BITX DIGI-TIA Build Update #1 Building the First 2 TIA Amplifiers

I started building the new transceiver today.   I am tentatively calling it the BITX DIGI-TIA.  Digi because it will have at its heart an Si5351 for BFO and VFO signal generation, and TIA because it will use Termination Insensitive Amplifiers (TIAs).  These TIA amps are designed to present a 50 ohm impedance not matter what impedance you connect to the other end.  This is a very useful feature when you are trying to get a certain impedance for a crystal filter in a bidirectional rig -- you want the same termination impedances in  both directions.

 

I built the "top" halves of two of the TIAs, using CNC-cut boards given to me by Pete Juliano.  Thanks Pete!  I like the boards, and I no longer have a thick coating of dried SuperGlue on my fingers.

 

Both amps seem to be performing  very well. Some numbers:

 

Current draw at 12 V (no signal) 30 ma.

 

Gain at 9 MHz (no load):  Amp 1:  27.2 db    Amp 2: 26.5 db.

 

I then took a 110 ohm load and put it across the output of Amp 1.  Gain dropped to 23.9 db (as you'd expect).  BUT HERE'S THE GOOD PART:  The input voltage from my homebrew sig generator stayed exactly the same.    Termination insensitivity. 

 

More on these amps (with a link to Wes's article) here:

 

http://soldersmoke.blogspot.com/2015/04/termination-insensitive-bitx-amps.html 

 

Next  I'll put the 9 MHz filter between these amps and measure the shape of the filter passband.

 



 

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

BITX DIGI-TIA Build Update #7: On The Air!

 

With lots of encouragement from Pete, I finally got the BITX DIGI-TIA on the air.  The first contacts were made yesterday. I have it on 40 meter SSB.  The finicky denizens of that audio-conscious band seemed to like the sound of the rig.   I was almost reluctant to tell them it is homebrew (no need to stir up trouble!)

 

The plug in filter arrangement seems to work very well.  This will allow me to put this rig on many other bands.  All I have to do is build some additional filter boards and upload modified versions of the software.  There is even space to make a plug-on socket for the crystal filter (the 9 MHz IF would not be cool for 17 meters).  

 

I'm really pleased with the RF power chain (the original BITX chain).  This time I built it all in a straight line along the back of the transceiver with lots of attention to shielding and grounding.  There were no instability problems.  The amplifiers did not try to be oscillators.  I was shocked!

 

I did have to reduce the gain of the three termination insensitive transmit amplifiers. Using the chart in the 2009 Wes Hayward/Bob Kopski article,  with just a few resistors you can set the gain.   I had built them with 19.4 db gain each.  This turned out to be too much -- the slightest amount of audio into the SBL-1 was driving the amplifiers to peak output.  So yesterday I changed all three amps to 15 db (I think that was what Farhan had in the original BITX).  It only took me about 15 minutes and it seemed to take care of the problem.  I am getting 7 or 8 watts out of the IRF-510.

 

T/R switching is very smooth and quiet using just two small 12V relays.

 

Thanks to Pete for the mil-pad boards and the encouragement (especially on the use of the Si5351).  Thanks to Farhan for the BITX architecture. Thanks to Steve Smith for the Yaesu filter.  Thanks to Wes and Bob for the TIA circuit.  Thanks to Thomas in Norway for the Si5351 software.  And Thanks to Allison for all the good advice.



 

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Adding Automatic Gain Control to the Termination Insensitive Amplifier

 

Earlier this month Paul VK3HN had a very interesting blog post about adding Automatic Gain Control to Termination Insensitive Amplifiers (TIAs).  

Termination Insensitivity is especially important in bidirectional rigs.  The shape of the crystal filter bandpass response is very dependent on the impedances presented at both ends of the filter.  In bidirectional rigs you are changing the signal path direction through the filter when you go from transmit to receive.  If the amplifiers at either end of the filter have impedances that vary depending on what is on the input or output of either stage, you will have great difficulty keeping the bandpass identical as you move from transmit to receive.  Termination Insensitive Amplifiers let you do just that -- they stay at one fixed input or output impedance (usually 50 ohms) independent of what is attached to the other end of the amplifier circuit.  This greatly simplifies impedance matching at the ends of the crystal filter. 

