Mike's 486 kHz receiver
As if being able to get home on Christmas Eve 2021 and then catching the Webb Telescope launch was not enough, Santa had another gift for us: Michael Rainey, AA1TJ, the Homebrew Hero of the Hobbit Hole, was back at it, melting solder. Mike threw together a regen receiver that allowed him to receive a transmission commemorating Reginald Fessenden's historic first transmission of phone signals. I was really pleased to once again be able to read about an AA1TJ radio adventure. Thanks Mike! Here is what Mike heard: http://soldersmoke.com/AA1TJ 920km.mp3
Mike wrote:
True to form, I began scratch-assembling my receiver yesterday afternoon just as Brian went on the air. Then again, a two-transistor regenerative radio for 486kHz isn't exactly rocket science. In any case, I was up and listening inside of a half hour.
What did I hear? Static. Just static. As a sanity test I quickly tuned down to 371KHz to find my favorite non-directional beacon, "GW," beaming in loud and clear from Kuujjuarakip.
Kuujjuarakip?
Kuujjuarakip is a tiny settlement of mostly Inuit and Cree inhabitants located up on Hudson Bay. The villages are primarily accessible by air and water so a robust radio beacon is an obvious necessity.
Satisfied that my receiver was working properly, I re-tuned to 486kHz. Back to static. On the bright side, at least there were no commercials. I continued listening intently until Vic called me to dinner. After the dishes were done I slipped back down to my underground radio shack for one last try.
I heard it right away. Beneath the static I heard a weak, out-of-tune, solo violin playing, "Oh, Holy Night." The signal strength varied wildly with ionospheric propagation. When the signal finally climbed high enough above the noise I ripped out the bipolar transistor audio amplifier stage, connecting my headphones directly to the junction field effect transistor detector output terminals. Of course the audio was far weaker now, yet I could easily follow the tune until it eventually faded away. Not bad for an estimated 15 watt ERP AM signal from a distance of 920km. And on 486kHz, no less, just a hop-skip-and a jump from the old 500kHz Maritime CW band; where countless ship radio operators went to send their last SOS.
Returning to the house, I emailed my reception report and included a short recording that I had made of it. Brian replied just after midnight; apparently, equally as stoked
"Yours’ is the best DX ever given your regen RX! Way to go! I just love it."
He went on to tell me that he was born and raised in Vermont, but he'd been working as a radio scientist down in Virginia since 1990. Told me his heart was still here in the Green Mountains and he was touched to learn his meager signal had found its way back there on Christmas Eve. All in all, a night to remember.
If you're still with me I hope you'll listen to the short NPR story in the provided link. It originally aired on the supposed 100th anniversary of this event. It's not just about radio history. It's about belief, memory and the myths we lug around in our heads. I thought it was well done.
Cheers,
Mike
Listen to what Mike heard. He says he "merely connected the mic input line of my computer across the headphone terminals. Some of the noise in the recording, - certainly the higher frequency stuff - is a byproduct of the computer. The headphone audio with the computer switched off was much more pleasant." Here it is: http://soldersmoke.com/AA1TJ 920km.mp3
NPR story (audio and text)
Posts
Thanks Bill,
ReplyDeleteBrain/WA1ZMS asked me to listen again for his 486kHz transmission beginning on New Year's Eve. Only this time he wondered if I might substitute an antique triode for the JFET in my regenerative detector. Unfortunately, I don't own any really old glass but I may have a quasi-fungible replacement.
The DM160/6977 was introduced by Philips/Amperex in 1957 ("Electronic Design Magazine" 7/1/1957) as a logic status indicator. It's essential a subminiature triode, sporting a P-15, phosphor-coated anode. A writer for the now defunct magazine, "Vacuum Tube Valley" observed (V-18)
"Scarcer is the DM160, also called 6977. This is my candidate for the world’s smallest glass electronic tube--barely 3/4" long and as wide as two match sticks. Philips, and their US division Amperex, tried to market the 6977 in
the late 1960s as a logic monitor for digital computers. Unfortunately, some radio collectors have found that it can be substituted for O1As in radios, by soldering it into a 4-pin UX base. It makes a very nice low-mu triode."
Audiophile vs. Radio Amateur tribalism aside, I have indeed employed the 6977 as a regenerative detector in the past, from 60kHz up to HF. Given the filament incandescence itself is barely visible, the blue-green anode glow is a welcome feature. Stronger signals even produce a 70's "disco-effect," only in miniature.
I had planned to be in the shack for Straight Key Night (SWL mode) anyway on New Year's Eve, so the Fessenden commemoration will be an added pleasure.
73,
Mike, AA1TJ