HP 3586C as a receiver?

There's quite a few HP 3586A/B/C selective level meters available out there. Makes sense, as they were designed for testing analog telephone trunks, and I suspect those are mostly bye-bye.

It's basically a very stable and accurate in frequency and sensitivity sideband receiver. You can use it as your basic shortwave or Ham band receiver as-is except for a few foibles:

(1) It has a 100 db range AGC control, but it jumps in very calibrated

5db steps, with no control of the attack or decay times.

(2) It has no simple manual AGC control, you know, like with a KNOB. It has keypad entry of sensitivity level, but that's very cumbersome.

(3) It has frequency readout to 0.1Hz, but at least on the "C" model it's the frequency of the center of the passband, which is 1.850 Hz off the usual "carrier" frequency specs.

(4) The selectivities are not particularly useful, varying among models: 20, 50, 200 400, 500, 1100, 1850, and 3100 Hz.

(5) The reinjected carrier is not tunable across the passband, likewise the passband is not tunable across the carrier frequency.

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Has anybody tried attacking these very annoying (to me) shortcomings as a radio?

(1&2) Look hard to do transparently, without disassembling and then modifying the code for the control program, which inconveniently is split across about 8 ROMS. The CPU is from Motorola, so it may be a

6800 variant.

It could be done by snipping off the DACs controlling the IF gain amps, but that's kinda ugly. Or using one of the options that's controlled by the main knob and redirecting it's DAC to the IF gain line, but that 's kinda ugly too.

(3) I havent figured out any kludges for, except by buying the "B" model, which I think has this as a three-button-press option.

(4) Looks changeable, as the filters are simple 8-pole LC ladders modeled at 62.5k ohms. Funny, in the older 1968 model 320 version, they used 18-pole active filters, and in this 1983 model, passive LC filters!

(5)

From the block diagram it doesnt look too hard to do (5), just

substitute a 50MHz 200 ppm pullable TXCO for the 49.98... final oscillator. But unless we also pull the previous LO in the other direction we will also be pulling the tuning, or at least the readout, which will be confusing.

Anybody have any thoughts?

Regards,

A_H

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Ancient_Hacker
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