Category: Farhan

Words of Wisdom from Farhan

I read the mail of the BITX20 group. Here is some good advice from Farhan:

I have often seen builders finishing an entire build, then powering it
up to face the frustration of a dead circuit. I suspect that the
trouble is with our kit building mind set. As a kit builder, we assume
that if it has worked well for a few hundred others, there is no
reason for it to not work for us. But the truth is more sobering …
Of the hundred odd components, any of them could get swapped by
another, or a bad solder, wrong polarity, etc. can all conspire to
thwart your attempts. The bitx manuals are really some of the best
produced in the recent years and yet, even with leonard’s videos,
troubleshooting kits is a challenge.
I am proposing a more elaborate, slower but surer approach to building the bitx.

It is as follows: build it one stage at a time, use one stage to test
the next. For instance, one could start with the bfo first. Just a
single transistor with the crystal. Then use an RF probe to check the
rf output. If there is no output, then sort that out before proceeding
to the next stage. With the addition of the buffer amp, the output
should go up. Then one could proceed to the audio amp. Injecting audio
from your mp3 player or computer could check that it works. Next,
replace the audio source with the mic amp, this tests the mic amp.
Now, if you add the two diode modulator, you should be able to receive
the dsb at 10 MHz on your HF transceiver.

This approach tests each stage individually and in isolation before
proceeding to the next. It also provides wholesome education to the
builder. In software industry, it is called a ‘test driven
development’ method of developing software.

In the end, this approach is no slower than the current approach,
except that surprises are not kept for the last.

I am sure that some of us can come out with a sequence of stages to
build where each stage is tested using the previous stage.

As much as bitx is about building it cheap, it is also about learning
your radio from inside. Bitx is also education on the cheap, don’t
give up that opportunity.

– farhan VU2ESE

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Hard Core! Wisdom and Ideas on Toroids

Gerard ZS5AAC

This morning the BITX20 mailing list has an interesting discussion of toroidal cores. I especially like Gerard’s use of the cores from old CFL bulbs. Farhan wraps it up with a great explanation of why we use ferrite cores in broadband transformers:
——————————
Over the years I built quite a few BITX’s. In the beginning I used the
toroids salvaged from CFL lamps. These worked quite well for the mixer
coils. For the filter coils I used 6mm bakelite slug tuned coils that were
stripped from old PYE radios. Wonder if anybody else experimented
along the same lines. I build my BITX’s Manhattan style and they work from the start with few minor tunings. Happy BITX’ing, Gerard, ZS5AAC.
—————————————
Bob
The purists may attack us on this, but what you propose is very
possible. I have been using a wooden-core toroid for several years as part of an antenna tuner.

http://qrp.webhop.net/Pictures/Webcam-1293651325.jpeg

http://qrp.webhop.net/Pictures/Webcam-1295140555.jpeg

I’m also using small plastic and wooden beads as toroid cores for
several other projects. Half inch long sections cut from thick-wall (schedule-40 or schedule-80) PVC pipe also makes good toroidal forms. Beauty of using non-metallic cores is that the core can be split to allow winding wire through the slot without having to thread it through the hole.

http://qrp.webhop.net/Pictures/Webcam-1289957121.jpeg = 1.4 uh

Bending an inductor back on itself in toroidal form concentrates the
magnetic field in the center, whether the core is metallic or non-metallic. This gives you similar self-shielding properties when using either type core material.

With non-metallic cores you no longer have to worry about core saturation, so running high current finals is not a problem.

Key to doing this is being able to measure inductance of 5 turns, 10 turns,
and 20 turns, so you can calculate and plot the effective AL of your wooden core toroids. Once you know this value you can make up a chart to tell how many turns are required for a specific inductance.

