uhf coax
Submitted: Wednesday, Dec 17, 2003 at 11:06
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hilux_4wd
is the rg58 coax used on 27 meg the same they use for uhf? - can i just use my existing cable setup (plug and mount) from my 27meg or do i need to buy a new one for uhf ?
Reply By: Well 55 - Wednesday, Dec 17, 2003 at 12:01
Wednesday, Dec 17, 2003 at 12:01
In a nut shell yes you, can just change the antenna.
AnswerID:
40460
Reply By: jeff-wa - Wednesday, Dec 17, 2003 at 12:15
Wednesday, Dec 17, 2003 at 12:15
27Mhz AM/SSB uses a 75ohm cable that will not work on UHF, UHF is 50ohm Rating like computer network cable.
Actually reading your post RG58 I beleive is the 50ohm, I don't know how the 27Mhz could have ever had any SWR tuned!
You will need a new arial however and you'll find 95% of UHF arials come with cable anyway, because the SWR is a bitch to adjust on UHF so they come pre-tunned. Just be careful not to change the length of the pre cut cable on your new UHF arial as it could come out of wack and damage your UHF rig when transmiting.
AnswerID:
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Follow Up By: joc45 - Wednesday, Dec 17, 2003 at 16:26
Wednesday, Dec 17, 2003 at 16:26
50 ohm is the norm for transceivers, regardless whether it's HF, 27meg or UHF.
RG58 is 50 ohm. RG59 is 75 ohm.
Unless you're installing a ground-independent UHF antenna, you will need to check/adjust the vswr of the antenna, as every installation is different.
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Reply By: stillthinkinaboutit - Wednesday, Dec 17, 2003 at 13:11
Wednesday, Dec 17, 2003 at 13:11
Jeff-wa
27mhz CB's use 50ohm coax not 75ohm.
AnswerID:
40463
Follow Up By: GaryInOz (Vic) - Wednesday, Dec 17, 2003 at 16:20
Wednesday, Dec 17, 2003 at 16:20
75 ohm coax is used on TV antennas and some electronic testing equipment.
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258064
Reply By: Member - AndrewPatrol - Wednesday, Dec 17, 2003 at 16:34
Wednesday, Dec 17, 2003 at 16:34
Bloody Hell , 5 different answers. This interests me too as i've just instaleed a new uhf and cut the cable a bit to fit it in. I also extended my AM aerial cable with a bit of coax i found in the shed. What have I done , who do I believe , How can I check it? The uhf seems to recieve ok and the am just hiss/hums- a guy at a radio joint said that its normal for AM's.
AnswerID:
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Follow Up By: ACH - Wednesday, Dec 17, 2003 at 21:04
Wednesday, Dec 17, 2003 at 21:04
Mate there's no need to panic! Maintaining the so-called "tuned" length of coax is a myth, whether it be for HF, VHF, UHF etc.!!! There are still folks who swear blind that you have to tune your coax - I say crap!!
As long as your antenna appears as a 50 ohm (resistive) load to the transceiver at the frequency/frequencies of operation, there's nothing at all to worry about. If you haven't got one, borrow/beg/steal/buy a SWR meter. This device basically tells you how much of the transmitted power is reflected back towards the transceiver. Without boring you with the intricacies of antenna theory, if you have an SWR as indicated on your meter (placed in line at the tranceiver end!!) of less than 2:1, then you're OK.
Same applies with your AM (27MHz) rig. But if you've extended your AM coax, did you use proper connectors or just "butt" solder the extension?
Look fwd to ur reply.
Cheers
ACH
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Follow Up By: Member - AndrewPatrol - Thursday, Dec 18, 2003 at 09:56
Thursday, Dec 18, 2003 at 09:56
Thanks ACH,
I used a joiner from Jaycar (an electronics mob) that insulates the inner wire from the outer braid, then checked for shorts between them with a muiltimeter. I'll go out on the highway and ask for a radio check to confirm 'cos to take off the roof console is a pain. I might take it to a radio joint if I have a problem after that.
Thanks
Andrew
FollowupID:
258113
Reply By: jeff-wa - Wednesday, Dec 17, 2003 at 16:35
Wednesday, Dec 17, 2003 at 16:35
I stand corrected, 50ohm RG58 for 27mhz is correct, however you will still not have to worry as a new UHF arial will most probally come with the cable already attached to the base, the last three I have bought were like that, either ground independant, elevated feed or std fibre glass cheapie.
AnswerID:
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Reply By: pete0002 - Wednesday, Dec 17, 2003 at 17:17
Wednesday, Dec 17, 2003 at 17:17
Replaced my AM set with UHF set and used the exact aerial cable and fittings, but purchased a new aerial a 6db from Dick Smith's and it did not come with cable.
Works fine, but my one mistake was I should have purchased a UHF set with the remote faceplate. Find my eyes cannot read as
well these days and my set is mounted low below the centre of the dash and I'M not spending dollars for a ceiling console.
Next vehicle will be set up betterer.
AnswerID:
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Reply By: chrisfrd - Thursday, Dec 18, 2003 at 16:40
Thursday, Dec 18, 2003 at 16:40
Hi guys,
It DOES matter about tuning your coaxial cable, but only for non-ground-dependent antenna systems, where the tuning length of the transmisison path includes the antenna radiator, with respect to ground (the car). but who in the F*ck buys ground-dependent antenna today?
Additionally, I set up a non-GD antenna a few months ago for a base station, using an 18dB yaggi, and it VSWR'd in pretty
well out of the box. In the bad old days of touchy low-tolerence transistorised front-ends, this would be a problem, but over the last few years (10 or so) most RF front-ends have been op-amps anyhow, so they can put up with a lot of sh*t before letting the smoke out.
I've seen trucks come back to me after a trip with antenna cables severed and they still work "perfectly".
AnswerID:
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