Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
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This is just so cool. Scott KQ4AOP has successfully homebrewed a ham radio receiver. He used the circuit Dean and I developed (with a lot of input from Farhan and others) for the High School receiver project. But Scott has had more success than any of our students. And I think he has had -- in a certain sense -- more success than any of us. After all, how many of us can say -- as Scott can -- that he used a homebrew receiver that he made to listen -- for the very first time -- to amateur radio signals? Scott writes: "Those first sounds were my first time ever hearing any Amateur Radio first hand!"
In the email below, you can see Scott's deep commitment to homebrew: "I want to build my own gear for 40m. I want to learn morse code. I want my first contact to be on my own gear." Wow Scott, the building of the receiver is the hard part, and you have already done that. I think you are well on your way.
In the video above you can watch Scott tune the entire 40 meter band and a bit beyond. You hear CW at the low end. Then FT-8. Then SSB. Up just above the top of the band I think you can hear our old nemesis Radio Marti. And this powerful broadcaster is NOT breaking through on the rest of the band. FB Scott. Congratulations.
----------------------------------------------
Bill,
Thank you for the quick response, direction, and pointers. I won't give up, and I am not in a rush.
I have wanted my amateur radio license since the early-to-mid-80s. I got my Technician and General in May of 2022 and completed my Extra in May 2023. I always wanted to understand how to design circuits, and I wanted to build them. I share that background to say that I have this impractical goal that I am stubborn enough to stick to (all due respect to you and Pete's advice on the topic of getting on the air). I want to build my own gear for 40m. I want to learn morse code. I want my first contact to be on my own gear. So, your blog and podcast really resonates with me.
I am only teaching myself at this point. It was the perfect project for my goals. I thought that if all these high school kids in Virginia, Canada, and Germany can do it, it was the sweet spot I was looking for.
The only transceiver I have was recently gifted to me. It is a Sommerkamp TS-788DX CB radio that allegedly works on 10m in addition to CB. I haven't connected it up because I wanted to stay focused on the HSR. I have a mentor who has gear that I can use to test the oscillator. I am not involved with the nearby ham club, but I know they would help if needed.
Bill and Dean - Thank you for sharing and documenting this receiver. I greatly appreciate you publishing the circuit, class notes, and build videos. That got me 75% to completion. I feel blessed that both of you chipped in and encouraged me through the troubleshooting to finally getting the receiver to start “breathing RF”. Those first sounds were my first time ever hearing any Amateur Radio first hand!
Ianis S51DX in Slovenia was the first call sign heard. Some peaking and tweaking remains to be done, but the receiver is working.
Congratulations to Scott KQ4AOP who got his Direct Conversion receiver working yesterday,
And congratulations to Armand WA1UQO who got his regen receiver working. I think all of us are following Farhan's advice and are taking some time to just listen to the receivers we have built ourselves.
It was great to get a comment from Paul VK3HN -- this led to a re-establishment of contact. Apparently Google knows who I have been e-mailing, so this great video appeared on my YouTube screen. Thanks Google!
-- Great to hear Paul's shout out to Pete Juliano N6QW, and Pete's concept of noodling.
-- Paul's emphasis on testing each stage independently is really important.
-- Wow, ferric chloride! It is great to see someone doing this (instead of just sending Gerber files to China).
-- Books. This reminds me that I have to get Drew Diamond's books.
-- Paul's comment on the usefulness of a general coverage receiver. Right on target Paul.
-- On the test gear, we can now add the TinySA Ultra. And you don't have to win the Lotto!
-- Finally, Paul is absolutely right on the need to constantly update and publish changes to schematics. I am guilty of not doing this. (I hang my head in shame.) This became a problem in our simple High-School receiver project -- I would make changes to circuits and fail to communicate these changes to Dean KK4DAS. Paul's method would have solved this problem.
