Category: BITX DIGI-TIA

My Manhattan-style Termination Insensitive Amplifier Production Line

You gotta love the name, right? It sounds like some sort of psychological condition. Perhaps someone who just doesn’t care if his girlfriend breaks up with him, or is indifferent to getting fired.

But no, we know that that’s not what it means.

I recently had to make three sets of TIA amps for my new 15-10 rig. First, I decided not to use the boards provided by Todd of Mostly DIY RF. You can see one of these boards above the tin shears in the picture above. Note how compact it is. Even though you would need two of these (one for receive, one for transmit) to get what you need for a bilateral rig like the BITX, using these boards (as I did on my 17-12 rig) saves you a lot of space. But this time I wanted to build a rig that is TOTALLY DIY RF. So out came the tin shears and the super glue.

First I decided on the Manhattan pad placement. I used a pattern that had worked on previous rigs. Pete is right — I use a lot of TIAs (but no, I have no tattoo of the circuit anywhere on my anatomy!). I scaled it down a bit, thinking that I could come a bit closer to Todd’s compactness.

Knowing that I would need three sets, I first made three boards. Then it was just a matter of soldering in the components: I did resistors, then capacitors, then, finally, the transistors. In this way I was able to put together the three dual TIA amps in a couple of morning build sessions. It was kind of tight and I had to be careful to avoid wiring errors or unintentional shorts. But it worked.

I like the TIA circuit. It lets me select the gain of a stage by simply using two resistor values from W7ZOI and K3NHI’s chart. And with this circuit I know that it will look like 50 ohms both ways. This is really important on bilateral rigs like this.

I don’t think there is anything wrong with using BITX-like bilateral circuits or TIAs or LC VFOs. This is all for fun right? I just like using these circuits.

My friend Pete is right in pointing out that the bilateral concept did not originate with the BITX — it has been around for a long time, going back at least as far as the Cosmophone. But I think Farhan’s BITX definitely moved it into the solid-state homebrew mainstream. Three cheers for Farhan for doing that.

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.

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:


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.

SolderSmoke Podcast #232 — Mythbuster, Pete’s Tube CW Rig, Pete’s DC RX and Simple SSB Rig, NanoVNA and TinySA, Very FB Mailbag

SolderSmoke Podcast #232 is available — Crank it in Robert!

Featuring a guitar intro by Pete “Bluesman” Juliano, playing his own composition: “Juliano Blues.”

Upcoming GQRP convention and the N6QW rig
Frank Jones and the FMLA — Possible Victory?
IBEW Stickers: NASA, Johns Hopkins APL….
Cycle 25 Lookin Better Today: SFI 93 SN 47
Pete’s Bench:
Toobular! A Tube Transmitter
SR-160
Simple SSB rigs around the world!
KI7NSS’s Pacific 40
Bill’s Bench
The Mythbuster and the Struggle Against the Urban Legend
W2EWL’s Cheap and Easy SSB
W4IMP’s IMP. Articles in ER by Jim Musgrove K5BZH and Jim Hanlon W8KGI
The Spirit of Homebrew SSB. From Electric Radio K5BZH December 1991
Reduced Front End Gain on the DIGITIA
Back on 17! HP3SS sells HBR receiver to Joe Walsh
Maybe another Moxon?
SHAMELESS COMMERCE DIVISION
Test Gear
NanoVNA — Alan W2AEW helped solve mystery of why NanoVNA not providing accurate readout of circuit impedance. Over driving. Need attenuator.
TinySA — Limited Resolution Bandwidth. But you can listen with it! See video on blog.
MAILBAG
— Google Feedburner to end e-mails from the blog 🙁
— Paul VK3HN — TIA AGC? Farhan and Paul looking into options
— Ciprian’s Romanian Mighty Mite
— Dino KL0S SolderSmoke GIF and graphical presentation on sideband inversion
— Allison KB1GMX helped me on 24 volts to IRF 510 issue.
— Dave K8WPE Wabi Sabi and Martha Stewart. And thanks for parts! 40673s!
— Steve N8NM building a 17 meter rig with 22.1184 crystals in a SuperVXO and a 4 MHz filter.
— Dean KK4DAS restoring an old Zenith. One hand behind your back OM.
— Pete Eaton debating SSB or DSB for 17. Go DSB Pete!
— Richard KN7FSZ a FB HBer. Asked about my solid-stating of Galaxy V VFO.
— Walter KA4KXX on benefits of no-tune BP filters like Farhan’s FB.
— Jack 5B4APL on Time Crystals and Homebrewing in the 4th dimension. FB OM!
— Moses K8TIY listens to the podcast with his young son Robert. Crank it in Robert!
— Farhan and the SBitx on Hack-A-Day
— Also Tom’s receiver from junked satellite rig on Hack-A-Day
— Todd K7TFC sent in beautiful message about the spirit of homebrewing. On the blog.
— Grayson KJ7UM was on Ham Radio Workbench with George Zaf
— AAron K5ATG running a uBitx with a homebrew tuner and antenna. Hope I can work him
— Heard Mike WA3O last night on 40 DIGITIA. Water cooled amplifier

