My fellow Vienna Wireless Society Member Ron WA6YOU is a real expert collector of QSL cards. He was rightly critical of a very crude homebrew QSL that I made a while ago. So when I got back from the Dominican Republic I decided I had to clean up my act. Some Googling, some printer ink, and some cardstock later, I came up with the above. I kind of like it -- it looks better (believe me!) than my earlier effort, but it retains an element of homebrew (I kind of made it myself).
The picture is of Juanillo Beach, the beach we use when in Cap Cana. This one was filled out for Mike KA4CDN, who was the only Vienna Wireless Society member I contacted from HI7.
I made about 38 contacts from HI7. If anyone out there worked me and wants a card, my printer is at the ready!
This is the Direct Conversion receiver that Dean and I have built. We plan to have students at a local high school build it, starting in early February. We would like to have some others build it, to make sure that the design is re-producible without problems.
Please build this receiver! But we ask that you build it exactly as per the schematic above and below. Innovation can come later -- for now we just want to make sure this thing works, that there are no errors in the schematic, and that it can be built by the students with minimum woe. Thanks in advance!
Dean or others with 3D printers may be able to supply the plastic form for the PTO inductor.
We know of one other builder, but he is having some trouble. We would like to confirm that this design is sound.
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Above is the screenshot of the LTSpice model of the 40 meter Direct Conversion receiver that Dean KK4DAS and I have been working on. I will post a larger scale version of the picture below. Click on the images for a better view. Comments welcome. Please let us know if you find any errors or mistakes. Realize that we wanted to keep this all simple, discrete, and entirely analog.
Here (I hope!) is the net list for the LTSpice model:
First, one of the surprising things about the LTSpice model: IT IS ALIVE! I never had a VFO or PTO actually turn on for me in LTSpice. This one did! So I just connected the PTO to the Mixer and the receiver works in LTSpice. I just put an RF signal at the receiver input, and you can see the resulting AF across the 8 ohm resistor at the audio amp output. I was even able to calculate the precise frequency of the PTO: 7078 kHz. As in the real world, in an effort to stabilize the frequency, I changed the capacitors to NP0 in LTSpice. Very cool. Dean joked that all we need is a way to get RF in and audio out and we will have made an SDR receiver.
About the receiver:
-- Four stages that will be built by students Manhattan-style on four copper clad boards: Bandpass filter, diode ring mixer, Permeability Tuned Oscillator (PTO), AF Amplifier.
-- The bandpass filter is a simple dual-tuned circuit device based on the info on the QRP Labs site. (Thanks Hans!) We out a 10k pot as an RF gain control between the antenna and the filter.
-- The mixer is a standard diode ring. We included a diplexer at the output using a circuit from the famous W7EL Optimized transceiver. (Thanks Roy!)
-- The Permeability Tuned Oscillator is a very simple and very stable Colpitts design developed by Farhan VU2ESE. We added a simple FET buffer using the circuit in Farhan's Daylight Again rig. (Thanks Farhan!)
-- The AF amp is a very simple three transistor amplifier based loosely on designs from Forrest Mims and from the Herring Aid 5 receiver. Both these designs use just two stages -- we added a third and put an AF gain pot between the first and the second stages. There is an impedance mismatch between the diode ring and the AF amp, but we found that most of the proposed solutions were more trouble than they were worth, so we left it as is.
--Thanks to Wes W7ZOI for his November 1968 QST article on the solid-state DC receiver. Wes's article inspired our efforts.
Dean and I have both built these receivers. They work very well. Dean has even decoded FT-8 with his. We used Radio Marti at 7355 kHz to test for AM breakthrough -- with the diode ring, the diplexer, and the RF gain control we were able to bring the AM breakthrough down to acceptable levels. You can see many videos of my receiver in action over on my YouTube channel: (355) SolderSmoke - YouTube
Here is a larger image of the schematic (click for a full view):
And here is a nicer schematic done by our friend Walter KA4KXX:
I was not going to buy this book. But then, Elisa and I were in a book store and there it was. I decided to take a look. I opened it to a random page: 2N3904. TRGHS. Sold.
It is really interesting.
You can order yours through the Amazon Search block in the right side column of the blog.