When I started building BITX rigs, I asked Farhan about the impedance matching problem.  He advised me to use TIAs on both ends of the filter and pointed me to a great 2009 article by Wes Hayward and Bob Kopski.  Using the information from that article, I built my DIGI-TIA transceiver, and I have used TIAs in almost all of the rigs I have built since that project.   

In his August 2021 blog post, Paul wanted to add Automatic Gain Control to the TIAs. He came up with a way to do this, but we worried that his circuit would have an impact on the impedance of the amplifiers. 

Yesterday, Wes Hayward W7ZOI posted on his web site a TIA circuit that lets us do it all:  Termination Insensitivity with Automatic Gain Control: 

http://w7zoi.net/tia+agc.pdf

I now find myself tempted to rebuild one of the TIA stages in my Mythbuster transceiver, adding the AGC circuitry from Wes's design. 

Thanks to Paul VK3HN for the blog post on this subject. And thanks to Wes Hayward for the TIA AGC design.  It is a real privilege to have direct input from Wes on questions like this. 

Retro QRP Rigs of the 1960's, 70's, and 80's -- Video by Mike WU2D

It is time to put aside (again!) all of the heated ideological arguments about the power level that defines "low power."  Just sit back and enjoy this wonderful trip down QRP memory lane. 

Mike's description of the simple, single-transistor QRP transmitter was really nice.   I recently made something similar: https://soldersmoke.blogspot.com/2023/02/first-qso-with-high-school-receiver-100.html  And Mike does a nice plug for our beloved Michigan Mighty Mite.  Go CBLA! 

The modular idea:  words to live by my friends. 

40673!  TT2!  And G3RJV's PW Severn - indeed, bow your heads!

Wow, the Ten Tec Power Mite (or Might!) -- I still want one.  Same for the Argonaut -- what a great name (sounds like a "magic carpet), and with SSB to boot!  I want to join the Argonaut cult! 

I have both the HW-7 and HW-8 (the HW-8 is heading to the Dominican Republic).  This video makes me want to fire up the HW-7.  Maybe on 40.  

My 40 meter homebrew rig (Digi-Tia) has in it the filter from that old Yaesu FT-7 rig.  The filter was given to me by Steve "Snort Rosin" Smith.  https://soldersmoke.blogspot.com/2015/05/bitx-digi-tia-build-update-2-installing.html  

Thanks to Mike for including me in the credit roll at the end.  What a great group of people -- it is a real honor to be listed with those folks. 

HB2HB: Contact on 40 meters with W0PWE

I got on 40SSB this evening and called CQ with my BITX DIGI-Tia.  Hooray!  Jerry W0PWE answered me with HIS 40 Meter DIGI-TIA.  His is still Al Fresco style.  Very nice.  We add this to the homebrew to homebrew scorecard.  Thanks Jerry!

Jerry's rig:

Amazing Homebrew/Boatanchors QSOs on 40 --Six solder melters in a row!

Al W8VR

After a day of happy tinkering with the Direct Conversion receiver I've been working on, I turned off the soldering iron and got on 40 meter SSB with my BITX Digi-Tia. 

First -- Steve W4IJ came back to my CQ.  Steve is a boatanchor enthusiast and has written for Electric Radio magazine.  FB. 

W4IJ Boatanchors

When Steve signed off, I got into a contact with Pete W8NBO.  We had spoken before and he had told me of a homebrew transmitter he'd built as a kid.  This time I asked for details: It was a 6AG7 oscillator to a 6L6 amplifier.  He ran it with an S38 (brave man!).  He described what must have been a very painful effort to hack (literally) the needed holes in the transmitter chassis using just a spike, a hammer and a file.  I told him this brought back my memories of similarly painful chassis work (mine was for a power supply for a Heath HW-32A).