Twisting wires together to make a transmission-line for bifilar or
trifilar windings is interesting because the impedance of that transmission line might affect performance of your transformer. It may require a bit of experimentation with an SWR bridge to tell when you have the best balance between twist pitch, wire diameter, and insulation thickness.
Arv – K7HKL
———————————————

Robert, Arv,
There are two types of coils used in the bitx – the broadband
transformers and the RF coils in the bandpass filter and oscillators.
You could easily substitute the rf and vfo/bfo coils with just about
any kind of coil – as long as you are hitting the same inductance and
Q. But there is a catch : a few years ago, I finally got down to
measuring the Q of the nylon tap washers that I had originally used.
The q was quite modest at 70. Wes made independent measurements with similar results (his paper is on www.w7zoi.net under technical stuff). In short, for good performance use good old air coils wound on a
cylindrical formers if you don’t use toroids.

About the broadband transformers. These need a material that has very
low loss, very high permeability. The reasoning is like this :
1. We need an transformer’s inductance such that the reactance is
at least 200 ohms at the lowest frequency. This puts the inductance at
around 30uH at 4MHz.
2. If we achieve 30uH through lots of turns (say 100), each turn will
exhibit capacitance with it’s neighbor and the large number of turns
will add up the capacitance so that the coil will provide enough
self-capacitance to resonate at an unintended frequency in HF leading
to pretty bad mixer performance.
3. The only way out would be to achieve the required reactance with
lower number of turns. This means using ferrites.
– farhan VU2ESE

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Toroidal Travails II

Steve Smith sent me a good article on broadband transformers. Reading through it, it occurred to me that perhaps using a heavier gauge wire in that PA output transformer might help. So I rebuilt the FT-50-43 transformer and put it in the final. No joy — output was still down around 1 watt. Then I tried adding two turns to the secondary (on his web page Farhan advises experimenting with the turns ratio in an effort to improve output). Again, no joy. So I went back to the FT-37-43 transformer with 12 turns on the secondary. This yields the best results so far: about 2.5 watts. Still a bit low, but for some reason, the smaller cores seem to do better. Toroidal transformer tweaking to continue… Stay tuned.

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Toroidal Transformers: Does Size Matter?

I continue to tweak and peak the JBOT amplifier in the Azores 17 SSB transmitter. On this version I used some FT-50-43 toroidal cores instead of the smaller FT-37-43 cores recommended by Farhan. This morning I was experimenting with the output transformer. I seem to get noticeably more output with a transformer made with four FT-37-43 cores than I do with one made with four larger FT-50-43 cores.

I noticed something similar on my previous JBOT: performance improved when I switched from some relatively large binocular cores and went to the recommended FT-37-43.

So, what do you guys think? Could there be lower losses using the smaller cores? Any other reason why the smaller transformers seem to be doing better?

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Another JBOT Amplifier

Over the weekend I built another JBOT 5 watt linear amplifier (design by Farhan). I used a nice piece of copper-clad board that Dave, W8NF, sent me (thanks again Dave).

This time I chickened out regarding the possible conductivity of the anodized heat sinks. I didn’t have any trouble with this on my first JBOT, but I worried that if the anodized layer gets flaked away, a heat sink might short one of those collectors to ground. To be on the safe side, I put small squares of Gorilla Tape on under the heat sinks. (PLEASE don’t tell me that Gorilla Tape is conductive!)

For T1 and T2 I used FT50-43 toroids instead of the TV baluns used by Farhan. He had recommended FT37-43’s as an alternative to the TV baluns, but I went with the slightly larger toroids. For T3 I rolled my own binocular core using four FT37-43 toroids stacked 2X2.

The amplifier has passed the smoke test. Next I have to put in the low pass filter (Steve Smith: Please note that I have left space on the board for the filter.) Then this version will face its real test when it goes into the 17 meter Azores SINGLE sideband rig.

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Another JBOT Amplifier

Over the weekend I built another JBOT 5 watt linear amplifier (design by Farhan). I used a nice piece of copper-clad board that Dave, W8NF, sent me (thanks again Dave).

