UHF Radio Aerials

Submitted: Friday, Sep 27, 2002 at 00:00
ThreadID: 2061 Views:2080 Replies:6 FollowUps:5
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I am currently running a GME Tx3200 with a GME 4.5bd colinear Ground Independent Antenna, the area that I live is mainly flat country and I was told that I would be better with a 6.5bd as I would get better TX & RX, (1) is this so (2) do I just buy the 6.5bd stainless whip antenna for around $25.00 or do I have to buy the whole colinear Ground independent base as well, Also who has the best 6.5bd Antennas?, GME, Mobile One, RFI .Etc, (Help Nigel)
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Reply By: Member - Nigel - Friday, Sep 27, 2002 at 00:00

Friday, Sep 27, 2002 at 00:00
Hi Mike, I'm not really an expert on antenna theory, but I'll share my thoughts. If you are in flat county you will benefit from more dB of gain, as long as the antenna doesn't bend (distorts your signal). You can get even more benefit out of the extra gain if you put your antenna higher as well. Lower dB is often better in hilly country as the transmission isn't as flat, so may get over small hills, etc

I have a GME 4.5 on a elevated feed (ground independant) on my Patrol. I recently purchased a "Polar" brand that had a 6.5 dB on a similiar elevated feed (for the wife's car), and this antenna certainly does a better job of getting a repeater some 70km away. The elevated feeds look almot the same in size and construction, so I can't see why the whips couldn't be swapped.

If your at all concerned then you can use a SWR meter to check the VSWR of each whip and as long as the reading are less than 1.5 then your ok.

I might swap the whips and see if the 6.5 works as well on my GME base. I'll let you know.
AnswerID: 6988

Reply By: Eric - Friday, Sep 27, 2002 at 00:00

Friday, Sep 27, 2002 at 00:00
Mike.
The extra 2 db would be hard to notice in a normal radio situation.
Much more important is to ensure the antenna is mounted correctly, ie clear of metal things in the signal path, this means not on the bull bar if you want to talk to a vehicle behind you. the centre of the roof is best.
as far as brand of antenna is concerned if they are all 6.5 db they will be the same at channel 20 but will be less than the 4.5 db at channels 1 and 40 because the higher the gain the narower the frequency range of the antenna.
Eric.
AnswerID: 6999

Follow Up By: Mudgutz - Sunday, Sep 29, 2002 at 00:00

Sunday, Sep 29, 2002 at 00:00
back to radio school for you........metal between the antenna and the intended target......balony.......the freq 477 mhz has a wavelength long enough to pass through the metal of a car body a 1.4 ghz signal is about 15cms wavelength so how long is the 477 mhz about 2 metres i think......so it would take an object that thick between the antenna and the intended target to block the signal and the extra 2db will
definatly be noticable since gain is an exponention measurement it may mean the difference on flat ground of up to 50km range....and finally gain has nothing to do with the frequency range of the antenna it is quite possible for a 4.5 db stick to have the same frequency range as a 9db stick..gain is the amount of amplification of a received/transmitted signal ....mine is on the bull bar i can talk to the car behind me.....and your gonna ask why when your under a metal awning doesnt your uhf work mine does.......think you need to check the loss of your antenna/cable/connections..... 1 dbm is good 2 dbm is bad....bet yours is 4 db plus if you cant talk to the car behind you when you had it mounted on the bar it is what kills most uhf rads that ive worked on .....and i am willing to bet even now with yours on the roof your radio works well in hilly country but the range is bleep poor in the flats regardless of the gain you have fitted ...would i be correct
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FollowupID: 3179

Reply By: Bob Y. - Saturday, Sep 28, 2002 at 00:00

Saturday, Sep 28, 2002 at 00:00
Mike, As Nigel said the 6.5dB aerials are better on flat country. The Polars are a good buy, give excellent performance and are very robust. Don't create much drag either. We use 6dB Colinnear "Kevlar" whips, by Antenna Agencies, on h'duty spring base, and find them good, but I would go for the Polars if you live in town. On our wagon, we've got one of these new GME 4700 series antennas, has about 6 different whips to select from. The 6.5 dB whip is good, but is about 2 metres long, and qiute bulky, so creates a lot of drag. We use the shorter 4.5 whip for long trips back to the coast. Like everyone says, get them as high as practicable. Oh yeah, the stainless whips tend to break, after lots of corrugations. See ya...
AnswerID: 7016

Reply By: mudgutz - Sunday, Sep 29, 2002 at 00:00

Sunday, Sep 29, 2002 at 00:00
yeah mike go for 6db you will get more range......go for an ae4011 from gme..the sod is about six feet long but its solid, put it on a good spring and mount the thing on the most solid part of the car you can find.....remember movement /vibration kills a good signal i suggest the bullbar as most 6 db sticks are over 1 m long so the roof as is suggested by some is not so practical
AnswerID: 7030

Follow Up By: Member - Nigel - Sunday, Sep 29, 2002 at 00:00

Sunday, Sep 29, 2002 at 00:00
I'd gor for that size myself if it wasn't for car parks. Enough hassle with the HF :)

BTW the 420-450 MHz amatuer band is the "70cm" band, so UHF CB should be slightly shorter in wave length.
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Follow Up By: Mudgutz - Sunday, Sep 29, 2002 at 00:00

Sunday, Sep 29, 2002 at 00:00
ok so 2metres was a bit long but it was a guess 70 cms ....still long enough for the car not to interfere.....
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FollowupID: 3182

Follow Up By: Darryn - Monday, Sep 30, 2002 at 00:00

Monday, Sep 30, 2002 at 00:00
Australian UHF (479/477 mhz) has a wavelenght of 62 cm (620mm).
Darryn
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FollowupID: 3189

Follow Up By: Mudgutz - Monday, Sep 30, 2002 at 00:00

Monday, Sep 30, 2002 at 00:00
cheers darren .....62cms is still long enough not to have the car body muck it up......
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Reply By: Brian - Sunday, Sep 29, 2002 at 00:00

Sunday, Sep 29, 2002 at 00:00
Mike Try this site It explains graphicly what the other post are talking abouthttp://www.gme.net.au/land/choose_ant.html
Brian


AnswerID: 7039

Reply By: Mike - Tuesday, Oct 01, 2002 at 00:00

Tuesday, Oct 01, 2002 at 00:00
Thanks all for your response to my question, I think Nigel is going to do what I wanted to know, can I put 6.5bd whip aerial on the GME 4.5bd colinear Ground independent that I have, Regards Mike.
AnswerID: 7076

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