Michael
This seems to me to be a classic case of RF mixing from one transmitter
into another. The cure for this is to install a circulator/isolator in
each feedline. The circulator does not allow RF from one transmitter to
feed back down the coax into the other transmitter. I have measured RF fed
from one transmitter back down the coax to another to be in excess of 5
watts on a 50 watt transmitter. This is one of the problems associated
with having more than one VHF transceiver located on the same or adjacent
tower.
I wish you the best of luck in curing this problem.
73's de Tom Manning
Pete B wrote:
> Sounds like front-end overload to me. Just my humble opinion.
>
> Pete
>
> -----Original Message-----
> From: Michael Singewald N1PLH [mailto:[EMAIL PROTECTED]
> Sent: Sunday, April 18, 2004 2:04 PM
> To: [email protected]
> Subject: [Repeater-Builder] Is there a relationship between 147.225 and
> 146.925?
>
> There are two machines on the same tower on these frequencies with
> one antenna about 20 feet directly over the other. Each machine is
> putting out about 30 - 50 watts. Each machine plays fine by itself,
> but as soon as the other tranmitter comes up the problems begin.
>
> Each machine has a different PL required to key up (67 and 77). If
> someone unkeys on 146.925 while 147.225 is keyed, the 925 which
> encodes a pl seems to get into itself and the 225. The 925
> transmitter also causes the same problem on the 225 receiver.
>
> These two are fine as long as the other is not keyed at the same
> time. Someone in the group has said that there is a harmonic causing
> this and those two repeaters just cannot be co located. I admit I
> don't know much about this, but how can a harmonic be causing this if
> they are both on VHF? I would think that mixing might possibly be
> responsible for this. The BpBr duplexers were just tuned so I don't
> think they are the problem. The SWR is flat on both machines as
> well. Also, both repeaters are new (1 Hamtronics, 1 Kendecom).
>
> How can I determine if the problem is mixing? If it is mixing, how
> can we fix it? Would a "crystal filter" on the receiver help?
>
> Neither of these machines are mine, so I am trying to gather info for
> the two affected groups, so thank you for any advice!
>
>
> Yahoo! Groups Links
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
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