[AMRadio] Trouble brewing ...


Bry Carling bcarling at cfl.rr.com
Tue Dec 17 08:30:04 EST 2013


Don

From a practical standpoint, can you tell us which commercial ham receivers or HF capable receivers have a synchronous detector like that?



Bry Carling
http://af4k.com
Sent with my iPhone 6


> On Dec 17, 2013, at 3:40 AM, "Donald Chester" <k4kyv at charter.net> wrote:
> 
> 
>>>>>> I once had asynchronous detector in a simple Sony ICF 2010 receiver. It
> was remarkably good on AM.
> 
> Bry Carling
> http://af4k.com
> Sent with my iPhone 6
> 
> 
>> On Dec 16, 2013, at 4:55 PM, "Brett Gazdzinski" <b.gaz at comcast.net> wrote:
>> 
>> That is why I love a sync detector that allows only one sideband
> reception.
>> It sounds just as good as normal with a lot less noise.
>> 
>> Brett
>> N2DTS >>>>>>
> 
> Actually, a  synchronous detector is basically designed to receive both
> sidebands, but with the full advantage of a product detector as opposed to
> an envelope  detector. If the receiver has variable selectivity, it may be
> narrowed to the point that only one sideband is received, which may be
> useful for dodging interference.
> 
> Some synchronous detector circuits have the internal capability of allowing
> the reception of only one sideband, using the phasing method of sideband
> rejection. But in this case it becomes nothing more than an old fashioned
> "sideband slicer", not a true synchronous detector. The synchronous detector
> functions by coherently demodulating both sidebands and vectorally adding
> them at the detector output, so that they reinforce each other. 
> 
> The only advantage of a synchronous detector when used to receive only one
> sideband of an AM signal, is that the PLL automatically locks the BFO onto
> the carrier frequency, thus eliminating the frequency error of a manually
> tuned BFO. Otherwise, this is nothing more than ordinary selectable sideband
> reception; you could do the same thing using any receiver with a narrow i.f.
> filter, BFO and product detector; just carefully zero-beat the carrier by
> turning the main  tuning control, with the BFO set to the edge of the
> pass-band. This cuts random noise in half, but reduces the signal by 6 dB.
> If the interference consists  only of random noise, the net effect is a 3 dB
> degradation of signal-to-noise ratio.  
> 
> Don k4kyv
> 
> 
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