Paul Kelley wrote:
>Kevin,
>
>That is one awesome repeater! Nice mix of GE and Motorola
>stuff. I sort of have the reverse situation with GE
>receiver / exciter and Moto PA.
>
>I have questions concerning the PA selection relays. I
>assume you have relays at the PA outputs as well as the
>inputs?
>
Correct. The Micor Mobile antenna relay is used backwards, as the
exciter input goes to the PL connector. The connection marked "R" or
receive is of course normally closed. This connection goes to the input
of the 110 watt PA, the other port (T) is going to the input of the 10
watt PA. At the other end exists the factory GE antenna relay that
originally connected the antenna to the receiver or amplifier output
(this amplifier was used in Basestation service before and had the relay
already in place). The output of the 110 watt PA goes the the normally
closed port of the output relay (the one that originally fed the
receiver). The output relay only engages when the GE tube PA is driven
(with RF and PTT) and of course is the PA that is selected.
> What type of relays are you using
>
A Micor Mobile antenna relay for the input power (400 mW), and the OEM
GE antenna relay used with the high power station (part number unknown,
but it looks and is similar in size to a Dow Key Relay) for the "hot
side" of the RF.
> and do you have some means of preventing them from "hot switching" while RF
> power is applied?
>
Sort of. By virtue of the way the output relay is driven, drive is
actually removed from the tube PA before the output antenna relay
switches. While drive and power already exists from the 110 watt PA, I
felt this was the lesser of the two evils.
> And if not, what happens in the event of a power failure while the machine is
> in use?
>
Since these relays are driven from a 110 volt derived source, they
simply drop out and the 110 watt PA takes over. It switches in a matter
of milliseconds and the user might only tell by his "S" meter.
> I mean do the relays handle it OK?
>
They seem to. In normal practice, the antenna relays are actually
switched prior to the channel element being enabled. This function was
incorporated into the Station Control Module by using the delays already
built into that module. While I'm not suggesting the way I do it is the
best, and while I don't make it a practice of hot switching the PA's, it
does work and hasn't given any trouble, yet; however it's only been on
the air a short time.
Kevin Custer
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