In this thread, we hack Heathkit's -104 lineup

[N8YX]

Revisiting the thread:

I started taking a look at signal paths through an FT-901DM, with a thought to converting the HR-1680/HW-104 IF scheme to the 8.9875MHz of the `901 series...allowing the use of a bunch of its readily obtainable filters. To do so means a lot of unnecessary circuit duplication. I think the better way to go is to stick with Heathkit's 3.395MHz IF then modify the Yaesu IF Shift/Rejection Tuning scheme to use a common Kenwood SSB filter (8.83 MHz) in the passband tuning circuit. The first and second roofing filters will be made from elements of the -1680 SSB filter - each configured in a half lattice arrangement.

This requires a redesign of all three boards in the receiver but I knew that much going in. Benefits of leaving the IF alone means I'll truly be able to track the transceiver via the receiver and direct VFO/HFO injection - no need for an RX Offset Adjust as used on the FL/FR-101.

If I can only find all the needed parts...

[N8YX]

Conundrums.

Heathkit only made two bandwidths of filters for these rigs: 2.1KHz (SSB) and 400Hz (CW). I would like to have an additional narrow filter option for each mode. Inrad used to offer a 1.8KHz and a 250Hz filter for the 104 line (3395KHz IF) but they're showing Out of Stock on the narrower of the pair.

What shall we do? Beg them to make 6 of each at $140 a pop, or convert the rig's IF frequency to something that is much more widely supported? 9 MHz (early Yaesu and Ten Tec), 8.9875 MHz (later Yaesu), 8.83 MHz (Kenwood), 5.645 MHz (Drake), ?

I can get a bunch of BFO crystals for everything but the Drake IF and since I'm going to use a DDS to generate the HFO premix signals I can make said IF anything I want.

Thoughts, especially from a birdie perspective?

[WØTKX]

9 Mhz kind of sucks for 17 meters, usually.

[N8YX]

9 Mhz kind of sucks for 17 meters, usually.

So 8.83MHz, then?

Single conversion like a TS820 or shall I also figure out how to shoehorn a 455KHz IF in there for the three receivers I'm building out of that pile?

[WØTKX]

I think the math works better, yea. I have an Omni D Series C that works on 17, but it's a bit flaky.

Works great on the other bands.

[N8YX]

That or 8.9875 - the FT90x/980 IF.

I have a bunch of filters for those rigs...and BFO crystals...NB/PBT/CAR boards which could be stripped of parts...

[WØTKX]

Doesn't take much of a frequency nudge from 9Mhz to stay out of trouble on 18 Mhz.

[N8YX]

8.9875 it is.

Next, an AD8951 controlled by a BASIC Stamp for HFO (band) and Mode selection. Hmmm...how to enunciate the ranges and modes in cool Heathkit Red fashion... :chin:

[WØTKX]

Nixie tubes, in Signal One fashion. ;)

[N8YX]

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