At this point we were joined by Arnie, W2HDI.   Arnie's rig is in Stowe Vermont, but he was running it remote from the South of France where he and his wife were celebrating their 50th wedding anniversary.  Arnie shared with us memories of similar chassis pain -- his were related to an external modulator that he built for a DX-40. I think he said that all he had was a hole punch and a file.  Oh, the humanity! 

Then Al W8VR joined the conversation.  Al said that he's been in the game so long that his early rigs were built using cigar boxes as chassis.  I pointed to a connection:  I noted that my BITX rigs are enclosed in what could be considered cigar boxes.  Al's QRZ page picture has a magnificent AM rack rig that he said was actually built twice.  There is also an HRO-60 in the picture.  FB. Check it all out at Al's web site.  Click on the mic for the write ups, the key for the pictures.  http://www.w8vr.org/

Then Dennis K0EOO called in.  Holy Cow!   Dennis and I spoke not long ago.  You may recall my enthusiastic write up of his beautiful 1974 SSB rig: 

http://soldersmoke.blogspot.com/2017/08/k0eoo-homebrew-ssb-in-1974.html

and

http://soldersmoke.blogspot.com/2017/08/more-on-k0eoos-amazing-homebrew-ssb-rig.html

This was almost too much.  Rarely will you spontaneously come across so many hams who have melted so much solder.  FB. 

Icing on the cake:   When I returned to the bench, I fired up the DC receiver and heard Mike KN4EAR talking about his BITX40.  I switched to the Digi-Tia and gave Mike a call.  He reports making many contacts with his rig. FB. 

TRGHS. 

Video (Audio) of N2CQR (me) on 40 Meters with BITX DIGI-TIA

This was the icing on the cake.  Ruben AC2RJ up in New York was monitoring as I called CQ with my BITX Digi-Tia last night on 40 meters.  He recorded the contacts that ensued.  I was really glad that he recorded VE3XBO describing his experiences with a BITX 40 Module at his local radio club -- The WAX Group of the Barrie Radio Club in Ontario. 

Farhan's module is really starting to show up more often on the band. On the 19th of April I talked to Bruce KC1FSZ -- he was on his Peppermint Bark BITX 40.  And on March 30 I talked to Josh KE8CPD on his BITX 40.

Click on the arrow (above) to listen to Ruben's recording.  Ruben has a nice YouTube channel here:
https://www.youtube.com/channel/UCXClX_GBzFQIiqTwgnt8qxA

HB2HB: N6ORS, W0PWE (and me!)

This is so cool.  Jerry W0PWE has built a magnificent BITX.   With a digital VFO and Termination Insensitive Amplifiers, I think it qualifies as BITX DIGI-TIA #2.   Running it "al fresco" he was tuning around on 40 and he heard DIGI-TIA #1 (mine!).  As soon as he finished soldering in the power amplifier, he put it on the air and, in his second contact, worked Keith N6ORS -- Keith was running his MIN-X rig.  Clearly TRGHS. Great work Jerry!

Hello Bill,

Jerry here W0PWE in Iowa. I save up your podcasts and listen to them when I travel. A year or two ago you and Pete got me interested in the BitX and I finally took action. I have plenty of other
projects I should finish but boy was it ever fun to start a new one. This morning I soldered the
last part in my newly hatched Bitx, drug it over to the operating position and had two great QSOs
with it. See attached photo shows the rig as it was during those QSOs.

When I finished my first QSO with W9SX, Keith in WI N6ORS called me. He was running a multi-band Bitx he had built and we had a great HB2HB qso. Awesome!

My rig is scratch built, mostly SMT and generally follows the 40M schematic that Farhan has on
his HFsignals page. I am using the Kopski/Hayward TIAs though and I designed a 6 pole crystal
filter for it since 6 of the 10 crystals I bought were very similar when I characterized them
with my PHSNA setup. It uses the Adafruit SI5351 board and I modified a sketch that LA3PNA wrote for the Arduino. 

