Hanks, WB0UIR National AN/FRR-59a receiver
Built for the navy in the early 60's, it's main features are independent
sideband reception and high tuning accuracy. It has over 60 tubes. It
has separate AM, USB, and LSB channels which account for a lot of them.
It has only one crystal oscillator running at one Mhz. The oven for the
crystal has proportional (straight line) temperature control which works
like the cruise control in your car, not like the thermostat on your
furnace. Stability is one part in ten to the seventh. All necessary
mixdown frequencies are synthesized from that oscillator using frequency
dividers and harmonic generators. The VFO covers a 100 Khz segment of
the band. You can let it run free for continuous tuning or lock it at any
0.5 Kc point. When locked, the tuning accuracy is the same as the
crystal oscillator. If ten to the seventh is not good enough they
provide a jack on the back to plug in an external standard. My HP
counter has a buffered 1 Mc output from it's 10811a oscillator and I use
it to get an accuracy of one part in ten to the eighth. Calibration is
easy. I just tune the receiver to 9.999, WWV, feed the USB signal to the
Timewave filter to strip off everything but the carrier, and measure
it's frequency. If it's not 1.0000 I tweak the fine adjust on the A3
support board for the 10811a oscillator in the HP counter until it is.
In the picture the lower unit is the RF/Converter, the upper
unit is the IF/Audio.