Message-ID: <000901c413ed$a230caa0$ee9bfea9@oben>
From: dj9dw <dj9dw@t-online.de>
To: rsgb_lf_group@blacksheep.org
References: <000001c41358$2d534c20$fce8c593@RD40004>
Date: Sat, 27 Mar 2004 12:21:21 +0100
Subject: LF: Re: Re: Receiving Setup
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Hello Jim &LF-group,
is the TX-antenne detuned, while you're receiving on the loop? (so ther is
no nearfield-coupling from the big one to the loop)?

Regards, Peter, dj9dw
----- Original Message -----
From: "James Moritz" <J.R.Moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, March 26, 2004 6:31 PM
Subject: LF: Re: Receiving Setup


> >James can we have a quick reminder of the set up you used last night.
>
> >thanks
> >peter G8AFN
>
> Dear Peter, LF Group,
>
> The receiving setup here is the same as it has been for the last couple
> of winters - the antenna is a 2m x 2m "bandpass" loop with preamp as
> described in the article downloadable from G3YXM's web site -
> http://www.wireless.org.uk/bploop.pdf
> Also on YXM's site is an article on the "lazy loop",
> http://www.wireless.org.uk/lazy.htm
> which is capable of similar results when used with a fairly big wire
> loop.
>
> The loop was aligned to null out Loran noise coming from a SW direction
> at my QTH - this also gives optimum pick-up for USA/Canadian sigs coming
> from the NW. The TX long wire antenna is not much use on receive here,
> due to  the level of 50Hz-related noise it picks up from the house
> wiring. The loops are located at the bottom of the garden, which is
> electrically the quietest place at my QTH. Audibly, the Loran clatter is
> eliminated, although there is quite often still some mains-related noise
> present. Using separate RX antennas located in the best available
> low-noise site seems to be the factor which has the greatest influence
> on results in my case. It does mean I run around in a panic every time a
> new buzzing noise appears...
>
> The receiver is an old Racal RA1792, which possesses decent sensitivity
> (about 0.1uV for 10dB SNR in 300Hz BW) at 136kHz. The internal OCXO
> frequency standard is also very handy for LF narrowband modes. The
> sensitivity vs. frequency issue is quite important - O.K., if the
> receiver goes deaf at LF you can get the required sensitivity back by
> using a bigger antenna, or a preamp. But this will increase the
> sensitivity of the system in the MF range, where it is already much
> higher than at LF. So it is then important to add sufficient
> pre-selection as well as increasing the signal level, in order to avoid
> assorted intermods, reciprocal mixing, and cross-modulation due to
> broadcast signals. Life is therefore a lot easier if the receiver
> sensitivity is fairly constant over the whole LF - HF range, like the
> RA1792. Especially if you live in Brookmans Park!
>
> I mostly use DL4YHF's Spectrum Lab for copying QRSS - It is considerably
> more complicated to set up and use than Argo, but I like the facility to
> change all the display parameters whilst looking at different types of
> signal and noise. Having said that, Argo is much simpler for the
> operator, and gives just as good results with weak QRSS signals, which
> it is optimised for.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>