VHFcontesting
[Top] [All Lists]

[VHFcontesting] more on MMT 432

To: "VHF TEST REFLTR" <vhfcontesting@contesting.com>
Subject: [VHFcontesting] more on MMT 432
From: "MICHAEL SAPP" <wa3tts@verizon.net>
Date: Thu, 17 Jul 2008 17:06:52 -0400
List-post: <vhfcontesting@contesting.com">mailto:vhfcontesting@contesting.com>
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.
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting

<Prev in Thread] Current Thread [Next in Thread>
  • [VHFcontesting] more on MMT 432, MICHAEL SAPP <=