I posted this video back in 2015, but it is so good that it is worth watching again. This is especially true now that I have the second edition of The Art of Electronics in hand, and in light of the fact that we recently had our own experiences trying to teach analog electronics to students.
Paul Horowitz is a real inspiration. He is still W1HFA, and QRZ.com has him living in Cambridge, Mass. So many great tech collaborations came out of that fair city: Car Talk and KLH, just to name two. And of course, Horowitz and Hill.
It was wonderful to hear Paul describe the origins and the evolution of The Art of Electronics. His description of the Electronics 123 course at Harvard was really inspiring. They were wise to limit the participation to 10 students (it seems that they eventually went to 2 sections of 10 students each). I think Dean KK4DAS and I came to the conclusion that it is better to have a small group of truly interested students than to have a large group of marginally interested students. (At the high school, we started with 70. That was far too many.) And it may be better to teach this stuff at the college level (high schoolers may be a bit too young). I want to get the third edition, and the book Learning the Art of Electronics.
Paul showed pictures of the class (near the end of the video). Classroom seating was seminar-like, with no pompous professor at a podium. The labs showed Rigol digital 'scopes in use.
And wow, the watch that Paul gave to Lady Ada is very cool.
It is all quite inspirational. Three cheers for Horowitz and Hill, and for Lady Ada.
Please my apologies for my late update on our DCR project. We started with the course in the semester break and once the semester started only a handful of students were able to finish their receiver. A long shelf of shame ....
Here is what we've got so far (those were finished at the end of April already). 3 nice DCRs completely sufficient to copy CW indoors without additional antennas starting from late afternoon. Strong stations can be heard all day. I found that coupling some 6m of wire with one or two windings to the ferrite core can boost the signal dramatically but can also increase noise.
The PTO is based on your design (Bill Meara N26QR & Dean KK4DAS) which was sparked by Farhan (VU2ESE) , except that I've swapped the FET for a NPN. The input amplifier and antenna is from the JUMA active ferrite antenna by Matti Hohtola (OH7SV), the band pass filter is from Hans Summers (G0UPL), the mixer and the headphone amplifier is inspired by Pete Juliano (N6QW), you told me that the diplexer (as well as the whole DCR idea) is attributed to Wes Hayward (W7ZOI) and the perfect schematics of Rick Scott (N3FJZ) where crucial to get me started in the first place. I enjoy keeping track of original sources, as I would do in science. This shows that even little achievements are based on the ideas of many other great people - and this is nothing to be ashamed of.
This was a lot of fun! Thank You!
Best and yours sincerely,
Andreas
Wow, the direct conversion re-engineering of education continues, this time at graduate-school level with biologists in Munich! Amazing.
Andreas points out that his group was also plagued by semester-related problems that caused many additions to the German shelf of shame. Let's hope that someday soon these builders will come to their senses and join the ranks of those who have finished their homebrew projects.
Looking at the schematic (below) of Andreas's project, there are a couple of significant differences from ours:
-- Their AF amp used a transformer-less push-pull design. We had considered this but abandoned it thinking that it would be too complicated to explain the workings of this circuit to our students.
-- Most significant, is Andreas's use of a ferrite rod antenna and an RF amplifier. I think a simple 33 foot quarter wave antenna (with a ground or a counterpoise) might work better. But hey, to each his own! The important thing is that a number of these receivers were successfully built. They look beautiful.
Congratulations to Andreas and the successful Munich homebrewers!
This is so cool. We have been getting reports from Daniel VE5DLD up in Regina, Saskatchewan, Canada. Daniel is a teacher and he has been building the receiver with a group of students.
They have been doing very well. They may end up having more success than we have had here.
This morning Daniel fired up his build of the receiver and it was inhaling 40 meter signals. You can hear the CW and the FT8 and you can also hear shortwave broadcast signals just above the 40 meter frequencies. Congratulations to Daniel! He is now one of very few radio amateurs who has homebrewed a receiver. I think his students will soon do the same.
