SolderSmoke Podcast #227: Solar System, SDR, Simple SSB, HA-600A, BITX17, Nesting Moxons? Mailbag

SolderSmoke Podcast #227 is available: 

http://soldersmoke.com/soldersmoke227.mp3

Travelogue

Mars is moving away.  Jupiter and Saturn close in the sky.  And the Sun is back in action – Cycle 25 is underway.  Also, the earliest sunset is behind us.  Brighter days are ahead.

Book Review:  “Conquering the Electron”   With a quote from Nikola Tesla. 

No real travel for us:   Hunkered down.  Lots of COVID cases around us.  Friends, relatives, neighbors.  Be careful.  You don’t want to be make it through 10 months of pandemic only to get sick at the very end.  SITS: Stay In The Shack. 

Pete's Bench and Tech Adventures:  

 Backpack SDR  keithsdr@groups.io

 Hermes Lite 2

 Coaching SSB builders

 G-QRP talk  

 A new source for 9 MHz crystal filters

 Bill's Bench: 

Fixing the HA-600A Product Detector.  Sherwood article advice. Diode Ring wins the day.  Fixing a scratchy variable capacitor.  Studying simple two diode singly balanced detectors.  Polyakov.  Getting San Jian frequency counter for it.

 

Fixing up the 17 meter BITX.  Expanding the VXO coverage.  Using it with NA5B's KiwiSDR. 

Resurrecting the 17 meter Moxon.  But WHY can't I nest the 17 meter Moxon inside a 20 meter Moxon?  They do it with Hex beams.  Why so hard with Moxons? DK7ZB has a design, but I've often heard that this combo is problematic.  Any thoughts?   I could just buy a 20/17 Hex-beam but this seems kind of heretical for a HB station.

Suddenly getting RFI on 40 meters.  Every 50-60 Hz. Please tell me what you think this is (I played a recording).  

MAILBAG:  

Dean KK4DAS’s Furlough 40/20

Adam N0ZIB HB DC TCVR

Tony G4WIF  G-QRP Vids.  Video of George Dobbs. 

Grayson KJ7UM Collecting Radioactive OA2s. Why?

Pete found W6BLZ Articles

Rogier KJ6ETL PA1ZZ lost his dog.  And we lost ours. 

Steve Silverman KB3SII -- a nice old variable capacitor from Chelsea Radio Company. 

Dave K8WPE thinks we already have a cult following.

Dan W4ERF paralleling amps to improve SNR. 

Jim W8NSA -- An old friend. 

Pete Eaton   WB9FLW    The Arecibo collapse 

John WB4GTW old friend... friend of: 

Taylor N4TD HB2HB  

And finally, we got lots of mail about our editorial.   No surprise: Half supportive, half opposed.  Obviously everyone is entitled to their opinion.  And we are free to express ours.  It’s a free country, and we want it to stay that way. That is why we spoke out.

Yesterday the Electoral College voted, finalizing the results.  All Americans should be proud that the U.S. was able to carry out a free and fair national election with record turn out under difficult circumstances. And all loyal Americans should accept the results. That’s just the way it works in a democracy.

We are glad we said what we said. It would have been easier and more pleasant to just bury our heads in the sand and say nothing.  But this was a critically important election and we felt obligated as Americans to speak out.  We'd do it again. And in fact we reserve the right to speak out again if a similarly important issue arises.  

Pete Juliano's Presentation to the 2020 G-QRP Club Convention -- Building SSB Transceivers

It is a great day my friends.  G-QRP has posted on YouTube the presentations made at their 2020 convention. TRGHS! Above you can see the awesome FB contribution of Pete Juliano N6QW.  I watched it live on Zoom, but have been waiting patiently for the opportunity to share it with SolderSmoke readers and listeners. 

There are many other great videos of convention presentations on the G-QRP YouTube channel.  Here is the link to the channel: 

https://www.youtube.com/channel/UClhe-ybLZzpnJh80VmFuS-A 

Be sure to subscribe and give many "thumbs up" to the presentations. 

I see that our friend Alan Wolke W2AEW has a presentation on the NanoVNA in that channel. FB Alan. 

Thanks to G-QRP for running this event and for putting these videos on YouTube. 

