The Sherwood SE-3 Synchronous Detector - Very Nice!

[Steve - WB3HUZ]

I have that article. It was a simple soft switch. Both detectors ran in parallel and the switch worked off the lock signal.

The IC9500 has that. Totally transparent.

Kewl. But can they do it for less than 10 grand  please
I saw a circuit in popular electronics article from the 70's that did it, not sure if
its totally transparent.  I want to incorporate it into
my homebrew synch detector, one of these days..
Just senses error voltage off the phaselock loop, and has delay circuit and, analog
switch to switch between the envelop and synch...

[w1vtp]

Al, in power sdr..

DON"T slide the whole filter.... just the one side-band...that may help.
Though  yes, you're right, every time you switch it resets the filter to center.


The syc am in power sdr is very slow...

SDRMAXII for QS1R, remembers the filter setting for each mode...
And the Sync AM locks on very fast (less than 1/2 second)

Bruce

It's exciting despite the aforementioned perceived shortcomings.  That DSP filter is amazing.  I have a sound / speaker system that goes down to 10 Hz -- sometimes I get a unwanted carrier just 20 Hz or so from the wanted AM sig.  I just pick either the upper or lower sideband (I use split VFO in my setup) to put the unwanted carrier just off to the other side away from the sideband components + the wanted carrier and then just slide the filter until the unwanted carrier goes off the side of the filter and !!poof!! - it's gone.

So between the SAM and the virtually square shape factor of the DSP filters the AM I hear rocks!  I'll have to check out that stuff you mentioned in your post

Regards, Al

[w3jn]

Chuck - The Drake R-8 does this, so does the Sony ICF-2010, and the FT-1000MP.

The Drake R-7 has a quasi-sync detector whereby the signal's carrier is amplified, limited, and mixed with itself.  If the carrier is off the passband a bit, it uses envelope detection.

I didn't pay nearly $600 for the SE-3 and I can certainly see how that could be a turnoff, especially when a softrock is so cheap.  Personally I vastly prefer a hardware solution to a software.   The SE-3 will never lay dormant for lack of the proper operating system, upgrades, drivers, etc.

I have a VERY expensive PC card for decoding RTTY, fax, etc., that's a doorstop due to no software/computer hardware to run it.

[WA1GFZ]

one thing to consider....when you are an old buzzard what is easier to work on an 813 or a 208 pin FPGA with .025 inch pitch leads.

[W3FJJ]

Chuck - The Drake R-8 does this, so does the Sony ICF-2010, and the FT-1000MP.

The Drake R-7 has a quasi-sync detector whereby the signal's carrier is amplified, limited, and mixed with itself.  If the carrier is off the passband a bit, it uses envelope detection.

Thanks John, I didn't know that, The only rig i have with A synch detector is Lowe HF-150, and its annoying tuning around in the synch mode. My hombrew  Synch detector is the is the same way...  Got a friend with a Drake
R8B, but hadn't played it much, did seem like a FB receiver, shame they don't make them anymore..

[w1vtp]

Here are a couple of links:

• For the technically inclined:
  http://www.arrl.org/tis/info/pdf/9209qex009.pdf
• For the "other method" using a limiting (saturated) amplifier:
  http://www.radio-electronics.com/info/receivers/synchdet/sync_det.php
  

I would think the phase locked method would be superior especially during deep selective fading where the local oscillator would continue to supply a "carrier."  I've heard this during very deep fading where you will hear the beat note start very briefly as the system loses lock and then as soon as the signal comes back up the system locks up again. 

Steve QIX, wonder if you have heard that effect on the Sherwood?

Al

[steve_qix]

Here are a couple of links:

• For the technically inclined:
  http://www.arrl.org/tis/info/pdf/9209qex009.pdf
• For the "other method" using a limiting (saturated) amplifier:
  http://www.radio-electronics.com/info/receivers/synchdet/sync_det.php
  

I would think the phase locked method would be superior especially during deep selective fading where the local oscillator would continue to supply a "carrier."  I've heard this during very deep fading where you will hear the beat note start very briefly as the system loses lock and then as soon as the signal comes back up the system locks up again. 

