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. 

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!

http://soldersmoke.com/soldersmoke232.mp3

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

Making a BIG Transformer from Scratch -- Video

Wow.  Watch this young guy make something very useful.  This video reminded me of the 16 de Marzo neighborhood in Santo Domingo, where I was able to get the RF choke and power transformer of my Hallicrafters HT-37 repaired.   This guy takes that a big step further.  He does lot with very limited resources, and does it in a workshop that many of us just wouldn't be able to tolerate. There is obviously a lot of skill in his production of this transformer,  and lot of wise re-purposing of materials.  

I think this shop is in Pakistan.  Three cheers for the Malik Transformer makers! 

Thanks to Rogier PA1ZZ for alerting me to this video. 

Video: E. Howard Armstrong and Early Radio

This is a really wonderful video. It might seem slow to those accustomed to faster-paced YouTube videos, but the information content is very high -- it contains a lot of pictures I hadn't seen before and audio of Howard Armstrong.  

I never knew that the name of the radio company Zenith was derived from the early callsign "9ZN." 

As a Northern Virginian, I like the reference to NAA Arlington.  

I used to live near Yonkers, N.Y.  I remember Warburton Ave.  What a fine shack young Howard had up in that cupola attic.  

The photo of Armstrong's breadboard was very nice.  My Mythbuster is in good company.

QRPers will get a kick out of the newspaper headline "New Radio Marvel Revealed!"  (They cut the power out from 20kW to 5 watts!) 

Thanks again to Dave Bamford W2DAB for sending me the book about Armstrong, "Man of High Fidelity" by Lawrence Lessing.  

Finally, I remember talking to Bruce Kelley W2ICE at hamfests.   He was a great radio amateur: 

https://www.qcwa.org/w2ice-01351-sk.htm

http://www.arrl.org/w1aw-bulletins-archive/ARLX020/1997

Be sure to check out the Antique Wireless Museum's YouTube Channel.  Lots of good stuff there: 

https://www.youtube.com/channel/UCX55peBhzeX1qps_VYXdLBA

We have the famous photo of Major Armstrong,

 but this is the first one I've seen of a slightly younger Captain E. Howard Armstrong. 

Mythbuster Video #17 Boxing it Up, Tuning Filters, Tapping a Heat Sink, QRO Dreams....

I made a cabinet out of scrap packing material. I show how I tune LC filters by squeezing the turns on toroidal inductors. I tap a heatsink and think about more power for the Mythbuster.

Joe Galeski's 1960 "IMP" 3 -Tube Filter SSB Transmitter, and the Spirit of SSB Homebrew

Here is another important bit of SSB history.  In  May 1960, Joe Galeski W4IMP published an article in QST describing his super-simple SSB transmitter.  While Tony Vitale's "Cheap and Easy" rig was a phasing design, Joe came up with a filter rig.  He built USB filter at 5775 kc.  With it, he ran a VXO at around 8525 kc. This put him on 20 meter USB. 

Here is the QST article: http://marc.retronik.fr/AmateurRadio/SSB/A_3_tubes_filter_rig_%28SSB%29_%5BQST_1960_5p%5D.pdf 

In discussing how to put this rig on other bands, Joe got the sideband inversion question exactly right: 

Thank you Joe!  

Joe even provides an comment that seems to capture an important element of the homebrew SSB ethos.  Joe homebrewed his filter, but he mentioned the possibility of using a store-bought filter: 

That's the spirit Joe!  

Along the same lines, Jim Musgrove wrote in Electric Radio: 

Having built Lew McCoy's Mate for the Mighty Midget receiver (which also used just three tubes), I can't help thinking that an IMP-ish transmitter would be an excellent complement to the Mate for the Mighty Midget.  

Jim Musgrove K5BZH knew Joe Galeski and wrote about him in the January 1992 issue of Electric Radio.  Jim wrote that Joe was an optometrist by profession. When OE1FF wanted to know the cost of building an IMP, Joe Galeski boxed up the original and sent it to him.  FB Joe. 

In December 1961 Joe Galeski published a QST article describing a transistorized version of the IMP -- this rig ran on 15 meters.  K5BZH wrote that Joe later published an article about a small, solid-state transceiver,  appropriately called "The Shrimp." 

