Getting More Rigorous About Receiver Design (Video)

As I finished up the receiver on my 17-12 SSB transceiver, I started to wonder -- how good is it?  

Sure, I could hear stations on both bands, and when I got started as a homebrewer that was enough for me. But now, I find myself wondering about receiver performance.  Did I get the gain distribution right?  Do I have too much gain ahead of the mixer?  Ahead of the crystal filter?  Is the receiver generating too much noise?  Can I hear the band noise?  If not, why not?  Do my circuits lose linearity in the presence of strong signals?  What is my dynamic range?

This is a big complicated subject that takes time to master.  

I am just beginning.  I found the video above to be very helpful. 

I was jealous of this fellow's audio spectrum analyzer, but then Tony G4WIF told me that the the analyzer that this fellow was using was really just a sound card and some software.  I quickly found a similar piece of free software that lets me do the same thing he did:  Look at the audio output of my receiver and watch what happens as I put an RF signal of varying levels into the antenna port.  

I am using Visual Analyzer, a free program out of Italy: 

https://www.sillanumsoft.org/   

 The author of the software seems very cool" 

My name is Alfredo Accattatis; I love electronics and software, and I have been working for years in commercial companies as software/firmware engineer and software designer. I've been writing programs for embedded systems (with DSP and MICROCONTROLLERS), for PC, for Avionic Computers and even for Mainframes, using C, C++, Pascal, Ada, REXX and assembly. I starting write VA during my free time just for fun and using (also) my DSP experience. The program was and is completely FREE.

More info about Alfredo here: 

https://www.sillanumsoft.org/about_the_author.htm

Do you folks think I need to buy the kind of True RMS Audio Voltmeter that is being used at the end of the above video? 

First Ever Contact on 12 Meters: Homebrew, QRP, SSB, DX (Video)

I've recently finished most of the circuitry on the 17-12 meter dual band SSB transceiver. I have had contacts with it on 17 meters, but until yesterday morning (March 22, 2022) I had not had any contacts on 12 meters. This morning I talked to Paul EA5JZ in Valencia, Spain. I was running the 17-12 rig barefoot at about 5 watts with the final being one RD06HHT FET. The antenna was my 75 meter doublet fed with window line -- I had to modify the tuner to get it to work on 24.9 MHz. It was very cool to have my first 12 meter contact be QRP, HB and with Spain.

There is a LOT of soul in this new rig.  Here is a partial list of contributors: 

-- Overall BITX design:   Farhan VU2ESE

-- Termination Insensitive Amplifiers (TIA):  Wes Hayward W7ZOI and Bob Kopski K3NHI.  

-- TIA boards from Todd K7TFC

-- ASK-1 Mixer from Armand WA1UQO

-- VFO design parameters from Joe Carr K4IPV (SK) 

-- VFO stability ideas from Frank Harris K0IYE and Mike Murphy WU2D. 

-- HT-37 Tuning Capacitor bought from e-bay at suggestion of Pete Juliano N6QW. 

-- Pine board base of the rig:  Frank Jones (SK) W6AJF's preferred building technique. 

-- DTC Band-Pass filter circuits from Han Summers G0UPL. 

-- Low pass filter values from G-QRP web site. 

-- Idea of using RD06HHT instead of IRF-510 in the final:  Pete Juliano

-- Heat sink from Chris KD4PBJ

-- Trifilar Toroids used in many places from Farhan VU2ESE.

Thanks to all.  73  Bill  

Receiver Dynamics -- How Good is my Receiver?

OK , so I've finished building my new 17-12 Dual Band SSB Transceiver.  I am now testing it out on both bands.   A big question I have is this: how good is my receiver?   Did I get the gain distribution right?   Is it generating too much noise?   Are any of the stages too vulnerable to distortion in the presence of large signals?  

These kinds of questions are at the heart of receiver design.  Many of us have for years just thrown together amplifiers oscillators and mixers, and have been pleased if we could copy signals on the ham bands.  But could we have been doing it better?   

This is a very complicated issue, and unfortunately much of the literature is plagued by jargon and unnecessary complexity.  Rarely do we find something that goes from the general to the specific and explains what it is we are trying to achieve:   We want the receiver to be sensitive, but we don't want it to be so sensitive that it distorts with strong signals.  It will make some noise, but we don't want the receiver's internal noise to be stronger than the noise coming in from the antenna.  The "front end" stages are very important because any flaws there will be amplified by the follow-on stages and will "cascade" down through the receiver.  Bandwidth is very important. 

This morning I found (again!) a document that defines terms in a very clear way.  Be sure to check out the footnotes mentioning Dave Newkirk and Wes Hayward!  FB!  Here it is:

https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/cryptologic-quarterly/Receiver_Dynamics.pdf

17 - 12 Dual Band SSB Transceiver On-The-Air

 

It is still completely al-fresco, with all the guts exposed, but I got it on the air this morning.  I was 17, running it through my CCI  .1kW  100 watt amp to a tuned doublet.   Four QSOs so far: HP3SAM, K5BM, N4ZUL, and II3WRTC.   