Adding 10 kHz of Coverage to My BITX 17

 

Solar Cycle 25 is underway.  The Solar Flux Index and Sunspot numbers are up considerably.  I have dusted off my old BITX17 transceiver.  This time around I am using it in conjunction with a waterfall display provided online by NA5B's KiwiSDR receiver, which is located about 9 miles east of me. This SDR receiver allows me to see the entire 17 meter band.   It was this panoramic display that made me pay more attention to the fact that the Variable Crystal Oscillator (VXO) that I am using in this rig prevented me from tuning the lower 10 kHz of the 17 meter phone band (18.110 -- 18.120 MHz). 

I use two crystals switched by a relay to cover the band. One is at 23.149 MHz, the other at 23.166 MHz.  The crystal filter is at 5MHz.  With a coil and some caps I could move the frequencies of the oscillator enough to cover 18.120 to 18.168 MHz (top of the band). 

When I first built this thing, I kind of wrote off the lower 10 kHz of the phone band.  I couldn't get the oscillator to work that low, and I was already satisfied with the top 48 kHz.  But the NA5B waterfall often showed SSB stations in that lower part of the band.  I wanted to talk to them.  So I started thinking about how to do this.       

Looking at my schematic (above) I remembered that most of the frequency lowering was done by L1, a 3.2uH toroid.  I figured that to go a bit lower, I would just have to add inductance.  But I didn't want to lower the frequency provided by BOTH crystals -- I just wanted to bring the frequency with the lower crystal down a bit.  

In my junkbox I found a 1 uH coil.  I disconnected the lower lead of the 23.149 MHz crystal from its connection to the relay.  I soldered the 1 uH coil between the crystal and the relay (see picture above).  This moved the lower limit down to 18.087 MHz. 

Now crystal one provides 18.087 - 18.144 MHz 

         crystal two provides 18.137 - 18.167 MHz

So now I have the whole phone band.  Bob is my uncle. TRGHS. 

This was a very quick and satisfying little fix. As Pete says WYKSYCDS: when you know stuff you can do stuff.  Indeed.  And as I re-build and repair gear that I built years ago, I am often reminded that as time goes by, we learn more. We end up knowing more and being able to do more.   

I am also planning on rebuilding my 17 meter Moxon;  this time I will make it better and stronger.         

"Radio, Radio" By Elvis Costello and The Attractions

Wow. At one point in the video Elvis C. climbs onto a radio chassis and sings while standing between two Thermatrons.  FB OM.  

And here is an interesting article about Elvis Costello's music, and opposition to Fascism. 

https://www.theatlantic.com/culture/archive/2020/11/elvis-costellos-armed-forces/617238/?fbclid=IwAR2vY3igpNXFijcHnPChvPQ96iKVWG4yjTjGPtj5Rr2ilQdSX-d6WR63fwc 

The Terrible Collapse of the Arecibo Dish: Climate Change, Hurricane Maria, and Funding Cuts. Also: China's New Dish

From https://www.thewrap.com/watch-crazy-footage-of-the-arecibo-observatory-collapse-goldeneye-video/  :

"Alas, over the 2010s it was battered by a series of severe, climate change-linked tropical storms and hurricanes, culminating in terrible damage inflicted by Hurricane Maria in 2017. Unfortunately the 2016 election led to a government unwilling to fund repairs. Though new sources of funding were cobbled together late in 2018, in late Nov. 2020 it was determined there was no way to safely repair the telescope and the National Science Foundation announced it would be decommissioned.

The decommissioning was supposed to proceed after NSF determined the safest possible method, but physics had other plans. So it is that on Dec. 4, the whole thing up and collapsed with almost no warning."

More info (from NSF): 

https://www.nsf.gov/news/special_reports/arecibo/index.jsp

Here is a good 2017 article that discusses the electronic and mechanical arrangements at Arecibo, and the budget cuts it was facing.  The article seems to almost predict the collapse: 

https://www.imeche.org/news/news-article/arecibo-funding-cuts-threaten-future-of-giant-radio-telescope

Here is a comment from someone who worked there and heard the collapse: 

Jonathan Friedman, who worked for 26 years as a senior research associate at the observatory and still lives near it, told the Associated Press news agency of the moment the telescope collapsed on Tuesday.

