开云体育

Hi:

As an alternative to using a Step Recovery Diode to generate the
harmonics it may be possible to use a modified A45 Module from a PRC-77
military radio. The A45 Module is called "One-megacycle spectrum
generator" and uses a PNP 2N2273 transistor to generate the harmonics
with a fairly simple circuit powered by +10 Volts. In the theory of
operation TM 11-5820-667-35 pg 2-22.3 "The sinusoidal 1-mc oscillations
are applied to spectrum generator Q2 (2N2273) through coupling capacitor
C3 (10 uuF) . The spectrum generator is normally cut off by the reverse
base bias applied through R4 (19k), and conducts only on the negative
half cycles of the 1-mc signal. A positive pulse, rich in harmonics, is
developed across transformer T2 and coupled to first mixer module A44.

This might be an excellent replacement for the impossible to get SRD.

73,

Brooke Clarke, N6GCE

Date: Tue, 01 Jun 2004 08:32:09 +1000
From: Morris Odell <morriso@...>
Subject: RE: hp 5100A /5110A synth set Spectrum Generator

Hi all,

When repairing my 5110A with the dud SRD last week I tried several
varactors and eventually found one from a junked cellular base station
tansmitter which worked very well. It is a stud mounted power device
used a tripler in the final of a ? FM transmitter aroung 800 or so MHz
judging by the appearance of the rest of the circuit. It's about the
size of an older style 10 watt power zener, but gold plated with a
ceramic insulated header. It is made by NEC and labelled "SV 888". After
the HP 5110A SRD oven assembly together with its control transistor Q2
was removed from the board, there was plenty of room to mount the diode
on a pair of stiff wire "legs". It's probably the only non-US made part
in the whole system now, which is a sobering thought when you think of
where comonents come from these days.

There is lots of this sort of equipment around at hamfests etc. It had
been sitting in my junk box for years - it just goes to show you should
never throw anything out!

The 5100A/5110A synthesizer is now working perfectly. The only other
parts that had to be replaced were a fuse and the "power on" neon
indicator in the 5100A, both glass components :-) It's a very impressive
performer!

I note the comments about other harmonic generators. There are lots of
ways to do the job, and I had briefly thought about the subject before
finding my diode. Going for a technology shift would have required a lot
of reworking of the 5110A and would have been a major effort. HP seemed
to like SRDs, they are in quite a lot of other equipment including range
extender plugins for various counters and also the 8708A synchronizer.
This is the first one I have seen fail.

Morris