Return-Path: Received: (qmail 15679 invoked from network); 4 Jan 2001 17:48:11 -0000 Received: from unknown (HELO murphys-inbound.servers.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 4 Jan 2001 17:48:11 -0000 Received: (qmail 15149 invoked from network); 4 Jan 2001 17:42:50 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 4 Jan 2001 17:42:50 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14EEGt-0000hv-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 04 Jan 2001 17:33:51 +0000 Received: from hestia.herts.ac.uk ([147.197.200.9]) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14EEGs-0000ho-00 for rsgb_lf_group@blacksheep.org; Thu, 04 Jan 2001 17:33:50 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from [147.197.200.44] (helo=gemini) by hestia.herts.ac.uk with esmtp (Exim 3.16 #4) id 14EEDr-000230-00 for rsgb_lf_group@blacksheep.org; Thu, 04 Jan 2001 17:30:43 +0000 Message-ID: <24606.200101041733@gemini> From: "James Moritz" Organization: University of Hertfordshire To: rsgb_lf_group@blacksheep.org Date: Thu, 4 Jan 2001 17:37:05 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 8bit Subject: LF: Stable frequencies / CFH Plots X-Mailer: Pegasus Mail for Win32 (v3.11) Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Dear LF group, If you have a receiver and signal source which can be tuned to 198kHz or one of the other stable broadcast frequencies, you can compare the frequencies with parts-per-billion resolution quite easily using spectrogram. Couple a sample of the signal source into the antenna circuit when the receiver is tuned to the broadcast frequency, and juggle the level of source and/or broadcast signals so they are approximately equal. Hopefully both signals will be within a fraction of a hertz of one another, so will appear superimposed as a single line on the spectrogram. However, as they drift in and out of phase, there will be peaks and nulls in the combined signal level. The frequency difference is the reciprocal of the period in seconds between 2 successive peaks or nulls, which can be measured with the cursor. If you choose an appropriate spectrogram time-base, and leave the set-up running for 1/2 an hour or so, it is easy to measure difference frequencies of the order of 0.001Hz, which is 5 parts in 10e9 at 198kHz. The only slight problem is that it does not tell you whether the difference is positive or negative, but that can be found by trial and error adjustment. I have tried this with 198kHz; also the Loran "carrier" at exactly 100kHz works, and might be more convenient if your reference signal is at a fixed frequency like 10MHz. Another possibility is to use a decade divider chain to obtain 1kHz from the reference; the harmonics in the LF range will be strong enough to make the comparison to an "odd" broadcast frequency. I was interested to see Rik's plots of the results from the CFH logging session (http://www.qsl.net/on7yd/t181200.htm) - as G3NYK suggested, deep fades do occur at different times at the different locations. The relative signal levels between different receive locations vary rapidly, so it is very likely that one person will be seeing nothing whilst their neigbor is getting good copy of a transatlantic signal. This suggests to me that, with marginal signals, there is not much point in going to very long dot lengths, or using very long "grab" sequences with BPSK software, since the signal will probably fade in and out in the time it takes to send a callsign. The propagation on LF seems to get more and more volatile as the distance increases It might be interesting if Alan were to make some plots with his logging gear while CFH is off-air (or on a different frequency when it comes back on again) of the noise level for comparison; after all, it is the signal to noise ratio which determines whether a signal can be received or not. Cheers, Jim Moritz 73 de M0BMU