Steve QIX, wonder if you have heard that effect on the Sherwood?

Al

So far, I have not observed this effect with the Sherwood.  It seems to stay well locked, even during deep fades.

[Steve - WB3HUZ]

It's all a function of the PLL loop time constant.

BTW, just for some historical perspective, QST had an article in the 1950's that covered synchronous detection and provided a circuit that could be built. In the late 60's, prominent (then, as he still is!) AMer, Bill-W3DUQ, had an article in 73 magazine on a sync detector he built.

[Bill, KD0HG]

Kind of like IBOC digital FM.  If you lose lock, it is supposed to automatically switch back to analogue.

Unfortunately, in the case of FM broadcasting, there as a slight time delay with the digital, and when reception becomes spotty and the signal rapidly switches back and forth between analogue and digital, the time differential is reported to become very annoying.

I couldn't say from personal experience because, like the case of AM stereo, I have never seen a receiver that had IBOC FM capability.

That's a function of lackadasical engineering, Don.

Depending on a station's equipment, the delay through FM IBOC encoding is around 8 seconds.
Unless hardware is changed, the delay doesn't change a bit, and once you've delayed the analog signal by the same amount, it should be in perfect sync.

There's a couple of ways to set the delay, one can use an IBOC modulation monitor, or more simply, one can use stereo headphones playing analog and digital in different ears.

I've got my FM synced to within 200 microseconds, and it stays put. Audio levels are within 1 db.

It really ticks me off when negligent engineering gives the technology a bad name. 

[W3RSW]

Interesting thread, bordering on the realm of an all SDR.

mentioned,

one thing to consider....when you are an old buzzard what is easier to work on an 813 or a 208 pin FPGA with .025 inch pitch leads.

That's true in the relatiely short term but in the long term, espceially in consumer electronics (which migrates to more specialized stuff like ham radio)... we'll be 'repairing' 208 FPGA equipment by just tossing the old board in the trash and replacing it with a whole new enhanced, probably different or upgraded FPGA board.   

Or the whole damn ADC and FPGA board...   or.... 

This is in addition to the upgrades of the software, especially in open arch. arena.

[Steve - WB3HUZ]

I've listened to close to a dozen stations, both AM and FM, running HD. I've never heard more than a slight delay between the digital and analog audio.

More propaganda from the HD haters.

[Steve - WB3HUZ]

It won't matter. The stuff will be like any other consumer junk. If it breaks, through it away and get a new one. If it's more than a few years old, it's obsolete anyway.

Interesting thread, bordering on the realm of an all SDR.

mentioned,

one thing to consider....when you are an old buzzard what is easier to work on an 813 or a 208 pin FPGA with .025 inch pitch leads.

That's true in the relatiely short term but in the long term, espceially in consumer electronics (which migrates to more specialized stuff like ham radio)... we'll be 'repairing' 208 FPGA equipment by just tossing the old board in the trash and replacing it with a whole new enhanced, probably different or upgraded FPGA board.   

Or the whole damn ADC and FPGA board...   or.... 

This is in addition to the upgrades of the software, especially in open arch. arena.

[k4kyv]

It's all a function of the PLL loop time constant.

BTW, just for some historical perspective, QST had an article in the 1950's that covered synchronous detection and provided a circuit that could be built. In the late 60's, prominent (then, as he still is!) AMer, Bill-W3DUQ, had an article in 73 magazine on a sync detector he built.

I have a near complete collection of QST's from that era.  Do you know what issue it is?  I have seen Bill's article in 73, but don't think I have that issue, but does anyone know which issue that was?  I'll try to find a copy.

The principles of synchronous detection were presented by Costas in the special SSB issue of IRE Proceedings that appeared in 1956.  I have that issue.

There is also a simplified circuit (using tubes) that appeared in GE Ham News, that used a rudimentary PLL circuit that worked by locking onto the AM carrier.  This was one function included in a multi-function "Sideband Slicer" circuit designed primarily for phasing-type SSB reception.  It would be very easy to build only this function, which would include maybe 4 tubes, and the audio phase shift network would not be needed.

