In article ,
(Michael Black) writes:

"Tom Holden" ) writes:
"Michael Black" wrote in message
...

snip

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!

I didn't see much response. The whole thing seemed to be propelled
by Stirling Olberg, and I never saw anyone else use the circuit in
a ham magazine article. Indeed, other than any followup letters,
there were no references to his articles. And nobody really seems
to know what's going on in the circuit.

I have bound volumes of HR going only to 1973 and did look up the '74
article to refresh my memory.

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.

Analog TV, both in North America and elsewhere, sends video sidebands
as mostly one of them with just part of the other sideband, and with the
carrier reduced to roughly half of what it would normally be with AM.
[so-called "vestigal sideband" with just a vestige of the lower one in US
NTSC standards] The resultant reduced carrier level is still good enough
to grab, limit-filter, and reapply in a mixer to recover just the video of
the
TV sideband. In the MC1330 application with TV carriers in the 50 MHz
range, balanced internal mixing and assorted internal capacitances
allow about 6 to 8 MHz video bandwidth detected with hardly any of the
carrier leaking through. Slight lowpass filtering can get rid of the
carrier.

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
detectors in an airborne receiver for an R&D project at RCA. Those RF
pulses were all 1 uSec wide at different RF carriers between 55 and 64
MHz and there was very little pulse distortion at the output of any one
detector without its input SAW filter. In the RF environment the RF
pulses would have up to 30 db variation in peak envelope power. The
MC1330 detector circuit wound up as a rather linear detector of RF
input amplitude versus video output amplitude over that 30 db range.
I was quite pleased with the results considering an impossibly small
space allowed for 8 detectors (non-optimized hand layout PCB was
about 1" x 1 3/4" for each detector). :-)

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

All in all, interesting stuff to see and consider!

Len Anderson
retired (from regular hours) electronic engineer person

In article ,
(Michael Black) writes:

"Tom Holden" ) writes:
"Michael Black" wrote in message
...

snip

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!

I didn't see much response. The whole thing seemed to be propelled
by Stirling Olberg, and I never saw anyone else use the circuit in
a ham magazine article. Indeed, other than any followup letters,
there were no references to his articles. And nobody really seems
to know what's going on in the circuit.

I have bound volumes of HR going only to 1973 and did look up the '74
article to refresh my memory.

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.

Analog TV, both in North America and elsewhere, sends video sidebands
as mostly one of them with just part of the other sideband, and with the
carrier reduced to roughly half of what it would normally be with AM.
[so-called "vestigal sideband" with just a vestige of the lower one in US
NTSC standards] The resultant reduced carrier level is still good enough
to grab, limit-filter, and reapply in a mixer to recover just the video of
the
TV sideband. In the MC1330 application with TV carriers in the 50 MHz
range, balanced internal mixing and assorted internal capacitances
allow about 6 to 8 MHz video bandwidth detected with hardly any of the
carrier leaking through. Slight lowpass filtering can get rid of the
carrier.

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
detectors in an airborne receiver for an R&D project at RCA. Those RF
pulses were all 1 uSec wide at different RF carriers between 55 and 64
MHz and there was very little pulse distortion at the output of any one
detector without its input SAW filter. In the RF environment the RF
pulses would have up to 30 db variation in peak envelope power. The
MC1330 detector circuit wound up as a rather linear detector of RF
input amplitude versus video output amplitude over that 30 db range.
I was quite pleased with the results considering an impossibly small
space allowed for 8 detectors (non-optimized hand layout PCB was
about 1" x 1 3/4" for each detector). :-)

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

All in all, interesting stuff to see and consider!

Len Anderson
retired (from regular hours) electronic engineer person

In article ,
(Michael Black) writes:

"Tom Holden" ) writes:
"Michael Black" wrote in message
...

snip

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!

I didn't see much response. The whole thing seemed to be propelled
by Stirling Olberg, and I never saw anyone else use the circuit in
a ham magazine article. Indeed, other than any followup letters,
there were no references to his articles. And nobody really seems
to know what's going on in the circuit.

I have bound volumes of HR going only to 1973 and did look up the '74
article to refresh my memory.

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.

Analog TV, both in North America and elsewhere, sends video sidebands
as mostly one of them with just part of the other sideband, and with the
carrier reduced to roughly half of what it would normally be with AM.
[so-called "vestigal sideband" with just a vestige of the lower one in US
NTSC standards] The resultant reduced carrier level is still good enough
to grab, limit-filter, and reapply in a mixer to recover just the video of
the
TV sideband. In the MC1330 application with TV carriers in the 50 MHz
range, balanced internal mixing and assorted internal capacitances
allow about 6 to 8 MHz video bandwidth detected with hardly any of the
carrier leaking through. Slight lowpass filtering can get rid of the
carrier.

