[time-nuts] LORAN C antenna thoughts from the group

Poul-Henning Kamp phk at phk.freebsd.dk
Tue Dec 21 22:14:39 UTC 2010


In message <AANLkTimSQsHE+YEhhhydw2V2Edj855SszT78mpQChz0o at mail.gmail.com>, paul
 swed writes:

>Is there a real advantage to a 4 or 6 foot big loop compared to a small
>loop?
>I use a 3 foot loop on wwvb/preamp and that works well.

There is a very good and simple explanation of the theory behind
loops here:

	http://www.vlf.it/octoloop/rlt-n4ywk.htm

Sensitivity rises with the area of your loop, so doubling the diameter
gives you four times the signal, which may or may not be a relevant
low number of dB.

>One other point on the wavefrom on loran c. It was constructed to minimize
>the impact of skywave influence on the receiver. Essentially making it
>easier for the receiver to distinguish between the two. Thast what I hadread
>in the loran docs.

Yes, this is why you should always zoom in on the 3rd positive
zero-crossing.  Inside the announced service areas, the skywave will
never arrive early enough to disturb the groundwave at that point.

>PS I thought the bw was +/- 10KC and even wider.

Yes, it is, but the amount of actual energy once you get past 
+/- 10kHz or 15kHz is very very limited.

The perfect bandwidth is where the S/N of the loran-C signal
is 1:1, but I have never found a good way to determine that
automatically.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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