I would like to review the QST article, and acquire a copy of W3DUQ's article.

[Steve - WB3HUZ]

I have (or had) all that stuff in a file at home. I will try to dig them out tonight, scan and email them to you.

[w1vtp]

<snip>

I would like to review the QST article, and acquire a copy of W3DUQ's article.

Me too!   BTW, I probably have the particular QST needed.

[n4wc]

I am currently looking at the June 1957 CQ Radio Amateurs' Journal.
On the cover is a picture of a DSB Synchronous Receiving Adapter for
DSB-SSB-AM-CW-NFM-PM-ETC
The article is on page 30 by John K. Webb, W0AHM.  He is listed with General Electric Company Light Military Electronic Equipment Department  Utica, NY.

The article seems to be a 'sort of' how to with schematic and theory.

I will try to get my wife to scan this article and send it to someone.

Bill Cook

[k4kyv]

My first experience with sync detection, or perhaps I should say pseudo-sync detection, was with an old pre-WW2 National HRO.

Those receivers use a tiny little capacitor to couple the BFO to the diode detector,  consisting of a couple of about 1/2" square metal plates separated by a wafer of bakelite that serves as dielectric.  The capacitance is too small to give sufficient coupling to properly demodulate SSB or even CW for that matter.  To get more BFO injection, I used that makeshift capacitor as a terminal strip and soldered a 100 pf mica cap across the terminals.  That gave plenty of BFO injection.

One night I was  listening on the band when it was totally filled with summertime QRN.  I could hear one or two slopbuckets but no AM.  Then I heard a faint carrier, so I turned off the BFO, and could tune in the AM carrier and hear traces of audio, but it was completely unreadable.  Fiddling around with the receiver I tried turning the BFO on again and zero beated.  As soon as I reached zero-beat, suddenly the audio popped up from nowhere out of the noise and the signal became at least partially readable.

I figured out what had happened; the BFO brute-force locked onto the AM carrier and coherently demodulated both sidebands, while the strength of the BFO was high enough compared to the sidebands that it acted  like product detecton, kind of like when you copy SSB with a diode detector by turning the audio wide open and run the rf gain way back.

As  long as I had that receiver, I often copied weak AM signals using that mode.  It worked if the AM carrier had near perfect stability and the HRO was warmed up enough that the frequency had stabilised.  It would lock on only when the free running oscillation was within about 30 Hz of the carrier, and it took only the slightest detuning from zero-beat to lose lock.

What makes the sync detector work so well is the use of a product detector to demodulate the signal.  With a diode or other type of envelope detector, the demodulated audio is the result of intermodulation of every discrete frequency  within the passband with every other discrete frequency.  The USB and LSB intermodulate with the AM carrier and with each other for the basic detection, but a QRM signal, for example an unmodulated carrier, intermodulates with USB and LSB and the AM carrier.  Any element of random noise intermodulates with the unmodulated carrier, the AM carrier, USB and LSB, and with all other elements of random noise within the passband.  With a large number of discrete frequency elements within the passband, the total number of intermodulation products becomes unimaginable, when you think of every possible difference frequency between every frequency element and every other frequency element.

With a correctly functioning product detector, the only output is from the product of the BFO intermodulating with USB, LSB, and with every element of QRM and random noise within the passband, but all the intermodulation products amongst all signal elements within the passband with each other is absent.  This results in a cleaner signal with far less interference.

Most of the apparent power advantage of SSB over AM is due to the action of the product detection process at the receiver, not the inherent power in the sideband(s) of the two modes.

But to coherently demodulate both sidebands of a DSB signal, the BFO must be exactly on frequency and in phase (or precisely 180° out of phase) with the original AM carrier.  Otherwise, the products of the BFO with USB and with LSB do not properly reinforce each other.  If the carrier is rotated 90° out of phase with the original, the audio products from the two sidebands cancel each other, so that the output of the AM detector is zero, and the signal becomes pure phase modulation.

A SSB signal can be thought of as a combination of amplitude and phase modulation, and it is possible to use that principle to generate SSB.

