antenna alterations for UHF
Submitted: Saturday, Dec 23, 2006 at 17:17
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Twinkles
I have a broken antenna. I was wondering if I cut off the screw on base and drill out the fibreglass to use the base again. On the antenna I cut off the plastic coating and expand the copper sheath, push and glue it into the base, solder the sheath onto the base where the original was, losing about an inch of length from the bottom. Will this work, not hurt my radio?
A friend said the arial is tuned by length and may damage the radio because of return power from the signal. Not really understanding what he was talking about I may be misquoting what he was saying. Never the less he said might damage my radio.
The arial is a fibreglass rod with copper sheath around it with wire twists in a couple of
places along it.
Reply By: Mike Harding - Saturday, Dec 23, 2006 at 17:33
Saturday, Dec 23, 2006 at 17:33
>I have a broken antenna.
I'm sorry to hear that; have you seen your doctor? :)
Your friend is correct - an "out of tune" antenna may damage your radio. You could try the repair you describe and ask someone with an SWR meter to test it for you - an Amateur Radio club in your area would do that as a favour I'm sure.
Mike Harding
AnswerID:
211808
Follow Up By: Mike Harding - Saturday, Dec 23, 2006 at 17:36
Saturday, Dec 23, 2006 at 17:36
A starting point to finding a club:
www.wia.org.au/info/clubs.php
PS. If you talk to them nicely they might even assist with the repair.
FollowupID:
471977
Follow Up By: Twinkles - Saturday, Dec 23, 2006 at 19:32
Saturday, Dec 23, 2006 at 19:32
Thanks Mike.
FollowupID:
471995
Reply By: disco1942 - Saturday, Dec 23, 2006 at 23:06
Saturday, Dec 23, 2006 at 23:06
Out of tune, broken or missing antennas destroying transmitters is a thing of the past - unless you disable the maximum power limiting circuitry on 25 W sets. This was however a problem with the first couple of generations of mobile radios (60s & 70s)
You do not have to purchase a complete antenna kit, just purchase a new 4.5 dB whip - they are cheap enough.
PeterD
AnswerID:
211838
Follow Up By: Twinkles - Sunday, Dec 24, 2006 at 00:25
Sunday, Dec 24, 2006 at 00:25
I have another antenna. I was going to fix this one to keep as a spare. Are you saying the repaired one will be OK and not damage the radio?
FollowupID:
472025
Follow Up By: Mike Harding - Sunday, Dec 24, 2006 at 07:23
Sunday, Dec 24, 2006 at 07:23
As Twinkles makes no mention of the make/model of radio he is using how can you be certain it has high SWR foldback circuitry?
Mike Harding
FollowupID:
472033
Follow Up By: Twinkles - Sunday, Dec 24, 2006 at 09:49
Sunday, Dec 24, 2006 at 09:49
The radio is a GME TX3400. looking on their site it gives this information:
Overvoltage Protection
"Special overvoltage detection circuitry protects the radio and warns of excessive voltage conditions by flashing the display."
The arial is on a spring base with a solid chrome section about 8" long with a short (about 2'6") fibreglass antenna screwed onto this.
The spare arial is about 4'6" long.
I thought I might get better reception with the longer arial.
FollowupID:
472047
Follow Up By: Bonz (Vic) - Sunday, Dec 24, 2006 at 09:56
Sunday, Dec 24, 2006 at 09:56
I had to cut 600mm off the end of my new whip cause it was hitting the fressing table in the bedroom
FollowupID:
472049
Follow Up By: disco1942 - Sunday, Dec 24, 2006 at 10:14
Sunday, Dec 24, 2006 at 10:14
Twinkles
Any "wet piece of string" will work and get you a little range. However for best range use you need a tuned antenna.
PeterD
FollowupID:
472053
Follow Up By: obee - Sunday, Dec 24, 2006 at 11:24
Sunday, Dec 24, 2006 at 11:24
keep the repaired job for emergency. Ok the radio is low power and may not
cook the final transistors but not efficient.
For anyone's info you can make emergency antenna from the coax by stripping away the outer copper sheath and folding it back down over the insulation. About six inches will for uhf but a meter would be better. Otherwise earth stripped back sheath to the chassis and keep the inner straight and vertical with what ever is handy
the formula for a straight antenna length half wave gives roughly 30 centimetres but other factors there are and like the man says, it needs to be tested (swr) and trimmed to get the best result.
owen
FollowupID:
472066
Follow Up By: Member - JohnR (Vic)&Moses - Sunday, Dec 24, 2006 at 13:36
Sunday, Dec 24, 2006 at 13:36
Bonz, I bet Marie was pleased you did, especially when she was standing in front of it. OUCH I bet you got the Drizabone off her quick too ;-))
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Follow Up By: Mike Harding - Sunday, Dec 24, 2006 at 15:23
Sunday, Dec 24, 2006 at 15:23
Got to watch those fressing tables Bonz - they can get aggressive!
Anyway a single tail is quite of out place for the bedroom, try a riding crop.
May the goat be with you.
Mike Harding
FollowupID:
472089
Reply By: Member - Bucky (VIC) - Sunday, Dec 24, 2006 at 07:31
Sunday, Dec 24, 2006 at 07:31
I break my antenna's all the time!,,,, no big deal , but I do run
mine with an Independant ground plane base
If you just snapped off the fiberglass bit, then just replace it they are cheap enuf
with " Independant ground plane " thats all you have to do . 4, 6 or 9 db gain, what ever you choose ( and I carry 2 spares )
Not too sure about those big white ones ,, at $200-400 + a through I would not want to be replacing them too often, ( would love one with 10-12 db gain for my next trip in
the desert ) Think I would try and patch them ( if possible )
Apperently if you prepared to drill a hole in the roof of your vehicle, then all you have to do is purchace one of those little " rubber dick " aerials, and you can achieve an excellent range, ( I believe it reaches out real distances ),, but but, it must be central, and of course
well sealed, was talking to a bloke In
Alice Springs caravan
park ( from Wodonga ) who has done just that..
Hope he reads this , and he may shed some more light
Cheers Mate
Bucky
AnswerID:
211854
Follow Up By: disco1942 - Sunday, Dec 24, 2006 at 10:32
Sunday, Dec 24, 2006 at 10:32
Another good elevated position that some acquaintances are using is a pole mounted on the spare tyre mounts and sticking up above the level of the loaded roof rack. On top of this mount a unity gain independent ground plane antenns (on some form of knock down knuckle for bush protection.)
Those big white sticks amuse me, their vertical beam width is only about 5 degrees (+/- 2.5 deg.)
The desert is not completely flat. If you get stuck in a
creek crossing you will be tilted at a much greater angle than that. The only good transmission direction is across the track. In one direction you will be trying to heat the earth and the other you will be talking to the satellites - not much good for advising your mates you are a little delayed. Also you will see these mounted on the bumper bar - any part of the antenna below the bonnet is wasted.
PeterD
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