Message-ID: <3C921829.BABF01F@usa.net>
Date: Fri, 15 Mar 2002 16:50:01 +0100
From: "Alberto di Bene" <dibene@usa.net>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: If you have downloaded PHD Radio...
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Jay Rusgrove wrote:

> Now to my question. What is used as the reference frequency for the BFO and can
> it be tweaked? I notice that with my GPS referenced receivers a known frequency
> output  makes the phase meter rotate about 1 revolution every 4 seconds or so.
> Is there a way to tweak the frequency right on as in Argo?

Jay and the group,
   thanks for your nice words.
What is used as the reference frequency for the BFO ?? Guess what ?
The sampling frequency of the sound card.... which generally is derived from
a cheap quartz crystal... the BFO is implemented as a  dual-output NCO,
producing quadrature signals for the half-complex mixers. The rate of updating
of the phase accumulator for the NCO is directly derived from the rate of
the callbacks from the MME subsystem of Windows, which in turn depends
on the hardware interrupts generated from the sound card.
So I cannot see any possibility to tweak it in hardware.
A software possibility could be to use the right channel of the Line In
(the mono input signal is on the left), to input a precise reference,
from which the software could somehow derive a correction factor...

Or, as in Argo, you could tell to the program "I know that this frequency is
xxxx Hz, do your math" .... I have to think about this.

Thanks for the feedback.

73  Alberto  I2PHD