The AM Forum

I've been testing a Sherwood Engineering SE-3 synch detector for a few days.

Having no experience with what a good synch detector can do, I am extremely impressed with the quality of the audio attainable from the unit.

For years, I've operated 75 and 160 meters at night.  The usual selective fading causes extreme distortion, even in my low distortion detectors.  However, with the synchronous detector, all of this distortion is gone !  Even in deep selective fades, the audio remains as good as ever.  That is very nice indeed.

Another thing I like about the detector is the unit's ability to quickly lock up during break-in QSOs.  The detector has an "AR" (Amateur Radio) position, which makes the detector synch up very quickly on any carrier within a few hundred cycles.  Even stations 1kHz or so away from the last station received are locked in nicely.

There are some other features such as a product detector for SSB and some settings controlling how the lock is obtained.  There is a speaker and headphone output if needed.  I connected the audio output to my usual station audio system, along with the other receivers.

I'm still getting used to the synch detector, however from what I see so far, I am rather amazed how good some of the better engineered stations really sound when the selective fade distortion is removed !

More later  :)

Regards,

Steve

Steve,

You have a Soft Rock Lite or similar, iirc??
How does that compare?

          _-_-bear

Steve

Interesting input on the Sherwood synchronous detector product. Thanks for posting it!

I support an implication contained in Bear's question:

All of the functionality of a synchronous detector, including all of the details of the algorithms Sherwood is using (for example) to perform synchronous detection in their latest product, can be readily performed with any of the SDR implementations.

This includes the ability to switch between fast lock-in with a wide capture range for round tables, and slower lock-in with a narrower capture range for situations where there is are interfering carriers, and one is not jumping between different members of a round table.

The existing Flex Power Power SDR application (available free from Flex) employs just one set of synchronous detector parameters (one choice of loop lock in speed and capture range)... but someone will probably add a feature that makes this user selectable (equivalent to normal and round table modes).

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.

[Of note, to use the Sherwood product with an i.f. that is different from 455kHz, one needs to use a mixer anyway, to convert the i.f. to 455 kHz]

Best regards
Stu

My SE-3 doesn't have an AR position so I modified it to speed the lock time; I posted my modification somewhere (in the Handbook section under Receivers I believe).  Still, in a fast-breakin session with someone off frequency a KC or so you end up missing a transmission now and then.

I measured the audio distortion from it (Agilent 8935 --> GPR-90 --> SE-3 -->8935 audio in) and it was under 1% pretty much everywhere above 300 Hz at 30-100% modulation (the 8935's notch filter doesn't go below 300Hz so its internal distortion analyzer can't measure below that frequency).

The only thing I've seen that beats the SE-3 is my HP 8901A modulation analyzer that checks in at .2% distortion or thereabouts.

It's a great accessory!  I have less than zero interest in dedicating a computer to a softrock, but that is an alternative for those who are willing to deal with all the inherent hassles with booting the computer, shack space, etc.

John, I thought the same thing until I measured 110 dB of dynamic range with Mercury. Now I can surf, send email, build projects and play radio at the same time.
The SE3 is cool, but big bucks.

YUP for $25 and a little time with the computer I gave up on any thoughts of spending $600 for a sync detector from Sherwood.
I'm not into specs that can only be seen by test equipment.
The SoftRock and the Flex software lock-in FB for me in the break-in mode.


Fred

And there's no spectrum display with the SE-3...or ~ infinitely variable filter bandwidths...or passband tuning...or adjustable notch filter (Perseus)...etc...etc...

The other night there was a slop bucket in close up above and another AM QSO 4 or 5 kHz below. With the aid of the spectrum display one can drag the filter bandwidth and put the upper edge of the filter just above the desired carrier...removing the slop bucket. Engage the notch filter and double click on the carrier below...it's gone. Run the filter as wide as possible, select SAM and sit back and enjoy. Only takes a couple seconds to set it up. If the situation changes you see it instantly.   

The SE-3 is a nice box for what it does, however.

The spectrum display alone makes it worth the money. You can monitor the whole phone band without turning a knob.

There's always something better or more desirable for someone' taste.

As you've seen Steve, sync detection is the way to go. For years I've been convinced most AMers much effort into perfecting the audio quality of their transmitted signal without similar efforts on the receive side. 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.