I designed and fabricated the boards for it using the software and process described by K7QO and
W5DOR. Toner transfer with the Hammerhill Gloss paper is working great. The heatsink on my IRF510 is a little light. I could smell the MOSFET warming up during a few of my lengthy transmissions with Keith.

Now the SWL report. While listening on the receiver portion of my Bitx last week I heard you on
7260 at about 0030Z. I think that was Tuesday or Wednesday. I wished I could give you a call but
at that point my PA was merely a few traces on the computer screen. Hope to hear you again on
40M.

73/72,
Jerry - W0PWE

SolderSmoke 264: CW TX, Repair if 17-12 Rig, AI and Repair, Back on 40m, HB for 2m, VWS WSPR Makers Project , MAILBAG

QSO May 8, 2026 with Lou EA3JE.  I was using my Mythbuster

May 12, 2026

SolderSmoke Podcast #264 is available for download: 

Audio:   http://soldersmoke.com/soldersmoke264.mp3

Video:  https://www.youtube.com/watch?v=_9FcfuqjZxA

We had a small recording glitch at the beginning of this video. But we didn't lose much. We talked about the success of the SolderSmoke Direct Conversion Receiver Project. We talked about the receivers built by Nader Omer ST2NH and Chuck Adams AA7FO. We also gloated a bit about our April 1 post -- you know, the (bogus! ) story about how the Administration is "Supporting Homebrew Radio." Let us know if you were taken in by this, even for just a few seconds. At that point, we were just beginning Pete's section. Here are the notes for the rest of the podcast:

Pete: 

Three CW transmitter projects featuring low parts counts.  Good results from Reverse Beacon Network. 

The goal in these projects is to raid the junk box and severely limit any new purchases of components.  Pete had no idea of the depth of parts he bought and just stashed away.   https://www.youtube.com/watch?v=5YLZ7aZpmxQ&t=30s

Bill: 

Fixing the 17-12 Rig.  Parasitic VHF Oscillations with the SK3050.  Good advice from Gemini. Killing NE602s. Fat Finger Syndrome -- hard to work with ICs.   Different freq when on transmit -- need for .1 uF cap on pin 8. Worked South Korea -- TRGHS. 

Putting the DIGI-TIA back on the air. On 40! And SW listening with the Q-31. 

Hard to homebrew for 2 meters.  Did some beacon experiments to Puerto Rico on last day in DR. 

SHAMELESS COMMERCE DIVISION: 

The importance of Patreon!  Thanks!  patreon.com/SolderSmoke

Mostly DIY RF!  https://mostlydiyrf.com/

Universe Today Podcast with Fraser Cain.  No Ads.  Great stuff.  Listen!   https://www.patreon.com/public-rss/75186?show=1744036

Dean: 

The VWS WSPR project.  

Mailbag:  

Ed N3EML  Heard me on 40 with my Digi-Tia

Grayson KJ7UM  Liked WWII training video: https://soldersmoke.blogspot.com/2026/05/radio-receivers-1942-training-film.html

Mike WN2A  -- Pete Juliano is our Shifu! (Lexicographer Steve Silverman KB3SII approves,)

Todd K7TFC Thoughtful comments on ARRL "Clean Signal Initiative."

Danny ON1MWS Regen with unusual variable capacitors. 

Mike WU2D  S-38, Nearfest,  Mu Metal.  https://www.youtube.com/watch?v=YUQ4xml1dSY

Charlie NJ7V  Interviews Mitch NK3H who homebrewed SSB transceiver. 

Charlie also had Don KM4UDX, President of the Vienna Wireless Society on the podcast. 

Bob KD4EBM -- El Cilindro. Radioactive Hospital Waste -- basis for a Ruben Blades song.  It was 1987 in Brasil.  Cesium 137 left in hospital waste.  

