Message-ID: <000b01c10791$bcad2240$d14c073e@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Subject: LF: Rx sensitivity again
Date: Sun, 8 Jul 2001 10:37:23 +0100
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Hi all, as Reg has released a new version of his Groundwave program, I
thought some results might be of interest, particularly to those struggling
to decide whether they are getting the best from their receivers. The
results are based on some figures that Dick PA0SE hase published previously
for the field strength of the German Utility station DCF39 on 138.83kHz, and
some measurements made here (Ipswich).

Using Dick's measurement for the field strength of the Madeberg station of
2mV/m, at a distance of 494kms, and the known output power of 50kW, we come
to a figure for the aerial efficiency of 80% over a ground condition of  7
(average ground). 80% may seem high for what we are used to with amateur
aerials, but this has been suggest by Gammal as the target for most
commercial installations. From the figures quoted for the big aerial at
Rugby GBR (16kHz) I estimate that that would have an efficiency of around
85% is used at 136kHz.

I am at a distance of about 700kms and using the same parameters leads to a
figure of 0.812mV/m here. Which is well inline with the signals I receive in
daytime from DCF39. This value also agrees well with the value measured by
Dick around Old Windor at last year's HF Convention (0.7mV/m).

 Reg has added a 'twiddle' capability to the program which allows the
incremental variation of several key parameters whilst watching the results
be continuously calculated. I found this very useful fo see the effect of
different parameters on the final value.

I think by using these figures in Reg's program , and possibly his other
programs for some aerial calculations, could help to check the effectiveness
of a receiving setup, certainly in the UK. The figures show that my aerial
is not as good as it should be, with an effective height of only 3m. This is
probably due to effects of surrounding trees. At this distance there seems
to be very little effect from daytime skywave although it is present. Look
for a slow fading of the signal to detect this. I suggest for most that the
ground values of 7 or 8 should give sensible field strength values. Of
course if you build Dick's field strength meter or use his technique of
measuring the signal on an untuned loop, you can get more exact results.

Reg's web site URL

http://www.btinternet.com/~g4fgq.regp/page2.html#S209
http://www.btinternet.com/~g4fgq.regp/grndwav3.exe

Well it will passes the time while the static makes the band unpleasant to
listen to. It seems to have chased away a lot of the activity this weekend.
I have only heard Bob and Tom.

Cheers de Alan G3NYK
Alan.Melia@btinternet.com