Ok you Johnson ghuru's out there, please read this.
I was asked by an area ARES group to lend a hand and convert an
EF Johnson CR-1000 series UHF repeater to amateur use. This is, of
course, free gratis on my part, I'll even chip in the ID'er since it's
for a good cause.
I cannot get the receive sensitivity where it should be. Initially
when I received it, the JFET located inside the preselector was blown.
I replaced it with a generic JFET but not an exact match.
At first I couldn't get the sensitity any lower than about 50uv and
several tuning screws were bottomed out in the row of helicals
suggesting the new frequency is beyond the range of the preselector. I
replaced the screws with a similar brass screw but about 3/8 in longer
and I was able to get the sensitivity down into the 10-15uv range,
obvioiusly a big improvement, but still way off. No screws were
bottoming out at this point.
I first retuned the receiver as per the factory manual. I did,
however, note the suggested minimum voltage reading I should see were
always lower. I've really never particularly paid strict attention to
these "should be about" readings, but all increased after the machine
screw changeout suggesting they could possibly increase more once the
proper sensitivity is reached.
Does anyone have experience with this repeater or the mobile chassis
it's patterned after? I can assume the helicals will need
modification, but that's why I asking the experts!!!!
The group that will own/manage this repeater are buidling their shack
this week and hanging hardline, so it looks like I may be the "holdup"
here. Please point me in the right direction...Thanks...de N5MZQ
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