This time I chickened out regarding the possible conductivity of the anodized heat sinks. I didn’t have any trouble with this on my first JBOT, but I worried that if the anodized layer gets flaked away, a heat sink might short one of those collectors to ground. To be on the safe side, I put small squares of Gorilla Tape on under the heat sinks. (PLEASE don’t tell me that Gorilla Tape is conductive!)

For T1 and T2 I used FT50-43 toroids instead of the TV baluns used by Farhan. He had recommended FT37-43’s as an alternative to the TV baluns, but I went with the slightly larger toroids. For T3 I rolled my own binocular core using four FT37-43 toroids stacked 2X2.

The amplifier has passed the smoke test. Next I have to put in the low pass filter (Steve Smith: Please note that I have left space on the board for the filter.) Then this version will face its real test when it goes into the 17 meter Azores SINGLE sideband rig.

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Homebrew SSB Portable from Australia

Peter Parker, VK3YE, is one of the true gurus of QRP phone. When I first started building DSB and later SSB rigs, I frequently found inspiration and ideas in Peter’s articles and web sites. This morning I came across this amazing video, produced just days ago, showing Peter and his new SSB transceiver in operation from a beautiful Australian beach. The rig is a 40 meter version of Farhan’s BITX-20. (I really like the frequency dial.)

Peter describes his rig this way:

It’s made from scratch, ugly style, with 99% being from the original design.
It covers 7 to 7.2 MHz, using a 9.05 MHz IF and a 2 MHz VFO.
I used a different microphone amplifier (I got more and clearer output than
the original with my electret mic) and a BD139 driver transistor.
The PA circuitry is also slightly different.
It’s been about my easiest and most trouble-free transceiver project to
date. Performance is excellent and a tribute to Ashhar. The furthest distance so
far was a 5/6 report from ZL (about 2000 – 3000km away).

The grand finale of the video is a four-way contact with homebrew rigs in use at all four stations. Excellent. Thanks a lot Peter.

Here is Peter’s web site: http://home.alphalink.com.au/~parkerp/

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Las Cruces QRSS Mafia Attacks Pensacola!


OM Dave, WA5DJJ, writes to us about a different kind of SKN — I guess this would be SLOWWWWWW Key Night!
———–
Dear Bill,

Hope you and yours have a very Happy New Year.

I agree that Ashhar Farhan is one of the guys that I also admire
mainly because he is trying a valid approach to get amateurs on
the air. His designs are easy to construct, use simple common
parts and work well. I got really tickled when he said that he
kept his parts in two plastic tool boxes. I have so much I have
a hard time keeping mine in a garage with some spillage over to
the storage shed. But alas, I need to downsize.

Keep up the good work with SolderSmoke podcast. You are reaching
a lot of folks and also making a difference.

Our Las Cruces QRSS Mafia had a New Years 2012 on the air celebration
on 30 meter this New Years. We got 14 transmitters on the air and
managed to jam the Pensacola Snapper with so many signals that Bill
couldn’t count them all. I attached the sheet I sent W4HBK to
mark the event. There wasn’t much room left but others still got
in the holes. We did have a lot of fun plotting the event and getting
the 15 guys installing antennas, building transmitters, and programming
keyers. So, there was a lot of activity here to do the deed.

Anyway, Keep the soldering hot and the projects going. I like your
rebuild of your 17M transmitter. Nice project.

Take care and have fun in 2012.

73 Dave
David R. Hassall WA5DJJ
WEBSITE: http://www.zianet.com/dhassall/


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Homebrew Hero: Ashhar Farhan, VU2ESE


I wanted to start off 2012 with something inspirational, and here it is: Ashhar Farhan’s work bench. I was visiting his site yesterday and found lots of good info, good humor and, indeed, inspiration. Be sure to check out his RF generator project. And the page that gives his thought on tools and test gear. All of it is wonderful — you’ll find lots of evidence of Farhan’s long-term case of The Knack, his efforts to put “soul into his new machines” (his kids are mentioned frequently in his descriptions of his projects), and his obvious qualification for membership in the International Brotherhood of Electronic Wizards. I really like Farhan’s efforts to design rigs that can be built with parts available all around the world — a JBOT amp of his design is percolating nicely in my 17 meter DSB rig, and has been crossing the Atlantic almost every day.