W2EWL's "Cheap and Easy SSB" Rig -- And The LSB/USB Convention Myth

In March 1956 Tony Vitale published in QST an article about a "Cheap and Easy" SSB transmitter that he had built around the VFO in an ARC-5 Command Set transmitter.  Vitale added a 9 MHz crystal-controlled oscillator,  and around this built a simple phasing generator that produced SSB at 9 MHz.  He then made excellent use of the ARC-5's stable 5 - 5.5 MHz VFO.  His rig covered both 75 meters and 20 meters.  Here is the article:

http://nebula.wsimg.com/2b13ac174f7f2710ca2460f8cf7d6b8b?AccessKeyId=D18ED10DA019A4588B7B&disposition=0&alloworigin=1

Because it used the 9 and 5 frequency scheme, over the years many, many hams have come to think that Vitale's rig is the source of the current "LSB below 10 MHz, USB above 10 MHz." This is  wrong.   An example of this error popped up on YouTube just this week (the video is otherwise excellent): 

First, Vitale's rig had a phasing SSB generator. All you would need to switch from USB to LSB was a simple switch.  And indeed Vitale's rig had such a switch. Pictures of other Cheap and Easy transmitters all show an SSB selection switch. So with a flip of the switch you could have been on either USB or LSB on both 75 and 20.  With this rig, you didn't even need sideband inversion to get you to 75 LSB and 20 USB. 

Second, even if hams somehow became so frugal that they wanted to save the expense of the switch, leaving the switch out (as suggested above) would NOT yield the desired "75 LSB 20 USB" that the urban legend claims that W2EWL.   As we have been pointing out, a 9 MHz SSB generator paired with a 5 MHz VFO (as in the Vitale rig) will NOT -- through sideband inversion -- yield LSB on one band but USB on the other.   

W2EWL's rig could not have been the source of the LSB/USB convention.  I still don't know where the convention came from. I am still looking for the source. 

But leaving the LSB/USB convention issue aside, Tony Vitale's rig is an excellent example of early SSB homebrewing, and of a very clever use of war surplus material.  In the January 1992 issue of Electric Radio magazine, Jim Musgrove K5BZH writes of his conversations with Vitale about the Cheap and Easy SSB.  Tony told Jim that this rig came about because the Central Electronics exciters required an external VFO -- they recommended a modified BC458.   B&W had recently come out with a phase shift network. Vitale went ahead and built the whole rig inside a BC458 box.  FB Tony! 

In the December 1991 Electric Radio, Jim K5BZH reports that Tony was recruited into the ranks of SSBers when he watched a demonstration of SSB by Bob Ehrlich W2NJR in November 1950. Tony very quickly started churning out SSB rigs.  His daughter Trish Taglairino recounted that when her father had "done something great again" there would be a parade of hams to the basement shack.  About 30 guys showed up when Tony put his first SSB rig on the air -- they sent out for beer.  

Thanks to Jim for preserving so much SSB history. 

Time Crystals, and Breadboarding in Cyprus in the 4th Dimension

 

We are always impressed by the way in which SolderSmoke listeners stay on the cutting edge (sometimes OVER the edge!) of modern technology.  I recently got this fascinating note from our friend Jack AI4SV, who is now operating under the hot sun of the Mediterranean island of Cyprus.  

Hi Bill,

It is brutally hot here in Cyprus during the summer, so we're spending a week at a rental on the beach -- no complaints in that regard. With all construction material back at the main house, I am free to daydream with no threat of actually building anything that I think of. The result: a new technique -- fourth dimensional design.

This probably popped into my head because I went to sleep right after reading an article about "time crystals" (https://www.quantamagazine.org/first-time-crystal-built-using-googles-quantum-computer-20210730/#:~:text=A%20time%20crystal%20is%20both,of%20what%20a%20phase%20is.), which are similar to physical crystals, but their pattern have symmetry in the time axis. I have to imagine that these things have some application in radio since oscillation is intrinsic to their state of existence. I don't want to think too much about them because it makes my head hurt.

Now, consider breadboarding. There isn't much to say about one dimensional circuits since current has to flow in a circle, but I suppose Franklin's kite was kind of one-dimensional: cloud, Franklin, earth. At least it had a key, so kind of relevant to radio, at least if you are a CW operator.

Two-dimensional circuit design would be a breadboard, particularly with surface mount components. Arguably three-dimensional if it's mulitlayer. Manhattan Island or Deadbug is more in the realm of three-dimensional, with components sticking up from the board, and true three-dimensional is probably best reflected in tube rigs with spider webs of wiring. I don't know who can think in terms of three dimensional layout like that, but it's certainly an art (kind of a blend of Escher, Dali and Bosch).