Hamilton  KD0FNR   Big fans of "The most interesting man in the world."https://soldersmoke.blogspot.com/2026/04/background-from-maine-on-most.html

Rhett KB4HG -- TW-100! Used on the OMRN. https://soldersmoke.blogspot.com/2026/05/the-tw-100-fly-away-transceiver-cw-ssb.html

What happened to Glenn KU4NO's homebrew rig? https://soldersmoke.blogspot.com/2018/07/a-rig-with-maximum-soul-5-band.html

Ryan KJ7KVD is listening to OLD SolderSmoke podcasts.  He will build a Michigan Mighty Mite. 

Will N5OLA restored a Heath SB rig.  We now know why they went to HW rigs.   https://www.youtube.com/watch?v=Bt2d1Ia8lqQ 

Paul G0OER -- Thanks us for PTOing the HB world, but sends us a video of a unique Eddystone receiver with 39 permeability tuned coils!  https://www.youtube.com/shorts/L4oQHU5_kQk?feature=share

Rick N3FJZ -- A very cool video today on his homebrew HF power amplifiers:  https://www.youtube.com/watch?v=-CUVAF4HyfY

Farhan VU2ESE -- I heard from him yesterday as he was landing in Chicago. 

Feedback on Farhan's FB Feedback Amp Video

As I said a couple of days ago, Farhan has put out a very informative video on amplifier design. During the video we can see him determine bias, feedback and load levels, then select component values. We then see him actually build the amplifier "ugly style" and use his Antuino to test it.  Fantastic.   

Watch Farhan's video here:  https://www.vu2ese.com/index.php/2020/06/18/feedback-amplifier/


I sent Farhan some of my reactions to the video.  In the hope of stimulating some discussion, I repeat them here: 

___________________

Wow Farhan, I really enjoyed your video and learned a lot.  You definitely have the Knack for explaining this stuff. 

I have been struggling to understand feedback amps for a long time.  I took up this topic on pages 187-190 of the "SolderSmoke -- Global Adventures" book.  I was more focused on the benefits of FB amps, and on how and why feedback affected input impedance.  

 I took notes as I watched: 

-- I liked the fulcrum analogy. 

-- Really wonderful how you describe the selection of components to get desired bias. 

-- Even better when you explain tapping down of RF coil to get 50 ohms to look like 200 ohms. Great stuff. 

-- Standardized on BNC.  FB! 

-- .1uF caps.  Love them!  No argument here! 

 

-- I copied your resistor list.  Will use it with Mouser. 

-- Saving the pigtails.  Indeed!

 

-- I like your ugly "resistors first" technique.  I may have to move away from Manhattan. 

--  Wow.  Ugly circuits IN SPAAAAACE!  FB!

 

--  2N3904   I always think it is EBC when looking at the flat end of transistor with leads facing down. Only had reverse pinout with PN2N2222.  EBC is my usual assumption.

 

-- I still have the big box of trifilars you left me.  I use them.  Thanks!

-- I like that VTVM in your Antuino.   Very handy. Want one!  Also, We need to get the Antuino to go down to below 455 kHz. 

-- I also like your dual Return Loss and SWR display.  I think in terms of SWR.  Return Loss sometimes messes me up. 

-- Didn't know about the Hold and Zoom feature on Antuino. FB.

 

-- Your measurement of the Q of the crystal was awesome.

  

-- I checked my soldering iron temp:  I'm at 480 C   A bit too hot. Will back off. 

 

-- Good description of need for an attenuator at amp output to keep it in Antuino's range.

 

-- As I watched you tug on the components after the solder cooled, I remember an old and silly admonishment from the ARRL Handbook:  NEVER  use solder for mechanical connections.  Ha!  They were WRONG!

 

-- Demonstration of the flatness of feedback was great.

 

-- I found your measurement of impedance using the SWR feature of the Antuino to be very useful.  Is there a chart relating the SWR/Return Loss to actual impedance values? 