AFTIA! The Audio Frequency Termination Insensitive Amplifier from W7ZOI

It really pays to check Wes Hayward’s web site. I looked yesterday and found something that we really need: A termination insensitive amplifier for audio frequencies — an AFTIA. Just last week I was looking at the AF amplifier of my Mythbuster rig, wishing that it had TIA properties. Now, thanks to Wes, we have a circuit available: http://w7zoi.net/audio-fba.pdf
And let’s not forget that it was Wes Hayward W7ZOI and Bob Kopski K3NHI whose 2009 article alerted us to the RF variety of termination insensitive feedback amplifiers.

Face the TRUTH! LOOK at Your Signal with an Antuino!

At first, I didn’t want to believe it. I was in denial. I wanted to shoot the messenger (in this case, the Antuino). How could my beloved HB 40 meter DIGITIA transciever have an output that was so…. so DIRTY! Everyone tells me it sounds great. But the little Antuino screen told a different story. Strong spurs up at 9 MHz and down at around 5.4. And lots of places in between. (In these display images, the center frequency is 7.2 MHz and each division to the left or right is 1 MHz.)

Farhan tried to get me to face the truth: “The frequency domain viewing of RF Signals is the opening of the third eye. Once you start seeing signals as a bunch of simultaneous sines, you will always be wary of the waveforms on the scope. In fact, time domain readings make little sense.”

 At first I blamed strong VHF RFI and my somewhat hay-wire test set up. My homebrew Rube Goldberg 20 db attenuator was probably picking up some of the VHF RF. But as I looked more closely at the output of the transceiver in the frequency domain, I gradually accepted that it was true. There were a lot of spurs. I have a general coverage receiver in the shack, and with it I could hear the little devils. And after some adjustment I could see them in the FFT display on my Rigol o’scope. An exorcism was definitely needed.

But first came a tightening up of the test setup. Pete advised me to do this. I had in the shack some really nice dummy load/attenuators from the HP8640B Signal Generator that Steve Silverman had given me (and that Dave Bamford had hauled across New York City for me). I ordered the necessary N connectors and adapters and soon my test setup improved a lot.


All this got me thinking about spurs. I consulted EMRFD and was reminded of a really great program in the LADPAC software pack that came with the book. The SPURTUNE program predicts spurs and tells you what to look out for. It is really illuminating. Try SPURTUNE.

Through this, I gained a better appreciation of the importance of the bandpass filter in an SSB transceiver. I’d always thought of it as something that allowed the other mixing product to be eliminated while passing the one you want. But I came to realize that it does a lot more than that — it also helps get rid of spurs. If it is designed right. Mine was not. I had plucked it out of an old QST article and had not paid much attention to it. All it needed to do was knock down the unwanted mixing product, right? And in my transceiver (9 MHz IF, VFO running 16.0 – 16.3) MHz that unwanted product would be way up at 25 MHz. It wouldn’t take a lot of selectivity to knock that down. But I’d forgotten about the closer-in spurs. Antuino reminded me of them. And SPURTUNE explained where they came from.

For the exorcism, I decided to use the bandpass filter design from Farhan’s BITX-40 Module. I had made the BP filter on this rig “plug-in” so it was easy to build a new filter.




I even checked out the filter design in a simulator. For this I use ELSIE. Another very useful program. Here is what ELSIE predicted for Farhan’s BITX40 Module filter:

I plugged the new filter into the DIGITIA and… SUCCESS! The big spurs that were bothering me were gone and the remaining spurs were all below 50db down from the main signal. Here is what it looks like now:


The Antuino is a very useful device. You can learn a lot from it, but you have to realize that this is not plug and play radio. You have to think about what you are testing, make sure you have the test gear set up properly, think about the circuit you are looking at, and be careful not to put too much RF into the device.

Three cheers for Farhan and his new Antuino! More on this soon. And we will talk about this on the next podcast.


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: Farhan in the SolderSmoke Shack! BITX, JBOTS, McDonald Straw Sig Gen, uBITX, Sweperino and more!

Thanks again to Farhan for visiting us. It was great to see his reaction to my humble implementations of his great designs. I got him to sign my BITX17. This was really a fantastic day for me and for my family.