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
detectors in an airborne receiver for an R&D project at RCA. Those RF
pulses were all 1 uSec wide at different RF carriers between 55 and 64
MHz and there was very little pulse distortion at the output of any one
detector without its input SAW filter. In the RF environment the RF
pulses would have up to 30 db variation in peak envelope power. The
MC1330 detector circuit wound up as a rather linear detector of RF
input amplitude versus video output amplitude over that 30 db range.
I was quite pleased with the results considering an impossibly small
space allowed for 8 detectors (non-optimized hand layout PCB was
about 1" x 1 3/4" for each detector). :-)

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

All in all, interesting stuff to see and consider!

Len Anderson
retired (from regular hours) electronic engineer person

In article ,
(Michael Black) writes:

"Tom Holden" ) writes:
"Michael Black" wrote in message
...

snip

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!

I didn't see much response. The whole thing seemed to be propelled
by Stirling Olberg, and I never saw anyone else use the circuit in
a ham magazine article. Indeed, other than any followup letters,
there were no references to his articles. And nobody really seems
to know what's going on in the circuit.

I have bound volumes of HR going only to 1973 and did look up the '74
article to refresh my memory.

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.

Analog TV, both in North America and elsewhere, sends video sidebands
as mostly one of them with just part of the other sideband, and with the
carrier reduced to roughly half of what it would normally be with AM.
[so-called "vestigal sideband" with just a vestige of the lower one in US
NTSC standards] The resultant reduced carrier level is still good enough
to grab, limit-filter, and reapply in a mixer to recover just the video of
the
TV sideband. In the MC1330 application with TV carriers in the 50 MHz
range, balanced internal mixing and assorted internal capacitances
allow about 6 to 8 MHz video bandwidth detected with hardly any of the
carrier leaking through. Slight lowpass filtering can get rid of the
carrier.

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
detectors in an airborne receiver for an R&D project at RCA. Those RF
pulses were all 1 uSec wide at different RF carriers between 55 and 64
MHz and there was very little pulse distortion at the output of any one
detector without its input SAW filter. In the RF environment the RF
pulses would have up to 30 db variation in peak envelope power. The
MC1330 detector circuit wound up as a rather linear detector of RF
input amplitude versus video output amplitude over that 30 db range.
I was quite pleased with the results considering an impossibly small
space allowed for 8 detectors (non-optimized hand layout PCB was
about 1" x 1 3/4" for each detector). :-)

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

All in all, interesting stuff to see and consider!

Len Anderson
retired (from regular hours) electronic engineer person

(Avery Fineman) wrote in message ...
[snip]
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.

I assume he is now a Silent Key - his call sign W1SNN is now
unassigned. Reading the preceding patent by Badessa, it seems more
complicated than what you describe but perhaps it boils down to that -
the complexity is in understanding the technique with which the
carrier is "synthesized" (his word). What you describe is a
"quasi-synchronous" detector; Badessa/Olberg talk about synthesizing a
carrier for suppressed carrier AM based on the carrier phase reversal
at zero crossings in the modulation envelope - the fundamental carrier
extraction also works on AM with carrier without the phase reversal
and it's my impression that the product detector itself oscillates at
the feedback loop filter frequency in the absence of a lockable
carrier.

The way my implementation behaves, I would say it has a synchronous
BFO. It sounds similar to a conventional BFO/product detector except
within the lock-in range, where it locks on to zero beat. I'm not sure
I have it functioning as Olberg intended or that Olberg's design is
consistent with Badessa's patent. The latter seems to claim phase
lock, except when there is a beat frequency. Both are silent about the
phenomenon I observe of an audio null on DSB AM carrier signals at a
certain point within the lock-in range. A couple have suggested that a
90 degree difference between carrier and reference would cause this -
(however,)it's not evident on SSB AM with carrier (e.g. CHU at
3330kHz). If so, then it would seem that the phase difference changes
across the lock-in range and passes through 90 degrees at one point
only. Wouldn't this be typical of all synchronous product detectors?

A hint that audio nulling may indeed have been a negative factor in
the RD is in Olberg's HR'78 article on the 10.7MHz RD where there is a
phasing network that does not appear in the earlier low frequency
models.

[snip]

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
[snip]

I have been quite pleased with the dynamic range of my RD in
combination with the output levels from the 2nd last IF amp of my
DX-394. I do hear a strong click on the initial pulse of strong
carrier for CW Morse characters that I have not yet concluded is
related to the AGC action of older receivers to which attributed some
overload problems. My modified AGC should have an attack of between 2
and 10 ms and I have turned AGC off and still get the clicks, IIRC.

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I have not compared my RD output to the envelope detector output under
controlled listening conditions. RD goes to my old stereo and Dynaco
A25 speakers; ED goes through the narrower bandwidth audio amplifier
of the DX-394 to a 4" speaker. When locked, RD sounds pretty clean!