-- Loved your description of how output impedance affects input impedance.  That is why you advised use of TIA amps in my DIGI-TIA.   But now I'm thinking that if I can accurately measure impedances of non-TIA amps, I can design L networks that will keep the crystal filter passbands ripple-free, right? 

-- Great explanation of the benefits of the 6 db pads at amp output.  Allison often recommends this. Now I know why. 

-- Wow!  Now I KNOW what that two-tone box you left with me is for!  Now I understand how it can be used to measure IMD on FB amps.  I pulled mine out just as you began to discuss yours.  Really cool. 

Thanks a lot Farhan for doing this.   These videos will be of long-lasting use to homebrewers around the world.  I hope we will see many more VU2ESE videos like this one. 

73  Bill 

BITX DIGI-TIA Update #4

 

Lots of progress over the long weekend.  Along the back you can see the three stages of the RF amplifier chain:  2N3904, 2N2218A, IRF510. I intend to add inter-stage shielding, and one long shield between the chain and the rest of the rig.   Front and center is the Si5351 board (code by LA3PNA).  Mic amp (which gave me a lot of trouble!) is to the right of the Si5351.   AF (RX) amp is to the left (2N3904 and LM386).  The big board in the center has the three Termination Insensitive Amplifiers (thanks Wes and Bob), the 9 MHz filter (thanks Steve Smith!) and the two SBL-1 mixers (thanks to Pete Juliano for the "mil-pad " boards).  And thanks to Farhan for the overall BITX concept and the TIA suggestion.  

 

In the upper right you will see where the plug-in low-pass filter will plug in (a better picture appears below).   I will use a similar plug-in for the band-pass filter.   Combined with the BFO/VFO flexibility of the Si5351, this plug in feature should allow me to cover many bands with this rig.    

 

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Alan Wolke's Drake 2-B (video)

Alan's video inspired me to do a little work with my Drake 2-B.  Nothing major -- I was just making sure that the passband knob is in the right setting.  I've complained that the Drake 2-B doesn't sound great on AM.  I recently noticed that my BITX40 DIGI-TIA sounds surprisingly good with AM signals -- I just treat them as SSB signals and zero-beat the carrier with my Si5351 VFO.  I wanted to try doing the same thing with the 2-B, and then make some comparisons.  I only heard a few AM signals this morning, so I will try again later today and will report results here.   

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

BITX DIGI-TIA Build Update #2 Installing and Testing Yaesu SSB Filter

Termination Insensitivity.  It sounds like some sort of psychological problem, but it is not!

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

SolderSmoke Podcast #180 Pete's Beam, Simple-ceiver, 2-B, Noodling, Homebrew and SDR?, "The Martian", Mailbag

SolderSmoke Podcast #180 is available:

http://soldersmoke.com/soldersmoke180.mp3

19 September 2015

PROJECT REPORT:
Pete's Antenna Project:  The Joy of Rotation!
Simple-ceiver
Bill fixes Digi-Tia (after breaking it)
Shack Configured for Winter (DX-100)
Working (a little) on the Drake 2-B

SolderSmoke words we forgot to mention:
Noodling
The Radio Gods
The Radio Art
The Grand Poobah
Magic Smoke
Lud(d)ite Curmudgeonism

SDR and the Homebrewer

"QSO Today" Interviews
Lady Ada interviews Paul Horowitz of "Art of Electronics"

SHAMELESS COMMERCE:  Book still free!
Start your Amazon purchases at our blog page.

Book Review:  "The Martian"

Great QSOs with W5NDS and AE5RM

MAILBAG

The Nauen Transmitter Station (Germany)

There is a lot of radio history in this shortwave transmitting station.  I came across it tonight with my BITX DIGI-TIA rig.  It was on 7.215 MHz transmitting in Indian (South Asian) languages.  But alas, the signals were not from distant India (home of the BITX!). Instead -- as often happens these days -- the signals were from a relay station.  In this case they came from  relatively nearby Germany, from the Nauen transmitter site.