As we were throwing a football around yesterday, I told Billy about Farhan. I mentioned that he lives in Hyderabad — Billy thinks that’s one of coolest city names on the planet and plans to work it into the plot of a novel he is working on.

Here is the site: http://www.phonestack.com/farhan/

Three cheers for Farhan! Happy New Year to all!

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Secret Listeners — The Voluntary Interceptors

Jim, AL7RV, and several others sent me the link to this really interesting video about the British radio amateurs in WWII. Real “stiff upper lip” spirit in this video. Musn’t grumble! Great stuff from Great Britain: http://www.eafa.org.uk/catalogue/5108

That regen receiver they showed looks a lot like the beast that I brought back from the UK with me. Once again, I am hearing the siren song of the diabolical regens….

Progress continues on my Indian-ized Azorean DSB transceiver (with JBOT amp). I now have the amp nicely stabilized (thank God!). Now I just need to get the output from the balanced mod close to the 1 mW PEP level needed by the amp. Should be done soon. And my cold seems to be going away, so maybe I’ll be able to share my tales of JBOT derring-do in a podcast this weekend.

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A Re-balanced Modulator for my Re-cycled Rig


My effort to bring my Azorean 17 meter DSB rig back to life continues. This is proving to be harder than I thought. I’m still taming my version the JBOT amp. It still seems to break into oscillation — I think the oscillation freq is around 1 MHz. But I am making progress.

I had to go back and work on the balance modulator circuit. I really like the simple two diode singly balanced mixer circuit. But my original Azorean board had, like the oscillator board, been through a few too many rounds of modification and repair. I decided to start over. See above. I even came up with my own little innovation on this circuit. Doug DeMaw’s original design called for a 100 ohm pot at the junction of the two diodes, with the signal coming off the tap. You adjust the pot to balance the circuit and null out the carrier. But I didn’t have a 100 ohm pot. Lots of 1K controls were available, so I put in two 50 ohm resistors in place of the pot, then put the 1k pot between the diodes, with the tap to ground. This balances things out nicely. See below.

I hope to get a podcast out next week, but I’ve been suffering from a nasty headcold that would have introduced all kinds of weird audio effects.

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Amplifier Woes — Help me! Help me!

When I look in the mirror and I see a haunted, obsessed look in my eyes. My wife senses that there is something wrong in the ham shack. She is right. I have an amplifier that wants to be an oscillator. Help me exorcise these gremlins! Guys, this problem is holding up the production of the next SolderSmoke podcast.

My JBOT amp works fine into a dummy load, but when I connect it to an antenna, it gets unstable. Here are some more details of the symptoms:

I am running the JBOT with a 5 element (two toroids, 3 caps) low pass filter (designed by Doug DeMaw and approved by Steve Smith).

With the antenna connected, all is well UNTIL I raise the power out (by varying the input) beyond about 1 watt. Below one watt, the amp is working fine, and it stable. As soon as I hit the 1 watt point, the amplifier seems to break into oscillation. This does not happen into the dummy load.

The antenna is a simple dipole fed by coax. It shows a low SWR. Even when I put an antenna tuner between the amp and the antenna and bring the SWR down to negligible levels, the instability problem persists.

With the amp disconnected from all other circuitry other than the antenna and the power supply, if I just touch the input capacitor, it breaks into oscillation. This does not happen when the amp is working into the dummy load.

I’ve bolstered the power supply filtering and decoupling. No luck. I tried some de-Qing of the transformers. No luck.

Any suggestions?

