Stefan
Your grabber seems to lack sensitivity on 137 Kcs. I am working stations at
good visibility and audio strength that are not visible on your Grabber but
closer to you than me.
I use QSO mode and get direct reports on my signal and do not need Grabbers
as Beacon operators do but thought you would like to have my observations.
Most grabbers in use also lack sensitivity compared to what I can see/hear
de Mal/g3kev
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Tuesday, January 18, 2011 6:26 PM
Subject: LF: DK7FC LF grabber(s) now GPS locked
> LF,
>
> After some time of maintenance, my LF grabbers
> (http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_Grabber.html and
> http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_LF_DX_Grabber.html)
> are now back on.
>
> Due to the cold days the institute was heated and this caused strong
> temperature changes (when opening the door and so on) and a visible
> drift of the signals in QRSS/DFCW60/120, so i decided to build a PLL for
> my 125 kHz IF. The current grabber RX is using a BF981, downconverting
> by 125 kHz and running 7 SpecLab instances.
>
> The 125 kHz signal is generated by a 8 MHz xtal and a 74HC4060, down
> dividing to 250 kHz (for the PLL) and 125 kHz, for the IF. The 250 kHz
> signal and 10 kHz signal is fed to a CMOS4070 XOR gatter that generates
> a regulation voltage as a function of the duty cycle. The waveform is
> smoothed by a RC circuit and fed to a 1N4007 (reverse) as the regulating
> part of the VCXO. 10 kHz comes from a GPS module that is the reference
> for all my grabbers.
>
> The system is running since some hours and seems to work fine. I will
> display the IF drift for some days. BTW i found that remote controlling
> the PCs is causing some overflows in SpecLab (if many instances are
> running). This causes a sudden drift / unlocking during the operation,
> can still be seen on my LF DX grabber. Just a hint for the remote
> controlling LF/VLF grabber runners :-)
>
> 73, Stefan/DK7FC
>
> PS: Tnx to Markus/DF6NM for many suggestions and advice!
>
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