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.  

First Use of Farhan's Antuino Scalar Network Analyzer

I was learning my way around Farhan's new Antuino this morning.  Very cool.  I decided to start with the Scalar Network Analyzer.   I've spent so much time measuring and plotting filter response curves BY HAND... the Antuino is an opportunity for me to move into the 21st Century.  

In the picture you see the results.  I was using a Heathkit SSB filter with the center frequency at 3.395 Mhz.   The Antuino was set for that freq, with the screen range set at +/- 10.  That means each division on the screen is 1 khz (right?).  The Heath filter is advertised as being 2.1 khz wide at 6 db down.  That pretty much matches what we see here.  

You can see ripple in the filter passband.  This is almost certainly the result of an impedance missmatch.   It looks to me like the Antuino is set up with 50 ohm inputs and outputs.   The Heath filter probably needs higher impedances to have a smooth passband.   I will try later to set it up for a smooth passband. 

It is easy to see how useful this device will be.  Thanks Farhan! 

More on the Antuino here: 

http://www.hfsignals.com/index.php/antuino/

Ham Radio in Germany 1955 (video)

Don't be deterred by the lack of English subtitles -- radio amateurs around the world will be able to follow what is going on in this very interesting 1955 film.  It is only about 14 minutes long. 

This video takes us back to a time when hams were hams and rigs were RIGS!

Note the German OM who apparently slept fully dressed (with necktie) in order to be ready to spring into action on the ham bands in the middle of the night.  That's dedication my friends. 

Also note the fellow sending out QSL cards that feature the schematic diagram of his rig.  Lots of solder melted in 1955.  Great stuff. 

Thank God for the Heaviside Schicht!    

FDIM Interview with Farhan VU2ESE

I didn't realize that our correspondent in Dayton/Xenia had interviewed Farhan.  There was a typo in the audio file name and I was wondering who this UV2ESE guy was.  A Ukrainian QRPer?   I was really pleased to find out that it was Farhan.  

In Bob's interview you will hear Farhan discuss the capabilities of his new Antuino (pictured above).  Pete's Antuino is in the mail, going transcontinental.  It should arrive in the Newbury Park Laboratory later this week.  

As for the spectrum analyzer that Farhan got me last year, I am waiting for retirement (soon!) to get that one going.  But there is a danger that the Antuino will leave little room for the older tech... 

In the interview you will hear Farhan talk about the Antuino circuitry, and about the roots of the three main devices in the Antuino box.  Very cool.  

Thanks again Farhan. And thanks Bob. 

Here is the interview:

http://soldersmoke.com/VU2ESE FDIM 2019.m4a

Farhan's Antuino page: 

http://www.hfsignals.com/index.php/antuino/

FDIM Interview -- NM0S on John Reinartz W1QP K6BJ -- Scandal on an Arctic Expedition?

John Reinartz, 1QP, at the operating position of WNP aboard the Bowdoin

Bob Crane W8SX interviewed Dave Cripe NM0S about his FDIM presenation on radio pioneer John Reinartz 1QP and later K6BJ. Listen to the interview here: 

http://soldersmoke.com/NM0S FDIM 2019.m4a

Here is Reinartz's obit in the New York Times: 

https://www.nytimes.com/1964/10/07/john-l-reinartz-pioneer-in-radio.html

Here is some background info on Reinartz: 

http://k6bj.org/Club_History/WhoWasK6BJ.htm

Dave Cripe's interview left me wondering what the north pole scandal was all about.   I found this passage from a book that seems to partially explain what happened.  Can anyone else shed more light on this unfortunate event?  

Antuino: Farhan's Compact RF Lab In-a-Box

I now have Farhan's latest invention, the Antuino.  Pete will have his shortly.  Very cool.  SWR meter and antenna analyzer, power meter and scalar network analyzer all in one box. I put an old-school knob on the rotary encoder -- it seemed like the right thing to do.  Soon I will be able to find out if my rigs have spurs or are somehow non-compliant.   I'm sure Farhan's "RF Lab in a box" will be an important addition to my test gear arsenal. We will be talking about this in upcoming podcast episodes. 

