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Re: LF: Re: CW...

To: <[email protected]>
Subject: Re: LF: Re: CW...
From: "James Moritz" <[email protected]>
Date: Sat, 7 May 2011 19:15:33 +0100
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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

Attachment: 136k_noise.jpg
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