Wow! CW finally gets some respect from the Silicon Valley guys! There is actually a Vibroplex bug in this video. And they note how USEFUL this will be for those afflicted with Fat Finger Syndrome (Pete's Disease). FB Google! TNX!
I was feeling kind of bad about the fact that there was one year in which we didn't do something special on the first day of the fourth month. That year was 2012. But looking back, we kind of did! The very next day, we posted this really awesome video from the folks at Google:
I did. Shep had as a sponsor the maker of a flying bird. It was a wind-up ornithopter powered by a rubber band. It was kind of like the one in the picture, but I remember mine as being yellow. My dad got it for me after hearing Shep talk about it on his program. Wow, what a sponsor! Shep must have made DOZENS of dollars from that deal!
It looks like Shep was pitching this thing in 1972, which was my first year in high school.
Walter KA4KXX in Orlando has been a prolific builder of rigs for many years, and has been a great friend of SolderSmoke: Here are some of the SolderSmoke podcasts and blog posts in which Walter's solder melting was mentioned: https://soldersmoke.blogspot.com/search?q=KA4KXX
As we approach the end of our current stay in the Dominican Republic, I could not miss out on the chance to work Walter with his homebrew rigs. Even though the space weather was stormy, and my dipole was droopy, we arranged to meet up on the high end of the 20 meter CW band this morning. See the results in the video above. A solid QSO with Walter. He says it is HB2HB, but truth be told I was on a uBITX that was built more by Farhan than by me. But this was a great contact. Walter started with a 50W rig, then switched to his 3 watt rig with a DC receiver. FB
Here is the e-mail I received from Walter after the QSO:
Dear Bill:
Many thanks for the great video, and when
you return to Virginia look for your mailman
to bring a postcard from me!
Just after your phone call this morning I scanned
the band from 14.025 to 14.300 and heard only one
SSB QSO at 14.347, and even now I only hear
a half dozen SSB signals, so that makes what
we did even more amazing.
The first photo below is my 3.5 watt NE602 direct conversion
rig which is about 2 years old. The transmit signal is created
by putting a 3 MHz VFO signal into an NE602 mixer with an
11 MHz crystal, so the rig can receive CW and SSB from
14.025 to 14.300 and can transmit CW anywhere in that range
with good frequency stability.
The bottom photo is my new full break-in CW 50W rig which
I just put on the air about a week ago and is still in the finalization stage.
I am not yet happy with it, but then again I am more particular
now than I used to be. It is really a trans-receiver with a single
conversion superhet receiver at the bottom of the board using
an NE602 pair with a 3-crystal 4 MHz 900 Hz bandwidth filter,
and a single 10.080 crystal VFO which is tuned with a polyvaricon
for operating between 14.061 and 14.068 MHz.
At the top is the VXO transmit section using a pair of 14.070
crystals pulled down into the operating range. This signal
is buffered and amplified to about 500 mW which is all that
the MRF101 RF Power Amplifier needs. Visible behind the
board is an AC-powered 24 VDC switching power supply which
is connected in series with the 12 VDC battery to
power the final stage with about 36 VDC. The main 12 VDC is
provided by a bench power supply which is not in the photo.
In both rigs the morse code key is the microswitch
at the lower right corner. (Way more handy and elegant
than your key, I might say?)
This morning each of these rigs was connected to its own
end fed half wave antenna, one in my backyard
and the other on the side of my house. My antenna analyzer
shows them to be essentially equal, but my 50W rig does
not like one of them at all.
Making our international homebrew-to-homebrew contact
today was a terrific ham radio experience, so thanks for all
We'll be heading back to the States soon and I was feeling guilty about
not having worked anyone from my home club (the Vienna Wireless Society).
On Wednesday night I Zoomed in to the club's Maker group -- this made me want
to make at least one contact with the club. Plus Walter KA4KXX in Orlando has
been trying to set up a sked on 20... This morning I saw that the SFI was up above 200.
I lengthened the dipole so it would resonate on 20 meters (on this trip it started on 20, went to 17, back to 20, down to 10 and now, back to 20!). I worked one station on SSB, then sent a text to the club's DX spotter group, saying that I would be calling CQ on 14.060 MHz. Soon I got a call from club member (and Maker) Mike KA4CDN. We had a nice QSO. Thanks Mike (video of our QSO above). I will try with Walter tomorrow.