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

For FM demodulation, he claims that converting the narrow-band crystal
filter that follows the feedback filter to an LC circuit makes a
frequency discriminator. In his Companion Receiver project, he
switches between the two filters for the two modes. My RD works with
the AM modes with/without the crystal filter (actually mine's ceramic)
and with an LC 455kHz resonator in parallel with the ceramic filter.
With straight wire, the lock-in range is on the order of 400Hz; with
the others, it can be reduced to less than the nominal 50Hz tuning
steps of the DX-394. I have yet to find a NBFM signal.

All in all, interesting stuff to see and consider!
So far, it has been all of that and the parts cost is low.


Len Anderson
retired (from regular hours) electronic engineer person

Good to hear from you,

Tom

(Avery Fineman) wrote in message ...
[snip]
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.

I assume he is now a Silent Key - his call sign W1SNN is now
unassigned. Reading the preceding patent by Badessa, it seems more
complicated than what you describe but perhaps it boils down to that -
the complexity is in understanding the technique with which the
carrier is "synthesized" (his word). What you describe is a
"quasi-synchronous" detector; Badessa/Olberg talk about synthesizing a
carrier for suppressed carrier AM based on the carrier phase reversal
at zero crossings in the modulation envelope - the fundamental carrier
extraction also works on AM with carrier without the phase reversal
and it's my impression that the product detector itself oscillates at
the feedback loop filter frequency in the absence of a lockable
carrier.

The way my implementation behaves, I would say it has a synchronous
BFO. It sounds similar to a conventional BFO/product detector except
within the lock-in range, where it locks on to zero beat. I'm not sure
I have it functioning as Olberg intended or that Olberg's design is
consistent with Badessa's patent. The latter seems to claim phase
lock, except when there is a beat frequency. Both are silent about the
phenomenon I observe of an audio null on DSB AM carrier signals at a
certain point within the lock-in range. A couple have suggested that a
90 degree difference between carrier and reference would cause this -
(however,)it's not evident on SSB AM with carrier (e.g. CHU at
3330kHz). If so, then it would seem that the phase difference changes
across the lock-in range and passes through 90 degrees at one point
only. Wouldn't this be typical of all synchronous product detectors?

A hint that audio nulling may indeed have been a negative factor in
the RD is in Olberg's HR'78 article on the 10.7MHz RD where there is a
phasing network that does not appear in the earlier low frequency
models.

[snip]

Olberg claimed that (in the '74 article) the "reciprocating detector" did
not handle overloads well. While I've not examined that in detail, nor did
I read HR in that year, I used the MC1330P in 8 simultaneous RF pulse
[snip]

I have been quite pleased with the dynamic range of my RD in
combination with the output levels from the 2nd last IF amp of my
DX-394. I do hear a strong click on the initial pulse of strong
carrier for CW Morse characters that I have not yet concluded is
related to the AGC action of older receivers to which attributed some
overload problems. My modified AGC should have an attack of between 2
and 10 ms and I have turned AGC off and still get the clicks, IIRC.

Offhand, after a long and thoughtful 20 minutes after reading Olberg's
'74 HR article, a narrowband (IF) filter could pass the carrier through to
any FM-style limiter IC, its output to a balanced mixer (differential,
double-balanced bipolar or FET) which could then output just the side-
band content of an AM unsuppressed-carrier signal. If the limiter gain
was high (that is, limiting threshold low), front end noise would get
through and appear at the demodulated output...but that noise band-
width would be only as high as the narrowband IF filter bandwidth.
Once a carrier was there, it would take over in the limiter and
demodulation would become essentially linear. Impulse noise
received could be reduced depending on the relative peak IF power
of noise pulse versus carrier...the limiter stage would take over and
pass the higher input level while suppressing the lower input level.

I have not compared my RD output to the envelope detector output under
controlled listening conditions. RD goes to my old stereo and Dynaco
A25 speakers; ED goes through the narrower bandwidth audio amplifier
of the DX-394 to a 4" speaker. When locked, RD sounds pretty clean!

I doubt that this "reciprocating detector" would be good for any FM
except quite narrowband FM...due to the bandwidth of the filter.
That was another claim by Stirling Olberg in the 1974 article. FM
carrier level would vary with modulation (although entire carrier plus
sidebands would remain constant) and that would mess up the carrier
reinsertion part of the "RD." Might be okay for PM. Have to do the
numbers to see if that is feasible and my 20 minutes was up. :-)

For FM demodulation, he claims that converting the narrow-band crystal
filter that follows the feedback filter to an LC circuit makes a
frequency discriminator. In his Companion Receiver project, he
switches between the two filters for the two modes. My RD works with
the AM modes with/without the crystal filter (actually mine's ceramic)
and with an LC 455kHz resonator in parallel with the ceramic filter.
With straight wire, the lock-in range is on the order of 400Hz; with
the others, it can be reduced to less than the nominal 50Hz tuning
steps of the DX-394. I have yet to find a NBFM signal.

All in all, interesting stuff to see and consider!
So far, it has been all of that and the parts cost is low.


Len Anderson
retired (from regular hours) electronic engineer person

Good to hear from you,

Tom

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