Daniel's students have built several of the boards and appear to be on the brink of full success.
Their PTOs look very nice.
The AF amps were the most challenging of the boards. Theirs look great. Excellent soldering.
We want the receiver project that we carried out at our local high school to serve has a model for others. After all, we got our inspiration from Farhan in Hyderabad. We want to see this kind of homebrewing continue. All of the information on this receiver is on our Hack-A-Day.io page:
We strongly encourage others around the world to find ways to use this project to teach analog electronics. We think the circuit strikes the right balance between simplicity and usefulness -- when they are done, the students will have a useful receiver capable of worldwide reception.
Please let us know if you are building this receiver; we are especially interested in the use of this receiver in student-focused group-build projects.
In our talks at the local high school we have frequently mentioned Ashhar Farhan, his Cubesat experience, and his use of a direct conversion receivers teach electronics to students in Hyderabad, India. So we were really please to have the opportunity to bring Farhan himself in to speak to the students we have been working with.
The acoustics in the room are not great, so you may have to listen carefully, but it is worth it. Farhan dispenses a lot of tribal knowledge and wisdom about satellites and about the value of homebrewing simple radio equipment.
Farhan VU2ESE was in Northern Virginia this week, on his way to the Four Days in May Event at the Dayton Hamvention. We had a great visit with Farhan. We took him out to the Thomas Jefferson High School for Science and Technology where he shared with the students tribal wisdom about building CubeSats and about building simple direct conversion receivers. Farhan's use of direct conversion receivers to teach homebrewing to students in Hyderabad inspired our efforts in Northern Virginia. We often referred to Farhan when speaking to the students here, so it was really great to give them a chance to talk to him directly.
From the high school we went to the local restaurant at which Vienna Wireless has its weekly lunch. Many of the people at this lunch are also members of the VWS makers group. This was a lot of fun.
Don KM4UDX even brought in his somewhat eccentric build of the uBITX transceiver designed by Farhan. Don's rig is labeled "The uBITX of Life." It has also been called "The Franken-uBITX." Whatever the name, Farhan was clearly pleased to see Don's handiwork.
I shot a lot of video during Farhan's visit (last time I failed to do this and regretted it). I will put these videos up on the SolderSmoke YouTube channel during the days ahead.
Dean KK4DAS, Mike KD4MM, and I had a good day at the local high school yesterday, even after a month of spring break and other absences. We thought this might have been our last session at the school this year, so we strongly encouraged the students to GET THE RECEIVERS DONE. We told them about the Shelf of Shame, and warned them not to half-way finish something that would gather dust at the bottom their parents' closet. They were close to success! It was time to finish the project.
We warned them not to be perturbed if the receiver doesn't work the first time they power it up. This is not "plug and play." The receiver would likely need some trouble shooting, or at least some peaking and tweaking. We noted that we often have to sort of coax a signal out of a newly built receiver.
We soon had the students come forward with two projects that were ready for final testing. Sure enough we found problems with both. The solutions provided a lot of educational fun.
The first group had not yet built the diplexer -- we advised them to skip over the diplexer for the moment -- just connect the output of the mixer to the input of the AF amplifier. We can't let the perfect be the enemy of the good! Build the diplexer later, but for now, get the receiver going. They did, and a few minutes later they were receiving signals from Mike KD4MM's transmitter (on the other side of the lab).
Then a second group came forward. We put a San Jian frequency counter on the PTO output. Uh oh. Trouble. Gibberish! A wonderful troubleshooting session ensued. With the student, we found that the signal was good at the output of the oscillator transistor, but NOT at the output of the buffer. At first we suspected that the buffer was bad, but it was not. Then we lifted the connection to the mixer and suddenly the buffer output was good. So the problem was in the mixer! When we disconnected the input transformer of the mixer from the diode ring, THE PROBLEM WAS STILL THERE. So the problem was clearly in the input transformer. Dean gave us a replacement transformer. Soon all was right with the rig, and this group joined the ranks of the successfully completed receivers.