[w3jn]

I am currently looking at the June 1957 CQ Radio Amateurs' Journal.
On the cover is a picture of a DSB Synchronous Receiving Adapter for
DSB-SSB-AM-CW-NFM-PM-ETC
The article is on page 30 by John K. Webb, W0AHM.  He is listed with General Electric Company Light Military Electronic Equipment Department  Utica, NY.

The article seems to be a 'sort of' how to with schematic and theory.

I will try to get my wife to scan this article and send it to someone.

Bill Cook

GE marketed a commercial sync detector in the 50's called the YRS-1 which is very similar to the design in this article.

I have a YRS-1, lightly modified to output USB and LSB simulatneously.  It works pretty well, but the sideband rejection isn't the best.

[WB2YGF]

Although the Sherwood product is nice, for less money one could buy a decent brand new desktop computer... and implement a Softrock or Softrock-like mixer to match any i.f.

Actually, for about the same price one could get a PC SDR receiver with Synch AM built in like Winradio for $499.

http://www.winradio.com/home/g303i-s.htm

[k4kyv]

Maybe the pendulum will swing more towards the center with better detectors and some people wising up to using special receive antenna and diversity reception.

I hope so!  It's such a waste to transmit a nice signal when it is immediately mangled by the receiver's poor detector and/or AGC.

But this has been going on since the mid 1930's.  By then, AM broadcast stations had the capability of transmitting hi-fi audio.  UTC LS series and similar quality audio transformers were available with 30-20,000~ frequency response or better, AM transmitters both composite (homebrew) and commercially built were on the air with no more than a few percent distortion, and microphones and studio equipment were available with specs that would still be classified as hi-fi to-day.

But very few AM broadcast receivers, from the 1930's all the way through the 1960's when FM finally became the preferred mode for the public, had audio quality that was a whole lot better than slopbucket.  Many of the old console floor model radios of the 30's used triode square law detectors with tremendous distortion.  The little plastic table radios of the 40's and 50's  had tiny little speakers with no effective baffle, and audio stages with telephone quality frequency response.  The vast majority of the superhets had  5 kHz selectivity at most, but with very poor skirt selectivity so that the frequencies above about 2500~ were severely cut but adjacent channel stations, and even stations two  channels away would still cause interference if they were very strong.

The broadcast industry spent tremendous sums of money to transmit high quality audio, and FCC regulations required a minimum standard of quality.  But the public was using receivers barely capable of better than space shuttle audio.

[Steve - WB3HUZ]

Here's a clip of K1JJ trying to QRM me using LSB as detected on a sync detector. First the detector is detecting both sidebands. Then the detector is detecting only the upper sideband. Notice the LSB interference is almost gone. This was an analog sync det. The cancellation would be even better with most DSP implementations.

[k4kyv]

But wasn't the detector still detecting both sidebands of the AM signal?  The AM audio did not change one iota while the interfering slopbucket almost completely disappeared. The sync detector has the capability of rejecting interference on either USB or LSB, while  still fully demodulating both sidebands of a DSB signal.  See the 1956 IRE Proceedings article.

[Steve - WB3HUZ]

It's like a phasing slopbucket rig in reverse. Yes, both sidebands are involved and in the IF passband. But only the audio from one sideband comes out of the speaker.

[k4kyv]

It is possible to configure a sync detector so that even though the interference on one sideband is suppressed, the audio from both the DSB sidebands comes out of the speaker.  The term for this is coherent detection.  The vector addition of both sidebands gives twice the audio voltage and thus a 6 dB power advantage. 

Normally, doubling the receiver bandwidth would increase the background noise by 3 dB, so demodulating audio from both sidebands would give only a 3 dB s/n ratio advantage.

Suppressing the interference from one of the sidebands cuts the noise in half and restores that other 3 dB.

[w3jn]

The SE-3 does not have a selectable sideband feature.

The YRS-1 does; however, I've never been able to get the matrix and phase shifters to the point where opposite sideband rejection is acceptable.  Also, the circuit Chuck FJJ posted has this feature as well.