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Reciprocating vs Synchronous Detector?
"Tom Holden" ) writes:
I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Michael VE2BVW |
"Tom Holden" ) writes:
I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Michael VE2BVW |
"Michael Black" wrote in message ... "Tom Holden" ) writes: I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. I got started on this from a schematic sent to me by a Czech ham/swl who also has a DX-394. He derived his schematic from a translation of one or more of the articles. I'm not sure he understands it because he can't explain well in English and my is Czech non-existent. The design uses discrete transistors, not many parts and is cheap. I have a breadboard version working, after a fashion. It does lock when within 200 Hz or so and sounds pretty good. I was initially puzzled by an apparent null or minimum audio in the centre of lock on DSB signals. It is fundamentally a product detector with a synchronised BFO, so the difference products of the two sidebands are anti-phase. I would assume that all synchronous demods use product detectors and would behave similarly in that regard. It definitely does better than the DX-394's envelope detector on DSB with selective fading and fades out very gracefully and cleanly on weak signals, although lock may be lost before signal is completely unreadable. At the moment my LO is very unstable with temperature. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. I found most of Olberg's HR articles at the Metro Toronto Reference Library but did not look for the IEEE Comm paper by Badessa, who I think was a colleague. I don't know if synchronous detectors were in vogue in 1971 and were known as such. Did Badessa and Olberg coin the name "Reciprocating Detector" because it was truly pioneeering work uninfluenced by the name that eventually dominated or were they trying to get a patent by tinkering with the fundamentals and giving it a different name. The only obvious thing I can see that may be different is the 500 hz filter between the local oscillator and the product detector (that's the part I haven't got working yet - a straight wire is the minimum requirement). When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Hence my posting. HR accepted 4 or 5 articles on the RD or receivers using the RD by Olberg and there appears to have been considerable response. I daresay that, if this Usenet group had been around then, there would have been some hot and heavy debates about the Reciprocating Detector! Michael VE2BVW |
"Michael Black" wrote in message ... "Tom Holden" ) writes: I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. I got started on this from a schematic sent to me by a Czech ham/swl who also has a DX-394. He derived his schematic from a translation of one or more of the articles. I'm not sure he understands it because he can't explain well in English and my is Czech non-existent. The design uses discrete transistors, not many parts and is cheap. I have a breadboard version working, after a fashion. It does lock when within 200 Hz or so and sounds pretty good. I was initially puzzled by an apparent null or minimum audio in the centre of lock on DSB signals. It is fundamentally a product detector with a synchronised BFO, so the difference products of the two sidebands are anti-phase. I would assume that all synchronous demods use product detectors and would behave similarly in that regard. It definitely does better than the DX-394's envelope detector on DSB with selective fading and fades out very gracefully and cleanly on weak signals, although lock may be lost before signal is completely unreadable. At the moment my LO is very unstable with temperature. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. I found most of Olberg's HR articles at the Metro Toronto Reference Library but did not look for the IEEE Comm paper by Badessa, who I think was a colleague. I don't know if synchronous detectors were in vogue in 1971 and were known as such. Did Badessa and Olberg coin the name "Reciprocating Detector" because it was truly pioneeering work uninfluenced by the name that eventually dominated or were they trying to get a patent by tinkering with the fundamentals and giving it a different name. The only obvious thing I can see that may be different is the 500 hz filter between the local oscillator and the product detector (that's the part I haven't got working yet - a straight wire is the minimum requirement). When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Hence my posting. HR accepted 4 or 5 articles on the RD or receivers using the RD by Olberg and there appears to have been considerable response. I daresay that, if this Usenet group had been around then, there would have been some hot and heavy debates about the Reciprocating Detector! Michael VE2BVW |
I have a Reciprocating Detector that I built from a kit of parts that I purchased
from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK Michael Black wrote: "Tom Holden" ) writes: I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Michael VE2BVW |
I have a Reciprocating Detector that I built from a kit of parts that I purchased