I think that seeing that two groups had finished helped motivate the others. Our announcement that successful completion would lead to a "Certificate of Completion" also helped. But most of all, I think the natural desire to finish the job and avoid the "Shelf of Shame" was pushing the students forward.
Other news:
-- Our stage-by-stage award program continued. Last time we awarded "The Torry" for the first successful bandpass filter; this time we awarded "The Audy" for the first successful audio transformers.
The Audies
-- We told the students that their work has been entered in a Hack-A-Day contest. Most of the info and files on the project can be found on the Hack-A-Day site. Check it out:
-- We also told the students about Walter KA4KXX's very generous offer of a reward for the first students to check into the Florida Sunrise net. (We had to make it clear that this offer is completely extracurricular and unconnected in any way from the school .) The students were clearly intrigued. Sunrise Net may get some new check-ins!
-- We provided instructions on how to build a simple 1/4 wave reception antenna. We also did a video.
We had thought that this would be our last session at the school, but at the students' request we will be back with them next week for another session. We think there are at least five more receivers approaching the finish line.
Travelogue: Cuba DSB and AM. Jose CO6EC and the Islander. We need more info, especially on the solid state Jaguey rig.
Bill’s bench:
Will the High School DC receivers get finished? Future uncertain. But the project was technically interesting. Great working with Dean KK4DAS. Battling AM breakthrough from Radio Marti. We joked that Dean has been listening to Radio Marti so much that even though he doesn’t speak Spanish, he has noticed an increased urge to liberate Havana.
Audio amps: Harder than we thought. Lots of variation in Hfe of 2n3904s. Oscillations. Not using feedback amps nor LM386s, nor push-pull. Simplicity is a design goal.
Fixing the tuning (bandspread) problem on the VFO was fun.
Antennas? A quarter wave with ground or counterpoise works well. We tried it. (59) An Antenna for the TJ 40 Direct Conversion Receiver - YouTube ---- Back to work on the uBITX. I chickened out on replacing the predriver with a BFR-106, but then – Just in time Todd K7TFC and his Mostly DIYRF came out with BFR106 boards! TRGHS. I will do the mods on two uBITX transceivers. I even bought a solder-sucking iron for the second job.
Winterfest Hamfest. Big success. Thanks VWS. HERRING AID FIVE! Simpson 260! QF-1, Another Radio Shack DMM, Eamon Skelton’s Homebrew Cookbook, Knobs, SWR meter. ----
Technical Note: Skype problems. Pete's Skype kept dropping out. Bad in the last podcast (#244). Three minute gap. I was ready to scrap the whole podcast when Dean KK4DAS offered to help. And he is obviously well qualified: https://potomacofficersclub.com/speakers/dean-souleles/ Dean went to work with AI. And he was able to fill the audio and the video gaps. Can you spot the three minutes of AI? Send me an e-mail with the time segment of the AI/Deep Fake portion of SolderSmoke 244. The first one with the correct answer will win a prize.
-- A New SPRAT arrived in the mail. PH2LB’s Gluestick on the cover. -- Will KI4POV – Awesome homebrew – on the blog. -- Sands, VK9WX listening to SolderSmoke on Willis Island! Wow. -- Andreas DL1AJG in Germany continues with the Electronics for Biologists DC RX build. -- Dean KK4DAS and his homebrew 10 meter DSB rig. -- Jim W2UO built a Michigan Mighty Mite and made a contact. -- Dave K8WPE and the E in IBEW. We need new stickers. -- Bob KC4LB – Surface Mount is SMALL. -- Bruce KK0S on the Herring Aid 5 Board. -- Chuck WB9KZY on Nuclear Monopole Resonance very cool video – on the blog. -- Alan WA9IRS wants a CW editor for his phone. Really. -- Vic WA4THR also working on uBITX power out improvement. -- Tobias weighs in on Kludge. As in Fudge. -- Tony G4WIF notes that when he changes his oil he often removes sludge, not slooge. -- Consultations with Lexicographer Steve KB3SII. -- Walt AJ6T says CW operating declined after FCC ruling in 1970s about callsigns. -- Ramakrishnan VU3RDD now VU2JXN has joined the VWS. An old friend of SolderSmoke. Urged us to launch a blog back in 2008. We announced his daughter’s birth - - now Ram is getting ready to build a DC receiver with her.