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! BITX40-BITX40 with KC1FSZ


This was very cool. I got on 40 SSB this afternoon with my trusty Digi-Tia. I heard a station saying he was running 5 watts… Hmm, could that be a BITX40? Indeed it was. And it was the Peppermint Bark BITX 40 of Bruce KC1FSZ that we featured a few weeks ago. He was up in Boston. K3MY was kind enough to let us have the frequency. Bruce and I had a nice contact. He told me he is working on a completely scratch-built BITX. FB. TRGHS.

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

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

HB2HB! KW4KD and N2CQR (video)

A couple weeks ago I ran into Jim KW4KD on 40 meter SSB. Jim is in Chattanooga, Tennessee. He was running a modern “black box” rig, but he mentioned that he had on the shelf two complete homebrew stations, one of which was for 40 meter SSB. He hadn’t used this gear in 40 years. I encouraged him to blow the dust off and get it on the air. Yesterday, Jim did just that. We met up on 40, first at 1730 local (my time) and again at 1930. Excellent! Another HB2HB contact. Check out the video (above). Thanks Jim.

 If you run into someone who mentions having some old homebrew gear, encourage them to blow the dust off and get it on the air.

Jim’s SSB rig:




N6ORS’s Min-X Crosses the Pond on First Contact

Very cool! Reports on new phone rigs keep coming in. It is great to see them in their “still out on the bench” condition. And reports of the first contacts are always exciting. I like the MIN-X name. This is indeed another testament to the contributions made to the radio art by our friend Farhan.
Hello Bill,

Well I just finished tweaking my new rig, I named it Min-X because I outright stole bits and piecesof the BITX and the Minima, thanks Ashhar. I made my first contact today and what a contact!
The contact was made with the rig as shown. The amp is a home brew FET push-pull.
I had a chat with Beth MW0VOW in South Wales! From Wisconsin to Wales on 15w PEP.
Oh, most of the rig was ‘noodled’ and constructed while enjoying you and Pete on the
SolderSmoke podcast.

Best 73,
Keith N6ORS

TIA-Tube Hybrids from Steve N8NM (Part 1)


 Last week Steve sent us a picture of his Straight Key Night rig which consisted of a homebrew thermatron transmitter and a TIA BITX as the receiver. I asked Steve for more info on the TIA BITX.

Bill:

Shot these right after making the first QSO using the TIA rig as the receiver. The Arduino and ‘5351 are still on a breadboard, otherwise, all of the PCB modules except the filters and PA are installed on the chassis.

The QSO was uneventful, which is a good thing!
73!
Steve

HB2HB! AC9JQ — N3FJZ on 40 with Homebrew Rigs

On Saturday October 24, Dean AC9JQ (Indiana) and Rick N3FJZ (Maryland) made contact on 40 meter SSB using Si5351/TIA BITX rigs. FB!:

Bill:

Dean and I made contact. We both were in and out most of the time, but conditions seemed to improve towards the end where I could understand Dean about 90%. Using the RST “by the book”, I would say he was a 33, 3 =(readable with some difficulty), and signal strength was 3=(weak), and based on what Dean was reporting, my signal back to him was the same – 33.

73 to you both.

Rick – N3FJZ.

HB2HB! AC9JQ and N2CQR Make Contact on 40 with Homebrew Rigs on Both Sides (with help from N3FJZ/HB)

This weekend brought another HB2HB (Homebrew to Homebrew) contact. We have been following with interest the 40 meter transceiver project of Dean, AC9JQ. Above you can watch a video of Dean’s rig in action before it went into the box. Earlier this month Dean achieved a remarkable “Double First” when he made his very first amateur radio contact. He was using his homebrew rig to do it. So his first contact was also his first homebrew contact. FB. More info on Dean’s rig and homebrew exploits can be seen here:
http://soldersmoke.blogspot.com/search?q=ac9jq

This week Dean got a decent 40 meter dipole up in the air. We arranged (via e-mail) to meet on 40 on Friday evening. We made contact, but conditions weren’t great. We tried again several times on Saturday, looking for open spots amidst the madness of the CQ WW DX contest. Rick N3FJZ joined us and also tried to make contact with Dean, but had no luck either. Daytime conditions didn’t allow for a good contact between Indiana and the Washington/Baltimore area where Rick and I are located.

Finally, last night after family obligations at both ends settled down, Dean and I found a relatively open frequency on 40 and made a good contact. A short snippet of it can be heard by clicking on the link below. Keep in mind that Dean was running about 2 watts to a dipole on 40 at night.

http://soldersmoke.com/HB2HBAC9JQ.mp3

Thanks Dean! Thanks Rick!