LF: Topband ionogram trace

[Andy Talbot <andy.g4jnt@gmail.com>]

Here's Peter's update on the 'unusual' topband split trace.   Might explain its cleanliness

 

Andy

www.g4jnt.com

 

---------- Forwarded message ----------
From: Peter Martinez <peter.martinez@btinternet.com>
Date: 4 March 2011 18:35
Subject: Re: Dopplergrams 12 years ago
To: Andy Talbot <andy.g4jnt@gmail.com>


Andy:

I had a look at the QRSS sample that G4AYT captured. Around the same time I was watching the signal from the Fairford ionosonde. This sweeps from 1625kHz, through top-band and on up to 13MHz. At that time it was clear that the Fcrit was getting down towards 2MHz so the F-layer was rising rapidly so this would have been responsible for the increasing negative Doppler shift he was seeing on one of the traces. In fact the MUF on the Fairford-Kendal path dropped below 1.7MHz at about 3 am that night. There was also evidence of night-time sporadic-E. This is sometimes known as Auroral sporadic E but it isn't 'auroral' in the sense we usually mean, but refers to patches of Es which drift south from the Auroral oval, probably initiated by the same particle precipitation that causes aurora. This Es activity could have been responsible for the non-Doppler-shifted trace that G4AYT saw. On a normal night only the F-layer would be reflecting on top-band.

Fairford now has a new ionosonde equipment, a Digisonde DPS-4D which I find is much easier to 'eavesdrop' on. The Digisondes are pulse sounders with the receiver co-located with the transmitter with the receiver synchronised to the transmitter locally. They didn't need to be locked to anything and they weren't stable. The new one behaves rather better, stepping exactly 25kHz exactly every 640mS (locked to GPS). I have my system stepping in sync and have some crude ionograms already and have confirmed that the pulse timing is accurate and stable. The next job is to implement the pulse-compression algorithm, which is very similar to that used by LORAN C.  This will give me real-time ionograms again, a facility I lost when the UK chirpsounders closed down last year.

73
Peter

----- Original Message ----- From: "Andy Talbot" <andy.g4jnt@gmail.com>
To: <peter.martinez@btinternet.com>
Sent: Thursday, March 03, 2011 7:59 PM
Subject: Dopplergrams 12 years ago

Hi Peter -
Cast your mind back.  We did some of the first Dopplergram tests on 1967kHz
back in 1998, and produced the plots shown

http://www.g4jnt.com/Download/1967jnt1.jpg
http://www.g4jnt.com/Download/1967jnt3.jpg
http://www.g4jnt.com/Download/1967jnt4.jpg

Can you recall the vertical span on the trace?   As far as I recall, your
EVM software decimated from 8kHz, then you set 80% of the samplinbg rate
as plot BW, so 3.125, 6.25Hz etc    But t'would be interesting to know for
sure.

Someone on the LF reflector (see below)  has just posted the plot of some
QRSS topband tests, and was "surprised" to see the trace splitting.  So I
looked out these to show what was done over a decade ago.

Andy



On 3 March 2011 18:55, Chris <c.ashby435@btinternet.com> wrote:

 Hi All,
Yesterday evening Pete, M0FMT, transmitted QRSS on topband for a test. An
unexpected effect was noticed with the trace splitting in two. Nothing new
or 'earth shattering' I expect, but new to us and worthy of further
experimentation.
See the result and conclusion on my website http://qsl.net/g4ayt on the
bottom of page 1.
I have never seen this effect on 137, even with quite strong audible
signals, maybe others have.
Vy 73,
Chris, G4AYT, Whitstable, UK.

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