maximising uhf range.

Post by **muppet_man67** » Mon Oct 25, 2004 12:59 pm

I got myself a 5w uhf radio and at the moment the arial is mounted to my old AM radio mount.
Im using the same Arial wire running to the uhf as what was used for the AM radio. The arial is your average run of the mill UHF black whip ariel. not unlike the AM whip ariel that was on it before. its about 3 feet high.

How should I set it up to make the most of my 5 watts? recomendations of specific products and brands appreciated.

thanks

Post by **phippsy** » Mon Oct 25, 2004 1:14 pm

AFAIK the coax for a uhf is a different weave to that of an AM lead. Also the different frequencies between AM & UHF mean that an AM ariel won't work too good with UHF radio. An elevated feed ariel is best for a 4wd wth a wire whipand spring base so if it hits trees etc. it just flexes and bounces back.
I'll try and find a link to an ariel makers site .

Post by **muppet_man67** » Mon Oct 25, 2004 1:31 pm

phippsy wrote:AFAIK the coax for a uhf is a different weave to that of an AM lead. Also the different frequencies between AM & UHF mean that an AM ariel won't work too good with UHF radio. An elevated feed ariel is best for a 4wd wth a wire whipand spring base so if it hits trees etc. it just flexes and bounces back.
I'll try and find a link to an ariel makers site .

thanks about the coax. I was wondered if it was different. I have a uhf ariel. sorry Ive edited the above post.

Post by **phippsy** » Mon Oct 25, 2004 1:50 pm

If it's not an elevated feed ariel, the ideal place for it is in the middle of the roof (or bonnet), but that's not always practicle.

Post by **LukeV** » Mon Oct 25, 2004 1:51 pm

An antenna like this would be nice. Use the 3dB for the hills and the 6 for the open highways. (from Prestige Communications

BTW - You want to use either RG58 coax for short runs, or RG213 for longer runs. (See here)

3 & 6.5db Ground Independant Explorer
Ground Independant
3 & 6.5db Gain Whips Supplied
Elevated Feed
Heavy Duty Spring
Extremely Robust
4.5m Coaixal Cable and Connector
Measures 900mm in 6.5db mode
Express courier delivery Australia-wide $5.00

PRICE: $99.00 (Including GST)

Post by **phippsy** » Mon Oct 25, 2004 3:52 pm

I snapped the 6.5 db ariel on an overhanging trees small branch b4 going to a s/s whip. But these are good, and seem to be a good price too.

Post by **Woop** » Mon Oct 25, 2004 9:04 pm

The best coax to use for the run to the antenna is either CELLFOIL or CELLFOAM. CELLFOAM is preferable but the other works just as well--it uses foil as its shield instead. Cable is the same size as conventional RG58 but with much lower loss. RG213 is ok as well but much larger in size and for the length that you would be using, not worth the hassles. G.M.E have a suitable elevated feed antennas if you cant find a large square flat spot to mount. KEep the antenna as far away from other antennas as possible--mounting too close to others can reduce radio sensitivity. Make sure its properly grounded..

Nick

Post by **crowey** » Mon Oct 25, 2004 10:27 pm

I have the CD900 antenna (made by RFI), and i cant speak highly enough of it.
It is fairly small and thin, and according to all the write ups on it, it is the best around at the moment. It's a 6.5db over 1/4 wave.

Post by **Jeeps** » Tue Oct 26, 2004 1:24 am

Although i think it's bullshit, a couple of 'blokes in the know' i've talked to have told me of a way to increase signal strength which sometimes works. It is done by looping the cable in a small loop where it comes out of the base of the antenna. This apparently increases quality of transmition as the cable acts as a signal generator as it pre-loads or some crap before the signal enters the aerial. They reckon it'll only work if the rest of the cable is as straight as it can be with minimal bends/kinds/turns and with no other loops.

Post by **dumbdunce** » Tue Oct 26, 2004 11:40 am

Jeeps wrote:Although i think it's bullshit, a couple of 'blokes in the know' i've talked to have told me of a way to increase signal strength which sometimes works. It is done by looping the cable in a small loop where it comes out of the base of the antenna. This apparently increases quality of transmition as the cable acts as a signal generator as it pre-loads or some crap before the signal enters the aerial. They reckon it'll only work if the rest of the cable is as straight as it can be with minimal bends/kinds/turns and with no other loops.

that is indeed BS.

one thing nobody has mentioned is the antenna BASE. if you are using an AM antenna base, with exposed terminals, they SWR will be crap and you will get marginal reception too. you need to use a UHF base where the coax screw into the base and the shield in not compromised all the way up to the antenna itself.

the "gain" of a UHF antenna is really a measure of the shape of the wave field radiated from the antenna. the higher the gain, the more flat the field, ie more like a disk. High gain antennas are awesome over flat grond or water and will give good performance as fas as you can see - to the horizon. Lower gain is better in hilly terrain or in urban areas where line of sight is not maintainable. At the end of the day UHF transmission is limited to line of sight (the waves can only go in a straight line) so terrain is usually the limiting factor long before distance becomes a problem. as an example, I live on the western facing side of the top of a hill in blacktown and have now trouble holding UHF conversations with people in the lower blue mountains approx 40km away using a stubby 3.5dB antenna but I cannot talk to people on the other side of my hill less than 2km away using any antenna unless I drive 200m to the top of the hill.

