[NLRS] Parts is parts

[Dr. Gerald N. Johnson, electrical engineer]

The ceramic block is likely a filter, could be replaced by another to
cover 902 or a home made one such as in the VHF/UHF chapter of some ARRL
handbooks or early 902 articles in QST by W0EYE.

For transmitter output tests a roll of 100' of RG-58 terminated by a
pilot lamp gives a flat load and a relative power indicator. The
brighter the lamp the more power is going into the coax. Start with a
#48. When it burns out go to a #47, then a #44, then a dome lamp bulb.
Not very expensive test equipment.

Yes you have to take control of the PLL/VCO, possibly tweak the hardware
rest frequency of the VCO.

I'm not kidding about using NBFM. It worked, and it can work again.

Offhand I'd guess the first IF frequency is at 45 MHz, and likely the
mixing is still fairly linear down to 10.7 MHz.

Two places to look for a schematic or service manual, (well maybe
three). E.F. Johnson at Waseca, the local two way shop that cares for
E.F. Johnson products, and epay. There are several hams at E.F. Johnson
that should be relatively willing to help other hams use their products.

If they are the 8615 radios with a 45 MHz split, they probably use the
same transmitter frequency for receiver LO so the first IF is truly 45
MHz. I have some Micor that do precisely that. Actually it looks like
most of the receiver is made of low band boards with one crystal for 45
MHz. And the transmitter is the exciter from a 450 MHz radio. Then they
split the 450 MHz power and run separate doublers for receiver and
transmitter and they have a circulator on the transmitter side to
protect the fragile PA transistor from high SWR at the antenna. Working
simplex seems to demand a pair of radios or rapid switching of the same
multiplier string (the Micor has room for several channel elements) from
transmit to receive channel elements, and my thought was to make up for
one being off tuned by adding a MMIC buffer stage, maybe 0404 or 1104 to
one of the sides. One of those projects that hasn't made it very far.

Possibly even with the off tuned ceramic filter, a preamp say with
cascaded 0604 MMIC before it would still receive well. There'd be a need
for that preamp to have some filtering in it.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.