The Sherwood SE-3 Synchronous Detector - Very Nice!

[Steve - WB3HUZ]

Here's an audio file demonstrating the binaural effect you can achieve with a properly wired sync detector. You'll need two speakers on your computer or better yet, put on a set of headphones. You are hearing the lower sideband in the left channel and the upper sideband in the right channel. You notice a strong AM station with the associated heterodyne and modulation products on the rights (upper side)but not on the left. Use your pan or balance control to verify.

With headphones, you get a very "spacious" sound. The desired audio comes from both channels but the noise from each channel is not the same, so it seems to fade into the background a little more. Neat effect and can even help sometimes on weak signals. It's really wild when tuning as the signal rolls across your headphones left-to-right or right-to-left, depending on whether you are tuning up or down in frequency.

[KM1H]

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

Don, in 1937 Hallicrafters had variable BFO injection on the SX-16 and followed with the SX-17. It worked very well on my friends 16 back in the 50's for AM reception, Shortly after that I got a HQ-129X and changed the very low value BFO coupling cap also to 100pf. It not only gave better CW reception (I still was a Novice) and less riding the RF gain but it was outstanding for BCB DXing. Later I found it to be a big AM help with crystal controlled 6/2M converters to a 7 mc IF.  I have no idea why Halli dropped that feature after just those two radios and also why others didnt pick the idea up. I do have a SX-17 now but havent used it much yet after the rebuild.

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.

Most but not all. Leaving Scott and McMurdo out of the discussion; in 1936 the move to better receiver audio was in motion. Of the big players in 35/36, Philco and Zenith were advertising "hi-fi" on select console sets and in 37 the Philco 37-116 had 2 IF stages with selectable bandwidth that Ive measured at 6 to 10 kc total 6dB BW. Nothing exciting by todays standards but it was a start. It sounds good also but I havent measured distortion or audio recovery.

Around the same time Hammarlund introduced the original SuperPro with continuously variable IF selectivity out to around 16 kc. You certainly cant fault the audio of the Zenith Stratosphere 1000Z either but that one is out of my price range for this week! Its about the price of a new LS9 Corvette.

All this sync detector talk will get me motivated to try the PC based approaches as mentioned; Ive learned a lot so far from the thread.

Carl
KM1H

[k4kyv]

Yes, a few de luxe receivers in the 30's were capable of hi-fi audio nearly to the fully capabilities of what the broadcast stations were putting out.  But I don't think anything at all was available from the end of WW2 through the 1960's capable of capturing the full quality transmitted by the stations as required under the FCC proof-of-performance standard.  Maybe one of two esoteric and very expensive receivers, but nothing on the general consumer market.  I'd say the audio quality transmitted by AM stations prior to the public's acceptance of FM was wasted on 99.9% of the listeners, and probably 99% of them didn't care.

[KM1H]

It all depends on what you mean by Capturing. etc.

The Scott 800B certainly met that criteria on the high end and RCA's Orthophonic series in the middle price range certainly can do that. I dont have many others of the 50-60's to compare but the tabletop Zenith MJ-1035-1 of 1965 certainly sounds good.

The Hallicrafters SX-62 series was marketed as a living room radio and not to hams. Halli specs the audio out to 15 kc. What it does on the BCB I havent measured but it can rattle the house with fine sounds; I play one thru the RCA Orthophonic audio deck and the other with the R-42 bass reflex. The SX-42 is almost identical and was aimed more to the ham. The S-47 is a scaled down version of the 42/62 and the chassis was sold to a few console manufacturers.

And dont forget the auto radios. It was pretty hard to beat the PP 6V6 Buicks and Cads with the built in HD 8" speaker or the Deluxe Mopars with PP 6AQ5's and a 6 x 9 built in. By the mid-late 50's they were all junk.

Carl
KM1H

[k4kyv]

Remember the mechanical vibrator power supplies in auto radios?

[KM1H]

Remember the mechanical vibrator power supplies in auto radios?

Of course I do, I rebuild those radios on a regular basis for customers.

With a good vibrator and buffer and the filtering in place the vibrator buzz is below the station and ignition noise. Turn the engine off to DX and even then the buzz is usually below band noise. I used to run my dads 52 Plymouth down regularly    These days its easier to clean up any remaining noise with filtering or a SS vibrator. Some radios are better than others.

Carl
KM1H

[af6im]

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.

Some HDFM and HDAM station engineers are better than others and have nearly eliminated the VERY annoying time difference between the audio on the analog and digital  signals. One local HDAM station had a time delta that was nearly a syllable long. I complained and they corrected it.

I like AM BCB and can receive analog, Motorola CQUAM stereo (yes, there still are a few CQUAM sigs and many Chrysler car radios can decode them) and the new HDAM stereo sigs. HDAM sounds a tad harsh and undersampled to my ear, but the specs suggest that it is just my analog attitude bias and not the signal itself.

73
AF6IM

[k4kyv]

HDAM sounds a tad harsh and undersampled to my ear, but the specs suggest that it is just my analog attitude bias and not the signal itself.

