At 03:59 PM 5/16/05, you wrote:
> >Look for 36-42mhz land mobile stuff. That's right, low band.
> >25-30MHz and 30-36mhz gear ends up on 10m, and 42-50MHz
> >gear ends up on 6m. Nobody wants the stuff in between,
> >and therefore it goes for parts value.
>
>Very cute!
>
>Of course there are a lot of radios out there, HTs and such too,
>designed for low power, with 10.7 MHz IFs..
These Motracs had 8.something MHz high IFs and 455khz low IFs..
>Carve in, and pull the same trick. Imaging could be a problem, but
>then a filter on the input should resolve that pretty well.
The stack that I set up 15-20 years ago used 36-42mhz LHT
Motrac receivers. One thing that I like about low band radios
is that the channel spacing there is 20khz. Many designers
put tighter filters in their low band radios than in their UHF
or high band radios.
We used a 432mhz satellite transverter with a blown TX stage
feeding a home-brew fully passive RX multicoupler. We went for
isolation in the multicoupler and lived with a lower voltage output
(the links had a high fade margin). Each Motrac RX was in it's
own shielded box (made from PC board material). The cabling
from the transverter to the multicoupler to the RXs was double-
shielded. We expected IF coupling between RXs but didn't
see any. Audio was pulled off the high side of the volume
control. COR was provided by a 2-transistor Schmitt trigger
circuit that read the squelch noise voltage and gave an
open collector output. The PL decode signal was acquired
from an open collector driver that read the audio mute line
and leaving the receiver in PL mode.
Images were prevented by having 5 adjacent link channels
spaced 20khz instead of 25khz (the low band Motracs had
IF filters designed for 20khz) and a single UHF pass cavity
was wide enough to pass all 5 link channels through to the
transverter front end (half db loops instead of 3db loops).
Mike
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