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
[email protected]
Villadreef 14 B-3128 Baal BELGIUM (JO20IX)
| 