Re: LF: Re: CW...

["James Moritz" <james.moritz@btopenworld.com>]

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

136k_noise.jpg
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