Tim & Folks:
I realized no one answered your IF retune question.....
>Actually there's one more compliaction with this one, which may or may not
>be related to the low power out. Someone modified it to have a 27Mhz IF
>instead. If I drive it with 28 Mhz it transmits at 433MHz.
>Could transmitting 1Mhz high cause it to have a great reduction in output
>pwr? Anyone have an idea of the output bandwidth range? I do not have
>capability to drive it with 27Mhz to test it.
> (Also..how do I retune it
back to 28MHz?)
Refer to the appropriate schematics available at
http://www.qsl.net/wa2wim/eme/eme.htm which are in a zip folder.
Both the rx and tx sides of the 28Mhz IF section have separate RF coupling
transformers. One or two turns of the respective inductor slug should be all
that is necessary to repeak them to 28 Mhz from 27 Mhz. An MFJ-259B analyzer
outputs around 5mw, so you can use the analyzer to determine curent resonance
and then tune for lowest SWR on the IF side back to 28 Mhz. If you use that
approach leave the DC power off to the transverter. If you can't get a low SWR
on the IF tx input then suspect something amiss with the tx IF input attenuator
or IF transformer. (Note: bypass the 1K resistor for low-level attenuator input
operation for this test) Same for the rx IF (but no attenuator). Mike wa3tts
P.S. I used this method to repair an old MMT 1296 rx converter---it had an IF
input transformer wiring fault that was immediately obvoius with the MFJ-259B
test. Actually I ended up ripping out the 2M IF preamp and installed a small
diplexer (p87, 1987 Mid-Atlantic Conf Proceedings, P. Drexler) and turned the
rx converter into a bi-directional tx/rx LO-Mixer for a 1296 transverter
project.
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