Termination Insensitivity -- Only Three TIAs in the World?

Termination Insensitivity.  Is this like when your girlfriend dumps you and you just don't care? 

No. It's more like this:

http://www.n6qw.com/TIA.html

Wes Hayward and Bob Kopski developed the Termination Insensitive Amplifier circuit back in 2009.  With a bidirectional rig it is important that the crystal filter face the same impedance in both directions.  Simpler bidirectional amps are impedance "transparent" in that their input impedance depends on what is on the output (and vice versa).  The circuit that Wes and Bob developed solved this problem:  these amps always look like 50 ohms.  That's very useful.  When I was building my earlier BITX rigs, Farhan suggested that I try the termination insensitive amp circuits.  On my latest project I followed his suggestion.  At the same time, Pete was building a new BITX, also using the TIA amps. 

Pete wrote to Wes and Bob and asked if anyone had followed through on their 2009 article by building a rig using this circuit.  Wes said that he was unaware of any TIA rigs.  It turned out that Tom Hall up in New York City had built one (video below). So I guess Pete's rig is TIA 2 and mine is TIA 3!  (But I was thinking, because of Pete's Italian ancestry, shouldn't we call his rig a Zia?)
Please let us know if you know of any other TIAS (or ZIAS!) out there.

Here is Tom Hall's very FB TIA:



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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.



 

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Moonbounce, Meteors and French Radar in Scotland

David GM4JJJ was the fellow who sent us the video of early Scottish moonbounce ops.  This morning he sent me a tale of woe involving some transverters and several BASTA! moments.  I will spare you all the painful details, but I really liked this paragraph about David's use of sigs from a French space surveillance radar:  

... While the transverter for 144 MHz was being tested out into my new homebuilt antenna I tried receiving the French space surveillance GRAVES RADAR on 143.050 MHz. It is easily detected here in Scotland via meteor scatter. It is also so strong that passing space hardware like the ISS reflect the RADAR and can also be detected, showing up on FFT displays with their rapid Doppler shift.  GRAVES is also easily detected by moonbounce, I could see it and hear it on my single 10 element yagi pointed at the horizon without a preamp. Even when the moon was at 15 degrees elevation here, and even higher in France the signal was strong enough to be picked up in one of the lobes of my antenna. You can actually see what the vertical pattern of the antenna looks like as the moon rises through the peaks and nulls of the antenna in conjunction with the constructive and destructive interference patterns caused by ground reflections and the direct path to the moon.

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Rigs vs. Radios: A Real RIG in a Real SHACK

Earlier this year Pete and I were talking about the use of the word "rig."  For me this is a hallowed term that captures much of the essence of ham radio.  Sadly, in modern parlance "rig" seems to be increasingly substituted by word "radio." If you are wondering what the difference is, well, I think this video presents a good example of a rig. 

There was a nice exchange of e-mails on QRP-L about this video: 

Jun 2 at 9:54 PM

Hi Bill.
I've operated a breadboard rig just to watch the electrons move thru the circuits but never worked such a kluged station yet.
73 de Ed, K1RID
(formerly KC1BBC)

 On Jun 2, 2015, at 21:30, Bill Cromwell wrote:
 Hi Ed,
I worked some lashups like Mike's. I still do. Once upon a time I "temporarily" taped a T-R relay under a shelf and used it temporarily enough months for it to come untaped and fall in the middle of a QSO! I finished the QSO anyway. I don't tape relays to the bottom of shelves any more but the top of the shelf is fair game. No relay ever fell *up*. I've worked Mike on the air. We have some of the same views.
  73,
  Bill  KU8H

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Mike Caughran (KL7R) Web Site

The links recently went bad, but fortunately Jim W8NSA saved the old site (most of it).  Thanks Jim.

http://www.commcenter-8.net/kl7r/


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 #6: Boxing it up!

 

Basic Basswood Box (From Michael's or Amazon)

 

Space cut out for Si5351 board and for AF Gain and Mic jack

 

Copper flashing placed (from Home Depot)

 

Amplifier Chain placed along the back

 

 

Note Plug-In Low Pass Filter

 

Starting to look Rig-ish

 

The View from Above

 

Still to do:

 

Socketry along the back (Antenna, 12V, external amp T/R control, Speaker, MAYBE:  IF connection).

 

 

Relay wiring (I'm trying to do this with just 2 DPDT relays: one for Low Pass Filter switching and External Amp T/R control,  and one for 12V T/R switching, and Bandpass Filter switching.

 

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BITX DIGI-TIA Update #5: Amplifiers Built and Tested

I have the RF amplifier stages done, and I worked a bit on the shielding.  This circuit board will be along the back, turned around, with the copper-clad shields between the amps and the rest of the rig.  In the picture you can see the small inter-stage shields, and one that put between input and output on the final.  All this in the probably vain hope of avoiding the Agony of Oscillation.   We'll see.  So far so good.  I get about 8 watts out of the IRF510 on 40 meters.  53db total gain for the three stages.  Of course, all this will likely change once the rest of the rig, the LP filter and an actual antenna are added.

 

As for the mic amp problems I mentioned last time, well,  I discovered on earlier BITX projects that one of the resistors in the base circuit needs to be changed from 10K to 39K.  It is kind of a long story (maybe for the podcast) but essentially I had to discover this AGAIN.  More details here:

http://soldersmoke.blogspot.com/2013/10/bitx-build-update-15-necessary-mic-amp.html 

 

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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.    

 

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Sage Advice on Homebrewing from WA3EIB

Bill, Pete,
 
Thanks for the sage advice.
 
You are absolutely right, I should stick to the plan and finish the project before tromping off in a different direction.
Anytime I've ever changed designs before I have completed a task, usually results in something far less than expected.
 
The real joy is completing a project and looking back at what was accomplished.
 
My own personal goals for the Minima Transceiver Construction include...
 
1. Build it from SCRATCH - Manhattan Style.
2. Start with modular construction - so that each circuit can be tested, troubleshot and modified in the future.
3. SMA connectors and coax to every stage so, I can divide and conquer the function of all modules.
4. Document the entire journey so I can actually see where my learning's took me.
5. Provide myself, a basic building block for future transceiver construction and designs.
6. Improve my skills, techniques and knowledge through my mistakes and understandings. 
7. Learn to SLOW DOWN, study, plan and write, in my own words, what the circuit(s) do and how they function.
8. Be a mentor to others and share what I have learned.
9. Be more of an Amateur Radio Experimenter and less of a Ham Radio Operator.
10. Continue to dream and design.
 
Each day should be NEW and EXCITING. There should be a thrill in every step of the way, even in the midst of failures.
 
Thank you both for taking the time to respond.
Thanks for the encouragement and sharing what happens on your own bench.
 
73's
 
Harv -=WA3EIB=-

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

More inspiration from Harv here:
http://soldersmoke.blogspot.com/2012/09/an-ode-to-old-time-radio-by-wa3eib.html

And here:

http://soldersmoke.blogspot.com/search?q=WA3EIB

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

Frank Harris and the Nobel Prize for Sideband

A lot of wisdom and good info in this chapter (and in the whole book);

http://www.qrparci.org/wa0itp/chap15.pdf

http://www.wa0itp.com/crystalsetsssb.html

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