Category: Farhan

Farhan’s High-School Direct Conversion Receiver Workshops in India

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.

Progress Report: High-School Students Build Diode Ring Mixers (Board #2 of 4). Hyderabad Soul Added to the New Machines

Dean KK4DAS works with students

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.

Farhan’s Direct Conversion Receiver

Thank God for the Wayback machine. For a moment I feared that this article about Farhan’s DC-40 receiver had been lost. (Phonestack is now some Vietnamese vendor. ) But the WayBack Machine archive came through for us.

https://web.archive.org/web/20171109081542/http://www.phonestack.com/farhan/dc40.html

Farhan’s receiver has been covered on this blog before, but it is especially relevant for us now that we are immersed in our own direct conversion receiver project. Farhan was working with his niece, who was a student. We are working with high school students.

I really like Farhan’s blow-by-blow description of the build. There are raw emotions here: He speaks of his hatred of LM-386s, and of how he thought of using the copper clad board as a projectile. His niece wonders about the possibility of evil spirits in the receiver. The battle against AM breakthrough is very familiar. (I like the RF choke idea.) You won’t find candor like this in QST or QEX.

Farhan’s DC-40 project was one of the inspirations for our high school effort. In fact, when we first went to the school, I left behind a direct conversion receiver that I had built. Taped onto the bottom of the receiver was a quote from the DC-40 article and a picture of the Wizard of Hyderabad. (See above, and click on the picture for a better look).

This week we will inject some more Farhan-ismo into our receiver. The time has come to build the mixer. Like Farhan, we will go with the diode ring. Winding the transformers would be very time consuming. I remembered that on his visit, Farhan had left me a box of trifilar toroids wound by the seamstresses of Hyderabad using FT37-43 cores. We will uses these in our build. They will add a lot of soul to the new machine.

SolderSmoke Podcast #243 — HI7/N2CQR, uBITX mods for 10 meters, High-School Direct Conversion Receiver Project Launched (Success!) Mailbag

DC RX and one of the PTO boards we built as demos last night.

February 10, 2023


SolderSmoke Podcast #224 is available.


http://soldersmoke.com/soldersmoke243.mp3

Video here: (32) SolderSmoke Podcast 243 (video) Hi7/N2CQR, uBITX, Success with High School Receiver Project – YouTube

Pete N6QW had technical difficulties this morning. He insisted that the show must go on. Pete will be back for the next episode.

Travelogue:

Bill in the Dominican Republic for all of January.

HI7/N2CQR Eastern tip of the island. uBITX and dipoles.

20, 17, 10. CW and SSB. SSB was tough and I had reports of RF getting into the signal.

Went to CW.

Worked VWS Mike KA4CDN, and Walter KA4KXX on 20CW.

Finally moved up to 10 CW. Lots of contacts. Even though uBITX very QRP on ten.

I am modifying the uBITX now.

Copper tape shielding to keep RF out.

Low power out not the fault of the IRF-510s. The problem is the 2N3904s.

Will replace with 2N2222 in To-18 cans.

Dean KK4DAS putting KD8CEC software into Arduino. I gave up.

Who sent me this orphan uBITX?

SolderSmoke Shack South in final phase of construction.

SHAMELESS COMMERCE DIVISION:

Patreon!

Bezos Shopping!

DC Receiver Project

Local High School radio club.

Simple: Like Herring Aid 5 and Wes’s original.

Farhan’s four stages:

BP Filter, Diode Ring, PTO, AF amp.

Simple Colpitts PTO SURPRISINGLY STABLE.

Simple and easy. No chips. No complicated circuits.

Guys have helped test out the design: Rick N3FJZ, Walter KA4KXX,

Daniel VE5DLD, Stephen VK2BLQ and others.

First session last night: We demonstrated build of the PTOs.

They worked (thank God).

Open Circuits book.

