Message-ID: <005d01cbb73f$1f1e8e70$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <4D35DB73.3070403@iup.uni-heidelberg.de>
Date: Tue, 18 Jan 2011 18:40:03 -0000
MIME-Version: 1.0
Subject: LF: Re: DK7FC LF grabber(s) now GPS locked
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Stefan
Your grabber seems to lack sensitivity on 137 Kcs. I am working statio=
ns at
good visibility and audio strength that are not visible on your Grabbe=
r but
closer to you than me.
I use QSO mode and get direct reports on my signal and do not need Gra=
bbers
as Beacon operators do but thought you would like to have my observati=
ons.
Most grabbers in use also lack sensitivity compared to what I can see/=
hear
de Mal/g3kev

----- Original Message -----
From: "Stefan Sch=E4fer" <schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
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.ht=
ml)
> 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, downconverti=
ng
> 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 genera=
tes
> 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 regula=
ting
> part of the VCXO. 10 kHz comes from a GPS module that is the referen=
ce
> for all my grabbers.
>
> The system is running since some hours and seems to work fine. I wil=
l
> display the IF drift for some days. BTW i found that remote controll=
ing
> the PCs is causing some overflows in SpecLab (if many instances are
> running). This causes a sudden drift / unlocking during the operatio=
n,
> 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!
>