40M Channelized SSB Transceiver retrofitted with a Heathkit SSB Filter

Описание: One of the best kept secrets is the Heathkit Crystal Filters as used in their many popular transceivers. As of this posting (May 2025) there are three of them for sale on eBay costing around $15.

Perhaps their lack of appeal is the Center Frequency is 3395 kHz and the lack of the matching BFO crystals. But with an Arduino and Si5351 this is not a problem.

What is a problem is single conversion designs with injection on the low side. Just like a 9MHz Filter and 17M that puts the LO essentially at the filter frequency. That same sort of problem with a Heathkit filter and low side injection where the center frequency and injection frequency are close. If you put the LO injection frequency on the high side, then not so much of an issue as a 3.395 MHz filter using a 10.5 MHz LO (sideband inversion) avoids that problem.

What is so cool is the Heathkit filters were actually fairly good as to skirts and ripple. Yes, an excuse to dust off your Nano VNA and play like you know what you are doing.

Now for those wedded to the TIA designs and would consider it heresy to use anything else, it is a simple 40:1 match from the TIA to the filter. This is easily done with a solenoid winding of 19 Turns tapped at the 3rd turn. Or two separate windings of 3 turns and 19 turns. 3^2 = 9 and 19^2 = 361. Thusly, 361/9 = 40.

I also tweaked and peaked the display, so it has a bit more color and the readout numbers are larger. It took only about 5 minutes to change the code from the Yaesu to the Heathkit.

You should have bought that filter ...

Them that know can make it go.

73's
Pete N6QW