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. 

The Wizard of Horseshoe Bend: VK2FC's Wonderful Projects

 

Google led me to VK2FC's amazing site.  I was digging up info on product detectors and I landed on Glen's description of his version of the W7ZOI Progressive Receiver.  Glen's website provides a very detailed, board-by-board description of how to build this great receiver.  I now want to build one. 

http://www.vk2fc.com/progressive_receiver.php

Glen's site has many other projects.  Check them out: 

http://www.vk2fc.com/index.php

And here he is, the Wizard of Horseshoe Bend: 

Thanks Glen. 

Diode Ring Magic

 

I continue to work on the product detector of my Lafayette HA-600A.   This work has caused me to brush up on my understanding of how mixers really work.   

I think one of the most interesting mixer circuits is the diode ring.  With just four diodes and one or two transformers, this device manages to take an incoming signal and multiply it by either 1 or -1 depending on the polarity of the local oscillator signal.  That is pretty amazing.  

Alan Wolke W2AEW did an excellent video on this: https://www.youtube.com/watch?v=junuEwmQVQ8

Inspired by Alan, I took my most recent homebrew diode ring mixer (with transformers from Farhan, diodes from Jim W8NSA, and a PC board base from the CNC mill of Pete N6QW) and hooked it up to two signal generators and an oscilloscope.   I had the local oscillator at 10 MHz and the signal oscillator at 7 MHz.   You can see my results in the pictures (above and at the end).  You can see the resulting difference frequency (3 MHz) in the broad up and down pattern.  And you can see the sum frequency (17 MHz) signal in the faster oscillations.  All you would need is some filtering to separate them out.  

I really like the RSGB Handbook diagram (above).  I think the bottom schematic with its crossed diodes really explains how the phase reversal takes place:  when the LO turns on D1 and D3 (the horizontal ones), multiplication by 1 takes place.  But when the LO turns on D2 and D4 (the crossed  diodes), up goes to down and down to up, creating phase reversal, or, in math terms, multiplication by -1.  

At a more basic level, mixing takes place whenever -- in a non-linear circuit -- one signal is controlling the gain or attenuation experienced by the other signal. A complex waveform results, a waveform that contains sum and difference products.  A circuit like the diode ring, that alternately multiplies by 1 and -1, is non-linear in the extreme, and the multiplication is controlled by the LO.  The results can be seen in the diagram's complex waveforms, on Alan's Tek 'scope, and on my Rigol.  And in those complex waveforms you can SEE the sum and difference frequencies. That is really cool. 

 

A Diode Ring Product Detector for the HA-600A? Problems.

Pete advised me to try this a week or so ago, but it took me a while to follow through and try it out.  

I got the two diode, one transformer product detector working well, but with it a new problem arose: 455 kHz energy from the BFO was leaking past the product detector back into the S-meter/AGC circuitry.  This showed up in the form of a constant S-3 reading when I switched to SSB/CW.  This was annoying. 

I figured the problem was that the only signal really being balanced out was the IF signal going into L1 of the product detector.  I took another shot at putting the BFO signal into this port, with the IF signal going into the unbalanced potentiometer port.   This did indeed take care of the BFO leakage S-meter problem, but once again the SSB did not sound great -- I think the old problem of simultaneous envelope and product detection returned.  

This was obviously a port isolation problem.  I remembered that the diode ring "doubly balanced" configuration has much better port isolation.  So on Sunday morning I built one, first in LTSpice and then on the bench.  

For the bench model I used some PC board pads out of Pete Juliano's $250,000 CNC machine.  For the toroids I used two trifilar coils wound by Farhan's dedicated staff in Hyderabad.  The diodes were sent to me by Jim W8NSA.  So there was lots of soul in this new machine. 

The circuit worked in LT Spice and at worked well when tested on my bench with my FeelTech (for the BFO) and HP8640B (for the IF signal) sig gens with my Rigol 'scope watching for the audio out.  

But I ran into some problems when I popped the new board in there in place of the old product detector:  The 455 kc BFO leakage problem is gone and the S-meter is where it should be, but...

-- I'm seeing a return of the old simultaneous envelope and product detection problem.  SSB was sounding scratchy again and indeed, when I removed the BFO signal from the diode ring circuit I could hear SSB signals making it into the audio amplifiers.  These signals sounded just like AM signals as heard through an envelope detector without a BFO. 

-- The diode ring circuit also had a very bad effect on how the HA-600A worked in AM mode.  It seemed like the new circuit was loading down the diode AM demodulator.   SW broadcast signals sounded awful in the AM mode until I disconnected the IF input to the diode ring circuit (this input is NOT switched -- it is always connected, even in the AM mode). 

So, for now, am back to using the two-diode, single transformer, singly balanced product detector with IF signal going to the balanced (L1) port and the BFO going in through the wiper of the 100 ohm pot.  

Any suggestions on how to overcome the problems with the diode ring circuit?  

Shortwave Listening

I was listening to Glenn Hauser's excellent shortwave listening show on WRMI this week, and he mentioned a technique that I had not been aware of:  listening for the harmonics of distant stations. This is apparently being done for medium wave broadcast stations, but also for stations in the lower frequency range of the shortwave bands.  If propagation makes it highly unlikely for you to hear the main frequency, perhaps propagation would be better for the the second or third harmonic.  This method is discussed here:   

http://www.pateplumaradio.com/genbroad/harmonics.htm

Here is some more background information on Glenn Hauser: 

https://en.wikipedia.org/wiki/Glenn_Hauser

Here is a real treasure trove of articles and recordings about the history of shortwave radio: 

http://www.ontheshortwaves.com/history.html

HB-2-HB Contact! N4TD's Amazing Homebrew 20 and 40 meter SSB Transceiver

 

Oh man, this doesn't happen every day.  Using my homebrew BITX 40 DIGI-TIA,  I had just finished a great QSO on 40 meters with Greg W8GP, talking about Heathkits and homebrew radio.   Then I got a call from Taylor N4TD.  He told me he is a SolderSmoke listener.  Then he just casually mentioned the really big news:  HE TOO WAS ON A HOMEBREW RIG! 

I told Taylor that this a rare occurrence.  He agreed. 

Taylor told me his rig is for 20 and 40.  It is a single conversion design with a 9 MHz IF and a crystal filter.  Using a Ukraine-made PA board, it puts out 50 watts.  

Taylor sent me some pictures and wrote: 

Hi Bill,

It was great to work you homebrew to homebrew.  As you said, that doesn’t happen very often.  I used a modular architecture for this radio.  The module size is the ExpressPCB miniboard  size, so they are less expensive and all the same size so they can be moved around.  All the boards are homebrew except for the final amplifier module.  The PA module I got from 60dbm in Ukraine through eBay.  I had tested this module before and found it to be solid, and it was more economical than building the PA from scratch.  It delivers 50W+ and has been reliable through all my sometimes abusive testing.  

73 Taylor N4TD

Taylors rig -- Top view

Taylor's rig -- Bottom view

The Dish -- Virtual Tour -- New Indigenous Name

Thanks to Peter VK2EMU for this update on the Parkes radio telescope.  Parkes is the subject of our favorite movie about an antenna:  'The Dish."   If you haven't seen it, well, you are just wrong. 

The video update is very nice, with an interesting juxtaposition of old and new test gear.  

But the coolest thing that Peter sent us is the story of the Parkes Radio Telescope's new indigenous name: Murriyang in the Wiradjuri language: 

https://www.abc.net.au/news/2020-11-09/the-dish-is-given-a-wiradjuri-name/12862452   

Thanks Peter.