UHF Radio Aerials
Submitted: Friday, Sep 27, 2002 at 00:00
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Mike
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)
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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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