Now comes fourth dimensional design - not just a theoretical abstraction, but a realizable method that would result in lower part count and simplify the operator interface to a single knob. The basic idea is that you have a design laid out in three dimensional space and that design is made time-variant in space. The simplest implementation would be a breadboard mounted in a track so it slides back and forth, like a desk drawer. Pulling it towards you puts it in transmit, pushing it away in receive. The secret sauce is that the rails have contacts and that the layout is designed such that the traces or pads on the board line up with contacts on the rails such that no relays are needed on the board. Some thought would need to be put in to assure that contacts are made in an appropriate order to avoid frying components.  

That's already fourth dimensional because the same board exists in two states and it can be one or the other, but not both at the same time. Superimposing transmit on receive would be bad, maybe world-ending.

There is no reason to stop there. This whole slide drawer sort of layout could be mounted on a rotational axis with contacts distributed around a tube surrounding the railings. Now you have band switching. Pull the knob to receive, twist it to go to 20 meters, push back in to transmit. That's only roll and translation in one axis -- four more to go, the practical implementation of which I will leave to the reader. Perhaps put mode (CW, SSB, etc.) on yaw, tuning on pitch (which seems natural), volume on y-translation, and RF gain on x-translation, and you would have a formidable 4D transmitter.

Clearly, this is too big to keep to myself, so I am sending it onward to you to share with the world for the benefit of mankind.

Hope all is well in the shack somewhere in the wilds of Northern Virginia. 

Cheers,

Jack

5B4APL / AI4SV

---------------------------------

My follow-up exchange with Jack: 

Jack:  When I read the title I thought you were going to comment on my BOLD decision to place a wooden front panel on my heretofore Al Fresco Mythbuster rig.  But I see now you have taken this to an entirely different astral plane!  Far out OM!  Really groovy.  The crystal thing really brings it into New Age relevance.  Whole Foods may want to get involved! 

I've long thought that the three dimensional nature of tube rigs is one of their most attractive features. You, my friend, are taking this one step further, into Einsteinian space time!  One problem I foresee:  How will hams "synch up" if they are moving through space time at different relativistic speeds?  This could be a real problem for the FT-8 folks and the WSPRers.  

Can I put your hyper-insightful message on the SS blog?   People need to know about this! 

73  Bill  

Hi Bill,

That was a BOLD design choice, but I like the aesthetic.

I'll let Joe Taylor grapple with the cosmic issues related to synching signals. The bigger issue may be regulatory in nature. I am not sure how Part 97 will deal with signals received before they are sent.

Yes, please feel free to share on the blog -- the world needs to know.

73,

Jack

Jack:  Another possibility:  Perhaps too much Cypriot sun?  Stay safe OM! SITS!   73  Bill 

Todd K7TFC on Pessimism, Optimism, and Homebrew Radio

In response to my blog post about Rob Sherwood, Todd K7TFC sent this very thoughtful comment.  It is so good that I wanted to put it up as a more visible blog post.  Thanks Todd. 

Todd wrote: 

Several of 4Z1UG's recent interviews have either hinted at or clearly expressed pessimism over the future of technically-oriented, homebrew ham radio. Of an age myself (another IGY baby) in which disgruntled cynicism is endemic, I nevertheless found their pessimism exaggerated and perhaps a little-too conventional.

Not that there's little evidence to back them up: recent retirements at QST and the magazine's thin technical coverage have not improved matters, and even QRP Quarterly recently found it necessary to spend more pages on UFOs in New Mexico than on VFOs in their readers's hamshacks. Even podcasts whose names might suggest otherwise--I'm thinking of Ham Radio Workbench--actually spend more time talking about store-bought black boxes, antennas, and cool things they've purchased (or want to purchase) than melting solder or winding coils. To be sure, HRWB, QRPQ, and even QST, make important contributions , but they do reflect the *proportional* decline of hands-on electronics.

For me, though, that the *proportion* of homebrewing, technically-oriented hams has declined is not as important as the actual numbers of hams so oriented. If their proportion is down to, say, five-percent of the total number of hams in the world, that's still *a lot* of homebrewers worldwide, and now that we interact in a truly-global theater of enthusiasts, we've never had it so good when it comes to the numbers of people who share our enthusiasms.