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JBOT Amplifier Installed in Azorean DSB Rig

I‘ve been remiss in posting to the blog, but I have a good excuse: I’ve been melting solder. I have working on the installation of my new Farhan-designed JBOT amplifier in my old Azorean DSB transceiver. I’m really enjoying this project, and I now see it as the first in a series. My shack has a number of creations that were built during the peak years of the last solar cycle, but have since fallen into disuse. Many of them were partially cannibalized — usually it was the RF amplifier that was taken out. The JBOT was just what I needed. I plan to refurbish all of these rigs, adding a bit of India to each one of them. This is very much in keeping with our “International Brotherhood of Electronic Wizards” ethos.

The installation went fairly well, but with all of the ups and downs that accompany this kind of project. The amp worked fine on the bench, fed with a signal generator and into a dummy load. But of course, life got more complicated when I installed it in the rig. Yes, it took off on me. This was no fault of the amplifier — I just needed to add some additional shielding. It is working fine now. See above. I moved it out of center stage and put it off in the corner to avoid feedback problems. More discussion of this in the next podcast (maybe this weekend).

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My JBOT 5 Watt Linear (Farhan’s Design)

There it is — my version of Farhan’s JBOT 5 watt linear amplifier. JBOT stands for “Just a Bunch of Transistors.” But I think Farhan is being modest. I really like the design, especially the effort to make this something that hams around the world can reproduce from readily available parts. For example, Farhan’s original version used TV balun cores for the transformers. I didn’t have any of those around, but I found three “mystery spec” binocular cores in my junk box. They seem to be working just fine. (I tested them a bit: Farhan had written that FT 37-43 cores would work. T1 has seven turns trifilar. Seven turns on my mystery cores yielded 13uH. On an FT 37-43 core 7 turns yields around 20 uH. Close enough — these are, after all, broadband transformers.)

Note how closely my build follows Farhan’s schematic (which you can see in the background). When building this circuit, I just kept Farhan’s web page on my computer screen, and scrolled up and down from his schematic to the photo of his version.

This is the first linear amplifier that worked the first time I powered it up. It didn’t release any smoke, or leave transistor burn tattoos on fingers, or try to be a 14MHz oscillator.

This version is going into my Azores-built 17 meter DSB transceiver. See how nice it fits:
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My JBOT passes the Smoke Test

Over the weekend I built my first version of Farhan’s JBOT. I really enjoyed building it. I soldered in the last connections this morning and I am happy to report that it passed the smoke test. More info (and a picture) tomorrow. Thanks Farhan!

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Comet Hits Sun, SFI up, Report from San Vito

The SOHO spacecraft caught some great images of a comet crashing into the sun. The YouTube clip above is from July. Here is NASA video of one that took place just last week:

http://www.nasa.gov/mission_pages/sunearth/news/comet-cme.html

Coincidentally I’m sure, the solar flux has increased significantly and the upper HF bands are working again. My 17 meter rigs still need final amps — I am ordering parts for Farhan’s JBOT circuit. (I plan to build three or four.) But because I had the 2B on 15 meters for the Sputnik event (still no Sputniks heard here) I noticed that DX was coming on that band. Using my HT-37 and a 40 meter dipole I easily worked several Europeans on 15 meter SSB. Especially nice was a long rag chew (using my rusty Italian) with Gianfranco, IZ4NPE, in beautiful Ferrara, Italy (a bicycle city).

Somehow tying this all together, I got an e-mail from Walter in San Vito, Puglia (the heel on Italy’s boot). Walter has one of those “dream jobs” for a radio amateur: He tracks sunspots!

Hi Bill,

Walter here from San Vito, Italy. Just wanted to drop a note to say hi and let you know that I’m enjoying your book. Thanks for making it available as a Kindle version. While reading, it brought back similar experiences with me as a youngster. I too was fascinated by airplanes and would ride my bike to the local airport and watch for hours as the planes would take off and land. My mom gave me my first airplane ride as a birthday present when I was 11. I have to admit that I was scared when we made our first airborne turn. I didn’t realize that a plane banks in the turns. I was also fascinated with shortwave radios and my best Christmas gift was a Radio Shack Globe Patrol (regenerative… hi hi) receiver kit. The gift from by grandparents was a Weller soldering gun (140 watts) to put it together with. Again, great job on the book.

