Dave, I have moved about 5 stations that were in Forrest Service use around 417
mHz, and have a few suggestions.
Buy a mobile 88 split receiver and don't attempt to change the 77 receiver
front end. I modified three of them by removing one quarter turn from each of
the helical resonators, and it is just not worth the effort. The mobile 88
split receiver will interchange with your 77 split receiver.
The exciter tuned right up, with no changes to any component values on each of
the 5 that I moved. If you buy a mobile for the receiver, the exciter will
also exchange with your 77 exciter.
The 77 split amp works just fine up in the ham band except for the low pass
filter on the board with the T/R relay on the output of the amp, if you have
one without the T/R relay. Remove the filter cover and parallel a #18 buss
wire with the existing wire that connects from the input cap to the output cap
across the three shunt caps. This lowers the inductance slightly and will
allow you to pass full power to the output. If the amp has a matching circuit
- a simple PI Network on the output, be sure to tune it up when you are through
with the LPF modification. Don't tune for max power - tune for a null on the
reflected power test point provided on the matching board. Not all amps have
the matching board, but pay attention if yours has one.
None of the other components in the station change with the 77 to 88 split
change. In fact, the audio squelch board from a VHF mobile or station will
interchange with the 77 you are moving to an 88 split.
By all means - buy or trade for an 88 split receiver and don't attempt the
quarter turn coil removal in the helicals. It just is not worth the effort to
heat the cavity for the heilcals enough to remove the coils and then get them
resoldered in the right place. The osc-multiplier board will not go to high
side injection like I prefer on a UHF M2. You would have to stay with low side
injection, and beware the pitfall in the receive frequencyarea described in a
note on the repeater builder site. I had a low side injection repeater
operating on 443.9 that had the problem until I changed to high side injection.
Good luck on your conversion.
73 - Jim W5ZIT
--- On Sun, 7/19/09, Dave Cochran <d...@n0trq.com> wrote:
From: Dave Cochran <d...@n0trq.com>
Subject: [Repeater-Builder] Convert 406-420mhz Mastr II to ham band
To: Repeater-Builder@yahoogroups.com
Date: Sunday, July 19, 2009, 10:05 AM
Okay guys, I might be biting off more than I know here, but
I've been
tasked out to try to get this accomplished for a new fledgling group
of hams here.
How much effort is really involved in converting a 406-420Mhz Mastr II
machine (combination ending in 77) up to the ham band?
Need to start learning more somewhere and this seems like a good avenue to take.
I'm sure someone must have written up a step by step guide for
re-tuning, I just have not found it yet. A point in the right
direction would be helpful.
Thanks,
Dave - N0TRQ