Envelope Detection Controversy

Save the Antenna – Book “Losing the Nobel Prize” K1JT

MAILBAG

–Dean KK4DAS 10 meter DSB! Tiny SA ULTRA! FB

–John AC2RL on Elmer W3PHL DSB guy

–AC3K reports inventor of Fender Stratocaster guitar was a ham: W6DOE

–AF8E was doing POTA. I worked him. He said my rig had presence. FB

–Alain F4IET FB DSB rig with mic in Cigar can!

–Daryl N0DP worked him on SSB. He is homebrewing

–Steve N8NM was in for repairs but is on the mend.

–Rick G6AKG working with sub-harmonic mixers and logic chips

–Paul HS0ZLQ Built DC receiver but looking for something else to build. No DSB!

–Steve AB4I – Coherer, Jagadish Chandra Bose, and Marconi

–Eldon KC5U Worked VK5QD right after me and mentioned SolderSmoke FB

–Todd K7TFC is building the DC RX.

–Tony G4WIF and Ian G3ROO using automotive relays for antenna switching. FB.

–Dave WA1LBP Great to hear from my fellow Hambassador (Okinawa)

Older post comments:

–Scott VO1DR was also in CF Rockey’s class! (Blog comment)

–Aurora Aug 4, 1972: Twelve people shared memories. (Blog comment)

–Will WN1SLG Googled novice call and was led to my Novice log.(Blog comment)

The 40 Meter Direct Conversion Receiver We Have Been Working On — Comments Welcome

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:

http://soldersmoke.com/DCRXLTSPICE.net

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:

Amazingly Cool MONTV Video on Direct Conversion Receivers with Glue Stick PTOs

I think this is one of Nick’s best videos. And he has made a lot of good ones.


This is a really excellent description of how a Direct Conversion receiver works. But more importantly Nick really captures the joy of building one of these receivers using discrete, analog components, including a Permeability Tuned Oscillator made from our beloved Glue Sticks.

Extra mojo comes in the form of a mixer designed by Pete Juliano using J310s to simulate a 40673 dual gate MOSFET. Fantastic. Icing on the cake comes from a W8DIZ AF amp out of SPRAT magazine.

There is a grand finale. I won’t spoil it. Watch the video. Suffice it to say that Farhan would be pleased with this.

Great stuff. Thanks Nick!

A Treasure Trove of Permeability Tuned Oscillator (PTO) Info and Links (Plus Info on Direct Conversion Receivers)

There is really great info on this page, and even more in the links at the bottom of it. While the page is about PTOs, the links often discuss their use in Direct Conversion Receivers. I really liked the Tin Ear receiver. And it was great to again come across the work of Alan Yates VK2ZAY. Alan very admirably admits that laziness caused him to use an LM386 audio amplifier in place of a more virtuous discrete transistor design.

https://qrpbuilder.com/pto_mechanism

I bought one of the qrpbuilder PTO kits and I will soon put it together. I have been having good results with a Glue Stick PTO and with a brass screw PTO form designed by Farhan and 3D printed for me by Dean KK4DAS.

LET’S GO PTO!

SolderSmoke Podcast #241 Mars, Direct Conversion, PTOs and Glue Sticks, Anniversary of the BITX20, Multus Proficio SDR, Boatanchor Station, MAILBAG

The board I use to test DC RX circuits

SolderSmoke Podcast #241 is available

Audio (podcast): http://soldersmoke.com/soldersmoke241.mp3

Video (YouTube): (215) SolderSmoke Podcast #241 October 28, 2022 – YouTube

Introduction:

Back on Mars. Opposition approaching. I have a Mars filter. And (like T.O.M.) a Mars globe.

N2CQR DXCC done

SolderSmoke in the WayBack Machine

Sticker news

PARTS CANDY — Don’t Scrimp with a Crimp!

Bill’s Bench

School DC RX projects — in Hyderabad and Northern Virginia.

