Back in the crystal controlled 1970's I used GE Mastr II and MVP exciter
boards as frequency sources for exactly what you are talking about. They
put out several hundred milliwatts of RF so a combination of resistive
attenuators and cavity filters and in some cases power splitters would bring
the level down to +7 dBm to drive a doubly balanced mixer or 2 or 3 in a box
I seem to recall that they had a fairly repeatable -6 dB or so conversion
loss and about 20 dB rejection from X-L and X-R.
I settled on the MiniCircuits SRA-5 after playing with a Vari-L DBM-182
which had a flat pack package. The relay can package of the SRA-5 worked
much better with my point to point in free space, micro coax brass board
kludge construction style of the period. It was ugly but it worked. If I
needed to put it on a hilltop I could bend up a cover and solder it over it.
An 820 mHz injection would bring my 1299 mHz signal down to a 478 mHz
frequency where I could get free radios. For the transmitters I used
varactor triplers to multiply up, deviation, frequency error and all. It
blew a few peoples' minds to see an EF Johnson 558 working full duplex on
1300 mHz.
They could not readily see the magic box under the seat that was doing the
conversion. Yes, the 558 had a varactor output stage so it was a varactor
driving a varactor, just asking for trouble. I seems I could always get
them tamed down after about a day of tweaking or until the temperature
changed a lot, then then they needed to get treaked a little more. I drove
around with a CE 15 in the car for work so it was no big thing to pop the
covers off and tweak on the fly.
I even built repeaters that used a common LO signal for both the transmit
and receive up and dowm converters. I would just order the crystals to land
on the tx RX or link frequency in the 470 mHz radios.
Fun while it lasted. got bored, had to duplex the radio since nobody else
was on FM. At least with duplex I could talk to myself.
I'm rambling too much, sorry.
td
wb6mie
10a.
Posted by: "David Struebel" [EMAIL PROTECTED] wb2ftx
Date: Mon Mar 19, 2007 11:14 am ((PDT))
Anyone help me.... I have a 1.2 GHz repeater, but no service monitor or
signal generator for these frequencies.
My service monitor, a Singer-Gertsch only goes up to 499.995 Mhz. I have
tried using the third harmonic in the 420-427 range but either the
service monitor is well filtered, or the signal is too weak to be picked
up by the 1.2 GHz receivers... I have thought about an external tripler
circuit... Any ideas on this or other possible solutions other than
buying a new signal generator (too costly).
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