"It sounded like a rumble. I knew exactly what it was," he said. "I was screaming. Personally, I was out of control... I don't have words to express it. It's a very deep, terrible feeling."  https://www.bbc.com/news/world-us-canada-55147973?fbclid=IwAR3RuwzTfJmqInrOOFB-nctknDzyB_VSr_qdNrjg9LbbxUnAbynKBv9stPQ

Here is an interesting WIKIpedia article on China's FAST dish, with comparisons to Arecibo: 

https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Spherical_Telescope#:~:text=The%20Five%2Dhundred%2Dmeter%20Aperture,County%2C%20Guizhou%2C%20southwest%20China.

Comparison of the Arecibo Telescope (top) and FAST (bottom) dishes at the same scale

Adios Arecibo

Receiving Signals from China's Chang'e-5 Lunar Sample-Return Mission

Background info: 

https://www.scientificamerican.com/article/chinas-change-5-mission-launches-to-collect-lunar-samples/

 A great report from Daniel Estevez EA4GPZ on radio amateurs receiving telemetry from Chang'e-5: 

https://destevez.net/2020/11/a-look-at-change-5-telemetry/

Radioactive Regulator Tubes -- OA2s! Who knew?

 

Pete found this amazing collection of articles by master homebrewer Ed Marriner W6BLZ.  They were published in a West Coast radio newsletter during the 1950s and 60s.   The above is from this collection.

I know that this kind of article upsets some people.  They will write in saying that they have using OA2s for 50 years with no ill effects.   Others will sarcastically say that we should just try to avoid eating the OA2s.  I know. Don't blame me.  Don't blame Pete.  You can blame the Navy. And Raytheon. And Cobalt 60 and Nickle 63. 

Adam N0ZIB's Direct Conversion Transceiver

This is obviously very cool, but looking ahead I think Adam should think about adding one more mixer, changing the bias on the TX amps, and adding a mic amp.   Boom:  A Double Sideband Transceiver.  

Pete wrote: When I was in the US Navy and a particular unit did something outstanding – the Command ship would raise the Bravo Zulu Flag  for a job well. Don’t know if you can see it there in MO but I have raised the BZ flag to you. Outstanding and congratulations.

Bill and Pete: 

Just finished a DC transceiver using Arduino nano, SI5351 (my sincerest apologies, Bill), diode ring mixer and lm386 audio amp.  The transmit portion is a two-stage class AB pre-amp (from EMRFD page 2.32), which is driving an IRF510 final (biased at 2.08 volts) from Pete’s design. Output is about 5watts into a CWAZ low pass filter, based on the design from here: https://www.arrl.org/files/file/Technology/tis/info/pdf/9902044.pdf

I’m using a manual TX/RX switch which is doing multiple things. It brings the Nano A1 LOW, offsetting the transmit frequency 600 Hz for CW, grounds the audio input to prevent deafness (learned that one the hard way), and it engages a relay that switches the antenna from the receiver to the transmit, and also turns on the transmitter stages. Keying is through the first stage of the pre-amp.  

I still have some tidying up to do, and I’m not sure the LPF works so well using two component inductors instead of all toroids, but I finished it today and made my first QSO into Ontario almost 1000 miles away.  It’s been great fun! 

73,
Adam
N0ZIB
Missouri

Rocket Knack

Truly amazing and impressive work.  Thanks to Hack-A-Day for the heads-up

https://hackaday.com/2020/11/27/so-close-to-landing-a-model-rocket-on-its-tail/#more-449440   

6EQUJ5 -- SNR, the Big Ear Radio Telescope, and the "Wow" Signal

https://hackaday.com/2020/11/25/the-wow-signal-and-the-search-for-extraterrestrial-intelligence/#more-448808

This Hack-A-Day article explains the significance of 6EQUJ5 on the paper readout of the Big Ear radio telescope.  It is a signal-to-noise readout. 

The article also has interesting information about the radio telescope that was used.  

