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:
Serving the worldwide community of radio-electronic homebrewers. Providing blog support to the SolderSmoke podcast: http://soldersmoke.com
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:
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?
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
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
As young James Clerk Maxwell used to say, "What's the go of it?" and "What's the particular go of it?"
I studied this circuit carefully when I was using it as a balanced modulator in my DSB rigs. I wrote up my conclusions in my book "SolderSmoke -- Global Adventures in Wireless Electronics."
BALANCED MODULATOR CONFIGURATION:
When I was using it as a balanced modulator, I had the RF "carrier" signal going into L1. This RF signal was 7 dbm, enough to switch the diodes on at voltage peaks. With the "center tap" of L2/L3 grounded for RF, this meant that when the "top" of L2 is negative, the "bottom" of L3 is positive. In this situation BOTH D1 and D2 will turn on and conduct.
When the top of L2 is positive, the bottom of L3 is negative and neither of the diodes is on. Neither conducts.
So we have the RF signal turning the diodes on and off at the frequency of the RF signal.
Audio from the microphone and mic amplifier is sent into the center tap connecting L2 and L3. The level of this audio is kept low, below the point where is could turn on the diodes. The center tap IS grounded for RF by the .1uF capacitor, but it is NOT grounded for AF. That is key to understanding this circuit.
In essence by turning the two diodes on and off at the rate of the RF signal, the audio signal is facing severe non-linearity through the diodes. We could say it is alternately being multiplied by 1 and 0. This non-linearity is what is required for mixing. We therefor get sum and difference products: Sidebands. At this point, Double Sideband.
The way the transformer is set up means the RF carrier signal is balanced out: Even when the two diodes conduct, the top of R1 and the bottom of R2 are of equal and opposite polarity, so there is no carrier signal at the junction of R1 and R2 (they are actually a 100 ohm variable resistor that can be adjusted to make SURE they balance out). So the carrier is suppressed and all that remains are the sidebands: Suppressed Carrier Double Sideband.
PRODUCT DETECTOR CONFIGURATION:
What happens when we use this circuit as a product detector in a receiver? Let's assume we are working with a 455 kc IF. If you run a 454 kc 7 dbm BFO signal into L1, it will turn the diodes on and off as described above. But you will NOT be able to put the 455 kc IF signal into the center tap of L2/L3 -- that center tap is GROUNDED for 455 kc. So you will have to run your IF signal into the resistors, and take the audio output from the center tap of L2/L3. This works. I tried it in my HA-600A. But there is a problem: Envelope detection.
In this arrangement, we are balancing out NOT the 455 kc IF signal, but instead we are balancing out the BFO. We don't really NEED to balance out the BFO -- it can easily be knocked down in the audio amplifiers, and IT is not responsible for the problematic envelope detection. We DO need to balance out the IF signal, because if that gets through we can get simultaneous "envelope detection" and product detection. And believe me, that does not sound good.
So I tried putting the IF signal into L1, and the BFO signal into the resistors (as shown above). I took the audio from the junction of L2/L3. This seemed work better, with envelope detection greatly reduced.
BUT WHAT'S THE GO OF IT?
But how is this circuit mixing in this configuration? The strong BFO signal is still controlling the diodes, BUT, with the BFO signal coming in through the resistors, when the top of R1 is positive the bottom of R2 is ALSO positive. In this situation D1 will conduct but D2 will not. The IF signal is facing a big non-linearity. This will result in sum and difference frequencies. The difference frequency will be audio. But with D1 and D2 turning on and off in a very different way than we saw in the balanced modulator, how does the mixing happen?
I think the answer comes from the summer 1999 issue of SPRAT, the amazing journal of the G-QRP club. Leon Williams, VK2DOB wrote an article entitled "CMOS Mixer Experiments."
Here is Leon's 74HC4066 circuit:
I think those two gates (3,4,5 and 1,2, 13) are the functional equivalent equivalent of the two diodes in our product detector. In Leon's scheme the VFO is supplying signals of opposite polarity. Ours is providing only one signal, but the fact that the diodes are reversed means that they act just like the gates in Leon's circuit. The transformer is almost identical to the one we use in the product detector.
Let's look at the output from Leon's circuit:
Steve N8NM built the HA-600A product detector both in LTSpice and in the real world. It worked fine in both versions. Steve even put the product detector into his S-38 receiver -- he reported it worked well there.
I too built the thing in LTSpice. Then I went and rebuilt the circuit on a piece of PC board. I connected the new circuit to the HA-600A, using my external FeelTech sig generator as the BFO. IT STILL SOUNDED BAD ON SSB.
At this point I started Googling through the literature. I found a promising article by Robert Sherwood in December 1977 issue of Ham Radio magazine entitled "Present Day Receivers -- Problems and Cures." Sherwood wrote:
"Another area that could use additional work is the product detector. As the name implies, its output should be the product of the two input signals. If BFO injection is removed, output should go to zero. If this is not the case, as in the Heath HW series, envelope detection is also occurring, which causes audio distortion."