The Sun has been keeping us busy at the Solar Observatory. I’m monitoring anywhere from 4 to 12 flares a day, 2 regions popped out of nowhere yesterday. The radio bands have been favorable with all the activity. I’ve got several projects in the works, a Genesis G3020 SDR rig is about 1/3 completed on the workbench now. It’s probably me when you see Puglia show up on the website spinning globe. Take care and keep the podcast’s coming. Ciao for now.
– Walter

I7/AC4IM

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A Good Day in the Shack — 2B Fixed, SPRAT Arrives

The temperature has dropped to around 10 C today. Fall is in the air. So it was appropriate for me to do some work on an old tube radio. (Several of our correspondents have reported similar seasonal urges to melt solder and to heat filaments.) This week my trusty Drake 2-B was giving me trouble on 17 meters. It was working on all other bands, but not on 17. Today I put it on the bench, pulled out the schematic and started troubleshooting. I quickly determined that the problem was, in fact, with the 22 MHz crystal. The 2-B has a 24.5 MHz rock for tuning the lower portion of the ten meter band. When I put that crystal in the “E” socket (where the 22 MHz crystal normally sits), the local oscillator worked just fine. Putting the 22 MHz rock back in the E socket resulted in no oscillation. And when I tried to the 22 MHz crystal in the 10 Meter socket normally used by the 24.5 MHz rock… nothing. What causes a perfectly good crystal to go bad like this?

Consulting the 2-B manual, I saw that I could also tune the 17 meter band by using (in socket D) a 14.21 MHz crystal from my junk box (it had been used in my 20 meter NE-602 DSB. transceiver). It works great. I’m listening to DK9KW calling CQ on 17 right now. Makes me want to fix up my homebrew 17 meter transmitter. (I need a final for it, and am thinking of using Farhan’s JBOT circuit). I may even buy some telescoping fishing poles and rebuild my Azorean rotate-able dipole (I have the mast and the wooden center support for the fishing poles). This magnificent antenna is shown above, spreading its wings above Sao Miguel island in the Azores (our home from 2000–2003).

Icing on the cake: I went out to the mailbox, and, instead of the usual pile of bills, there was a SPRAT 148 and the G-QRP Club’s Members Handbook.

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Links from #111: W7ZOI, VU3ICQ, AA1TJ

Here is the excellent discussion of bi-directional amps I mentioned. From the web site of W7ZOI:
http://w7zoi.net/Bidirectional%20Matched%20Amplifier.pdf

Here is Farhan’s new JBOT 5 watt final amplifier:
http://www.phonestack.com/farhan/jbot.html

Here is the mysterious (and perhaps diabolical) Xtaflex from AA1TJ (the first rig EVER to promise “buns of steel.”)
http://mjrainey.googlepages.com/xtaflex

Deep Solar Minimum

Farhan alerted us to this. From the NASA website:

April 1, 2009: The sunspot cycle is behaving a little like the stock market. Just when you think it has hit bottom, it goes even lower.
2008 was a bear. There were no sunspots observed on 266 of the year’s 366 days (73%). To find a year with more blank suns, you have to go all the way back to 1913, which had 311 spotless days: plot. Prompted by these numbers, some observers suggested that the solar cycle had hit bottom in 2008.
 Maybe not. Sunspot counts for 2009 have dropped even lower. As of March 31st, there were no sunspots on 78 of the year’s 90 days (87%).
 It adds up to one inescapable conclusion: “We’re experiencing a very deep solar minimum,” says solar physicist Dean Pesnell of the Goddard Space Flight Center.
“This is the quietest sun we’ve seen in almost a century,” agrees sunspot expert David Hathaway of the Marshall Space Flight Center.
For the rest of the article:
http://science.nasa.gov/headlines/y2009/01apr_deepsolarminimum.htm?list830785