A cosmically interesting troubleshoot. But I'm not sure about their explanation. Why would the intermod disappear when they moved the Parkes Radio Telescope off of Proxima Centauri?
Tuesday, October 26, 2021
Monday, October 25, 2021
Putting a Ceramic Filter in the "Mate for the Mighty Midget" Receiver
It is really simple. I had one of the +/- 3kHz (6 kHz wide) 455HT filters on hand. The spec sheets call for 2000 ohms at both ends, but looking at the schematic it appeared that I already had high impedance on both sides of the filter. I put a .001 uF cap on the input side to keep the DC voltage off the filter (see above and below). This capacitor allows us to avoid the dreaded problem of electro-migration that is so nicely described by SV8YM here:
Tasos also provides a good description of the innards of those little black boxes that contain ceramic filters.
Once you get the filter in your receiver, you have to carefully place the BFO signal in relation to the filter passband. I have trouble properly sweeping 455 kHz filters -- my HP8640B will not go that low. Nor will my Antuino (I need to modify the code -- someone help me please). I know the NanoVNA will do the job, but I just couldn't seem to get it to work. So I went "old-school" and manually swept the filter using my FeelTech sig gen and my Rigol scope. This gave me a rough idea of where the passband was. I put the BFO on the low end of the filter passband, at 451 kHz.
With this filter the MMM RX has become a real asset. The 6 kHz bandwidth allows for nice reception of both SSB signals and AM sigs. I may try to use one of the +/- 2 kHz filters (4 KHz wide), but so far I have not been able to find a source for this part.
Sunday, October 24, 2021
WA9WFA's Mate for the Mighty Midget 1966 QST Receiver
Scott WA9WFA and I have been exchanging e-mails about his Mate for the Mighty Midget receiver project. This morning I finally took a look at Scott's we page on this effort. There was a lot there that resonated. For example:
"I remember the moment very clearly. June 1966 I was sitting in a lawn chair reading a stack of QST's that I had brought along to the summer cabin. The February 1966 issue the Beginner and Novice section introduced the "Mighty Midget Transmitter", a 10 watt crystal controlled transmitter. The April 1966 issue Beginner and Novice section introduced the "Mate for the Mighty Midget" which was a three tube super-heterodyne Novice type receiver. Over the course of that summer I read and re-read those articles a jillion times. Being 13 years old, I didn't have the electrical or mechanical skills to pull off such a project so I could only dream about it. In 1970 I bought a handful of the parts. In 1976 I bought more parts. In 2021 I decided to build it while I still had the ability to do it. This project is only my second homebrew radio project so I am still learning things every second of the way...
While I am not expecting to much in performance, the 13 year old in me is ever hopeful that this 1966 Novice receiver will be the most wonderful radio ever made. 73, Scott WA9WFA"
Scott's MMM RX page:
Scott and I are now both updating the MMM RX by substituting 455 kHz ceramic filters for Lew McCoy's FT-241 crystal filter. I have my filter wired in now, and it is working well. Scott plans on soldering his in today. I will post on this mod soon.
On his QRZ.com page, Scott notes the need to fight the temptation to further soup-up this simple receiver: "I did have to resist the temptation to add another audio stage, a mechanical filter, AGC, 2nd IF amplifer stage, etc..."
Exactly right Scott. Resist the temptation. Simplicity is a virtue. I do use an outboard, powered computer speaker, but I justify this by telling myself that I just don't want to use headphones. But I could use headphones, so this is OK. OK?
Scott's QRZ.com page:
I must add that I think the yearning of Scott's inner 13 year-old can be fulfilled by the MMM RX. I think it is pretty wonderful. It is -- in my view -- not as good as a Drake 2-B, but it is FAR better than an S-38E, and it is better than a Lafayette HA-600A (wjm).
Friday, October 22, 2021
Tribal Knowledge: Pete N6QW on "How to Make Things Work"
BUILD IT LIKE THIS
Yesterday Pete Juliano published a blog post that contains an enormous amount of tribal knowledge and good advice for homebrewers. As I read Pete's post, I thought back on my own failed teenage efforts at homebrewing -- the Herring Aid Five fiasco came to mind. I also thought of Farhan's comments about his similar frustrations with early homebrewing efforts (though I find it hard to believe that Farhan EVER had trouble making something work).
