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Message-ID: <3.0.1.16.19990414085752.2f3f44f8@mail.cc.kuleuven.ac.be>
Date: Wed, 14 Apr 1999 08:57:52
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: good signals - deaf receivers
In-reply-to: <37133A8B.26E94D6D@phonakcom.ch>
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At 14:37 13/04/99 +0200, you wrote:
>>>From HB9ASB, JN36pt
>
>Now the band gets also busy here in Central Europe. Last weekend I've
>heard 17 different callsigns and sometimes it sounded like a "dialogue
>des sourdes": Strong signals but they did not hear each other. 
>Alarming is the increasing number of stations with good signals and
>mediocre receivers. It seems to me, that the real challenge on the LF
>band is the receiving part and I think there is still a lot of work to
>do. This includes also directional receiving aerials. 
>I am aware of the fact that some locations suffer from heavy local QRM
>or Loran-splatter or have more Luxembourg-effect than others. On the
>other hand are receivers suffering from front end overload,
>inappropriate AGC-characteristics and large bandwidths far from the
>optimum.
>
>
>73 de Toni
>
>
I can only agree with Toni. As owner of a QTH with very low man-made noise
(QRM) but unfortunately poor 'ground conditions' (and thus rather low ERP)
I know all about the frustration of hearing stations with 'armchair copy'
and not being able to work them.
With the very nice PA-designs of G3YXM and G0MRF it is easy to get several
hundred Watts RF, but maybe now it is about time to focus more on the
receiving side.

My experience :
I use my 13m high and 26m long inverted-L antenna also for receiving and if
I connect this antenna directly to my TS440 I hear nothing but
intermodulation products in the 135.7-137.8kHz segment. After adding an
attenuator (10-40dB in 10dB steps) between antenna and RX a small miracle
happens, all the sudden the band is clear and the weak ham-signals can be
heard. Although I have only a 500Hz CW filter I can narrow the bandwidth by
using the IF-shift and centering on 400Hz instead of the 'default' 800Hz.
For my TS440 I found out that I have the optimum between signalstrength and
'intermodulation-surpression' when I receive the DBF39 (or DCF39) signal
with about S7. By adding more attenuation I loose the weak signals in the
internal RX noise, with less attenuation the intermodualtion-products show up.
So maybe this 2 tips may be a help to others :
1. Use an (adjustable) attenuator between antenna and RX, focus on best
ratio between the wanted ham-signals and the unwanted IM-products. And
don't worry if the s-meter is not moving.
2. Use the IF-shift to narrow the RX bandwidth, it helps if you go from the
default 800Hz 'beat' to 400Hz.

73, Rik


Rik Strobbe  ON7YD
rik.strobbe@fys.kuleuven.ac.be
Villadreef 14  B-3128 Baal  BELGIUM   (JO20IX)