A discussion on sync detection

MTScannerNut

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Very informative article. I have an early production Icom R75 with sync detection. I've been playing with it and if it is making any difference I can hardly tell. On the other hand, the sync detection on my R8600 makes a very noticeable difference and the improvement is easily heard.
 

majoco

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I have an ex-Marine Debeg 7313 which was also badge-engineered by Skanti, Hagenuk and Siemens as far as I can gather. It only receives CW, AM or USB. For the USB product detector it uses a TBA120 IC and the carrier insertion frequency of 1.4MHz +/- a little is synthesised somewhere else. However on AM the signal is fed into the input transformer of the product detector but also fed into a limiting amplifier on the same IC which strips off the modulation, amplifies the remaining carrier and applies that to the other input of the product detector - the normal CIO for USB is disabled of course. The AM IF amplifier has a very broad characteristic so combined with the synchronous detection give a fine not-quite-HiFi sound and I have never heard it come out of lock. I have attached the schematic and the explanatory text for info.
 

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mbott

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13dka has written several excellent articles for SWLing.com.

--
Mike
 

Direwolf131

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Very informative article. I have an early production Icom R75 with sync detection. I've been playing with it and if it is making any difference I can hardly tell. On the other hand, the sync detection on my R8600 makes a very noticeable difference and the improvement is easily heard.
You will never realize any true synch performance out of the excellent Icom R75 absent serious mods, mods which come close to the original cost of the receiver itself. On the other hand, you have absolutely no need for a working synch detector on any working R75 as they are absolutely spectacular at capturing all HF/AM signals via ECSS, which in my 45 years has always equaled or exceeded any synch detection circuitry right from the gate!

The R75's stability in SSB is just superb, I listen to all HF/Utility/Broadcast on my R75's via ECSS, one of the greatest utility receivers ever produced, as far as I am concerned synch is a pointless gimmick I have never seen really live up to its vaunted expectations, even on professional sets costing 3-4 X the original cost of an R75.
 

GB46

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The only way to tell that my R75 is in AM synch mode is by the indicator on the LCD, as it makes absolutely no difference in the received signal. It does have give a slight pop when tuning away from lock, but it's useless. On the other hand, the R75's 1 hertz tuning step is very useful for zero beating when using ECSS.

Back in the 90s I had a Sony ICF-2010, and its synch mode greatly reduced the effects of fading. It didn't stay locked on the signal very long, however; I had to retune quite often.
 

GB46

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Meant to mention that mine is an early version of the R75, over 21 years old by now.
 

mbott

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After using my 2010 since '91 and needing to replace the R75 I sold, I did pick up an older R75 with the synch detector. This one didn't have the DSP unit, so that was ordered prior to the radio even shipping to me. Upon receipt, I added the DSP unit and sent it on to Kiwa for their synch detector magic. There is a slight improvement in the signal quality using the synch detector now, but I didn't have it long enough prior to sending on to Kiwa to say it wasn't there before.

As for the 2010, I don't think I've encountered the drifting issue. That synch detector can spoil one. :)

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GB46

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As for the 2010, I don't think I've encountered the drifting issue. That synch detector can spoil one. :)
I no longer have mine, but while I did, I discovered a little trick with the synch detector quite by accident:

After tuning in a USB signal, I inadvertently switched the radio to synch AM. Out of curiosity I started fiddling with the tuning dial, and actually managed to clarify the signal with more pleasant audio than I ever got in USB mode. People I shared this with contradicted me, claiming it couldn't have worked, due to the absence of a carrier in sideband signals, but I know it worked for me. My guess is that the 2010's AM synch must have been injecting a carrier of its own, and producing the same effect as ECSS.
 

ka3jjz

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That is pretty much how sync is supposed to work - basically put, it's replacing the carrier that was originally received and detected with one internally created which is more stable and free of fading effects. But how well it works is a very touch and go thing- some manufacturers do it right, others....

Mike
 

bearcatrp

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You will never realize any true synch performance out of the excellent Icom R75 absent serious mods, mods which come close to the original cost of the receiver itself

Can you elaborate on this? Just bought a used R75. What serious mods?
 

mbott

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You will never realize any true synch performance out of the excellent Icom R75 absent serious mods, mods which come close to the original cost of the receiver itself

Can you elaborate on this? Just bought a used R75. What serious mods?
The Synch-AM mode on the Icom R75 was only available on the early production models. Not sure exactly when that was no longer available on the R75. Later models don't include it. Instead, they had the UT-106 DSP unit installed. I don't believe that there is a way to upgrade a later model with Synch-AM. I believe Icom dropped the Synch-AM in the early- to mid-2000s.

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Mike
 
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