Hi Alan,
Sorry for the slow reply; I was waiting for responses to see
what hardware locking ability potential users already had.
All but one had the ability to drive their receiver's
reference from a GPS-derived frequency standard, so R2 is
on the back burner for now, anyhow.
The narrow filter reduces the number of "visible" lines,
and so degrades the S/N of the locking signal, because it
is mixed with band noise and QRM. Careful level adjustment
would minimize the problem, but there are many constraints:
The impulse resulting from the 1 pps excitation would have
to be much larger than the general noise level, but not
clip the A/D, while the noise (with buried desired signal)
level would still need to be high enough that A/D quantizing
noise and other errors did not degrade the signal too much.
Your keyed oscillator idea is interesting, but it appears to
introduce another unknown. For example, if the 136 kHz oscillator
drifted up 0.01 Hz, it would affect the audio in the same way
as the receiver LO drifting down 0.01 Hz. One way to resolve
this ambiguity would be to digitally divide the 136 kHz into
the audio range, and feed that into the sound card, too.
Do you have a simpler solution?
73,
Stewart
----- Original Message -----
From: "Alan Melia" <[email protected]>
To: "LF-Group" <[email protected]>
Sent: Sunday, February 22, 2004 4:08 AM
Subject: LF: WOLF development
Hi Stewart, with reference to R2, I suppose the injection of the 1pps into
the RX input with provide some "pseudo-Loran" lines for frequency locking.
If the 1pps was used to "key" a simple 136khz oscillator, this would produce
a comb of 1Hz spaced lines in the right area all locked to the GPS. This
would allow easy control of their level, which is often a problem when
putting a calibration signal up even on QRSS. This is a technique of
frequency synthesis used back in the old days when PLLs occupied a couple of
racks and consumed a few kW.
The necessity to use an SSB filter width might be a problem in Europe where
there are many strong signals around. I presume that the rise-time with a
narrower filter is the problem extracting accurate enough timing?? Having
got frequency sync data at RF could timing data be put into the soundcard at
audio....possibly on the other channel?
Great ....I look forward to seeing the final solution.
Cheers de Alan G3NYK
[email protected]
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