HF autotune near UHF?

Submitted: Monday, May 23, 2005 at 16:52
ThreadID: 23239 Views:1675 Replies:3 FollowUps:1
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Gday all
I am pondering the mounting of my Codan 9350 autotune on the bullbar (I've read the archives and know the legal considerations... I'm in NSW) but was wondering if I need to worry about maximising the distance between the UHF aerial and the HF?

Are there interference issues? What about the CDMA/GSM aerial?

Any help appreciated.

cheers
JohnN
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Reply By: joc45 - Monday, May 23, 2005 at 17:16

Monday, May 23, 2005 at 17:16
Technically, for the purists, it's not a good idea; the proximity of the HF to the UHF antenna, esp if it's within 1/4 wavelength, can affect the UHF antenna performance and vice versa. But everyone seems to get away with it. The same goes for uhf and CB antennas almost next to each other and GSM.
The RF power from one is unlikely to get past the input filters of the other's receiver, so receiver damage is unlikely.
The UHF RF transmitted power is not likely to affect the electronics of the autotune HF, as it's already pretty-well screened from the HF. But I'd check this aspect just to be sure.
But as a techie, I wouldn't do it myself.
Gerry
AnswerID: 112451

Reply By: Michael Carey - Monday, May 23, 2005 at 20:32

Monday, May 23, 2005 at 20:32
You should try and have the HF antenna as far away as possible from ALL other antennas. Although most modern UHF's have diodes limiting the power getting to the receiver circuit, the amount of RF getting back to the radio from closely spaced antennas isn't good.
On my old 4wd, I had a Codan 8558 autotune antenna mounted on the tray near the back of the cab. A hella work light was mounted on the frame about 300mm away from the antenna. When I transmitted on the HF, enough energy was getting back through the lights DC cable to cause the LED illuminated switch to glow quite brightly. Imagine how much would come back through an antenna and coax cable!!

AnswerID: 112484

Reply By: JohnN - Tuesday, May 24, 2005 at 10:19

Tuesday, May 24, 2005 at 10:19
Thanks for these answers. I wonder how far is far enough. Space becomes limited for aerials.

cheers
JohnN
AnswerID: 112565

Follow Up By: signman - Tuesday, May 24, 2005 at 10:38

Tuesday, May 24, 2005 at 10:38
I would try and keep the UHF about 1/4 wave away from the HF antenna. That distance is about 700mm.
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FollowupID: 368780

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