We have reached the point where we have to decide on an antenna for the high-school direct conversion receiver. It needs to be simple and easy. It needs to be something that students can easily install from a bedroom window in an apartment or a town house.
We thought about an End Fed Half Wave, but 66 feet of wire seemed to be too much, and the EFHW would require both coax and the construction of a transformer. That seemed like too much.
So here is what happens with just 33 feet of wire (1/4 wave on 40 meters), with another 33 feet as a counterpoise. I found that the counterpoise worked just as well spread out on the bedroom floor as it did hanging out the window along the outside of the building. As you can see in the video, the counterpoise is really necessary with this kind of antenna. It makes a big difference.
We know that the students could have dispensed with the counterpoise by connecting the copper clad boards to a cold water pipe, but that might be difficult for them. So we went with the counterpoise.
After the antenna demonstration I ramble on a bit about the high-school construction project, and where the students could go from here.
One of the receivers. (l to r) AF, PTO, Mixer, BP filter
The students continue to make great progress on their direct conversion receivers. Yesterday they were enthusiastically sitting down to workbenches, building Manhattan-style circuits, working directly from schematic diagrams. It was really impressive. They are building receivers.
This week we had two sessions of about two hours each. We introduced the final board: the audio amplifier. Many of the students began work on this amplifier; others were catching up with work on boards presented earlier.
The AF amp is their most challenging board: It used 14 Manhattan pads and about 26 components. We warned the students that amplifiers often aspire to be oscillators. We told them to pay attention to layout, and to keep their leads short.
One of my builds, and a Manhattan board pattern
At first, the students just built the first stage on the AF amp board. They tested this, then moved on to build the other two stages.
By the end of Friday, two groups had completed the build of the AF amplifier board.
We think there are about 13 receivers in production. Some are near completion, others will need more work.
On Thursday of next week those teams that have completed all four boards will put the circuits together and will test the entire system. They will then add all needed front and back panels and socketry.
We really want the students to complete as many of these receivers as possible. Exam season and the end of the school year is approaching, so we have to get this done. We will remind students that they don't want to that person who ALMOST finished a project! We will urge them to GET IT DONE! They can tweak it and mod it later. This kind of tweaking and modification is part of the homebrew experience.
We have been presenting awards to the students who are first to complete each stage: The winners of the PTO board competition got a copy of SolderSmoke: Global Adventures in Wireless Electronics. Those who won the mixer competition got a W1REX Hamfest Buddy transmitter. Thanks Rex! And this week we presented an award to the students who were the first to complete their bandpass filter. You've heard of the Tony, the Emmy and the Grammy? Well, we presented "The Torry" (from Toroidal). The trophy was made from a toroidal winding tool made in Alaska by KL7FLR. I explained to the students who had made it. Thanks Paul!
For the capacitive element in the LC circuit we have
essentially two 660 pF caps in series.This results in a total capacitance of 330 pf.I measured 362 pF.
To get a resonant frequency of 7.0 MHz with 362 pF we need
1.428 uH.
To get 1.428 uH on the PTO coil form we need about 21 turns
of wire.
