[time-nuts] VLF Phase-tracking receivers.

Kenneth G. Gordon kgordon2006 at frontier.com
Sun Aug 10 12:26:45 EDT 2014


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.

Yes.

> 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.

Thanks again,

Ken W7EKB



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