The HP 3586C Selective Level Meter, often used as a receiver, is easily
modified to receive high frequency digital broadcasts that use Digital Radio
Mondiale modulation, for general purpose reception with Winrad, and to use
other receiving software not dependent on complex (I&Q) inputs to a sound
card. The modification only requires adding a connection from an existing
jack internal to the instrument to the back panel.
The first conversion in the HP 3586 series is to 50 MHz, where a 10 kHz wide
crystal filter sets the maximum receive bandwidth, followed by a conversion
down to 15.625 kHz. There is a SMC connector test point on the A10 card on
the top side of the 3586 where this signal appears. The test point output
impedance is 1000 ohms and the signal level can be over a volt with high
level inputs. To find this test point, disconnect the line cord and remove
the top cover, which requires removing the two plastic feet at the rear top,
and loosening the captive screw at the rear center of the top cover. The
SMC jack is well marked and is one of only a few connectors without a cable
attached. If your unit does not have the crystal oven option, it is easy to
run a short coax jumper to an added BNC connector placed in one of the
several unused holes on the back panel. I used a BNC connector with
isolated ground as the internal circuit ground in the 3586 series is
isolated from the chassis, but there are probably other ways to get this
signal out of the instrument. I didn't find any DC on this jack, which is
attached through a 1000 ohm resistor to the output of a op amp, but adding
an isolation capacitor might be a good idea, although I did not. A 1:1 600
ohm transformer, the once common Radio Shack one in my case, avoids
grounding issues between the 3586C and the PC sound card. Results using the
modified unit for DRM broadcast reception with Dream software and ssb/cw
with Winrad have been excellent, but I did have to invert the spectrum (a
Dream software option) to get the DRM reception working.
While you have the top cover off, check the battery on the A80 card, which
is vertically mounted and the card closest to the right rear of the unit
when viewed from the front. These batteries often leak after long use and
can damage the board, the connector, and the +5, -12, and +12 volt power
supplies. Except for early production units, normal operation is possible
without the battery, which can be unsoldered or clipped out. Minor leaks
can be cleaned up with a solution of vinegar and water.
These modifications are done at your own risk and may void the HP warranty.
Roger Thompson
AD5T
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