Direct Conversion Receivers — Keeping it Simple, Learning a Lot. A step beyond the Michigan Mighty Mite. Do we really need 100db? Do we really need to shield VFOs? Farhan’s super-simple and stable Colpitts PTO. Audio amps, 1000-8 transformers and rolling your own LM386

PTOs and Glue Stick PTOs. Paul Clark WA1MAC. Brass vs. Steel bolts. #20 thread vs. #28 thread. Backlash Blues. The best Glue Sticks.

2 meters and the VWS. Bill has a Baofeng.

SHAMELESS COMMERCE: MOSTLY DIY RF

Pete’s Bench

20th Anniversary of the BITX20 Pete’s early BITX rigs.

Computer Woes

The Multus Proficio SDR rig

Simple SSB in China BA7LNN

Things of beauty: Tempo One, NCX-3 and a SBE-33

MAILBAG

— NS7V is listening.

— Graham G3MFJ sent SPRAT on a stick.

— Nick M0NTV FB Glue Stick and 17 Shelf videos.

— Dino KL0S HP8640 Junior

— Mark AA7TA Read the SolderSmoke Book

— Steve EI5DD Connaught (Ireland) Regional News

— Dave K8WPE Planting the seeds of ham radio interest

— Peter VK3YE Ruler idea on PTO frequency readout

— Michael AG5VG Glue Stick PTO

— Tobias A polymath with UK and Italy connections. And cool tattoos.

— Alain F4EIT French DC receiver

— Michael S. was in USMC, working on PCM/TDM gear

— Alan Yates writes up Amazon transformer problem

— Todd VE7BPO, Dale W4OP, Wes W7ZOI

— Farhan VU2ESE sent me an sBITX

— Todd K7TFC The Revenge of Analog

— Jim Olds Building QRP HB gear


The Multus SDR rig Pete discussed

The older rigs Pete mentioned


My version of DC RX that Farhan is working on

My PTO with VK3YE’s ruler frequency readout


DC Receiver: 100db Gain? Diplexer? VFO in a box?

Here is a progress report on Direct Conversion Receiver developments. Dual Tuned Circuit, Diode Ring with Diplexer, PTO VFO from Farhan’s Daylight rig, two stage 49 db BJT AF amp with a transformer. It works very well. I discuss: Shielding of the VFO — necessary or not? Why brass in the PTO? Do we really need 100db in a receiver, especially with ear buds? Sourcing the AF amplifier’s transformer. Using W7EL’s diplexer. (I think it has solved my Radio Marti breakthrough problem). Developing a DC RX circuit that can be built by students. I end with a bandsweep of 40 meters that includes CW, FT-8, SSB, and AM

Listening on 40 with a Glue Stick PTO in a Direct Conversion Receiver; Some PTO History

Thanks to Paul WA1MAC for this idea. He first shared it with us via the SolderSmoke mailbag in 2008! Sorry it took so long for me to try one Paul.


The PTO itself is an old idea of course. Here is an article from 1966:
OM faced the problem of having to keep track of frequency while turning the dial many times. He was hoping to use a turns counter — in 1966 we didn’t have the San Jian frequency counters. I note that his PTO looked a lot like the one KK4DAS 3D printed for me (using file from Farhan).

And some background on PTOs: https://sites.google.com/site/randomwok/Home/electronic-projects/permeability-tuners-last-stand

Paul Clark’s Dollar Store PTOs made with Glue Sticks or Chap Sticks

A few weeks ago Pete Juliano and I got some e-mails from Paul Clark about his use of Chap Sticks and Glue Sticks (acquired at a Dollar Store!) in Permeability Tuned Oscillators.

Dean KK4DAS, Mike KA4CDN and I had been experimenting with PTOs following Farhan’s use of one in his new Daylight Again transceiver. We are also looking at simple circuits for use in Direct Conversion Receiver builds for high school students.
Yesterday, I noticed a Glue Stick on the floor under my bench. TRGHS. I built one of Paul Clark’s PTOs and used it with the circuit from Farhan’s Daylight Again rig. For the ferrous material, I just glued (!) a .5 inch toroid (I think it is #7 material) onto the moving internal part of the glue stick. For the coil I used a total of 9 turns of #20 wire, with a tap at 2 turns. You can see the results in this video.

