The (slightly grainy) taste of success

(As I mentioned earlier, this and previous posts are re-worked versions of posts originally made late last year.)

Straight after I finished building, testing, & installing the new PSU, I hooked the laptop up to the FRG-7700 and decoded the following images:

Oddly, I don't recall ever having received & decoded HF fax on the FRG before. As far as I can remember the last time I toyed with fax/RTTY/etc was back in the mid 80's, initially using a Tom Moffat-designed FSK decoder (and later a home-brewed narrowband FSK detector with PLL-based drift compensation) plugged into an old ex-army R210 receiver & decoded on a Microbee (or, for RTTY, sometimes plugged straight through a current loop interface to a Siemens T100). I remember receiving wefax maps from VMC & VMW, Japanese language news fax from Kyodo News Agency, and North Korea's RTTY news (which was always a bit sporadic and I believe shut down for good a few years ago), but to tell the truth you can only receive so much unreadable news & Dear Leader propaganda before it gets boring. When I later bought the FRG it was about the time people were starting to develop soundcard-based software decoders on the PC - but seeing & understanding the troubles with the early software & knowing that the result wasn't that interesting, I didn't bother with it myself.

Anyway, the weather faxes above are from VMC, the Australian BOM's marine weather station for the east coast, located about 750km away in Charleville. Frequency was 5100kHz, and the antenna used was a modified version of Charles Wenzell's amplified loop. The loop is sitting on the window sill just above the radio, in a concrete slab and brick flat full of CFL / computer / TV / WiFi noise, in a block of flats full of similar noise sources, in the middle of the radio-noisy suburbs. As evident from the images - particularly the first - S/N was highly variable but averaged around 15~25dB.

All in all, given the limitations, I don't think they're too bad. It was certainly very easy to copy & decode with a decent radio & all-software decoder; much easier than the old R210 and Microbee setup! What's not evident is that the radio really needs a proper alignment - tuning is non-linear at the bottom, and about 50kHz short at the top, of every band. Both of those issues are well-documented symptoms of age in the FRG-7700 and easily fixed by following the alignment proceedure in the service manual. Also it has a fair bit of drift (which the software handled just fine); even after warming up for an hour or so, the FSK tones shifted by about 200Hz over 30 mins. That's a bit more of a concern, and probably due to the many electro & several polyester capacitors throughout the set. Hopefully it'll settle down as the set gets used and soaks a bit more, or at least is simply BFO drift (I don't yet have a stable enough reference to tell). I don't really want to have to replace all those caps...