Sherwood Sync

[N8AFT]

Please tell of your experiences using an outboard sync detector, such as the SE6 for ham AM use. I can't find any reference other than for BCB and SWL AM uses, even on their website. Receiver here is a Miltronix EAC R390a... Thanks, Lane.

[k4kyv]

I have been using one with my 75A-4 for several years, and wouldn't be without it. I would recommend the later version with the "AR" mode, which makes it much easier to operate on the ham bands in a QSO where stations are usually not zero beat with each other.  I pull the signal off the last i.f. stage where it feeds the diode detector.  Pulled out the diode detector tube to get easy access to the i.f. signal, and pulled out the 6AQ5 audio output tube to save power drain and reduce heat generation.

It was expensive, but I got mine essentially as an even swap for a tube-type Collins audio peak limiter I was no longer using. Thanks to a friend I was able to get it at a deep discount, and then turned round and sold the peak limiter to a recording studio hobbyist for a more than what I paid for the Sherwood.

It not only enhances AM reception compared to the diode detector; the audio quality of SSB is better that what I could ever get with the stock Collins product detector, beyond comparison.

With AM signals, the audio quality of strong stations is improved, selective fading reduced or eliminated and it pulls weak signals out of the noise and through the interference, sometimes making the difference between perfect readability and marginal or no copy.

[flintstone mop]

It is supposedly the best for SWL and getting rid of the dreaded selective fading distortion..........BIG bux

Fred

[N8AFT]

 Thanks Don, As they say, "ask the man who owns one"...Lane

[WBear2GCR]

They say that you can do the same trick with free downloadable software, a computer and a <$100 SDR receiver - for example a "Softrock".

Put the SDR board at the IF freq and tune the thing with the receiver...

The software has a sync detector mode...

                     _-_-bear

[w3jn]

I have the SE3 which I modified to improve the lock time.  I think Sherwood adopted that mod with the "AR" switch.  In any event, I documented that mod here on the site somewhere; it amounts to adding a switch and a resistor.

Like Don I wouldn't be without mine.  There are many who like to run over 100% positive modulation, and diode detectors in receivers will tend to distort at anything much above 80%.  The Sherwood produces absolutely fabulous audio.

The only downside is if you're in a roundtable with a bunch of guys with drifting VFOs, sometimes someone will drift far enough that the thing won't lock, or will take a while to lock.  Then you're the bad guy yelling at everyone to get on frequency 

[k4kyv]

It's not so hot for receiving Timtron's SBE, either.

[kg8lb]

 A fantastic box.  As Dons says , the improvement in weak signal copy is amazing .The Sherwood flat blows away any SDR that I have ever seen . Even the $3500 type !  It works without the need to bring an unsightly computer and monitor into the shack.

 BTW:  Anybody want to buy a turn key SDR ?   

[N8AFT]

  More convincing evidence..ThankYou, I'm about ready to take the plunge after that one...lane

[SM6OID]

Hi!

Since more than a year I've got a SE-3, I'm very happy with it.
I'm using it more or less every day with my R-390A.
Be sure to use a good speaker and you can get fantastic audio.

[Pete, WA2CWA]

A fantastic box.  As Dons says , the improvement in weak signal copy is amazing .The Sherwood flat blows away any SDR that I have ever seen . Even the $3500 type !  It works without the need to bring an unsightly computer and monitor into the shack.

 BTW:  Anybody want to buy a turn key SDR ?   

Had one several years ago. Worked fine. Then, got the Flex 5000 with excellent sync detection and great audio. Got rid of the SE-3.

Lots of monitors/computers in the shack can be very functional and great eye candy.

N0KGM Shack:

[k4kyv]

The down side is that Rob Sherwood keeps the circuit as proprietary information.  No schematic is included with the documentation.  They are good about helping with technical problems, however.  Mine had a problem with the BFO sometimes dropping out of oscillation.  I called them up, and they recommended that I send it back. Turns out the FET used in the oscillator wasn't optimum for the circuit, so they replaced it with another type, and it worked fine, and they returned it with shipping charges on their dime. They said that they went on to apply that same change to all factory production.

They are good about helping you troubleshoot the unit and will explain step-by-step over the phone how to make certain repairs and/or upgrades as well as alignment, but no schematic. It doesn't look like it would be too difficult to reverse-engineer or trace the schematic if one really wanted to go to the trouble.

One problem they have had with production is acquiring the parts.  Things like the little toggle switches and Miller RF coils they originally used in production have become unobtanium. They had to revise the oscillator circuit for that reason, and that was the reason for the FET problem.