This question of actual numbers versus proportions can be seen in the most common modes of operation as well as on the hardware side. SSB long ago passed CW as the mode-of-choice, and now SSB is in decline *proportionally* as the weak-signal digital modes seem to be taking over. But when the bands are open, you can still tune through the lower portions of most bands and find *plenty* of CW ops at all levels of speed and clarity. CW is not dead, and in fact it's easier to learn than ever before. I expect a proportion will always see CW as essential to ham radio--enough in fact to keep them supplied with contacts to satisfy their retro-cravings and keep the tradition alive.

I may be in the last quarter (third?) of my life, but the older I get the more I come to believe in living *three-dimensionally*. The "X" is my own time and place (a west-coast Boomer), the "Y" is my own time but other places and cultures, and the "Z" is other eras, times, and places. The "other eras and times" in the ham-radio context means I don't have to abandon tank circuits and crystal filters and vacuum tubes *merely* because other and perhaps objectively-superior technology is now at my disposal. I can use the new stuff and the old stuff, too. I'd even argue that to abandon all use of older technologies means there's been no *growth*, only "progress."

We see this clearly enough in other aspects of the human endeavor. The computer may have totally replaced the typewriter, but it hasn't replaced pen, ink, and paper. The internet may be a superior repository of knowledge than printed books, but books and magazines are still widely used and are in some ways superior to online media. Microwave ovens cooking prepackaged, processed, and *manufactured* food are more efficient, but no one denies a meal made with raw whole foods and hand-prepared is better.

I expect there will always be plenty of people living three-dimensionally as hams with whom I resonate. There's already a high SWR between me and *most* people anyway. I've grown comfortable with a more-narrow bandwidth--73, Todd K7TFC

------------------------

Todd's Web Site: https://mostlydiyrf.com/

Sam KD2ENL's Homebrew Integrated Circuit Chips

Sam Zeloof KD2ENL does some really inspirational work on the homebrewing of IC chips. We first posted about this back in 2018, when Sam was 17: 

https://soldersmoke.blogspot.com/2018/05/youngest-homebrew-hero-17-year-old-sam.html

Sam has some very impressive gear  -- I found myself wondering if that could really be a home lab. But it is.  It is apparently in his garage in New Jersey.  Hack-A-Day reports that Sam got a lot of the gear on e-bay.  And they note that living near Princeton University (great dumpsters!) also helped.  Here is some background on Sam's workshop: 

https://hackaday.com/2018/11/19/of-roach-killer-and-rust-remover-sam-zeloofs-garage-made-chips/

and

https://hackaday.com/2017/02/25/the-fab-lab-next-door-diy-semiconductors/

Sam and his brother Adam KD2MRG are students at Carnegie Mellon University in Pittsburgh. 

Thanks to Hack-A-Day for alerting us to this: 

https://hackaday.com/2021/08/14/the-zeloof-z2-intergrated-circuit-has-100-transistors/

KI7NNS's "Pacific 40" Simple SSB Transceiver

Here is the amazingly beautiful "Pacific 40" build of the Simple SSB transceiver.  The builder is Kacy KI7NNS.  This was part of the Vienna Wireless Society group build led by Dean KK4DAS.  The design is from Pete N6QW.  

Here is more info on Kacy's rig, and on a recent SOTA activation.  

https://drive.google.com/drive/folders/1azj3e7skUE5QFpa4kRCARoeivrawhIAZ

 Congratulations to Kacy KI7NNS for a really nice rig. 

Grayson Evans KJ7UM on the Ham Radio Workbench Podcast

 

OM Grayson was on the HRWB podcast with George Zaf and company. This was a really informative and entertaining session.  For example, when asked if special precautions are needed when working with thermatrons, Grayson replies, "Well, try not to swallow anything... and don't sit on the thermatrons."  Words to live by my friends.  Grayson's story about cooking Tektronix scopes in a refrigerator re-purposed as an oven (after cleaning the 'scope with a Home Depot power washer) is the kind of practical advice that readers of this blog REALLY NEED!  

But seriously, I learned a lot just listening to Grayson talk about thermatrons with George and the HRWB crew.  

The interview includes nice shout-outs to SolderSmoke, SPRAT/G-QRP, and Electric Radio magazine. 

Check it out:  https://www.hamradioworkbench.com/podcast/hollow-state-design

Stay to the end for some thermatron-related password management advice from George. 

Thanks to Grayson and to all the folks at HRWB.