Message-ID: <006e01cbba45$d1de2ee0$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <004a01cbb99f$182a38f0$0401a8c0@xphd97xgq27nyf> <D10349FA0B32494DADCF5748099ADACF@JimPC>
Date: Sat, 22 Jan 2011 15:05:34 -0000
MIME-Version: 1.0
Subject: LF: Re: Re: Alpha benchmark
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Jim
I cannot notice any difference between 9 Khz and 12 Khz as far as
sensitivity is concerned in relation to antenna atmospheric noise.
Using a calibrated selective voltmeter gives the same presentation across
this frequency range.
Observing the selective voltmeter shows no change nor does the AF presented
to the Spectrum display.
de Mal/G3KEV

----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, January 21, 2011 8:59 PM
Subject: LF: Re: Alpha benchmark


> Dear Mal, LF Group,
>
> What you suggest might be useful as a benchmark for Alpha beacon
reception,
> but not so helpful for 9kHz reception. The problem is that the relative
> noise level often varies a great deal between 9kHz and 11.9kHz, so you
could
> have good Alpha reception and poor 9kHz reception, or vice versa.
>
> Where Alpha beacon reception tests could be useful is for assesing
receiver
> frequency stability - remembering that accuracy and stability of the order
> of milli-hertz or better is *essential* for 8.97kHz amateur tests.
> Monitoring the Alphas using spectrogram settings for DFCW-600 or slower
over
> a period of at least several hours or preferably days is a simple way of
> assesing receiver drift at these levels. You can see examples at DF6NM's
and
> DK7FC's VLF grabber pages.
>
> For assesing receive system sensitivity, and local noise levels, you
really
> have to do it at 8.97kHz directly. A quick check is to generate a
> spectrogram using QRSS3 settings - the display should be dominated by QRN,
> which should totally mask any receiver noise. Usually there will also be
at
> least a few spectral lines from man-made sources present, especially
> harmonics of 50Hz, but many others can be present too. At my QTH, levels
of
> this man-made noise vary greatly from one day to the next, as does the
QRN.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>