I think it is really useful, a very nice way to get good frequency control using an item available in most super-markets (I bought two glue sticks at Harris Teeter yesterday!). This continues a long ham radio tradition of using household items for ham projects — we started with breadboards.

Some of Paul’s coils:

Some of Paul’s data:

Here’s the data I got in testing these on the NanoVNA:
Burt’s lip balm
16t #24 insulated
brass tubing ferrule
80pf
9.93mhz-10.80mhz
3.21uh-2.714uh
Dollar Store PTO Forms in 3 sizes
Small Jot Glue Stick (8 for $1.25!)
1 3/8″ of #30 enameled close wound
waiting brass tubing to fit cup
80pf
2.980mhz with no core, I’m waiting brass tubing to fit this one (we have no hobby stores around here anymore that stock the K&S music wire and brass tubing assortments)
35.65uh
Medium Playschool Glue Stick
36t #30 enameled
1/2″ copper water tubing
80pf
2.96m-3.380m
36.13uh-27.72uh
Large JOT Glue Stick
1/2″ copper water tubing
80pf
28t #24 insulated
4.995m-5.625m
12.69uh-10.00uh

Bandsweep with the New Homebrew 40 meter Direct Conversion Receiver

It is inhaling nicely but some improvements are still pending. Click on the video above to see and listen to the bandsweep done on 40 this morning.

— The front end consists of capacitive divider input impedance matching circuit, followed by one LC circuit and an FET RF amp.

— The VFO is a super-simple Colpitts design by Farhan. The two feedback capacitors do double duty in the LC tan circuit.

— I am using an old variable capacitor instead of the PTOs that we have been experimenting with.

— The mixer is singly balanced using one trifilar toroid and two diodes. We have found out that even with these three simple devices, there is significant variation in how people connect them to VFO, RF in and audio out. I think we have found the best way to do this: Be sure to put the VFO on the primary of the transformer, and let this signal turn the diodes on and off.

— For the AF amplification, I have one FET, followed by two BJTs. I have a small audio transformer between the speaker and the final AF amp. There is plenty of audio.

You may wonder why, after all the SSB superhet transceivers, I am building a simple Direct Conversion receiver. Well, we hope to help a bunch of high school kids build one, so we need to be really familiar with how it works. And I find that as simple as it is, there is still a lot to learn in a project like this.

A Bout of Direct Conversion-ism in Northern Virginia — DC Receivers Under Construction

There I was, minding my own business, when suddenly I was dragged into the construction of Direct Conversion receivers.

Here is a video about my latest effort. But I feel the urge for more simplification — I may go back to the seminal DC receiver designed by Wes W7ZOI and presented in the November 1968 issue of QST. It is on page 15 here: https://worldradiohistory.com/Archive-DX/QST/60s/QST-1968-11.pdf

Building Farhan’s PTO — But Is This Really a PTO?

Farhan has a PTO in his Daylight Again transceiver. This caught the attention of homebrewers around the world. Walter down in Orlando built one. Dean KK4DAS and I have built versions also. Dean has a 3D printer and made the coil support used in my version (above). Thanks Dean!
I had a little trouble at first because one of the capacitors I had in there was not NP0, so the device drifted a lot. But once I straightened that out (I put in a Silver Mica cap in its place) the oscillator became very stable. Mine moves about 25 kHz with each turn of the bronze screw — this is nicely linear tuning. But I think I will have to use a San Jian counter to keep track of the frequency. The long plastic tube on mine is there to eliminate had capacitance effects.

One of the guys in the Vienna Wireless Society questioned whether we should really call this a PTO. After all, bronze has a permeability equal to that of free space. So we are not really changing the permeability. Frank Harris points out that the bronze screw really acts as a shorted secondary. What do you guys think? Is this a PTO, or do we need another acronym to describe it?

