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

[N8YX]

Late-night eBay surfing netted me an SB-104 with noise blanker and CW filter installed, but no PA assembly or heat sink included.

Perfect for the "HR-104" portion of the project, and I got the thing for about the price of the filter and noise blanker alone.

This is going to be a proof-of-concept experiment where a near-9MHz IF is used with a digital readout rig: The counter unit is preloaded to 6.604MHz when a 3.395MHz (OEM) IF is employed. Obviously, I'll have to change that to get the readout working correctly with a different IF scheme.

Better to find a cheap test bed than a pricey one.

[kb2vxa]

That's also the difference between a prostitute and a call girl, no comment on the frequency counter.

[N8YX]

A couple days back I got a complete but non-functional SB-104A (including CW filter and noise blanker) for a decent price. One more of those to go along with a couple SB-604s, an SB-230 and perhaps one more junker 104 for cabinet and push buttons then I can begin to build and modify this station.

[N8YX]

Now comes decision time for the IF/HFO/BFO portions of this here project. I want to use an IF frequency which is fairly common (think parts scavenging and filter availability) and which was used in enough HF sets that the odds are good I can snag a bunch of HFO premix crystals (think Yaesu FT90x, 101ZD) for use on the new HFO boards I'll design.

The easiest way to approach this task - bar none - is by the use of a BASIC Stamp and a pair of DDS units to generate all required frequencies. I've heard some not-so-favorable comments regarding the average AD9850's spectral purity when run above 30 MHz...and this rework will require a max HFO frequency of around 43MHz.

Best thing to do here is to get my Stamp debugger up and running then write some test code and put the DDS on my spectrum analyzer to see what's up. I may be able to filter out any spurs that aren't too close in.

The SB104 uses a preloadable counter arrangement to drive its readout. Changing the IF will require changing the preload values in order to properly display the tuned frequency, as it's counting the premix signals. Looks like it's time to order parts needed to build up one of these boards which is DIP switch programmable, then after completion hook a generator running at a calculated frequency to its Input port and see if the higher IF premix frequency can be counted properly.

ETA: This exercise would be a whole lot easier if I could lay my mitts on a bunch of CW filters with 3395.7KHz center frequencies, and in 600/500/400 and 250Hz bandwidths. Then the entire IF chain wouldn't require redesign. :roll:

[WØTKX]

http://www.google.com/patents/US3938048

Searching that filter frequency of interest, looky what I found. :chin:

[N8YX]

Interesting read, Dave. The Kenwood TS-520/R-599 rigs also used a 3395KHz IF but their CW filter's center frequency is (surprise!) different from that of the SB-104's filter. I'm beginning to consider a change to the earlier generation CW offset of 3395.4 if I keep the IF "stock". Lots more of those filters floating around and it would be relatively easy to modify a 400Hz unit to a narrower bandwidth.

[N8YX]

I got hold of another 104-specific CW filter and a 3395.4KHz crystal today, but the thought of narrower bandwidths - especially on CW - keeps dancing through my head. Next, what if we take that "Tune" position on the Mode switch bank and make it something useful...say, true FSK?

When I construct an "HR-104", the entire right side switch bank will be dedicated to mode selection and power. The left side will have a button to activate the noise blanker and the rest will be used for filter selection. AM, SSB 2.1KHz, SSB 1.8KHz, CW 400 Hz...and possibly something using this:

http://www.google.com/patents/US5051711

If I have enough real estate for extra knobs I'll add a variable bandwidth tuning control to the rig and incorporate some method of electrically shifting the vari-filter's center frequency based on mode. This would also be neat to incorporate in the pending HR-1680 projects and maybe in the SB/HW-104s themselves. A BFO Board redesign will be required in all cases to accommodate the extra filters and offset control signals.

[K7SGJ]

I got hold of another 104-specific CW filter and a 3395.4KHz crystal today, but the thought of narrower bandwidths - especially on CW - keeps dancing through my head. Next, what if we take that "Tune" position on the Mode switch bank and make it something useful...say, true FSK?