21 turns on our coil form yields 1.440 uH and resonates with
362 pf at 6.9708 MHz
That’s pretty close to what we need, but the problem
arises when we screw in the brass tuning screw. This reduces the inductance and raises the frequency. Putting the screw
all the way in reduces the inductance to 1.138 uH resulting in a resonant
frequency of 7.8414 MHz.So with a coil
this large (that we must use if we want to tune down to 7.0 MHz) we end up with
a tuning range that is far too large.We
only need 7.0 to 7.3.In effect, this
means that we end up using only a small portion of the tuning range:We can turn the screw approximately 34 times,
but only 6 turns keep us within the range of 7 to 7.3 MHz (the 40 meter
band).There is about 50 kHz per turn of
the dial.This makes tuning
difficult.It becomes more difficult to
separate stations and tune them in.It
would be better if we could tune across the band using more turns of the dial.At least 15 turns of the dial would be
nice:That would mean about 20 kHz per
turn.But how can we do this?
Possible solution #1:Steel screw with tighter pitch on the turns.
Just using a steel screw slows the tuning rate down.In a normal PTO we increase the inductance
(and reduce the frequency) by gradually introducing a ferrous material that
increases the inductance of the coil, pushing the frequency of oscillation
down.But our brass screw is
non-ferrous.This means that putting it
into the core does not change the permeability of the coil.The permeability of brass is the same as that
of air.
What does happen, however, is that introducing the brass screw
into the coil causes currents to flow in the screw.These are called eddy currents. In effect they become shorted secondary coils.
And they have the effect of lowering the
inductance of the coil – this is why the frequency of the oscillator increases
as we screw in the brass screw.
When you use a steel screw you get both effects: As you
screw it in, eddy currents flow in the screw, reducing the inductance and
increasing the frequency of oscillation.But you are also introducing ferrous material – this pushes in the
opposite direction, increasing induction and lowering the frequency of
oscillation.I think the eddy current
effect dominates, but the increase in permeability pushes in the opposite
direction.This means that with a steel
screw you have to use more turns to cover the same frequency range. And that is what we want.
But there is more:steel
screws are also available with tighter (#28) thread pitches. The Hillman 45479 uses this tighter thread pitch. This too means that more turns are needed to
move through the same tuning range. Again, that is what we want.
I found that using a steel screw with #28 thread pitch allowed
for the coverage of the 40 meter band in approximately 11 turns of the dial.That is much better than what we got with the
brass screw:About 27 kHz per turn
instead of the 50 kHz per turn that we got with brass. But it is not quite good enough.It would be better if we could use the
entire range of that PTO coil form.
Solution Two:Add
a fixed inductor in series with the PTO coil.
After some noodling, I decided to split up the
inductor:A portion of it would remain
fixed, the other portion would continue to be tunable.
I estimated that I was starting out with a coil of about
1.428 uH.So I just put a 1 uH choke in
series with the variable inductor and reduced the variable coil to about .428
uH (about 9 coil turns).This worked,
but it worked a bit too well!It would
not tune the entire 40 meter band.So I
figured I needed less fixed inductance and more variable inductance.I found an air-cored coil in my junk box and
cut it so that it measured about .650 uH.I added turns to the variable coil, going to a total of 15 turns.This REALLY worked well and yielded the 26 or
27 turns to tune across 40 meters that you can see in the video.
TWEAKS:
Later, I tweaked it a bit more: With 15 turns of #22 wire on the variable inductor, a steel screw tuned from .791 uH (screw out) to .662 uH (screw in). I put one additional turn on the fixed inductor, making it .749 uH, or about 8 turns of #22 (wound tighter on a cardboard tube from a coat hanger than was the coil on the variable inductor). With these coils I could tune from 6.9772 to 7.386 MHz. That's a bit more than we need but this allows us to keep the tuning away from the ends of the coil where tuning is more likely to become non-linear. I am able to go from 7.0 to 7.3 MHz in 23 turns of the dial. And the tuning is quite linear: The first turn from 7.0 MHz moves the frequency 12 kHz. At the mid-point of 7.150 MHz, one turn of the dial moves the frequency 12 kHz. At the high end, going down from 7.3 MHz, one turn of the dial moved the frequency 11 kHz. That, for me, is VERY linear tuning. You probably will have to adjust the coils a bit (just squeezing the turns together or spreading them apart) to get the tuning range where you want it.