This has been a really fun project. I never built an oscillator like this before. I will probably follow up by building the rest of the Daylight Again rig.

BTW WA6OTP has a nice PTO design: http://www.wa6otp.com/pto.htm

Thanks again to Dean, and to Farhan.

Fixing Up An Old Homebrew Rig — Barebones Superhet and VXO 6 Watter

I’m not exactly sure why I pulled this old rig off the shelf, but I’ll write up what I did — I often use this blog as a kind of notebook. I can look back and easily see what I did on my last encounter with the rig.
The receiver is Doug DeMaw’s Barebones (aka Barbados) Superhet. This was my first superhet receiver. I built in in 1997. The transmitter was my first real homebrew project — it is the VXO 6 watter from QRP classics. I built it in the Dominican Republic, probably in 1993 or 1994. I built the power supply so that I could say that the entire rig is homebrew.

This rig is getting a bit long in the tooth: The receiver is built with 40673 Dual-Gate MOSFETs, an some of the transistor cans have gotten rusty. The frequency readout on the receiver is the top of a coffee can fitted onto the reduction drive behind the tuning knob from a Drake 2-B (not MY 2B!).

Here are two 2013 videos that I did on this receiver:

— I put the crystal filter back in CW mode. I had widened it so that I could listen to 20 meter SSB, but I decided to go back to its original configuration. When I built the receiver in 1987, I didn’t characterize the crystals — I just used the capacitor values that Doug DeMaw had in his article. I pretty much did that again this time, just putting caps that are close in value to what Doug had. DeMaw used color burst crystals at 3.579 MHz. So I guess this would be a GREAT receiver for the Color Burst Liberation Army!

— I used My Antuino (thanks Farhan!) to check the passband. Here is what it looks like. I just put the Antuino across the 10k resistors on either side of the input and output transformers. The coil cores had become very loose — I just tried put them in the right place. I may need to put some wax in there to allow them to better stay in place. I think they could have used toroids instead — that would have been easier. One of the transformer connections was open — they don’t work well that way, once I fixed that, the passband looks like this:
— Each of the horizontal divisions is 500 Hz. The passband is not pretty, but it is OK, and I didn’t feel like doing too much work on this to get it in better shape.

— The filter peak was a bit lower in frequency than expected. I found that trimmer cap C3 in series with the BFO crystal would not allow me to lower its frequency sufficiently. So I moved C3 to a position in parallel with the crystal. With this mod, I could get the BFO frequency to 3578.69. This produces a 690 Hz tone when the received signal is at the peak of the IF passband. Opposite sideband rejection is quite good.

March 2013 Rebuild of the VXO 6 watter

— I didn’t have to do any real work on the transmitter. The RF amplifier in the transmitter had served for a time as the RF amp in by 17 meter DSB rig (I had added a bias circuit, which I removed when I put the amplifier back in Class C). Some time ago I rebuilt the oscillator circuit (which had been literally cut off the board when I used the amplifier in the DSB rig).

— I did have to reconfigure the muting circuit — the T/R switch in the transmitter switches the antenna and also — through a two wire circuit — cuts off 12 V DC to the transmitter when in receive mode.

— For sidetone I just put a small piezo buzzer through a 1k resistor between 12 V DC and the key line.

It all worked fine — I talked to three stations on the high end of the 20 meter CW band.

SolderSmoke’s 2006 Interview with Farhan (and pictures from his 2019 visit)

Farhan in N2CQR shack with ET-2 on bench
October 2019

Here is the YouTube version of the SolderSmoke Podcast #34

https://youtu.be/q-L4IE9f1aA

Farhan with Bob Bruninga WB4APR (SK)
https://www.qrz.com/db/WB4APR

With Bill and Abe Lincoln
With Einstein
Correcting an Einstein equation
With Elisa

Tuning Bill’s BITX 20

Daylight Again on the Sunrise Net! Walter KA4KXX Builds a PTO

Dear Bill:


I had never built a PTO, but after reading Farhan’s Daylight Again Transceiver article I cobbled one together with parts and pieces I had on hand. My observations so far are as follows.