Check out the Wikipedia page:

https://en.wikipedia.org/wiki/Nauen_Transmitter_Station

Arduino Problems -- Back from the Ledge

As I was struggling through this, someone -- who will remain nameless -- told me that because of all the technical problems resulting from the many Arduino IDE "upgrades," suicide prevention hotlines now answer all calls with an automated question:  "If you are calling about an Arduino problem, press 1 for assistance."

It got pretty ugly but with the help of Tom up in NYC I managed to get through it. First he convinced me that it is indeed POSSIBLE to upload the latest version of the IDE -- the dreaded 1.6.7.   I just had to REALLY get rid of earlier versions.  This got me past the horrible Bundled Java Runtime Environment problem (who thinks up these names?).

We then worked with the libraries needed to upload the AD9850 code of Richard AD7C.  You see, I work on Arduino stuff.   Then I stop.  18 months pass.  I forget all I learned.  Then I start over.  The pain begins again.  In an effort to break this cycle, I am now taking notes (in the inside cover of Mario Banzi's book).

I am using the AD9850 with a Kanga Arduino shield designed by Paul M0XPD.   It takes the AD9850 output, divides by 4 and puts it out as 2 square waves in quadrature.  I use this with my R2 phasing receiver.   The problem was that the display on the Arduino showed a freq 4 times the actual tuning freq.  Believe me, this gets old fast.  I considered just getting a San Jian freq counter and supergluing it on the top of the DDS box.  I was going to connect this to the square wave output.  That would have given me one readout with the actual receive freq, and another (on the Arduino) showing the (4X) freq coming out of the AD9850.  But that would have been too much of a Kludge. Tom talked me out of it and modified the code so that the Arduino display shows the actual receive freq.   Thanks Tom.  

Armed with the new IDE and with my knowledge of Arduino basics refreshed, I was able to reload the LA3PNA Si5351 code into my 40 meter DIGI-TIA.  But not before having to swap out the Arduino that drives the Si5351.   One Arduino happily accepted the code, another did not.  Why?  Who knows?  It is a digital mystery.  Those little 1s and 0s are fickle you know.

The Radio Gods rewarded me for all this.  At about 5:45 AM today I was listening to a very friendly SSB roundtable on 160.  The guys were getting ready to sign off.  The last one ended the conversation by asking the others to "Be kind.  Smile at your neighbors."  Nice.
Then WFAX AM started the broadcast day at 6 am, wiping out my 160 meter reception.  Next project:  High-Pass filter at 1.7 MHz.

BITX DIGI-TIA Build Update #3 Video of Receiver in Operation

A few things I forgot to mention in the video:

That USB port on the front panel has already come in handy.  I needed to switch the tuning increment from 1 kHz to 100 Hz.   I just went into the Arduino program, removed one zero, and then re-uploaded the code.  

I also put to use the sideband inversion rule-of-thumb:  My IF is at 9 MHz.  I want to receive signals in the 7.2 MHz range, and I want the VFO running ABOVE the IF frequency.  So obviously the VFO will be running at around 16.2 MHz.  So, rule-of-thumb time:  Will I be subtracting the frequency with modulation from the frequency without modulation?  Yes I will!  So, there will be sideband inversion.  This tells me where to position my BFO frequency.   The signals on 40 start out as Lower Sideband.  But as explained above, by the time they get to the filter they will be inverted and will be upper sideband signals.  So I need to put the BFO slightly BELOW the filter passband so that I can tune the signals in such a way as the sidebands fit into the filter passband and have the proper frequency relationship to the BFO to allow for demodulation. I put it at 8.9986 MHz.  With the Si5351, changes to the BFO and VFO frequencies are very easy.

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Re-purposed Computer Power Supply Box Provides a Home for a BITX Transceiver

Jaydip VU3JOJ came up with a really inventive way to box up his new BITX transceiver.  Nicely done. I especially like the way he put the speaker  in the space intended for the fan. Very nice.