Above we see a large N6QW prototype breadboard. Note how it is easy to see where the various stages start and stop. This is key to understanding and troubleshooting a complex rig. If you want to see the antithesis of this approach, here it is:
DO NOT BUILD IT LIKE THIS
This was supposed to be an 80 meter DSB transceiver. The builder (who will remain anonymous) obviously didn't get it to work. I think he should try again, using Pete's methodical approach.
Check out Pete's great advice here:
Thanks Pete!
Wednesday, October 20, 2021
Super-Regeneration is Super-Strange
Farhan VU2ESE is largely responsible for this. He has recently been talking about VHF. (More about this in due course.). This started me thinking about my failed effort in London to get on 2 meter AM. My plan was to use the transmit portion of this HW-30 (above) with a 2-to-10 downconverter and my trusty Drake 2-B for receive.
Tony G4WIF also bears some responsibility: When I expressed interest in Farhan's VHF work, Tony sent me two articles from SPRAT. Both of them were about super-regenerative receivers.
Farhan's comments caused me to pull the HW-30 out of storage. I started poking around the transmitter. But then I noticed something: On receive, the AF amplifier was obviously working. Then, when I tuned through the 2 meter band, the rest of the receiver seemed to be working too. I fired up the HP-8640B sig gen on 2 meters and turned on the AM modulation. Indeed, the old receiver was inhaling!
This launched me into an effort to understand how super-regenerative receivers work. There are a lot of really weak explanations out there. You get the distinct impression that the person explaining the circuit does not understand it himself. This makes explaining it very difficult. I am not the only one to notice this phenomenon: Mike WU2D commented on this in one of his excellent super-regen videos. This one:
Mike very kindly said the operation of this circuit seems like "magic." I was thinking more in terms of Voodoo.
Howard Armstrong discovered super-regeneration years after he invented plain old regeneration. The new discovery came around 1921.
It looks like VHF guru Frank Jones had very early misgivings about super-regeneration. In his 1934 classic 5 Meter Radio Telephony, Jones seems unenthusiastic about the circuit and about our ability to understand it: "To explain, simply, exactly how this form of detection takes place is not a simple matter, but some of its characteristics are easy to visualize." In this book, Jones goes on to predict that super-regens will be superseded (!) by superhets. Indeed, in his 1961 book VHF for the Radio Amateur there are no super-regen circuits; all the receive systems are down-converters to HF receivers.
Still, with that HW-30 hissing away right next to me, I feel I need to understand how the super-regen works. I'm not there yet, but I'm trying. Here are some good resources:
A good article from Wireless World 1946:
A student's write up of his effort to understand:
But the best so far (for me) is from Frederick Terman (one of the founders of Silicon Valley) in his 1943 classic Radio Engineer's Handbook. Click on the images for a clearer view.
I will definitely try to get the HW-30's 5 watt AM transmitter going. I am not so sure I'll do anything with the receiver. I think this is a matter of picking your battles and "finding joy." I didn't find joy in FT-8, so I stopped working with it. Same with my HA-600A, DX-40 Novice rig. Same with CW in general. And the same with SDR. I suspect that super-regen receivers may also fall into this category. I mean, let's face it, if you are not fond of ordinary regens, is there any real chance that you will like SUPER-regens? Even Frank Jones seems to have disliked them. And there is a reason Howard Armstrong moved on to superhets -- they are better! But still, that receiver is hissing away at me... Stay tuned.
Tuesday, October 19, 2021
Homebrew Tiny Space Telescopes from the Netherlands
It is good every once in a while to step back from our electronic work benches and take a look at what other kinds of builders are making. Hack-A-Day led me to this wonderful video from Holland. There is great background information on telescopes, but the really great part is the interview with the Dutch fellow who is actually making -- in his home workshop -- these tiny telescopes. Icing on the cake: One of them will be used in a student Cube-Sat project in Oregon.
Be sure to stay to the end for an intriguing presentation by Dr. Liam Fullersheit.
