I have several repeaters on one tower .2 uhf commercial 473.575 and 489.10mhz and 3 VHF 70meg repeaters  70.300mhz,70.5875,70.725mhz and i am having desense issues on both  70.5875mhz and also 473.575.Would i also require installing isolators on each of these repeaters..any thoughts?
Thank You,
Ian Wells,
Kerinvale Comaudio,
-------Original Message-------
Date: 04/06/06 01:32:28
Subject: Re: [Repeater-Builder] Frequency Spacing?
At 4/5/2006 07:27, you wrote:
>How close, frequency spacing wise, can a couple of VHF (2 meter) repeaters
>in the same equipment room on the same short tower be made to work well
>without much trouble or extra expense? How does 45 Kc. with same 600 Kc.
>offset sound? What will work this close and what won't?
If the offset is the same, closer is actually better since the duplexer of
each repeater will protect each RX from both TXs, both in RX notching of TX
& TX noise suppression at the RX freq.  However, isolators on both TXs are
a MUST, otherwise you will 2A-B mix in both TXs & end up TXing 45 kHz above
& below your two outputs.  Try to keep the two antennas as far apart as
possible.  If you can't separate the antennas much, you might need dual
isolators on both TXs.  I've seen two TXs 20 kHz apart at the same site mix
strong enough to be heard 10 miles away, even though both systems had
single isolators.
When dealing with close-freq. TX spacing, equipment shielding seems to be
more important for some reason.  Stay away from converted mobiles as
repeaters, or plan on using a separate RX in an RF-tight box with EMI
Bob NO6B
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