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Author Topic: poor swr with new hf install  (Read 801 times)
WB9NXC
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Posts: 1




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« on: August 21, 2001, 11:37:16 PM »

Just put an alinco 70th with a spider antenna with a 8ft antenna cable in my 1988 jeep, problem is I did a stainless steel mount like the one in QST. And I can't get any better than a 2.1 swr on all bands except 40 where 1.3 is 7.250-260 where it goes up also. When I hold the shaft of the spider all swr's go below 1.4....I have been told to increase the resistance to the antenna but no one had a real answer how....The radio and antenna work great in the blazer but not here.  Any ideas?Huh?
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KR4JA
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Posts: 37




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« Reply #1 on: August 22, 2001, 12:43:11 PM »

It just sounds like a poor ground.  Make sure you have good bonding on your vehicle, such as copper braid straps connecting the steel mount, to the frame, which is bonded to the tailpipe, doors, hood, etc.  Just keep "bonding" things together until your SWR falls to a reasonable level.
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KL7IPV
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Posts: 984




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« Reply #2 on: August 23, 2001, 12:55:26 AM »

Did I read that right, you're holding the antenna and reading the RF output at the same time?? You're HOLDING the antenna and not gettting an RF burn? DON'T DO THAT!! Check all the grounds. I used a Hustler with multiple antenna coils, and I had the same problems on some vehicles  and not others. I used a tuner in my mobile all the time. I think the spider will have the same interaction problems between coils and a tuner may be the answer. It actually made it better for me because I even tuned to bands not coiled and the tuner allowed me to "cheat" a little and I was able to work all bands using just 4 coils. Sure saved time if I was on the highway and didin't want to stop to add or change band coils. I used an MFJ mobile tuner and it worked for many years. Good luck
73,
Frank
KL7IPV
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K4SUS
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Posts: 7




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« Reply #3 on: September 04, 2001, 11:33:30 AM »

You say you are only using 8 ft. of feedline. Try increasing that to 17-18 ft but do not coil it up. 2.0-1 swr is really not that bad anyway. 73 Tom K4SUS
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N4ZYV
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Posts: 90




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« Reply #4 on: September 08, 2001, 09:02:02 PM »

If you know so little about RF safety that you are grabbing the antenna while transmitting, I would suggest you take up painting flowers or maybe knitting.
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Guest

« Reply #5 on: September 12, 2001, 10:19:53 AM »

The safest thing this particular ham can do is to substitute a shielded dummy load for the antenna. A side benefit of making this change is that the SWR will be 1:1 across all bands!


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W2DI
Member

Posts: 133




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« Reply #6 on: September 13, 2001, 01:40:40 PM »

I used the DX70 with many mobile antennas and found that the best way to work multi-band is with one of the small matching units at the antenna - like the mfj-910 (about $20). These capacitive units will tweek your antenna resistance and get the match right on. Plus, by getting the swr down, you'll get better acceptable bandwidth before the transceiver folds back. They install within a foot or so of the antenna and really work great! Usually you'll use the same setting on the higher freqs but will have to switch it for 40 and 80. Give it a try. Good luck, 73.

Joe
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KG4L
Member

Posts: 3




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« Reply #7 on: October 26, 2001, 12:31:51 PM »

I had a similar problem with a Hamstick -- I couldn't adjust the
whip for a good SWR in the band, except when I was parked under
a friend's tree.  Then it worked beautifully.  We played with it for
a bit, and realized it was capacitively coupling to the tree.  The
antenna seemed to "want" some capacitance before it would
resonate in-band.  So I grabbed a couple of 1000pf 3KV
capacitors out of the junk box and kludged them onto the antenna
mount (big ring lug under the antenna, faston tab under a setscrew).
The 500pf parallel capacitance made the whole setup happy.
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