|[AMRadio] Trouble brewing ...|
b.gaz at comcast.net
Mon Dec 16 16:55:23 EST 2013
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.
----- 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
> 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
> 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
> 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
> 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
> 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
> more noise with DSB, the actual improvement in s/n ratio is only 3 dB.
> net improvement from combining the upper and lower sidebands is 3 dB over
> each one of the sidebands transmitted alone, exactly what would be
> since the total sideband power of both the sidebands is twice that of each
> Don k4kyv
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