I have on my shelf John Kraus W8JK's wonderful book "Big Ear Two -- Listening for Other Worlds."  John Kraus is the guy who built the Big Ear.  In a reminder of how new radio technology really is,  Kraus got his start in radio as a ten year-old boy in 1920.  He ripped the wire out of the ignition coil  of a Model T Ford to make a tuning coil for a crystal radio.  He took the earpiece out of the family telephone.  His father gave him a chunk of Galena.  He used the crystal radio to listen to the early broadcasts of WWJ in Detroit. 

VK3YE's Super Simple Phasing Receiver

Really simple, really nice.  I like the innovative way they achieved the RF quadrature: they did it by splitting and phase-shifting the RF signal, not the VFO signal.  I also like Peter's use of the AM broadcast signal to demonstrate the sideband suppression. Then, SSTV for icing on the cake. 

Wrapping up the HA-600A Product Detector Project -- Let's Call Them "Crossed Diode Mixers" NOT "Diode Rings"

This has been a lot of fun and very educational.   The problem I discovered in the Lafayette HA-600A product detector caused me to take a new look at how diode detectors really work.  It also spurred me to make more use of LTSpice.  

In the end, I went with a diode ring mixer. Part of this decision was just my amazement at how four diodes and a couple of transformers can manage to multiply an incoming signal by 1 and -1, and how this multiplication allows us to pull audio out of the mess. 

But another part of the decision was port isolation: the diode ring mixer with four diodes and two transformers does keep the BFO signal from making its way back to into the IF chain.  This helps prevent the BFO signal from activating the AGC circuitry, and from messing up the S-meter readings. LTSpice helped me confirm that this improvement was happening:  in LTSpice I could look at how much BFO energy was making its way back to the IF input port on the diode ring mixer.  LTSpice predicted very little, and this was confirmed in the real world circuit. (I will do another post on port isolation in simpler, singly balanced diode mixers.)  

At first I did have to overcome some problems with the diode ring circuit.  Mine seemed to perform poorly with strong signals: I'd hear some of the "simultaneous envelope and product detection" that started me down this path.  I also noticed that with the diode ring, in the AM mode the receiver seemed to be less sensitive -- it was as if the product detector circuit was loading down the AM detector.  

One of the commenters -- Christian -- suggested putting some resistance into the input of the diode ring circuit.  I put a 150 ohm pot across the input, after the blocking capacitor. The top of the pot goes to the capacitor, the bottom to ground and the wiper to the input of L1 in the diode ring circuit (you can see the circuit in the diagram above).  With this pot I could set the input level such that even the strongest input signals did not cause the envelope detection that I'd heard earlier.  Watching these input signals on the 'scope, I think these problems arose when the IF signals rose above .7 volts and started turning on the diodes.  Only the BFO signal should have been doing that.  The pot eliminated this problem.   The pot also seemed to solve the problem of the loading down of the AM detector.  

With the pot, signals sounded much better, but I thought there was still room for improvement.  I thought I could hear a bit of RF in the audio output.  Perhaps some of the 455 kHz signal was making it into the AF amplifiers.   I looked at the circuit that Wes Hayward had used after the SBL-1 that he used as product detector in his Progressive Receiver.  It was very simple:  a .01 uF cap and 50 ohm resistor to ground followed by an RF choke.  I can't be sure, but this seemed to help, and the SSB now sounds great. 

A BETTER NAME? 

One suggestion:  We should stop calling the diode ring a diode ring.  I think "crossed diode mixer" or something like that is more descriptive.  This circuit works not because the diodes are in a ring, but because two of them are "crossed."   From now on I intend to BUILD this circuit with this crossed parts placement -- this makes it easier to see how the circuit works, how it manages to multiply by -1, and to avoid putting any of the diodes in backwards.

I prefer the bottom diagram

A KNOWN PROBLEM? 

I'm left wondering if the engineers who designed the HA-600A were aware of the shortcomings of the product detector.  It is really strange that my receivers lacks a 12V line from the function switch to the product detector. And it is weirder still that the detector works (poorly) even with no power to the transistor.  What happened there?  

When you look at the HA-600A manual, you can see a hint that maybe they knew there was a problem.  For CW and SSB, the manual recommends leaving the AF control at the quarter or halfway point, then controlling loudness with the RF gain control.  This would have the effect of throttling back the RF gain (and the potential for product detector overload) when strong signals appear.  MGC in addition to the AGC.  Any memories or insights on this would be appreciated.