from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK Michael Black wrote: "Tom Holden" ) writes: I've been tinkering with an add-on project for a RS DX-394 receiver based on Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published in Ham Radio in 1972 to 1978. Has anybody had any experience with this design. Is it fundamentally any different from a synchronous detector such as the NE602 design by OH2GF in the current ARRL Handbook? Tom I've read those articles, and specifically reread them last year, and for the life of me I really not sure how it's supposed to work. The way he explains it, it sure seems like there is some specific little bit that is happening in there. If I'm remembering, he claims it works for FM too, and I don't see how it could demodulate FM if it was just a synchronous detector. He references some professional article or paper as the source of scheme, and one would hope if someone could get ahold of that, what is going on might be clearer. When I did some searches on the internet last year, I sure didn't find anything more about it. A handful of Usenet posts, none of which added to the scheme or even an understanding of it. Michael VE2BVW |
Bob, thanks forcoming back. I'm delighted to connect with someone who has a
RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
Bob, thanks forcoming back. I'm delighted to connect with someone who has a
RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
Hi Tom,
I haven't built any of the detectors but read some on them awhile ago. I believe that if you get a null that the lock up is happening at 90 degrees out of phase. That cancels the audio. I remember reading something about that in one of the articles and that there was a way to adjust it but the rest is foggy. There is an article on the Costa system in the old CQ SSB handbook. 73 Gary K4FMX On Sun, 13 Jul 2003 21:44:18 -0400, "Tom Holden" wrote: Bob, thanks forcoming back. I'm delighted to connect with someone who has a RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
Hi Tom,
I haven't built any of the detectors but read some on them awhile ago. I believe that if you get a null that the lock up is happening at 90 degrees out of phase. That cancels the audio. I remember reading something about that in one of the articles and that there was a way to adjust it but the rest is foggy. There is an article on the Costa system in the old CQ SSB handbook. 73 Gary K4FMX On Sun, 13 Jul 2003 21:44:18 -0400, "Tom Holden" wrote: Bob, thanks forcoming back. I'm delighted to connect with someone who has a RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
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Avery Fineman ) writes:
Stirling's description isn't quite good enough in the '74 article covering the included "reciprocating detector." The principle is that of simply filtering out the carrier, amplifying it, and mixing it back with the incoming carrier-plus-sidebands. At the output the carrier, mixed with itself, becomes a DC level. The sidebands mix with the amplified-and- limited/filtered carrier to result in the original audio. Motorola used the same principle in the MC1330P video detector chip introduced in the early 1970s (1972?). The 1330 had what amounted to a limiter ahead of the mixing stage. The so-called "capture effect" of the limiter will output the stronger signal which, in this case, is the AM carrier. For the "filtering" (as Olberg called it), the 1330 used a simple resonant circuit tuned to the carrier frequency. While the MC1330 internal schematic is not well layed out for clear understanding, it is different from the reciprocal detector. Unique to the RD design is the fact that the filter is at the output of the differential amplifier, what it sees at it's input is not just the incoming signal, but the incoming signal modified by the output of the filter. That seems to be a key to the design. The MC1330 splits the incoming signal, with one path going to a mixer, and the other path going throught a limiter and filter which then feeds the other input of the mixer. It's behaviour is obvious, ie limit the incoming signal so it's you get a constant amplitude carrier and mix it with the incoming signal to beat it down to baseband, and shows up in plenty of designs, both before and after the Badessa patent. There was an article in Ham Radio for September 1970 about the MC1496 double balanced modulator, and Roy Hejhall specifically mentions it's use as an AM detector in a similar scheme. He said that a limiter wasn't even needed since the 1496 will limit with enough signal. The same thing is stated in the MC1496 datasheet though you have to dig a bit to find it since it's under the "product detector" heading. The filter in this scheme is optional, because not only is there the 1496 example but I've seen similar schemes with no filter. The same scheme shows up in that fairly recent QST article about a synchronous detector (it's been in the Handbook too), though there it's labelled as "quasi-synchronous" and it's merely a side circuit to the main part using a PLL. But if you look in old literature it gets the "synchronous detector" label. What is a puzzle is why Olberg did not reference such articles, because they were halfway there to explaining the reciprocal detector, and what is vague in his articles is what makes the RD different. One thing is certain. That "amplify the carrier, limit it and use it as a locally generated carrier" scheme will not work with SSB, unless the original carrier is not well suppressed. And it's not going to work with CW either, since beating a carrier, as you say, against itself will result in DC and double the carrier. There'll be no beatnote. Since the RD is claimed to work on these modes, something else has to be going on. Michael VE2BVW |
Avery Fineman ) writes:
