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Re: LF: Rugby LORAN measurement?

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Subject: Re: LF: Rugby LORAN measurement?
From: "Peter Martinez" <[email protected]>
Date: Mon, 10 Apr 2006 07:56:37 -0000
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The design of an MSF receiver, intended to recover the carrier frequency to any great accuracy, needs to be able to reject the existing 'unwanted' signals either side of the carrier. These are only about 15dB down and at +/-1Hz. I am referring to the 1 sec timing pulses (gaps). The disturbance from this 1Hz source has to be attenuated by a very large amount if it isn't to affect the output of the frequency standard. If we suppose that MSF receivers in service can achieve this, they shouldn't suffer any problem from unwanted products which are somewhat further away, at 6 and 8Hz, and are already a long way down. I cannot detect them here which probably means they are more than 70dB down.
I know it would be nice to be rid of the LORAN interference, but this line
of reasoning may not be a means to that end, and in any case it wouldn't
help amateurs close to the other LORAN transmitters. I understand the Rugby
site must close in a year or so and they are looking for an alternative site
for the 60kHz MSF transmitter. The question becomes whether the LORAN
transmitter will also move to that new site or whether it will close down.
The long term future of LORAN has always seemed shakey but it doesn't look
as if it will be killed-off until there is a European second-source for
satellite-based position-finding, and that seems some years away yet.
Peter G3PLX

The accuracy of MSF is 2 parts in 10E12, so systematic interference even a long long way down may well have an effect. It will depend on the design of the receiver and whether it has a front end filter that has high rejection at +6Hz, -8Hz, but prior to the LORAN transmitter.

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