The structure of the rig is basically BITX. 

The blue boards you see are TIA boards developed by Todd K7TFC. 

No major problems to report.   I will try it out on 12 meters  soon.  The receiver was working well on that band. 

Flick Lives -- More from a Great Web Site about "Jean Shepherd"

Jim Clavin has some really great stuff on his FlickLives website: 

http://www.flicklives.com/index.php?pg=318

Much of this stuff I had never seen.   Like the picture he has of young Shep in his shack.  I wonder how old he was in this picture.  He appears perturbed.  Perhaps his Heising Modulator was distorting?

Jim dug up all of Shep's licenses and got the names and callsigns of all the hams who were active from Shepherd's  hometown during the years Shep was living there.  I think I can recognized some of the names -- Shep talked about some of these guys when talking (on WOR) about ham radio.  Boles.  Stan.  Good times. 

The CQ Guest editorials and the various articles are a lot of fun.   Some things never seem to change. 

Thanks Jim! 

EXCELSIOR! 

Help! Can You Write the Software to Control the MAX2870 Board?

 

It is not every day that you get the chance to help a master homebrewer like Pete Juliano N6QW.  But today is just such a day.   Pete asks for some coding help: 

https://n6qw.blogspot.com/2022/03/march-18-2022-help-software-programmer.html

The Radio Gods would be pleased if you help.  The Mojo and Juju levels of all your projects would increase.   If you can help, please do so.  

Colin M1BUU's Homebrew Manhattan SST

 

Wow, especially on St. Patrick's day I think it is appropriate to say " 'tis a thing of beauty. "

Colin did a great job on his homebrew version of the SST transceiver. It looks like his is on 30 meters.   I especially liked his description of the troubleshooting that followed the construction.  the assist provided by AA7EE's blog was especially cool, and demonstrates the long-lasting power of internet-shared tribal knowledge. 

Colin wrote (on Facebook):  

I was inspired by Bill and his adventure with the SST-20, so I started gathering a few parts last year to build a Manhattan SST. I did a joint SOTA activation with a fellow homebrewer ham at the end of January and we started talking about classic portable CW rigs, it turned out that we both had an SST build on our 'list'. I was challenged to build the SST for the next joint SOTA activation!

It took a lot of effort and a few late nights but I did manage to produce a rig capable of making QSOs for a joint SOTA activation of Fair Snape Fell, G/SP-007. I'd done a solo activation of Pendle Hill G/SP-005 a few days before with the rig for a trial run and I discovered that the AF was very low. After some troubleshooting I noticed that I'd soldered the LM386 gain set capacitor to an incorrect pad. Doh! I fixed my error and the rig had much more gain.

I found that with the improved AF gain, the rig would squeal if the gain was turned up. I was ready to give up really, but after a cool off period, I began researching the issue and it turns out that it's very common and indeed I found posts from 1997 about it! It seems as though my recreation was so faithful to the original, I'd included the original flaws too! I added in a 0.1uF cap and resistor connected to pin 5 of the AF amp chip as per the suggestion on Dave AA7EE's blog and now the squealing has stopped.

I'd made 14 QSOs during the joint SOTA activation, so I considered my challenge to have been met! It's been a bit of an epic build!

73, Colin, M1BUU

Pete N6QW Looks at Tapped Capacitance Impedance Matching

 

For some reason we are more accustomed to impedance matching using tapped coils than we are with the use of tapped capacitors.   This is too bad because tapped capacitors are a very useful impedance matching tool.  Pete recently looked at this technique.  Check it out: 

http://n6qw.blogspot.com/2022/03/march-7-2022-pipsqueak-20m-ssb.html 

VK2BLQ's Two-Tube Regen with a SolderSmoke Dial

 

Thanks to Peter Marks VK3TPM ("a bloke with too many hobbies") for alerting us to this magnificent homebrew receiver with the especially magnificent tuning dial.   

http://blog.marxy.org/2022/03/a-two-valve-regenerative-receiver-for.html 

We have used old CDs as dials for many years.  I have one on my Q-31 Quarantine SW receiver.  But never have we seen one with SolderSmoke emblazoned on it. FB OM. 

Stephen VK2BLQ should make sure that those 6U8s haven't gone old on him.  I recently replaced the 6U8s in my Mate for the Mighty Midget with 6EA8s.  This seemed to rejuvenate the receiver.  

Also, it is shame that Stephen doesn't keep that rig at 12 volts.  250 V?  Yikes.  As I often say, you CAN hurt yourself with 12 volts, but you really have to work at it.  Not so with 250 V.   One hand behind your back Stephen! 

Thanks to Peter and Stephen. 

"Fashion" for Fans of LC Analog VFOs

 

Get this shirt (and much more like it) here: 

https://www.cafepress.com/k1nssartforshacks/8326230?fbclid=IwAR24e2gpyu93pV7Mj3srT4iBLnA7agsV7FpC9EWHFax4qf4ck5o9dwiOLK4

Note:  There is no rotary encoder shirt.