Multiple UHF atenna's - Bullbar

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mitch
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Multiple UHF atenna's - Bullbar

Post by mitch » Tue Mar 22, 2011 2:49 pm

G'day

Quick question, hopefully simple answer. I want to mount 2 UHF antenna's on my bullbar. Do they need to be a certain distance apart or does it no particularly matter? One will be hooked to a Uniden and one to a Icom, if that matters.

Cheers
Mitch

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bodyguard
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Re: Multiple UHF atenna's - Bullbar

Post by bodyguard » Tue Mar 22, 2011 3:32 pm

I would personally mount them about 500mm apart, this allows for 1/4wave groundplane effect on or about 144mhz
Cheers
BG


UBC9000XLT, UBCT8, BCT15X, UBC92XLT, Kenwood R-5000, PSR-410 , KG-UVD1P

mitch
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Re: Multiple UHF atenna's - Bullbar

Post by mitch » Tue Mar 22, 2011 3:36 pm

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Last edited by mitch on Wed Dec 17, 2014 1:15 pm, edited 1 time in total.

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Azoic
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Re: Multiple UHF atenna's - Bullbar

Post by Azoic » Wed Mar 30, 2011 1:02 am

Antenna phazing is somewhat complex, and interaction is similar.
The optimum spacing to avoid interaction is more than 1/4 wavelength for receive, and more than 3/4 wavelength if they are both used for TX.
Best distance for UHF is 110 cm apart. The 477 Mhz UHF wavelength is 69 cms (approx.) so add another 1/2 wave to be safe.
For ease, use 70 cms as UHF wave, + 35 cms as a safety. This giving 105cms. Add another 5cms for security and be satisfied your OK to TX on both at one time.

mitch
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Re: Multiple UHF atenna's - Bullbar

Post by mitch » Wed Mar 30, 2011 6:51 am

Does it matter if both don't transmit at once? Only one will ever be transmitting at any time, the other may be recieving something (diff. channel) while im transmitting, but certainly wont both transmit at same time.

Mitch

Kevaclone
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Re: Multiple UHF atenna's - Bullbar

Post by Kevaclone » Fri Apr 01, 2011 3:55 am

I wouldn't worry too much. at best the you'll get desensing of the RX radio when TXing on the other(all that means is that the RX will not hear anything and remain quiet) and at worst the RX radio will open up and you'll get feedback

Since you're using a Uniden for RXing I'd say it will suffer no matter how far the antennas are apart, especially if the Icom is 25watts
and beside having an antenna in your line of vision, ie; right in front of you, when driving is a real pain

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