1. The frequency-determining capacitors (shown on the schematic as three 470 pf) are very critical, so I feel the usual experimental cut-and-try technique is a must, even using all NP0 and C0G types.

2. After I built the 2 MHz version like the article (see first photo), the stability was terrific, but when I tried building the companion Daylight Again crystal filter, I was only able to get a bandwidth of 1.6 kHz, which is too narrow for my taste in an SSB radio, so I decided to build the same filter design but with 11 MHz crystals, where I could easily achieve a 2.8 KHz BW.

3. Therefore, now I needed a higher frequency VFO, so I merely reduced the capacitance (from about 1200 to 370 pf) without changing the coil and I am very impressed with the performance of my 4 MHz PTO (see second photo). The bandspread easily covers the entire 40M band, CW and Phone.

4. However, whenever I transmit on the 40M Phone band, I like to first set my VFO within 10 Hz of the operating frequency. That way, if I talk for five minutes or so and get up to 15 Hz of drift (which is quite common with many radios when I operate portable outdoors in the sun and wind), it will not be noticable and I avoid receiving any “you are off-frequency” chastising. But the shortcoming I have with this PTO inductor is that the 1/4-20 bolt has a coarse thread, so it is very difficult for an old fellow like me to get within even 20 Hz of a particular frequency just using this common bolt. Therefore I believe a better choice would be the fine thread 1/4-28 two-inch brass threaded bolt which is available from industrial supply houses like McMaster-Carr. However, for CW use or those with a very steady hand, the 1/4-20 works well enough.

5. I solved my fine tuning problem by adding a varactor circuit using a common 1N914 diode in series with a 100 pf capacitor, operating from 0 to 6 volts. Another advantage to adding this feature is that since I have not so far enclosed my PTO, I can mount the varactor potentiometer several inches from the PTO so my hand capacitance does not affect the frequency like when tuning with the bolt.

6. An easy way to “do the math” in my case with the common Sanjian counters is to simply create a small lookup table listing half a dozen common frequencies and stick it on the radio. For example, 90% of the time in the morning I am tuned to my favorite SouthCars Net frequency of 7251, so using a BFO setting of 10,999.900, I simply set the PTO to 3,748.90 on the 6-digit 10 Hz resolution counter I normally use (see third photo).

7. I am currently using my Daylight Again PTO on a daily basis with an NE602 receiver, and I am thinking of adding a locknut to the bolt so it does not wiggle when I jostle or move the radio, essentially giving me a crystal replacement oscillator that I can use for any single 40M frequency. To date I have been able to listen for hours at a time indoors without even any touch-up of the varactor fine tuning.

8. Also, if continuous frequency readout is desired without building a noise filter circuit board, a separate power supply for the counter is a solution. For portable operation I use Lithium Polymer radio control model airplane batteries which are light, small, and cheap, so one 12V 2000 mAH battery for the transceiver (allows a half hour of transmitting at 15 watts) and a much smaller 12V 350 mAH battery with a series resistor to reduce the current and brightness of the counter has worked well for me.

73, Walter KA4KXX
Orlando, FL

SolderSmoke Podcast #239: Hex DX, VFO Temp Comp, DC RX, Polyakov!, DX-100, Wireless Set, Farhan’s “Daylight Again” HDR rig, MAILBAG

N2CQR Hex Beam Aimed at Europe


SolderSmoke #239 is available for download:

http://soldersmoke.com/soldersmoke239.mp3

TRAVELOGUE:

James Webb Space Telescope. Mars returning to opposition in early December.