You guys really have to listen to this. This is culturally important. In this 1965 radio broadcast, Jean Shepherd describes his teenage struggles with parasitics and other technical problems in his homebrew 160 meter transmitter.
He describes the sound of parasitics on a signal, saying that they sound as if the signal is being attacked by "debauched erotic locusts."
He really nails it in describing the scornful, dismissive tone that many hams use in telling their fellow radio amateur that there are problems with his signal. ( I have recently been on the receiving end of this kind of treatment.)
He observes that no one is more worried, "than a man who has built something and can't get it to work." Indeed.
During a date with a girl from his high school, he is so obviously preoccupied with his transmitter trouble that she tells him that something is wrong with him and that his mother "should take him to a doctor."
And he describes the joy that comes when you figure out the problem and get the thing to work.
The REALLY good stuff begins at about the 25 minute point.
This is simply awesome. At almost every minute of this video, I found myself thinking, "Yea, I'd screw that up." Even the simple stuff, like cutting out the cockpit windows: "Yea, I'd screw that up too."
I was sorry to read this morning of the passing of Homebrew Hero Arnie Coro CO2KK. As we see in one of the obits, Arnie got his start in radio at age 12, with the gift from his father of a chunk of galena, a coil, and some headphones.
Here are some of the SolderSmoke posts about Arnie:
HNY from HI7! In keeping with SolderSmoke tradition, I recorded the above greeting. If you look over my right shoulder, or in the picture below, you can see the apartment building we will be moving into (at least for the winter months) later this year. There will be a small shack on the top level. And yes, a telescope.
This morning I fired up the uBITX on 20 CW and made two Straight Key Night contacts. My key is the straightest of the straight -- a homewbrew thing made from an old hack-saw blade, copper tape, brass screws, scrap wood, and duct tape. Picture below.
"It is not the critic who counts; not the ham who points out how the homebrewer stumbles, or where the builder of rigs could have built them better. The credit belongs to the ham who is actually at the workbench, whose hands are scarred by solder and metal and glue; who strives valiantly; who errs, whose amp oscillates again and again, because there is no effort without error and shortcoming; but who does actually strive to build his rigs; who knows great enthusiasms, the great devotions; who spends himself in a worthy cause; who at the best knows in the end the triumph of homebrew achievement, and who at the worst, if he fails, at least fails while daring greatly, so that his place shall never be with those cold and timid operators who neither know victory nor defeat.”
When "direct conversion" receivers came along in 1968 (the concept existed before, just not the name), it was to build simple receivers. They took over from regens (which of course for the purpose of CW and SSB, were "direct conversion"), and kind of bumped simple superheterodyne receivers out of the magazines.
And they were easy to build, so long as the meaning of the dots were standard, but good performance was elusive. Endless articles about better mixers or more front end selectivity, and still the same basic results The Heathkit HW-7 comes along, and endless mods to that, but still no perfection.
Slowly the move was back to simple superhets, especially with some of the early seventies ICs intended for radio, and then ladder filters came along (actually they came early at least by 1974 from the UK and/or France, but while they got mention in North America early-ish, it took some years before the KVG filters were pushed aside and ladder filters got the spotlight).
And then wham, in the mid-eighties someone caught on. The problem with direct conversion receivers wasn't the mixer (well not once it was a balanced mixer) or lack of front-end selectivity, it was the matter of properly terminating the mixer. The problems that had been there all along were gone. And direct conversion receivers started their climb to being complicated receivers.
I guess it was that receiver by Gary Breed in QST circa 1986 with diode balanced mixers and termination that changed things. A new concept, but not really, I remember an article in QST in 1974 where a DBM diode mixer for VHF was properly terminated, and yet the concept went no further until a decade later.
Actually, I think there is a tiny bit about mixer termination in "Solid State Design for the Radio Amateur" but it never went so far as to say "this is what we need".
Or perhaps that tiny transceiver by Roy Llewellyn in QST was the first, I cant' remember. It certainly used a diode mixer with termination for the receiver.
And that set the stage for Rick Campbell's various receivers, all counting on termination of the mixer.
The ideas can often be there, but not applied because technology doesn't allow it yet, or just not looking that far beyond this month's construction article.
