Re: LF: DF6NM 23-09-2011

[Gary - G4WGT <g4wgt@tiscali.co.uk>]

Hi Marcus, LF,

Pleased it provided useful feedback.

I am hoping to optimise the system, both from the receiver stability & SpecLab. The receiver is quite good but does show temperature stability issues at these narrow systems. I am considering trying a similar sound card receiver to the one Stefan DK7FC has recently posted in his mails.

I am not at all sure about sound card sampling correction at this frequency range, I have no problem at the 8.970kHz range with using the MSK transmissions at VLF but with the narrow bandwidth of the system at 137kHz it presents a different situation for me.

Thank you for your suggestions, I will try them in due course.

73, Gary - G4WGT.

On 24 September 2011 17:55, Markus Vester <markusvester@aol.com> wrote:

Hi Gary,

 

this is excellent, and much appreciated! I had basically tried to provide a readable signature on Chris' grabbers, but in the end QRSS 1200 turned out to be a bit fast for those. I guess the general concept is more suitable for straight unmodulated carriers...

 

Your screenshot reveals my transmit instability near the end of the "N", when my (DHO-based) samplerate locking temporarily failed, and the audio frequency jumped by 20 mHz. Do you have plans for further optimization? The Loran line visible on 137780.419 (Anthorn et al) may come in handy to evaluate sensitivity and stability during development.

 

One thing I would perhaps suggest is to activate the "one pixel per FFT bin" option in Speclab. If you don't, and zoom in instead, the brightness of each pixel is driven by the highest power from a number of adjacent FFT bins, which in effect increases the visible noise level significantly. Of course the downside is that the visible range becomes quite narrow, requiring TX stations to cuddle closely around a prescribed QRG to be seen on the grabber slot. On the other hand, you can still move the slot around a posteriori, and manually search for possible missed activity.

 

Best 73, and thanks

 

Markus (DF6NM)

 

From: Gary - G4WGT

Sent: Saturday, September 24, 2011 12:26 PM

To: LF Group (RSGB)

Subject: LF: DF6NM 23-09-2011

Hi Marcus, LF,

Please forgive the frequency accuracy & stability on my experimental very slow (2 mHz) SpecLab screen but the signal is clearly visible.

Receiver - JRC NRD-345

Antenna - PA0RDT Mini-Whip at 9 metres

73

Gary - G4WGT