Stirling's description isn't quite good enough in the '74 article covering the included "reciprocating detector." The principle is that of simply filtering out the carrier, amplifying it, and mixing it back with the incoming carrier-plus-sidebands. At the output the carrier, mixed with itself, becomes a DC level. The sidebands mix with the amplified-and- limited/filtered carrier to result in the original audio. Motorola used the same principle in the MC1330P video detector chip introduced in the early 1970s (1972?). The 1330 had what amounted to a limiter ahead of the mixing stage. The so-called "capture effect" of the limiter will output the stronger signal which, in this case, is the AM carrier. For the "filtering" (as Olberg called it), the 1330 used a simple resonant circuit tuned to the carrier frequency. While the MC1330 internal schematic is not well layed out for clear understanding, it is different from the reciprocal detector. Unique to the RD design is the fact that the filter is at the output of the differential amplifier, what it sees at it's input is not just the incoming signal, but the incoming signal modified by the output of the filter. That seems to be a key to the design. The MC1330 splits the incoming signal, with one path going to a mixer, and the other path going throught a limiter and filter which then feeds the other input of the mixer. It's behaviour is obvious, ie limit the incoming signal so it's you get a constant amplitude carrier and mix it with the incoming signal to beat it down to baseband, and shows up in plenty of designs, both before and after the Badessa patent. There was an article in Ham Radio for September 1970 about the MC1496 double balanced modulator, and Roy Hejhall specifically mentions it's use as an AM detector in a similar scheme. He said that a limiter wasn't even needed since the 1496 will limit with enough signal. The same thing is stated in the MC1496 datasheet though you have to dig a bit to find it since it's under the "product detector" heading. The filter in this scheme is optional, because not only is there the 1496 example but I've seen similar schemes with no filter. The same scheme shows up in that fairly recent QST article about a synchronous detector (it's been in the Handbook too), though there it's labelled as "quasi-synchronous" and it's merely a side circuit to the main part using a PLL. But if you look in old literature it gets the "synchronous detector" label. What is a puzzle is why Olberg did not reference such articles, because they were halfway there to explaining the reciprocal detector, and what is vague in his articles is what makes the RD different. One thing is certain. That "amplify the carrier, limit it and use it as a locally generated carrier" scheme will not work with SSB, unless the original carrier is not well suppressed. And it's not going to work with CW either, since beating a carrier, as you say, against itself will result in DC and double the carrier. There'll be no beatnote. Since the RD is claimed to work on these modes, something else has to be going on. Michael VE2BVW |
"David J. Windisch" wrote in message
news:3f13ee31_1@newsfeed... Hmmmm. Been a long time since I thought about the r-d. IIRC #1: It (the reciprocating detector) would detect SSB and c-w, and it was silent between SSB bursts and c-w characters. Hmmmmmm. My RD implementation behaves like a BFO, no silence like you recall. Heterodynes 5kHz and higher with a wide IF. Olberg's hr 74/09 article says "Through regenerative feedback Q1 and Q2 form a simple oscillator operating at the filter centre frequency". When not locked onto a carrier ("nonsynchronous mode") he said, "the reference level is no longer completely amplitue controlled by the input signal". That seems to suggest that as a locked on signal becomes weak, the amplitude of the reference signal will diminish until lock is lost and rise when it becomes unlocked. He went on "but it does have signal-induced phase fluctuations", whatever that means. I do notice a tendency for the reference signal (BFO) to pull on signal strength and also on keyed carrier or bass speech energy close to the lock-in range. The latter can sound like a lf resonant belch. The narrower the lock-in range, the less susceptible it would seem, but then with no better than 50Hz tuning steps and some drift to contend with, we can't be too narrow. IIRC #2: It was best preceded by mode-suited, steeply-sloped filtering. I recall speculating, back then, that its operating principle was to generate the bfo signal by ringing a bfo tank, offset from the incoming signal, with the bursts of incoming signal. When the tank ceased oscillating, the r-d output was silent. A mode-suited, steeply-sloped filter ahead of the r-d would help keep its bfo tank from being rung by unwanted (off-frequency) signals. It would certainly prevent them beating against the product detector's self oscillation. The filtering of the reference signal inside the RD is supposed to be fairly narrow but not so narrow as to make lock difficult. The narrower the filter, purportedly the greater the immunity to impulse noise. In my current implementation, I use a ceramic resonator paralleled by a white top 455kHz IF L-C resonator. Olberg showed just an inductor in parallel with a quartz crystal, the inductor apparently chosen to resonate with the crystal's interelectrode capacitance at the crystal's frequency. My LC ratio is much lower and is perhaps not as effective at suppressing wideband noise but I can tune for a tighter lock range than Olberg recommended. The bfo offset required for these modes, and thus non-synchronousness of the