Dear Jim,
Thanks for the foort to set up this comparison! I suppose the local
noise is rather equal distributed. Of course i can reduce the effect of
DCF39 but HGA22 would be E-W. Anyway, on a sunday morning HGA wouldn't
be as strong as DCF.
I switched a 10th order Butterworth filter (2 kHz BW) and a
noiseblanker (12 dB threshold, 2 ms ramp time) in front of the the small
CW filter. This removed the DCF bursts and sferics very well, without
affecting the CW signals significantly.
Maybe your RST was 119 so at least this was excellent suitable to do
such filter tests!!! I copied your "73" since this is a well known word
in daily CW operation. As i was starting to improve my CW speed in 2002,
the first words i understood in QRQ were "73" and "599" and so. This was
the case again today, although not limited by my CW reading skill ;-)
Well, i have a 44 turn loop for 137 kHz, about 3 mH. BW is below 1 kHz.
I will so some tests in the near future and have enough place there on
the roof of the institute.
What do you think is better, the 44 turn loop or a 1 turn loop? I think
a 44 turn loop is rather narrow band while a 1 turn loop is rather broad
band, right? If so, the 44 turn loop is preferable here due to DLF,
DCF39, DCF49 etc...
Thanks very much so far. Mybe i have some questions later :-)
73, Stefan/DK7FC
Am 07.05.2011 20:15, schrieb James Moritz:
Dear Stefan, LF Group,
Using a loop antenna might bring the needed few dBs but means more
effort and adjusting. Anyway i will do some tests soon.
I have attached a 200Hz bandwidth spectrogram showing a comparison
between the noise level received here today using a loop oriented E-W
and a vertical antenna. I adjusted gain levels so that the received
level of DCF39 was exactly equal on both antennas. The loop noise
level in the right half of the spectrogram clearly includes less QRN,
and also the Loran C lines are nulled quite effectively, compared to
the vertical signal on the left. So for aurally receiving signals from
DL, the loop definitely improves SNR by a few dBs on this occasion.
Of course, the improvement which can be obtained depends on such
things as the relative directions of signal and noise sources, and
whether local QRM sources are predominantly E field or H field, so one
cannot say if one type of antenna is going to be better than another
without doing the experiment. At this QTH in the southern UK, the E-W
loop works well for European reception, since the closest Loran
stations at Lessay and Anthorn are roughly N - S, and much of the QRN
seems to come from the south. In DL, I imagine the direction from
DCF39 and HGA22 would be important, due to the strong sidebands from
these stations. The mains QRM here sometimes affects the loop more
than the vertical, and sometimes the vertical is worse, so it pays to
have both!
Cheers, Jim Moritz
73 de M0BMU
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