Post by **muppet_man67** » Tue Oct 26, 2004 12:00 pm

one of those links said that AM is better for hilly country. why is this?

Post by **dumbdunce** » Tue Oct 26, 2004 12:09 pm

muppet_man67 wrote:one of those links said that AM is better for hilly country. why is this?

AM will reflect off a variety of surfaces, including some atmosphereic layers under certain conditions (skip), so under certain conditions it can perform better in hilly country.

google for 'AM radio bounce skip' and you should find some answers.

Post by **the_smoo** » Tue Oct 26, 2004 12:37 pm

AM is a lot lower frequncy than UHF..

AM 27MHz,

UHF 300Mhz to 3000MHz..

Lower frequencies can travel a lot further than the high freqs..
You might of noticed that you pick up AM stations a lot longer than FM stations broadcasting from similar locations.. part of the reason is due to the lower frequency of operation of the AM station..

SKIP occurs when the AM signal bounces of the the atmosphere and "channels" itself over huge distances.. only happens when conditions are right..(as dumbdunce mentioned.)

Post by **muzza_fattire** » Tue Oct 26, 2004 1:29 pm

dumbdunce has got it right....
Although in hilly country, you will want a less directional antenna (low gain) more because the receiver may not be on the same plane as the transmitter, ie. your car is at the bottom of a hill and the other is at the top or your car is on a steep slope. If you have a more directional antenna, there is not enough power transmitted in the vertical plane.

Also in regard to mounting the antenna in the middle of the roof...
This is only required when the antenna in ground plane dependant. If so, it needs at least 1/4 wavelength of reflective material the whole way around.
If the antenna is ground plane independant it does not require this. Not sure if it benefits from having it though...

Post by **the_smoo** » Tue Oct 26, 2004 1:36 pm

heres some more info on what muzza_fattire is talking about..

http://www.marcspages.co.uk/tech/antgain.htm

and some selection info
http://www.marcspages.co.uk/tech/antchose.htm

Post by **Davidh** » Tue Oct 26, 2004 10:35 pm

AFAIK the coax for a uhf is a different weave to that of an AM lead.

AM and UHF both need 50ohm coaxial, any 50ohm coax cable should work fine for both types of radio, be it RG58, RG213, or if you REALLY need to, LDF5. You really couldn't use RG213 in the car though. It's too thick and hard to bend around corners. The loss is so little, it's not worth it for cb's.

Although i think it's bullshit, a couple of 'blokes in the know' i've talked to have told me of a way to increase signal strength which sometimes works. It is done by looping the cable in a small loop where it comes out of the base of the antenna. This apparently increases quality of transmition as the cable acts as a signal generator as it pre-loads or some crap before the signal enters the aerial. They reckon it'll only work if the rest of the cable is as straight as it can be with minimal bends/kinds/turns and with no other loops.

I've done a few antenna installations in the past and I was told first off that the loop is purely there so you can change antenna's or connectors in the future and you don't have to pull up more cable. Maybe these "guys in the know" saw installations and assumed it helped signal strength.

Post by **Utemad** » Tue Oct 26, 2004 10:40 pm

UHF operate on a higher frequency as said before. However the lower frequencies rely less on line of sight. Although the more open an area the better. Can't quite remember all the details but lower frequencies penetrate better.

However AM would be pretty much useless as it is not really used anymore. So even if you could reach someone they probably only have a UHF :lol:

Post by **mkpatrol** » Wed Oct 27, 2004 8:59 am

Utemad wrote:UHF operate on a higher frequency as said before. However the lower frequencies rely less on line of sight. Although the more open an area the better. Can't quite remember all the details but lower frequencies penetrate better.

However AM would be pretty much useless as it is not really used anymore. So even if you could reach someone they probably only have a UHF

Am is not used for local transmissions much any more but it is still used by the enthusiast to talk long distance on sideband. Any night on the weekend a conversation can be struck with anyone around OZ if the skip is right.

Post by **muzza_fattire** » Wed Oct 27, 2004 10:49 am

Davidh wrote:I've done a few antenna installations in the past and I was told first off that the loop is purely there so you can change antenna's or connectors in the future and you don't have to pull up more cable. Maybe these "guys in the know" saw installations and assumed it helped signal strength.

Most people put a loop in the cable so that if water somehow gets inside the coax then it will pool in the loop and not progress further down the cable ie. towards expensive equipment.
I guess it would also be handy to have a little slack for future mods aswell

Post by **Utemad** » Wed Oct 27, 2004 10:55 am

muzza_fattire wrote:
Davidh wrote:I've done a few antenna installations in the past and I was told first off that the loop is purely there so you can change antenna's or connectors in the future and you don't have to pull up more cable. Maybe these "guys in the know" saw installations and assumed it helped signal strength.

Most people put a loop in the cable so that if water somehow gets inside the coax then it will pool in the loop and not progress further down the cable ie. towards expensive equipment.
I guess it would also be handy to have a little slack for future mods aswell

You have to run out the slack somewhere. I have heaps of slack coax in the ute. Digital phone antenna, UHF antenna, old CB cable, AM/FM cable. Combined with all the other electronic stuff I have added I almost can't cose my glove box for all the wires running behind it :lol:

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maximising uhf range.

maximising uhf range.

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