bfo with the incoming signals, I think, might help to support, to some degree, the speculation above, as well as to explain the use of "reciprocating", rather than "synchronous", as part of the name. The "reciprocating" nomenclature seems to be related to switching the path between opposite phase legs of the product detector on the carrier phase reversals that occur with zero crossings of the modulation envelope of a suppressed carrier AM signal. Perhaps he borrowed it from "reciprocating engine" metaphor. The inventor, Badessa, did not use the term in his patent. Thinking about it now, I simply can't recall any attraction other than novelty ;o) It does seem to me to be an inexpensive synchronous/nonsynchronous detector for all AM modes (and possibly NBFM) that can be easily constructed for low frequencies, eg 455kHz. I'm sure my parts cost is only about $10 compared to $150 for a kit that uses the Sony ICF2010 parts. I'd like to try a 2010 as many extol the virtues of its SD and see how they compare. My main complaint with the RD (or, at least, with my RD) is the audio null that occurs at one point in the lock range. 73, Dave, N3HE and 73 to you. Tom VE3MEO |
"David J. Windisch" wrote in message
news:3f13ee31_1@newsfeed... Hmmmm. Been a long time since I thought about the r-d. IIRC #1: It (the reciprocating detector) would detect SSB and c-w, and it was silent between SSB bursts and c-w characters. Hmmmmmm. My RD implementation behaves like a BFO, no silence like you recall. Heterodynes 5kHz and higher with a wide IF. Olberg's hr 74/09 article says "Through regenerative feedback Q1 and Q2 form a simple oscillator operating at the filter centre frequency". When not locked onto a carrier ("nonsynchronous mode") he said, "the reference level is no longer completely amplitue controlled by the input signal". That seems to suggest that as a locked on signal becomes weak, the amplitude of the reference signal will diminish until lock is lost and rise when it becomes unlocked. He went on "but it does have signal-induced phase fluctuations", whatever that means. I do notice a tendency for the reference signal (BFO) to pull on signal strength and also on keyed carrier or bass speech energy close to the lock-in range. The latter can sound like a lf resonant belch. The narrower the lock-in range, the less susceptible it would seem, but then with no better than 50Hz tuning steps and some drift to contend with, we can't be too narrow. IIRC #2: It was best preceded by mode-suited, steeply-sloped filtering. I recall speculating, back then, that its operating principle was to generate the bfo signal by ringing a bfo tank, offset from the incoming signal, with the bursts of incoming signal. When the tank ceased oscillating, the r-d output was silent. A mode-suited, steeply-sloped filter ahead of the r-d would help keep its bfo tank from being rung by unwanted (off-frequency) signals. It would certainly prevent them beating against the product detector's self oscillation. The filtering of the reference signal inside the RD is supposed to be fairly narrow but not so narrow as to make lock difficult. The narrower the filter, purportedly the greater the immunity to impulse noise. In my current implementation, I use a ceramic resonator paralleled by a white top 455kHz IF L-C resonator. Olberg showed just an inductor in parallel with a quartz crystal, the inductor apparently chosen to resonate with the crystal's interelectrode capacitance at the crystal's frequency. My LC ratio is much lower and is perhaps not as effective at suppressing wideband noise but I can tune for a tighter lock range than Olberg recommended. The bfo offset required for these modes, and thus non-synchronousness of the bfo with the incoming signals, I think, might help to support, to some degree, the speculation above, as well as to explain the use of "reciprocating", rather than "synchronous", as part of the name. The "reciprocating" nomenclature seems to be related to switching the path between opposite phase legs of the product detector on the carrier phase reversals that occur with zero crossings of the modulation envelope of a suppressed carrier AM signal. Perhaps he borrowed it from "reciprocating engine" metaphor. The inventor, Badessa, did not use the term in his patent. Thinking about it now, I simply can't recall any attraction other than novelty ;o) It does seem to me to be an inexpensive synchronous/nonsynchronous detector for all AM modes (and possibly NBFM) that can be easily constructed for low frequencies, eg 455kHz. I'm sure my parts cost is only about $10 compared to $150 for a kit that uses the Sony ICF2010 parts. I'd like to try a 2010 as many extol the virtues of its SD and see how they compare. My main complaint with the RD (or, at least, with my RD) is the audio null that occurs at one point in the lock range. 73, Dave, N3HE and 73 to you. Tom VE3MEO |
Hi Tom, I was waiting for a thunderstorm so I could answer your question. We
finally got one. You get maximum audio in the center of the passband as long as the regenerated carrier is in phase with the original carrier (suppressed or not). With the RD it is in phase. It's hard to tell what lock range I get since I have a DDS local oscillator that only tines in 10kHz steps. I believe that since my RD uses a xtal, the lock range would be in the ballpark of a hundred cycles. As far as noise rejection, I also have an envelope detector in my receiver and I can switch between it and the RD. I cannot tell any improvement on static crashes. I tried my electric shaver as a noise source and the RD may have had slightly less noise - but not enough difference to write home about. Bob Tom Holden wrote: Bob, thanks forcoming back. I'm delighted to connect with someone who has a RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