[K5UJ]

Does Sherwood put proprietary circuits in epoxy blocks?  That's the one thing I don't like about an old Orban compressor I have, there are a couple of these modules in black epoxy blocks because Bob Orban didn't want anyone to reverse engineer anything.  I understand the desire to protect intellectual property, but it is annoying if you are trying to fix a problem.  Bob O. is a swell guy and very helpful though, probably like Rob Sherwood.

[k4kyv]

It's all on a circuit board, no epoxy blocks.  It's been a while since I had the box open, and I don't recall if it is 100% poke-through-the-hole construction, or if some SMT is used.  As far as I could tell, it's all off-the-shelf components.

[kg8lb]

A fantastic box.  As Dons says , the improvement in weak signal copy is amazing .The Sherwood flat blows away any SDR that I have ever seen . Even the $3500 type !  It works without the need to bring an unsightly computer and monitor into the shack.

 BTW:  Anybody want to buy a turn key SDR ?   

Had one several years ago. Worked fine. Then, got the Flex 5000 with excellent sync detection and great audio. Got rid of the SE-3.

Lots of monitors/computers in the shack can be very functional and great eye candy.

N0KGM Shack:

  No comment regarding "eye candy" .. a subjective matter. Meat and potatos works fine for some of us  I can accept that the Sherwood is not as impressive looking to some folks as a wall of monitors may be. I still find the Sherwood better performing than the Flex 5000. An elegant application, not having to tie up all that real estate with ugly screens and computer boxes, keyboards etc in order to use it is a huge plus for us .  The Wizard of Oz look was never a goal here . 

 

[K5UJ]

It's all on a circuit board, no epoxy blocks.  It's been a while since I had the box open, and I don't recall if it is 100% poke-through-the-hole construction, or if some SMT is used.  As far as I could tell, it's all off-the-shelf components.

Okay thanx Don; maybe I'll get one someday.  For now I manage to get by with the 75A-3 with its product detector mod, outboard p.p. audio amp, and most recently a cheap h.b. filter I wired into one of the slots using a murata 6 khz ceramic filter, blocking cap and two load resistors on a breadboard with pins to seat into the space for the mech. filters.  A 6 or 9 kc mech filter B (or C?) type is unobtainium but so far I have been happy with the six buck ceramic filter.   Its skirts are not vy steep so it is more like a 7 or 8 kc filter on strong sigs.

[w3jn]

Here's the link to the mod I did

http://amfone.net/Amforum/index.php?topic=15782.0

[WQ9E]

For those wanting to try their hand at building an add on sync detector the article by Dave Hershberger W9GR in the April 1982 issue of Popular Electronics would be a great starting point.  It allows either DSB or choice of sideband and has various sync modes to deal with different conditions.  It is on my list of to do projects.

[w3jn]

Thanks, Rodger!  Here's the article.  As a bonus it includes a I/Q phase shifter network so you can select USB or LSB.

http://www.epanorama.net/sff/Radio/Receivers/Synchronous%20AM%20Radio%20Detector.pdf

[WQ9E]

John,

Thanks for posting, I was going to scan my copy later tonight.  In my notes about the article I also found the following:


NOTE: The article has a published correction in the July '82 issue of "Popular Electronics" on P. 6 in Fig. 4, pin3 of IC8 should be connected to pin 11 of IC2 not pin10.

There is also an unpublished correction where the "ENV" (i.e. Envelope Detector) position of switch S1B should be ground (GND) and not N.C. as shown

[N8AFT]

  Glad I posted the topic as it opened up to some real good stuff...Sherwooder should arrive today...Thanks for all the positive replies..The Ham equipment supplier here in Ohio was happy to get the business during this their slow season...
 
   73 Lane.

[k4kyv]

Thanks, Rodger!  Here's the article.  As a bonus it includes a I/Q phase shifter network so you can select USB or LSB.

The Sherwood allows one to select USB or LSB by choosing the "offset" mode, and manually tuning to one side of the carrier or the other without losing lock.  Of course, the receiver must have the option of narrow enough selectivity to select one sideband over the other.

Some commercial sync detectors are said to run the I/Q psn all the time, so you can receive only one sideband at a time. These are more like the old fashioned phasing type "sideband slicer" of the 50s, than a true sync detector.  A true sync detector must have the capability of receiving both sidebands at the same time in order to take advantage of the vectorial summing of USB and LSB to produce the demodulated audio. This is known as "coherent detection".

Receiving one sideband at a time on a phasing type slicer is no different from tuning in an AM signal on a normal SSB ricebox by switching to USB or LSB, and zero-beating the carrier. It may be useful when there is strong interference on one of the sidebands, but you sacrifice the advantage of coherent DSB detection when both sidebands of the signal are usable. The narrow selectivity filter built into the receiver is likely to be more effective for rejecting the unwanted sideband.