I checked my circuit. When I removed the BFO signal from the product detector, envelope detection continued. In fact, with the receiver in SSB mode, and with the BFO disconnected, I could listen to the music of WRMI shortwave. It seemed that Sherwood was explaining well the problem I was having: Simultaneous envelope and product detection was making SSB sound very bad in my receiver. What I was hearing just seemed to SOUND like what you'd get with a mixture of product and envelope detection: "scratchy" sounding SSB. This also seemed to explain why SSB would sound fine when using the diode detector with loosely coupled BFO energy -- in that case it would be envelope detection only, with no ugly mixture of both kinds of detection.
Finally, I needed to find a way to use the BFO in the HA-600A with the new product detector. Obviously I needed more BFO signal -- I needed about 7 dbm, enough to turn on the diodes. I converted the outboard product detector board into a simple amplifier and put it between the HA-600A BFO and the BFO input port of the new product detector. This works fine.
A few issues remain:
1) The output from the HA-600A BFO through the above BFO amp (and across the 50 ohm resistor) is NOT a pretty 455 kc sine wave. But the peaks of the distorted wave appear to be enough to turn on the diodes, and when I look at the voltages across each diode (on my two channel 'scope) I see mirror images -- one is on when the other is off. Is this good enough?
2) Moving the BFO input from L1 to the junction of the two 50 ohm resistors (that is actually a 100 ohm pot) has big implications for how this mixer works. With the BFO energy going through the toroid, BOTH diodes are being alternately turned on and turned off. But both are on, and then BOTH are off. With the BFO energy going in through the other side, one diode turns on when the other is off. I think the mixing result is the same, with AF coming out of the output port, but the way the mixer works in this configuration is very different. Does this sound right?
In our last podcast we took a few minutes to share with our listeners our views on the U.S. election and who we think they should vote for. Here is the text of what we said. We stand by every word.
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Just days before a very important U.S. election we feel obligated to express our opinion and to let our listeners in the U.S. know who we think they should support.
Some of you will think this is inappropriate -- we
disagree. Several of the long-running
and more recent themes of SolderSmoke are wrapped up in this election:
SolderSmoke is all about global community, the
International Brotherhood of Electronic Wizards. Trump just rejects the idea of global
community. He is all about building walls, imposing travel bans, rejecting
refugees, circling the wagons, and blaming our problems on foreigners. This is one of the reasons we oppose him.
SolderSmoke is all about Science and Technology. Trump is
anti-science. He is a climate change
denier. That's another reason we oppose him.
Speaking of science, since the onset of the pandemic we
have been urging SolderSmoke listeners to protect themselves, their families,
and their communities by following the advice of doctors and scientists. We urge them to socially distance, and to
wear masks. We even invented an acronym in support of this -- SITS – “Stay In
The Shack.” Incredibly, Trump has been
pushing in the opposite direction: He ridicules
the use of masks. He calls our leading
doctors "idiots." He stages super-spreader
events at his rallies and at the White House. Look, more than 200,000 Americans
have been killed by this thing. I know
five people who have buried close relatives.
Yet Trump STILL treats this virus as some sort of political hoax. This is one of the many reasons we oppose
him.
We are both military veterans. We have both been offended by the way Trump
-- who is a draft dodger himself -- has disparaged those who have gone into
harm's way for the United States. We
remember what he said about John McCain.
His scorn for veterans and service members is another reason we oppose
him.
There are many other reasons to oppose Trump, but those are
the ones we feel are most relevant to SolderSmoke.
Election day is Tuesday.
PLEASE, for the good of the country and the world, get out there and
vote against Trump. Wear your mask and stay safe as you do so, but get out and
vote. Especially if you are living in
Florida, North Carolina, Georgia, Pennsylvania, Wisconsin, Michigan, Arizona,
Texas, or Omaha, Nebraska, please help vote Trump out of office and please urge
your friends and relatives to do the same.
SolderSmoke Podcast # 226
http://soldersmoke.com/soldersmoke226.mp3
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About the U.S. election
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Mars: Setting early, will have to shift to evening observation. Weather has been poor.
Sunspot Cycle 25 is underway -- SFI 78, SN 32
The Gliessberg cycle
Pete's Bench: #49, #50, uSDX, Hermes Lite
Bill's Bench: HP8640B, Global Specialties Corp 6000 counter, Lafayette HA600A.
MAILBAG:
Peter VK2EMU Sent me copy of 1947 Handbook. Thanks Peter
Brad W1BCC Spotted 10 S-38s for 80 bucks on Craig’s list. What’s going on here?
Dale K9NN sent both Pete and I care packages with very cool part, including DG Mosfets
Stuart ZL2TW sent me Les Moxon’s Antenna Book. TRGHS. Moxon will be back!
Alvin N5VZH got his receive converter with a little Tribal Knowledge from SS.
GM4OOU The Bitsy DSB rig from Scotland
Peter VK3YE DSBto DC incompatibility SOLVED
Paul VK3HN's Digital SWR and Power Meter and Low band AM TX VFO/Controller FB Videos.
VK2BLQ alerts us to article about Jac Holzman of Elektra Records.
AA0ZZ great message on assembler language and writing software the hard way.