Hi Tom, I was waiting for a thunderstorm so I could answer your question. We
finally got one. You get maximum audio in the center of the passband as long as the regenerated carrier is in phase with the original carrier (suppressed or not). With the RD it is in phase. It's hard to tell what lock range I get since I have a DDS local oscillator that only tines in 10kHz steps. I believe that since my RD uses a xtal, the lock range would be in the ballpark of a hundred cycles. As far as noise rejection, I also have an envelope detector in my receiver and I can switch between it and the RD. I cannot tell any improvement on static crashes. I tried my electric shaver as a noise source and the RD may have had slightly less noise - but not enough difference to write home about. Bob Tom Holden wrote: Bob, thanks forcoming back. I'm delighted to connect with someone who has a RD. Do you not get null or minimal audio at zero beat in the centre of the passband with your authentic RD? I thought that this would be the normal response of a product detector on symmetrical sidebands - the negative frequency product would be antiphase of the positive frequency product. There is no such null on a SSB with carrier signal such as CHU. What lock range do you get? Without the 455kHz filter in the feedback loop, I get about 400Hz. With a ceramic resonator of unknown interelectrode capacitance, I have been trying different values of parallel inductors and getting lock range of 100 Hz or less. Do you find that the RD suppresses impulse noise and static crashes? 73, Tom VE3MEO "Bob G. Mahrenholz" wrote in message ... I have a Reciprocating Detector that I built from a kit of parts that I purchased from W1SNN back in 1972. I use it at 455kHz in an AM broadcast receiver to eliminate selective fading. The IEEE Comm paper by Badessa lists the patent on the RD that you can look up. Also if you get a null in the center of the lock range you may be locking 90 degrees out of phase with the carrier. Bob K4QQK |
"Bob G. Mahrenholz" wrote in message
... Hi Tom, I was waiting for a thunderstorm so I could answer your question. We finally got one. Great! You get maximum audio in the center of the passband as long as the regenerated carrier is in phase with the original carrier (suppressed or not). With the RD it is in phase. I get minimum audio near the centre. It's hard to tell where centre is with 50Hz steps. Tried reversing phase of feedback loop and got no oscillation, no audio. I'm wondering whether a phase shift network might be needed in the connection of the feedback loop to the product detector base. In Olberg's 10.7MHz version (hr 78/10), he describes a phase shift network on the input signal to the product detector. The unshifted signal also feeds the biased half-wave rectifier/reciprocating switch, as it does in the original version, which lacks the phase-shifted input to the PD. It's hard to tell what lock range I get since I have a DDS local oscillator that only tines in 10kHz steps. I believe that since my RD uses a xtal, the lock range would be in the ballpark of a hundred cycles. As far as noise rejection, I also have an envelope detector in my receiver and I can switch between it and the RD. I cannot tell any improvement on static crashes. I tried my electric shaver as a noise source and the RD may have had slightly less noise - but not enough difference to write home about. That's what I get with my RD variant, too. Do you hear heterodynes with your RD as you tune between stations and approach lock? In your e-mail you indicate that you hear only white noise in the absence of signal. Bob 73, Tom |
"Bob G. Mahrenholz" wrote in message
... Hi Tom, I was waiting for a thunderstorm so I could answer your question. We finally got one. Great! You get maximum audio in the center of the passband as long as the regenerated carrier is in phase with the original carrier (suppressed or not). With the RD it is in phase. I get minimum audio near the centre. It's hard to tell where centre is with 50Hz steps. Tried reversing phase of feedback loop and got no oscillation, no audio. I'm wondering whether a phase shift network might be needed in the connection of the feedback loop to the product detector base. In Olberg's 10.7MHz version (hr 78/10), he describes a phase shift network on the input signal to the product detector. The unshifted signal also feeds the biased half-wave rectifier/reciprocating switch, as it does in the original version, which lacks the phase-shifted input to the PD. It's hard to tell what lock range I get since I have a DDS local oscillator that only tines in 10kHz steps. I believe that since my RD uses a xtal, the lock range would be in the ballpark of a hundred cycles. As far as noise rejection, I also have an envelope detector in my receiver and I can switch between it and the RD. I cannot tell any improvement on static crashes. I tried my electric shaver as a noise source and the RD may have had slightly less noise - but not enough difference to write home about. That's what I get with my RD variant, too. Do you hear heterodynes with your RD as you tune between stations and approach lock? In your e-mail you indicate that you hear only white noise in the absence of signal. Bob 73, Tom |
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