[w3jn]

The Sherwood can demodulate USB or LSB by adjusting the BFO knob, but it doesn't have a I/Q phase shifter/matrix to eliminate the unwanted sideband as the W9GR project has.  As you noted Don this is a SSB phasing exciter in reverse.  The Central sideband slicer operates the same way but doesn't have a phase-locked BFO - if it did, it would be an ideal sync detector.

There are a few such sync detectors using the I/Q to eliminate the opposite sideband I'm aware of - TMC made one, which was part of the DDR series of receivers; GE made the YRS-1 in the early 50s, and there was a mil SSB converter which did it as well, the CV-178 or something like that. 

The difference between the "sllicers" or SSB detectors such as the Central Electronics, the TMC CV-591, and the B&W is that they don't have phase-locked BFOs - hence, they're not synchronized.

[k4kyv]

The Sherwood can demodulate USB or LSB by adjusting the BFO knob, but it doesn't have a I/Q phase shifter/matrix to eliminate the unwanted sideband as the W9GR project has.  As you noted Don this is a SSB phasing exciter in reverse.  The Central sideband slicer operates the same way but doesn't have a phase-locked BFO - if it did, it would be an ideal sync detector.

There are a few such sync detectors using the I/Q to eliminate the opposite sideband I'm aware of - TMC made one, which was part of the DDR series of receivers; GE made the YRS-1 in the early 50s, and there was a mil SSB converter which did it as well, the CV-178 or something like that. 

The difference between the "sllicers" or SSB detectors such as the Central Electronics, the TMC CV-591, and the B&W is that they don't have phase-locked BFOs - hence, they're not synchronized.

True, but you don't actually need the phase locked BFO to receive one sideband only. It doesn't sound as good unless you carefully zero-beat the  carrier and the receiver doesn't drift, but it still provides satisfactory reception - as a SSB signal. To receive both sidebands, the carrier MUST be locked, otherwise USB and LSB will actually interfere with each other and reception will be garbled.

I found a G-E slicer at Dayton a few years ago, but the seller wanted too much for it.  I believe it does have a PLL carrier lock function without the phasing network enabled, so it would function as a DSB sync detector much like the Sherwood.

Then, there is the Costas Loop, which can demodulate DSB suppressed carrier, using the phase relationship between the sidebands to establish the reference point to lock the BFO to the missing carrier. The problem is, that during long silences with no modulation, the BFO has time to drift off lock, and may produce a popping sound at the beginning of the next syllable as it re-locks.

My first experience with a  crude form of synchronous detection was with an old pre-WWII HRO. The stock circuit has a tiny capacitor, just a couple of pf, to couple the BFO to the diode detector. It works for CW, but the BFO injection is not strong enough for good SSB reception.  I bridged a 100pf capacitor across the original one, and it worked satisfactorily for CW and SSB.  One night I was trying to pull a weak AM signal out of the background noise when there was heavy lightning storm static. I tried zero-beating the weak AM carrier with the BFO on, when suddenly the audio popped right out of the noise and the signal became readable. The BFO had brute-forced locked onto the carrier and I was experiencing coherent synchronous detection.  I used it that way from time to time, but it was a real PITA to keep the BFO locked, since even the slightest drift in the receiver tended to be enough to pull the BFO off lock. You had to be tuned to within 10 or 20 cps of the carrier for it to stay locked in.


 

[w3jn]

True, but you don't actually need the phase locked BFO to receive one sideband only. It doesn't sound as good unless you carefully zero-beat the  carrier and the receiver doesn't drift, but it still provides satisfactory reception - as a SSB signal. To receive both sidebands, the carrier MUST be locked, otherwise USB and LSB will actually interfere with each other and reception will be garbled.

Yes, but the I/Q phase shifter and matrix actually REJECTS the opposite sideband - just like a phasing SSB exciter in reverse.  If you take a look at the skizmatic that I posted, you'll see that the BFO is fed to two product detectors, with 0 degree and 90 degree shift.  The outputs of these product detectors are the I and Q channels respectively.  Then each channel is fed thru a 90 degree allpass filter and I/Q are added or subtracted, as appropriate, to select the desired sideband and reject the undesired sideband.

I found a G-E slicer at Dayton a few years ago, but the seller wanted too much for it.  I believe it does have a PLL carrier lock function without the phasing network enabled, so it would function as a DSB sync detector much like the Sherwood.

It does have carrier lock and a phasing network, and USB or LSB can be selected while rejecting the opposite.  Its opposite sideband rejection's not great - perhaps on the order of 25 dB.  I modified mine so it outputs both sidebands independently.  Fed into a stereo amp, USB is the left speaker and LSB is the right; as you tune thru a carrier it gives a spatial definition as the beat tone appears to be zipping through the room!