Differences

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--- vlf [2023/12/23 09:54] – [Setup and Testing] ei3jdb
+++ vlf [2024/06/30 14:06] (current) – [Setup and Testing] ei3jdb
@@ Line 1: / Line 1: @@
 ====Introduction====
-Although there are no ham bands for VLF, there are VLF transmissions that hams can receive.  This page is about how to receive the transmissions from the Alexanderson transmitter at Grimeton in Sweden, sent on Alexanderson Day (2nd July) and Christmas Eve (24 December) every year.
+Although there are no ham bands for VLF, there are VLF transmissions that hams can receive.  This page is about how to receive the transmissions from the Alexanderson transmitter at Grimeton in Sweden, sent on Alexanderson Day (Sunday closest to the last day of June) and Christmas Eve (24 December) every year.
+===SAQ Grimeton===
 The Grimeton transmitter is the last surviving example of an Alexanderson transmitter, generating 200kW of RF at 17.2kHz using a direct alternator: a slotted magnetic disc that weighs more than a family car spinning at over 2000RPM.
 The transmitting station is now a [[https://grimeton.org/en/|museum]] and the transmissions are arranged by the [[https://alexander.n.se/en/|Alexanderson Association]]
+===Soundcard SDR===
+The receiver described here is a computer soundcard and GNURadio Companion combined to make a VLF Software Defined Radio.  Since the frequencies are very low they are within the range of high fidelity audio equipment -- so a soundcard can capture the radio frequency.  Yes, you really plug an antenna into your soundcard!
 ====Hardware====
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 So an ''aplay -l'' output like this
 {{grimeton-aplay.png}}
 should become an input to the Audio Source properties like this
 {{grimeton-audiosource.png}}
 Then you may need to enable your input with ''alsamixer''
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 Here is what my input looks like with 100 microvolts at 17.2kHz
 {{grimeton-siggen.png}}
 and here is what it looks like when connected to my antenna
 {{grimeton-ant.png}}
 To connect the output of GNURadio to another application, I used the PulseAudio Volume Control tool.  The input of the application should be the monitor of the output that GNURadio is using -- probably your active sound device.  I was able to set this up with FLDigi, although FLDigi doesn't like mode switches, so set to CW before selecting the input.
-After that, you should be all set.
+After that, you should be all set.  If you are able to receive other VLF transmissions then SAQ should be OK.  I have been able to receive the RDL station in Krasnodar, Russia on 18.1kHz. This is an interesting station as the output is intermittent and the modulation mode varies. Most of the submarine stations send with military-grade encryption but RDL sometimes sends codes in clear using CW-FSK — Morse code encoded as CW. By choosing narrow band and tuning off-centre it is possible to receive only the mark signal and filter out the space signal, which makes it possible to decode the Morse by ear or with fldigi.
+If you can receive RDL you should be able to receive SAQ.
 The Grimeton transmitter seems to schedule tests on the day before the actual transmission, so you should have a chance to test your rig before the transmission day.
-Good luck!
+===Windows Setup===
+To find your soundcard in Windows please follow [[https://wiki.gnuradio.org/index.php/Audio_Source#Windows|these instructions]]
-===Windows Setup===
+===QSL?===
+Here is a recording of the afternoon transmission on 30th June 2024: {{ :grimeton-20240630.mp3 |}}
-//Please someone with a Windows computer put something here!//
+If you heard the transmission, the Alexanderson Association have an online QSL form for your signal report on their [[https://alexander.n.se/en/|home page]].