Mike N2HTT did a nice write up of the new device: 

https://n2htt.radio/2019/05/26/hello-antuino/

And here is the info from the htsigs.com page: 

http://www.hfsignals.com/index.php/antuino/

Thanks Farhan! 

KG7SSB -- Homebrew SSB in Tuscon -- Learning from the BITX40 Module

On Sun, May 26, 2019 at 1:45 PM William R Meara wrote:

Dale: 

  I was talking to Jim W9UD on 20 SSB today.  When I told him I was running a homebrew transceiver he mentioned that he talked to another guy who is on the air with homebrew SSB gear -- you! 

There are so few of us Dale.  I felt compelled to send you an e-mail.  

What are you running?  

After several years on DSB, I started building separate SSB receivers and transmitters, mostly for 17.  Lately I am running versions of the Indian BITX transceiver. 

Please send info on your homebrew SSB projects. 

Thanks,  

Bill N2CQR

Hi Bill, 

I have two radios that are completed to date. I started out building the BITX 40 transceiver from scratch and also a companion 60 watt solid state linear rf amplifier. Then I decided to construct the second transceiver for 20 meter using some of the BITX design concepts and mixed with the UBITX design for additional rf amplification. It too is amplified to about 25 watts output. The 20 meter rig is my favorite radio at this time but I am going to go a different direction on my next build. It's presently just in the design stage but I'm thinking about using the MC1350 integrated circuits for the IF amplification and for the front end I may try using a FET rf amplifier. The beauty of the bitx design is the use of wide band amplifiers that don't have a tendency to oscillate. But, the new design I'm working on will have more shielding between critical circuits and I will use a small amount of negative feedback in the high gain circuits. The reason for changing the radio to a higher impedance design is to simplify the design build. I will basically build a receiver that I can reverse the signal direction over to transmit using the same amplifiers and filters. This will cut in half the amount of circuit building however it will increase the switching circuit complication associated with this new design. 

Today I'm beginning the build of a 100 watt rf linear amplifier design using the kit parts from China (minipa 70) amps. This provides the transformer components and circuit boards. I purchased two kits of parts and I have a large heatsink to build it on. I'm working on a current sensing circuit for protecting the final FETS.  It  will run 4 IRF530's tied together with a splitter and combiner for the input and output matching transformers. It should produce at least 100 watts at 75/80 meters and maybe a little less on 40 meters but 20 meters it will drop off to about 60 or so watts. 

I'm just having as much fun as a guy can have playing around with the homebrew radio's and like you say there's not many doing it these days. I love operating a radio that I built vs. running a factory made radio. I have two commercial rigs on my bench and a couple of Collins radios but the homebrew takes the lead. 

Jim W9UD has become one of my ham friends this year. We end up talking every week or so on the air and keeping touch with local weather conditions.

Side Note:

I wanted to build a SSB radio since I was a young lad with a technician license in the early 60's. SSB came into the picture many years after I was first licensed.  Then move forward to 2015 my ham license had long ago expired during my time in the Vietnam war. I spent several weeks studying the tech, general and finally the extra class exam information and passed on through that adventure. So I decided it's time to build my own radio from scratch. So I started to look online and in books and I still didn't have the confidence to begin building. Then I ran across Farhams BITX 40 and I thought why not buy this radio and just use it as a model of how sideband circuits work. So I did just that and I got it working fine I took the radio and placed it on the test bench and began circuit analysis and signal level evaluation until it all made perfect sense. This is accomplished while transmitting so the levels can be seen on the oscilloscope. Just kill the voltage on the final stage of the bitx. I put a 1khz signal on the mic input. That was just about the only thing I used the bitx 40 rig for and I still keep it handy when I need information. 

Good hearing from you I hope I haven't over done this reply but I really enjoy talking about this subject.

73's Bill.... keep up the building and good luck on your next radio. 

Dale KG7SSB

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And of course, Pete N6QW knows Dale and has been talking about SSB with him for some time...