Ok Doug
The frequency pairs are
TX 473.575  RX 478.775MHZ
TX 489.100 RX 483.900MHZ
TX 70.300  RX 72.800 MHZ
TX 70.5875 RX 72.0875 MHZ
TX 70.725 RX 73.225MHZ
 
 
Thank You,
Ian Wells,
Kerinvale Comaudio,
 
-------Original Message-------
 
From: Doug Bade
Date: 04/07/06 01:24:28
Subject: Re: Fw: Re: [Repeater-Builder] Frequency Spacing?
 
Ian;
         I do not think you suppled enough info for us to answer
that. While isolators are always a good idea at sites where there are
multiple transmitters, the specifics of why in the preceding
discussion is for specific problems due to exact offset paired
repeaters in the same site working in close proximity with probable
antenna coupling contributing to potential intermod as a
result....isolators are probably mandatory in that case.
 
         That specific site set of conditions as was being discussed
may have no relevance to you unless your pairs all have same TX-RX
offset, and the transmitters are capable of cross coupling energy
among themselves and thus create intermod for your receiver(s). 70
Mhz isolators will not be cheap... so I would not jump there without
proper diagnostics...
         You did not tell us what your receive frequencies are, or
are these simplex stations??? 70 mhz is not a repeater band we
recognize here, I am unaware of your licensing schemes for this band
in Australia....
         Same question applies for your uhf... specifics would be
helpful for analysis of your exact inputs and outputs...at 470 here
we use 3 mhz offset... at 450 we use 5 mhz offset... Rules vary by locale....
 
Doug
KD8B
 
 
 
 
At 01:03 PM 4/5/2006, you wrote:
>
>
>
>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
>feedthroughs.
>
>Bob NO6B
>
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