Monday, October 18, 2021
No Longer On the "Shame Shelf" -- Pete Fixes His KWM-1
I think a good troubleshoot is almost as satisfying as a successful homebrew. And we can sense that high level of satisfaction in Pete N6QW's description of his repair of a Collins KWM-1:
I liked Pete's troubleshoot/repair story, but -- as is often the case -- I struck by his turn of a phrase. I think Pete has added something important to the SolderSmoke lexicon:
THE SHAME SHELF
Most of us have a shelf like this. I have an HW-101 on mine. Pete shows us that there is hope -- there is path off of the shame shelf. You just have to know stuff.... Or have IBEW friends like Pete who can advise you.
Sunday, October 17, 2021
2 Meter Homebrew: The Fredbox (Video)
I predict a rebirth of interest in 2 meter homebrew. This will probably hit around Christmas time. The impetus will come out of Hyderabad, India. At this point, I can say no more.
I was thinking about all of this today. I remembered "The Fredbox." G3XBM's report on this fantastic rig was carried on this blog before it was even a blog. And the Fredbox goes back much further in time -- back to the mid-1970s. It must have been great fun to have QSOs with this rig in Cambridge England back in the day. G3XBM actually crossed the English channel with this 10 mW rig. FB.
When I was in London (2003-2007), G3XBM's post on the Fredbox got me interested in 2 Meter AM. I had a down-converter that let me listen, and I went as far as modifying a Benton Harbor Lunchbox for the proper AM transmit frequency. I don't think I made any contacts, but I still have the bits and bobs of this rig, so if anyone in the Northern Virginia area wants to get on, please let me know -- I will blow the dust off this project and will build a 2 meter antenna.
Here are more details from G3XBM on The Fredbox:
Hans G0UPL got into the Fredbox in 2009 and 2016:
Wednesday, October 13, 2021
SolderSmoke Podcast #233: PIMP, Boatanchors, Novices, MMM, Heathkits, DC Receivers, Mailbag
SolderSmoke Podcast #233 is available.
http://soldersmoke.com/soldersmoke233.mp3
Travelogue: Cape Cod. SST. Marconi Site.
The WFSRA: The World Friendship Society of Radio Amateurs.
Pete's Bench:
The Pimp.
The NCX rig.
The Collins.
The many DC receivers built worldwide.
The parts shortages are real! Several key radios on hold. Si5351 sub.
Talk to G-QRP convention
Bill's Bench:
FT-8. Not for me. I tried it.
Novice Station Rebuild.
Globe V-10 VFO Deluxe.
Selenium rectifier removal CONTROVERSY?
Not crazy about my Novice station. Not crazy about CW.
Mate for the Mighty Midget. Again.
Mike W6MAB -- Detector problems LTSPICE Check
One more mod for MMM RX. Ceramic filter at 455.
Dropped screw inside tubular cap on Millen 61455 transformer.
Talk to the Vienna Wireless Society
Thinking of a Moxon or a Hex beam.
BOOK REVIEW Chuck Penson WA7ZZE New Heathkit Book. http://wa7zze.com
Mailbag
-- New SPRAT is out! Hooray!
-- Todd K7TFC sent me copy of Shopcraft as Soulcraft. FB.
-- Dean KK4DAS building an EI9GQ 16 W amp. FB.
-- Jack NG2E Getting close on Pete's DC receiver.
-- JF1OZL's website is BACK!
-- Tony K3DY sent link to cool books.
-- Sheldon VK2XZS thinking of building a phasing receiver.
-- Peter VK2EMU has joined the WFSRA. FB!
-- Ned KH7JJ from Honolulu spotted the Sideband Myth in the AWA video.
-- Chris M0LGX looking at the ET-2, asks about the variometer.
-- Pete Eaton Nov 64 anti HB rant in november 1964 QST. Wow.
-- Josh Lambert Hurley spreading FMLA stickers in the UK. FB
-- Stephen VE6STA getting ready to melt solder.
-- Got a great picture of Rogier PA1ZZ back on Bonaire.
-- Farhan reading the manual of Hans's new digital rig.
-- Paul G0OER wonders if FMLA getting ready to move on 5 meters.
Saturday, October 9, 2021
Recent Homebrew Projects from Jan PA3GSV (of "Mate for the Mighty Midget" Fame)
Recent talk of the Mate for the Mighty Midget receiver and Pete's PIMP SSB transmitter brought me back in contact with the work of Jan, PA3GSV. I took a look at his QRZ.com page and found that he has some projects that rival even his seemingly unbeatable MMM RX project.
Check it out for some real homebrew eye candy:
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