Thanks for the report Steve.  As you know I'm using the computer / FlexRadio method but the end is approximately the same.  Minimal selective fade distortion, and eliminating the need for special receiver mods other than bringing out the IF to a SoftRock, mixer conbo.  Can you give out any details for your application of the Sherwood?  I know you had to accommodate for your IF freq.

I love it

Al

Hi Al,

I hooked it up to my 75A3, which has an IF transformer in place of one of the mechanical filters.  In this mode, the receiver is a good AM receiver.  I wrapped a wire around the last IF amplifier tube's plate pin (yes, a tube!), and went into a 10pF capacitor, then into a piece of audio cable to the Synch. detector.  There is a pot on the detector main board to adjust the input level, if it's too high (which it was with my particular connection).

Anyway, that's how I hooked it up!   8)

Regards,

Steve

More response from yours truly.

• Jay -- I don't recall your setup but it sounds like a FlexRadio
• Steve -- Yeah, how about trying out "the other approach?"  I'd be interested in a comparison
• I especially like the marriage of the old with the new in my case.  Not only can I slide the filter around graphically on my computer screen, adjusting the width, position but also, I can more accurately use the on-board notch filter on my OLD FT-301 and visually walk it in over the noise towards an offending heterodyne and get rid of it. 
  
  I also like the 10 band RX equalizer in the PowerSDR program -- I can customize the fine audio coming out y'all's great AM stations to fit my 72 year old ears.
  
  I DO have a problem with the lockup time in round tables if someone is 1 KC off or off the edge of the filter - I'll either get that descending tone of the lockup search and miss the first part of the station's comments or in the other case just a ssb sounding sig 'cause he's off the edge of the very sharp DSP filter

I've read Sherwood's excellent web page - they have a lot of good resource material!  Guess the only downside of the whole Sherwood experience is the cost.  They do offer some pretty good service to those who do not have the time nor inclination to DIY this excellent mode of receiving AM

I've included an attachment on how I did my setup

73 Al

Al...I was previously using the R-390-A / Softrock / PowerSDR...but the Perseus currently in use is an A/D right off the antenna like the Mercury or QS1R.

 

Maybe, instead of a whole software defined radio, a software defined detector, or i.f. strip and audio stage would be a good compromise.

That's what you have (with some other added functionality) when you hang a Softrock or other downconverter off the IF if an existing receiver and use Flex or other SW on the back end. Going this route is cheap and easy, if you already have a computer to use.

A feature I like to see on today's Synch Detectors, is an auto mode. Here, it knows whether
the detector is locked or not, when its not, it automatically switches to a conventional
envelope detector. This way you can tune around and it will use envelop detector, if you
stop tuning and stay with in capture range, the synch detector will lock and switch automatically
to it. 

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.

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...

SMOP in the sdr world.....Simple Matter of Programming

Charilie  excellent point.  From my experience point of view -- the FlexPowerSDR has an odd response when manually going from Synchronsis detection AM (SAM) to AM -- it forgets where I set the filter window - usually off to one side to maximize high freq response, and centers it.  While it isn't a major problem it sure is disconcerting to see it happen.  Maybe the Flex people will correct the problem at some point.  For things to be transparent that feature of remembering where the filter was set by the operator would be important.

BTW -- I'd rather just point and click on the choice between the two choices within the program (SAM & AM) rather than have software make the decision.  Also, my choice would NOT be going between a conventional envelope detector and SAM - the straight AM detection in my FlexPowerSDR program is still miles ahead of my envelope detector.

I apologize for straying a little off the point -- the Sherwood people have some excellent resources on receivers etc.  I highly recommend visiting their web site and looking at some of their reference material.  Thanks Steve for bringing some visibility on the subject of Sync Am detection!! :) :)

73, Al

Al,
I don't have that problem but usually just select one of the bandwidths on the display. Maybe it happens when you do variable BW??

Yes -- sometimes I slide the filter off a bit to get rid of a heterodyne but if I switch from SAM to AM it centers the filter.

Al

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)

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

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

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.

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.

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..

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.

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.

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. 

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

mentioned,

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.

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.

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.

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.

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.

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

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

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.




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

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.

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

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  ;D  These days its easier to clean up any remaining noise with filtering or a SS vibrator. Some radios are better than others.

Carl
KM1H

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

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.

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

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

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.

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