SM-220 / BS-8 Converter for FT-1000D

By Chris Codella, W2PA

December 2006

The Kenwood SM-220 station monitor can be fitted with an optional band scope module.  The BS-5 module, meant for use with the TS-520 series transceivers, takes an input IF of 3395 kHz, and the BS-8, meant for the TS-820 series, takes 8833 kHz.  Because the Yaesu FT-1000D has a first IF output at 73.62 MHz, a converter is required to use them together.

I built such a converter using an NTE-7164 single-IC double balanced mixer (equivalent to the venerable NE-602).  The schematic is shown below (click it to see a full-sized version):

The components associated with the local oscillator should be close to those specified above.  The others are less critical but should still be within a few percent.  L1 and L3 don't have to be variable as indicated - my converter has fixed inductors and works fine - but tuneable ones might enable you to peak things up a bit better than I did.

The basic design is fairly general.  Changing to appropriate component values, it can be used to convert a wide range of transceiver IF stages for use with the BS-8 or BS-5 and SM-220 - or any other panadapter or band scope for that matter.  Other variations and improvements might include adding an IF amplifier stage - I find I need to run the vertical gain on the SM-220 quite high to get a decent display. I could also spend time reducing noise in the system.

My converter is built into a small project box and powered by a 6VDC “wall wart” adapter, and connected between the FT-1000D and SM-220 using 50-ohm shielded phono (RCA) jumper cables.

An example signal trace is shown here:

It's not quite as nice as a digitally derived spectrum display on a computer screen, but it's not bad.  This example was taken using the 20kHz display width.  The multiple traces in the photo are due to a mismatch between shutter speed and scan rate.

One flaw in this system is the display of spurious mixing products.  Since the first IF output from the FT-1000D is taken before most filtering occurs, such signals will appear as strong peaks on the display, but you won’t hear anything as you tune across them because they don’t make it further downstream in the receiver’s IF chain.