[time-nuts] VLF Phase-tracking receivers.
mfeher at eozinc.com
Sun Aug 10 14:54:06 EDT 2014
Unless on what you were working on it had a different meaning, MSK means
"Minimal Shift Keying". It is still a PSK modulation of any order, however
the transition between significant phase locations is not instantaneous,
but, shaped in various ways to smooth the transition. This results in a
waveform that has a minimal AM component which then consequently reduces
spectral regrowth when amplified by a non-linear amplifier. Allows for
closer channel spacing, and is generally nicer, at the expense of additional
complexity. 73 - Mike
Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Kenneth G. Gordon
Sent: Sunday, August 10, 2014 12:27 PM
To: paul swed; time-nuts at febo.com
Subject: Re: [time-nuts] VLF Phase-tracking receivers.
On 10 Aug 2014 at 6:24, paul swed wrote:
Hello again, Paul. Thanks for replying. Please see below.
> On iPhone
> Yes but those stations are fsk so the offsets an issue.
As I understand it from back in the 1970s when I was first working on this
sort of thing, the modulation is not FSK, but "MSK" (whatever that is) at
something like 25 to 50 Hz, and the Navy installed the necessary equipment
in the 1970 time-frame to assure that the transmitted signals are
phase-stable. The same thing, apparently holds true for GBR and some of the
other stations like those. Russian, for instance.
I have no idea what, exactly, has occurred in this area since then though.
> We may assume the transmitter is accurate.
> But how accurate?
That is a good question. I have no idea at this point. I'll try to find out.
> Then the fsk generator
Well, as I said above, it is not FSK....exactly...
I DO know that the Navy had problems when they first tried FSK with their
antenna tuning methods. Due to the extremely hi "Q" of their antenna
systems, any useable frequency shift (at the receiver) was so great that it
pretty much threw their antennas out of tune on either mark or space. Thus,
they had to use a different method. I never did learn what that method was.
Perhaps now is the time for me to find out.
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