YMMV – Keep it simple!
Like they used to say in the commercials:Your Mileage May Vary. There are many ways of doing this.The objective is smooth tuning across the 40
meter band.I think that by varying the
pitch of the variable coil turns you could get a more linear tuning response (please let us know if you have any luck).You might also be able to get similar results
by changing the amount of capacitance in the feedback network (which is also the
frequency determining element in this simple Colpitts oscillator).But remember that simplicity and a low parts
count were also our objectives in this.This mod adds only 1 part (the fixed inductor), requires the removal of
some turns from the main tuning cap, and perhaps the replacement of the brass
screw with a steel #28 screw and nuts.
We might present to the student this problem and our search for a solution. This would be a good example of how homebrewers work to make their rigs better and easier to use. It illustrates well the design dilemmas that can come up, and how amateurs like us can come up with solutions.
Farhan came up with the idea of having high school students build their own receivers. We followed his lead -- there are now several such projects underway around the world.
The simple but effective Colpitts circuit that Farhan recommended.
Farhan sent this picture yesterday. If you look closely you can see the students holding their homebrew 40 meter Direct Conversion receivers. You can even see that they are using the same kind of PTO coil forms that we are using here. Farhan reports that 11 receivers were built by 33 students. A few more are being finished and will soon be active in Hyderabad.
I was really blown away by this picture. We are doing the same things on different sides of the world. Our students will like this. It will be as if they are seeing people of the same age building the same receivers 7,500 miles away.
In our last session I mentioned to our students that Farhan of Hyderabad had given us the toroidal transformers that they are putting into their mixers. I told them that in ham radio, when we use parts given to us by a friend we add "soul to the new machine." And I said that Farhan would be coming to see them in May. They were really impressed.
We are starting to see similar efforts in different parts of the world -- Andreas with university students in Germany, Daniel with high school kids in Canada. We hope there will be others.
We've been giving out prizes for the first team to complete each stage. I wanted to give one of the teams a little oscillator that could b heard with their receiver. So this morning, using a 7040 crystal from the AF4K (SK) company, I threw together a one transistor oscillator. It has just 8 parts, including the key:
I had a low pass filter in the antenna tuner. The antenna was a low-to-the-ground 40 meter dipole. The transmitter was putting out around 100 milliwatts.
N2CQR's Ten Minute Transmitter
The Reverse Beacon Network showed that I was getting out quite well:
Then I thought, wait a second, let's make a contact with the prototype high-school direct conversion receiver.
With the receiver hooked up, I again called CQ on 40 CW. BOOM! Very quickly Alan W4AMV in Raleigh NC came back to my call. Wow! That's 222 miles. And a quick check of QRZ.com revealed that Alan is a homebrewer. Then Google reminded me that his work has been featured on the SolderSmoke blog. TRGHS.
I was so excited during this contact that I almost forgot to film it. But I did manage to get some short clips of the QSO in progress. You have to listen carefully, but you can hear our calls in there while Alan is transmitting (listen for the lower tone):
UPDATE (Feb 27 2023): I asked Alan about the rig he was using: "A PLL EXCITER DRIVING A PAIR OF FETS PUSH PULL ABT 50 w to an inverted L at 55 feet. The Rx a single conversion 9 MHz IF and it is connected to an active antenna in the trees out in the woods abt 25 feet up. Uses an automotive whip antenna about 3 feet long. "
Alan's Rig
This little contact is a reminder of the fun that can come from using simple, homebrew, QRP gear. It is really amazing that the very first contact with this receiver was with another homebrew station. This all reminds Dean and me of something we have been telling the students: the little DC receiver they are building is not a toy -- it is capable of being used in real, long-distance contacts.
