 60 meters fairly well...   For 80 meters I use a 80 meter whip and I made a simple bracket out of heavy aluminum to so that I can mount both whips at the same time.  There is small interaction but for mobile use I find I get very acceptable results...  I like to switch between 20 meters and 80 meters especially on my afternoon commute but in the morning 80 seems to be the key...    Have fun and keep experimenting...
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N4ZKF
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« Reply #11 on: January 06, 2006, 02:45:40 PM »

I use the new Icom 7000. I had a small screwdriver antenna which I will not name. I just went today to AES and bought the Icom AH-4 tuner and the Icom 2 whip to go with it.
I am getting the same signal reports and I don't have to change modes, flip a rocker switch, change modes again and talk.
I just hit the tune, 2 seconds later I'm having a QSO.
Don't waste the money. Keep the whip.
I love the new setup.
The screwdriver is going back to AES.

73 Dave n4zkf
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