Re: LF: EbNaut 137.477 kHz 1 Dec

[Markus Vester <markusvester@aol.com>]

Hi Joe,

> a fax of Tangles' forehead

Yes those lines on the narrow spectrogram were indeed reminiscent of cat's whiskers ;-)

> use the stable DOXCO to divide out or synthesise an LO signal and mix it in an SBL-3 as Stefan has done

But that would imply building a complete LF receiver from scratch, including an image reject filter and some gain stages. A possibly quicker alternative might be to use your existing receiver and only inject an weak pilot tone from your DDS (eg. 137500 Hz) to the antenna, and then engage SpecLab's frequency offset detector to eliminate any receiver drift. That way soundcard samplerate drift won't be corrected, but that will have little effect as long as the difference between the pilot and the desired signal frequencies is less than a couple of 100 Hz. I have successfully employed that method on MF to compensate the significant drift of my freerunning FiFi-SDR, and was able to decode a number of EbNaut transmissions (including yours) around 477.7 kHz.

Best 73,
Markus (DF6NM)


-----Ursprüngliche Mitteilung-----
Von: jcraig <jcraig@mun.ca>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 2 Dez 2016 7:15 pm
Betreff: Re: LF: EbNaut 137.477 kHz 1 Dec

Hi Markus and Stefan,

Thank-you for for your efforts in receiving and decoding the message. This
is encouraging -- it's good to know everyhing still works after the
hardware clean-up in the shack. I'll take care of forwarding the message
to Poldhu.

The slope and bends in the high res bpsk specrogram were intentional.
The element period T increased as a function of time and the bends are
actually curves due to the 1/T relation of the sideband deviation
from the carrier frequency I think.

It was a (poor) attempt to send a fax of Tangles' forehead (see
attached). She has been reminding me that she is interested in
getting a message from Gizmo and so I've been giving some thought
about reception. An idea is to use the stable DOXCO to divide out or
synthesise an LO signal and mix it in an SBL-3 as Stefan has done,
then to feed the product and a reference into the Spectrum Lab.

73 & TNX AGN
Joe VO1NA