Isn't HDAM also significantly compressed?  How else can they make the stream fit within the bandwidth restrictions on an AM channel or fit three simultaneous streams within a normal FM channel? I am wondering how HD® quality would compare to that of MP3, which sounds harsh to me and less than CD quality.  But the MP3 degradation in quality doesn't seem to bother the public, which has fully embraced the technology.  And admittedly I have never listened to MP3 over a full fledged living room stereo system with power amp and full size speakers.  That may improve the sound, or it could make the deficiencies in quality even more obvious.  I have listened to MP3 sound over a docked iPod and yes, the sound filled the room, but still it was no full-fledged stereo system.

Now, back to the topic.  I am currently trying out a Sherwood SE-3, and hooked it up for the first time last night, to my 75A-4.  These are preliminary observations, with the unit jury-rigged to the receiver, real JS style.

I was highly impressed with its performance on all modes.  The built-in envelope detector is much cleaner than the receiver's stock diode detector.  With synchronous AM detection, the quality of some amateur and AMBC stations approaches that of broadcast FM, and it seems to pull weak AM signals out of noise and QRM, signals that would be marginally readable with the envelope detector.  I then tried listening to SSB and CW.  Again, the audio quality of SSB is far better than what I ever heard with the stock Collins product detector, and CW signals using the 300~ filter seemed to have more clarity and less ringing effect, making copy substantially easier when using the narrow filter.

The only real problem I encountered so far was that in synchronous AM mode, when there is no carrier for the BFO to lock onto, it tends to drift to the side until it reaches several kHz away from the passband mid-frequency.  When I pressed the "lock" switch, it would always instantly lock back on, but one thing I found annoying was that when I switched to envelope detection and then back to sync mode, the BFO would be way off and have to re-lock.  Also, during transmit, I normally switch the receiver to stand-by via the T/R relay.  When I returned to receive, the BFO was again way off, and I had to wait for it to re-lock or else press the manual LOCK function, which essentially made going from transmit to receive a two-switch operation.  However, during a late night/early morning QSO on 160, it remained locked perfectly if I kept the receiver on during transmit, which is no problem, since I automatically mute the audio, and an external BNC coax relay grounds the antenna input to the receiver during TX to protect the front-end rf coil.  My own carrier kept the BFO close enough to instantly lock when I went back to receive. Turning the receiver to stand-by during transmit serves no real purpose, so this shouldn't be a real problem.

When listening to a roundtable QSO, it would take only about a half second to automatically lock onto a station that was considerably off frequency from the station that previously transmitted.  I have not yet heard any fast break-in AM QSO's to evaluate its performance under those conditions.

[w1vtp]

To quote from Don KYV:

"Now, back to the topic.  I am currently trying out a Sherwood SE-3, and hooked it up for the first time last night, to my 75A-4.  These are preliminary observations, with the unit jury-rigged to the receiver, real JS style."

Don and others in this thread. 

This whole topic has been very interesting to me.  I have been using Flex-Radio's PowerSDR for a few weeks now with my Yaesu FT-301 and have found the Sync AM to be a very pleasant experience.  I have found that during a fast and spirited breakin QSO that it is best to go to regular AM detection that the software offers.  The frequency response is excellent - I especially enjoy the low frequency end.  I am limited presently to 6 KC due to the filter in the 301. 

I have a Flex 5000a on the way and am looking forward to the experience.  The panadapter is useful even in the narrow window of my present hookup -- I'm looking forward to the broad band display with the "5000a"

We'll see how much of the high end I can enjoy with these 72 year old ears.  HI FI Am is GREAT!

Al

[KC9GMF]

Now back to the topic

Yes, lets do that.
Now while SDR's are great and its the first thing that we
power up when we power up the shack (most of the time).

But, the SE3 can be used with many of our favorite BA
and SS stuff w/455kc.

My all time favorite combo when the bands are not crowed
is the SX-28A's last IF out into the SE3 then back into the 28's
phono input and back to the 6V6's and a R42 spkr. 
Ladies and Gentlemen this is true AM aka Angle Music!
Bypassing the 28's detector is the icing on cake, along with
the low noise floor of the 28.
Yes % THD is important but this is such a warm and
robust way to listen to AM, and no "latency" I might add...!

Tom
KC9GMF

[k4kyv]

How did you connect the SE-3 to the '28?

I pulled out the 6AL5 detector tube from the 'A4 and stuck a piece of wire into pin 2 receptacle, which is soldered to a small mica cap, into a piece of shielded audio cable.  An alligator clip soldered to the shield is clipped to the base where the tube shield goes on.  Like Steve, I had too much i.f. signal and had to turn down the pot to keep the unit from overloading.

The audio output feeds the same outboard amp I have been using with the A4 all along.

That's kind of a JS setup, though, and I am trying to figure out a better, more permanent way to do it.

[KC9GMF]

Don,

I'll have dig out my notes, as I remember it was
a balancing act with a small mica and resistor out
of the 28. I did not remove the 28's detector, just sample
the IF pre/detector (last IF can?)
That way when I pull the 1/4" jack out
of the phono " input"  the 28 it returns to normal operation.

Then on the back of the SE3 there are pre-punched
holes (4)  for extra RCA jacks, there I put more jacks with
different R's to the input for lo-mid-hi for different receivers,
1)R8500,  2)SX28a, 3)up and coming SP600, and 4) ???.

I'd prefer to put that input pot on the back ofthe SE3, but Sherwood
recommenced against it, but then...

Like I said, I'll have to look this up, its been 4yr's or more
that I did this.

Tom