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Here's a clean, stable local oscillator that can be used to provide up to +17 dbm anywhere in the 1000-1400 MHz range. Typically, one would use this as the base L.O. for a microwave transverter, or as a source for a beacon amplifier. In fact, I use this same board in my 23, 13 and 9cm transverters, and as a driving source for the 23cm beacon (also described on this site). The board shown does not yet have the crystal installed at Y1, which is a standard 5th or 7th overtone AT-cut crystal. When ordering crystals, asking for a turn point at 50C is a good idea; this allows the use of a crystal oven for even greater thermal stability. Just one more option to consider...
You'll
need to provide a couple of filters; one for
the inter-stage filtering between U1 and U2, and another at the output of U2.
Fortunately, these are small and easily constructed; the resulting signal is
very clean, with at least 50db suppression of the adjacent oscillator harmonics,
as shown in the picture to the right. The filtering is even more effective if
the crystal is in the 150-199 MHz range.
The basic lineup is a low-noise Butler oscillator driving a
high-gain MMIC (U1). U1 is driven into saturation, and generates harmonics well
into L-band. One of these harmonics is selected by a
filter between U1 and U2, amplified by U2,
and cleaned up again using a second filter at the output of that stage. The
beauty of this arrangement is that only one adjustment is required...the crystal
"peak" trimmer is adjusted for a reliable crystal start, and the filters do the
rest. Selecting a different value for the "net" capacitor can provide a coarse
frequency adjustment. The "peak" capacitor allows only fine adjustment of
frequency (it's main purpose is to peak the output of the oscillator).
Just
for illustration, here's a picture of one way you can set one of these up.
Here the board is fully loaded and wrapped in a tin sheet enclosure.
Fastened to the bottom cover of the enclosure, and connected to terminals on the back side of the board, is one of the filters mentioned above.
Note the mounting method for the 7808 regulator (soldered to the enclosure wall) and the feed-through capacitor for the 12v supply.
The second filter (not yet attached) will be mounted to the
top cover.
Shown below is the complete schematic and a component layout
close-up; for crystals in the 150-199 MHz range, use 22nh at L1, 5-20pf at
"peak", 150nh at L4 and 330 ohms at R8.