This appears to be one of the new BITX 40 meter "modules" described in yesterday's blog post.  FB!  How fortunate the new board fits in the power supply boxes.  That's very lucky.

You know, I had an old computer power supply in my hand  just yesterday.  I almost threw it out.  Obviously that would have been a mistake.

Today was a BITX day.  Using my BITX DIGI-TIA on 40 I had a long QSO with Rich N3TDE.  Rich has a BIT20 built from a Hendricks kit acquired at Dayton.  He takes it with him on the Appalachian Trail.  

TRGHS! HB2HB! Homebrew Extravaganza on 40 Meters!

AC7M HB Amp and HB Power Supply

I was flying solo last night.  Everyone else in the house was out.  So I turned to ham radio for some company.  And I was rewarded.    

I called CQ with my BITX DIGI-TIA rig and was immediately answered by Doc AC7M in far-off Twin Peaks, Idaho.   Doc was running a K3 to a homebrew solid state full gallon amp.  And get this -- Doc had also homebrewed the 3 kw switching power supply.  I looked at my store-bought supply and felt like an appliance operator.  I hang my head in shame.

As we discussed solid state amplifiers, we were joined by another builder of silicon after-burners: Don K9AQ, who called in from a beautiful cabin in rural Wisconsin. Don's amp is based on the venerable EB-104 design.   

Both Don and Doc talked about the work of W6PQL.   He has a really amazing site devoted to homebrew solid stat amps, and he is selling lots of great boards and parts for this kind of project:
http://www.w6pql.com/  

As I finishing up with Don and Doc, I got a very welcome call from an old friend from the SolderSmoke community: Dino KL0S.  He as booming in from Williamsburg, Va.  Dino has an amazing workshop.  He is building a serious vertical antenna for 160 meters.  Dino is going for the DX.

Dino's Bench

At this point Mike WA3O in Pittsburgh called in.  And get this:  Mike heard me on his new BITX 40 Module.  The Radio Gods Have Spoken! (TRGHS!).  We switched up to 7.285 MHz where I fired up my BITX 40 Module for a BITX40-BITX40 QSO (albeit not at QRP levels).
We should definitely make more use of 7.285 for BITX40 and other HB QRP SSB QSOs.  1930 EST (0030 Z) seems like a good time.

Finally, just when I was thinking that things couldn't get any better, they did:  Armand WA1UQO called in from Richmond.  Armand and I collaborate on parts acquisition at Virginia hamfests.  We specialize in the contents of the musty cardboard boxes found under the tables.  We discussed the DISRUPTIVE influence of Farhan's BITX 40: All around the world, other homebrew projects are being literally pushed aside on workbenches to make room for that fantastic little module from Hyderabad. 

I was very pleased to hear that Armand is building an analog VFO for his module, using a coil in the 4 uH range, wound on a piece of cardboard tube from a coathanger.  The inspiration for this kind of coil (which I now have in THREE rigs) came from Farhan, who used sipping straws from fast-food restaurants as coil forms in a sig generator that he built years ago.  This week, seeing a Facebook picture of my daughter and me in a restaurant with drinking glasses in front of us, Farhan asked if I had brought home the straws. 

Mythbuster Video #15 The Mythbuster Signal As Seen in the NA5B WebSDR

Mehmet NA5B has an excellent WedSDR receiver in Washington D.C., about 9 miles east of me. I often use it to check my signal quality. I think this video shows that the 10 pole crystal filter is working and is producing a signal with very sharp drop-off outside the 2.7 kHz passband. You should focus your attention to the passband (yellow vertical lines) near 3895 kHz. That's me.

Once, when I was describing my 40 meter DIGI-TIA to an SDR guy, he seemed surprised that I was using a -- gasp -- crystal filter. "Your skirts must be atrocious!" he said. My HDR sensibilities were deeply offended.

I had hoped that the 10 pole crystal filter would produce skirts so nearly vertical as to make my signal indistinguishable (in the waterfalls) from the SDR signals. At least at this low signal level, it appears to be working.