[AMRadio] Trouble brewing ...


Bry Carling bcarling at cfl.rr.com
Mon Dec 16 17:07:04 EST 2013


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
> 
> ----- Original Message ----- From: "Donald Chester" <k4kyv at charter.net>
> To: <amradio at mailman.qth.net>
> Sent: Monday, December 16, 2013 3:58 PM
> Subject: Re: [AMRadio] Trouble brewing ...
> 
> 
>> Bry Carling wrote:
>>> 24KW PEP for parity? I think not.
>>> 
>>> Bry Carling
>>> http://af4k.com
>> 
>> 
>> For parity in talk power, you would need the same total sideband power for
>> both modes. 1500 watts of peak sideband power for AM translates to 3000
>> watts of fully modulated carrier power, since only on voice PEAKS does the
>> modulation hit 100%. The modulating signal must be 50% of the carrier power
>> to modulate 100%, or 1500 watts of power in the two sidebands combined at
>> voice peaks to fully modulate the 3 kw carrier. 1500 watts of sideband power
>> is 1500 watts of sideband power, regardless of whether all the power is
>> concentrated into one sideband, or distributed into two sidebands. The
>> carrier is just "there" for a reference; it neither adds nor takes away
>> anything from the talk power
>> 
>> With SSB, the receiver passband need be only one half as wide as with DSB,
>> so you get a 3 dB s/n ratio advantage with SSB due to the narrower passband
>> at the receiver, which lets in only half the random noise. That would
>> represent a 3 dB improvement for SSB. But, with DSB, the voltages from two
>> sidebands add vectorally, so that the peak voltage at the receiver detector
>> from the  two  sidebands combined adds up to twice the peak voltage that
>> would result from each one of the sidebands received individually. P =
>> voltage squared X R. Doubling the voltage by vectorally combining the two
>> sidebands gives twice the voltage or 4 times the power of each sideband
>> taken individually, or 6 dB. But since the receiver passband allows in 3 dB
>> more noise with DSB, the actual improvement in s/n  ratio is only 3 dB. The
>> net improvement from combining the upper and lower sidebands is 3 dB over
>> each one of the sidebands transmitted alone, exactly what would be expected
>> since the total sideband power of both the sidebands is twice that of each
>> one.
>> 
>> Don k4kyv
>> 
>> 
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