A team from the Vienna Wireless Society was back in the local high school Thursday and Friday of this week, helping the students finish their variable frequency oscillators and build their diode ring mixers. Club President Dean KK4DAS was in the lead, and did an amazing job working with the school and procuring all the needed parts. Mike KD4MM and Don KM4UDX provided patient and understanding help to the students.
Students at work on the receiver
On the oscillators, the students had to add about six parts to install a buffer circuit built around a J310 FET. They also had to replace some of the 3D printed coil forms for the main-tuning variable inductor. (Dean KK4DAS made some really nice forms -- see below.) Several teams of students experiences were very pleased to get their oscillators running.
Manhattan Mixer Pads
Then it was on to the diode ring mixer. We had planned on having the students wind their own trifilar toroids, but we realized that this might be too much -- it would add a lot of time to the build, and would introduce a lot opportunity for error.
One of Farhan's transformers
I remembered that Farhan had given me a big supply of FT-37-43 trifilar toroids that had been assembled in Hyderabad. We decided to use these transformers. We reasoned that this was not a big deviation from our DIY ethos -- after all, we didn't ask the student to wind their audio transformers, nor did they wind the RF choke in the VFO buffer. But we faced a problem: the Hyderabad transformers were all wound with the same color wire on all three turns. This would make it hard for the students to figure out which wire went where (there were 12 such wires on each mixer board!). I figured out how to do this: The night before, I soldered together the center tap wires, and I twisted together the input coil wires. We told the students to first solder the center taps in place, then solder the two free wires to the diode ring, and finally untwist the input coil wires, soldering in these connections. This worked.
How the transformers were prepped
Before we started, I gave the students a quick class on the essentials of mixers. And I pointed out that we were using transformers made in Hyderabad India and donated by our friend Farhan. I told the students that whenever we include parts given to us by a ham radio friend we are adding "soul to the new machine." Indeed, Farhan's toroids added a lot of soul.
We have been insisting that the students have each stage tested before moving on to the next. This week we used signal generators to put RF and VFO energy into the mixers, and oscilloscopes to make sure that audio was coming out.
One of the test set-ups for the mixers
The students are making good progress. After today's session we did an estimate of where each of the projects stand at this point:
We are building 15 receivers. Oscillation without the buffer: 11 Oscillation with the buffer: 5 Mixer built and tested (but no diplexer yet): 5 Mixer working, diplexer built 2
During the next month or so the students will build the bandpass filter and the audio amplifier, and put all the boards together to complete the receiver.
"SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
http://www.amazon.com/dp/B004V9FIVW
Wanted: Matching speaker for NC-183D
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Does anyone have a excellent condition 10" version of the matching speaker
for a NC-183D they would like to sell?
If so, please contact me at wd4lur@gmail....
Photos from the Stuart Hamfest 2024
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Many thanks to SWLing Post contributor, Mike (VE3MKX), who shares the
following photos by Ben (VE3ST) of the Stuart Hamfest 2024 held in Florida:
Photo Gal...
Dale Goes “SOTA-Lite” with the Elecraft KH1
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Many thanks to Dale (N3HXZ) who shares the following field report:
SOTA-Lite with the KH1 by Dale (N3HXZ) My KH1 Edgewood Package finally
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Handy breakout board for Raspberry Pi Pico
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Ugly Construction!
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Here’s a little project I put together on a whim about 18 months ago. It
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New QRP Cluster Online From OM0ET and OM6APN
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By DX EXPLORER
DX EXPLORER
Paul OM0ET and Peter OM6APN recently launched a new cluster dedicated to
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What’s all this? In 10 seconds, A high performance, 7MHz, 5 watt SSB rig
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The early buyers of the sBitx board set who bought it for $270 USD might
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A Simple Speech Processor
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Over the last few weeks I had been thinking to build a small AF speech
processor to add to...
A New Look for your uBitx!
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Adding a "Cool Blue" Display to your uBitx!
The standard "green background" with black lettering frequently reminds me
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