When I construct an "HR-104", the entire right side switch bank will be dedicated to mode selection and power. The left side will have a button to activate the noise blanker and the rest will be used for filter selection. AM, SSB 2.1KHz, SSB 1.8KHz, CW 400 Hz...and possibly something using this:

http://www.google.com/patents/US5051711

If I have enough real estate for extra knobs I'll add a variable bandwidth tuning control to the rig and incorporate some method of electrically shifting the vari-filter's center frequency based on mode. This would also be neat to incorporate in the pending HR-1680 projects and maybe in the SB/HW-104s themselves. A BFO Board redesign will be required in all cases to accommodate the extra filters and offset control signals.

The B+, don't forget the B+, and ground it.

This is a great project, Fred. I enjoy following it. I wish I had the time (or more accurately the $$) available to do stuff like this. I guess I should be satisfied with all the building/modifying I did back in the day, while walking uphill in the snow, both ways, rebuilding the filaments in my 6743 and 6146s.

[N8YX]

This is a great project, Fred. I enjoy following it. I wish I had the time (or more accurately the $$) available to do stuff like this. I guess I should be satisfied with all the building/modifying I did back in the day, while walking uphill in the snow, both ways, rebuilding the filaments in my 6743 and 6146s.

The funny thing, Eddie, is that I'm attempting this on the cheap. On Page 1 we started with a $20 SB-614 (with all knobs and circuitry intact, but with a front panel which has most assuredly seen better days). That scope and another like it were destined for the conversion bin, to be made into a pair of "SC-7" units - which is the one piece of equipment Drake never offered for their otherwise comprehensive lineup.

Their soon-to-be-superfluous concentric knobs got me wondering about the type of functionality I could add to an SB/HW-104 or an HR-1680. Then I began to take a look at what Benton Harbor DIDN'T offer in the way of 104-line station accessories. A few came to mind, though at least two of these actually did make it to prototype stage before being killed off:

A synthesized remote VFO with digital frequency readout
A matching antenna tuner (the "SB-670")
A companion receiver, a la the R-820 or R7
A panadapter display, like the SB-620
Whatever else one can dream up with spare full or half-sized cases and matching control knobs, trim, etc

I'm not going to hack "collector quality" accessories here with the exception of one of the SB-614s. It'll become an SB-624. The rest of the stuff? Give me your poor, your downtrodden, your destined-for-the-scrap-heap green boxes and I'll build some useful things from them.

Why? Maybe the odd magazine article of the very late 70s/early 80s which featured the Heathkit series made a lasting impression on a newly minted ham...and said ham was determined to have such a lineup. Some day.

Truth of the matter is, my Omni VI/Opt 3 will slap a "stock" SB-104 into RF oblivion. But I think I can fix that, in part or in whole. ;)

[N8YX]

Some updates - and a reminder that I'm going to have to brush up on my German. First, a few neat links I've found on the subject. I really need to get ahold of the DK4 and do some collaborating:

http://dk4sx.darc.de/sb-104.htm
http://dk4sx.darc.de/sb-104a.htm

I bought four of Mike, WB8VGE's (Heathkit Shop) LED display conversion kits last year. But then I ran across this:

http://www.qsl.net/k/k8lbh//K8LBH/Display.html

The 10MHz digit is controlled by the bandswitch - it isn't counted directly. The 1MHz digit is preloaded to a "6" via hardwired logic in the counter circuit but this can also be changed to other values. And....there's enough space in the readout window for an extra digit.

IMG_0438.jpg

Using DIP resistor packs instead of discretes saves space and allows me to add one more digit along with control logic. Thus, the 10M A/B band positions (28.0 and 28.5, respectively) become xxx.000.0 or xxx.500.0 - with the hundreds and tens digits controlled by external logic sources. Perfect for the addition of a set of transverters for weak-signal SSB/CW work, and with direct frequency readout to boot.

One or two of the discarded SB-6xx accessory cases will be used to house the transverters and control logic. A call to Down East Microwave ought to net me some data about repackaging their wares and the physical dimensions thereof.

Last week I won a pair of HW-104 junkers on eBay; both come with filters and noise blankers. A working 104A/SB-604/HP-1144A is inbound. First order of business is to replace its questionably-designed +5/+11V regulator circuitry with the LM-350K solution that Pat, 'mhz described a few years back. Then, it's on to modifying the first of the digital rigs. The analog stuff - HW/HR/HX gear - will be done later.