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Author Topic: -->Help me Please with my mobile HF<--  (Read 2169 times)

Posts: 14

« on: January 06, 2002, 10:38:12 PM »

I have an SUV with my new 706m2g,an Am-Com Autotenna system and a straigh run on RG8x going to my HighSierra 1500. The HS1500 antenna is grounded quite heavily with a 3/4" copper pipe flattened out and connected to a paintless area that I grinded away on the body panel. I have 8awg going from the
battery to inside of the car of which everything connects. The radio is not grounded to the car only the autotenna unit is grounded to the radio to help with better SWR readings.

--> Problem I noticed that the Am-com box is not quite as accurate as my YS-60 connected to the system and my manual tuning. With a dummy load on the radio the YS-60 reads 1:1.5 VSWR, about 95 watts output on a common 6 meter repeater freq.
With the antenna connected I show 25 watts(approx) reflected and only around 50-60 watts forward.

--> Biggest problem is that when I key down on 80 meters to adjust see the VSWR with my YS-60 meter the damn rear brake lights go on when keyed up! What the hell is going on here?
Not to mention the meter doesn't even move when testing on 80 meters. If any of you know of a good website that can walk me through some very good information and to-do's for mobile HF please let me know. This week I have ordered a better cable
for HF and UHF/VHF (LMR-240), I went to this because the shield velocity is 90% like my LRM-400 at home and the losses are nearly 1/2 or better.

Also how accurate are the Am-Com boxes for tuning SWR?

Disconcerted Ham'r in the car.

Posts: 4

« Reply #1 on: January 28, 2002, 07:02:18 PM »


Just read your request on your HF mobile woes.

Sounds like the feedline is not the issue.

Any car, boat plane that a HF radio is in with a 100 watts or so will get into "stuff" you don't want it in.

The grounding of your units is a major focus and should be # 1 before the radio is turnedon the first time.

In all of our haste to "Get on the Air" many dollars and efforts have gone up in smoke because we rushed.

I am stressing grounding because it is KEY to the reduction of resonanting circuits within your car.

Whenever a circuit is triggered by HF fundamentals or harmonics the source / entrance of the RF must be found and eliminated or grounded.

Your system is unique and only you can do the legwork needed but read the handbook about bypassing RF to ground with inductors and capacitors and you will prevail.

There is no quick fix or bandaid.

Check your grounding of major components between negative terminal of the battery and all points you think are "grounded".

Less than a .4 ohms is your target.

Use a Fluke grade digital meter.

Flat strap of copper or silver brade as wide as available is called for.

Ground your exhaust at three places 1 point being at the tailpipe and the other near the inlet of the cat converter.

Wide braid is needed to be flexible and RF effective.

Doors, trunk lids and hoods are needed to be grounded by braid.

On your tailights going on... do the above grounding first then see if the problem continues.

Be truly forewarned, the air bags can be as easily adversely affected as your tailights.

Frank Giambrone

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