BILL’S BENCH

Hex Beam K4KIO – on roof – TV Rotor – 20-17-12 Lots of fun. Working Japan regularly, Australia, South Africa on long path 17,000 miles. 52 countries SSB since July 11.

VFOs and Temp stabilization. Dean KK4DAS found my ceramic resonator VFO for DC receiver drifty. He was right. So I built a real LC Colpitts VFO. Got me into temp stabilization. A new hobby! An obsession. HT-37 and Ht-32 parts. Ovens? WU2D’s second VFO video. Understanding thermal drift and how to address it. Split stator caps. Cut and try.

Built a Polyakov DC Receiver. https://soldersmoke.blogspot.com/2010/03/polyakov-plus-dual-band-receiver-with.html Lauser Plus. Lauser = Imp or Young Rascal! DK2RS. He used a ceramic Resonator VXO at 3.58 MHz. Mine works great on 40 with VFO running 3.5 — 3.65 MHz. See schematic below.

On 40 AM with DX-100 and MMMRX. DX-100 died. 12BY7 VFO buffer went bad. How common is failure in this tube type? Nice QSO with Tim WA1HLR about the DX-100.

Got my Dominican license: HI7/N2CQR! SSSS on the way. Thanks to Radio Club Dominicano and INDOTEL.

Getting more active in the Vienna Wireless Society.

BOOK REVIEW:

“The History of the Universe in 21 Stars” by Giles Sparrow. Written during the pandemic. Published by Welbeck, in London. https://www.amazon.com/History-Universe-21-Stars-imposters/dp/1787394654 Also: From “Atoms to Amperes” by F.A. Wilson available for download. See blog.

SHAMELESS COMMERCE DIVISION:

Todd K7TFC getting ready to launch “Mostly DIY RF.” I used his TIA boards in my 1712 rig. He will have boards like this and much more. Stay tuned.

I need more viewers on YouTube. They want 4,000 hours IN A CALENDAR YEAR! Please watch!

FARHAN’S NEW “DAYLIGHT AGAIN” RIG. Analog. VFO. Comments, observations. We need to get him on the podcast. Maybe two shows: SDR and HDR.

PETE’S BENCH

Time very limited. But still sharing lots of tribal wisdom.

Wireless set with tubes!

Tool recommendation – Air compressor

MAILBAG:

Farhan VU2ESE – Speaking of big antennas “Whenever I look at the huge construction cranes in Hyderabad, I always think how one could make 160m, 4 element yagi using it as a boom..”

Todd K7TFC in Spain, spotting Log Periodics in Madrid.

Andreas DL1AJG: Can Biologists fix Radios?

Janis AB2RA Wireless Girl. Expert on Hammarlunds. And was my first contact with the Tuna Tin 2. She too was HB!

Peter Parker VK3YE on Owen Duffy VK1OD

Lex PH2LB on homebrew radio

Would this really be homebrew? Mail from H-A-D article on FM receiver

F4IET a DSB rig from France

Ciprian got his ticket YO6DXE

Josh G3MOT sent us a good video about the Vanguard satellite and IGY.

Dave Wilcox K8WPE bought Chuck Penson’s Heathkit book.

Rogier — So many great articles and links from PA1ZZ

Bill AH6FC Aloha. Retiring. Wants to build. Mahalo!

Grayson KJ7UM Working on an Si5351. Gasp.

Mike KE0TPE viewing YouTube while monitoring 6 meters. He will have a lot of time to watch!

Chris KD4PBJ spotted Don KM4UDX from VWS FB

Mark WB8YMV building a superhet. Having trouble with 455 kc IF can filter.

Walter KA4KXX Great comment on the Daylight Again rig.

Ramakrishnan Now VU2JXN was VU3RDD. Found lost Kindle with SolderSmoke book on it. Building SDR rig from junk box. Trouble with the LM386.

Pete, Farhan and Tony: Shelves of Shame

Daylight Again by Farhan
The Polyakov receiver I built yesterday (from SPRAT 110, 2002!)