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Saturday, 4 January 2014

A disk-what? Ah, a Discone!

Well,

Today has been a day of antenna fiddling. The first thing I did was put up a Discone antenna on the front of the house:


This is supposed to be a general coverage receive antenna from 25MHz to over 1.3GHz plus it is resonant for transmit on the Amateur 6M, 2M, 70cm and 23cm bands.

Here's what it looks like connected to the return loss bridge and Spectrum Analyser:


The markers at the bottom of the image above show the resonant points we are interested in and it does indeed seem to be a reasonable match to 50R at those frequencies (as is a 50R resistor, of course). How good an antenna it is remains to be seen. I am hoping this will hear more of LEO satellites than the collinear I have.

We have had some more really bad weather over the last few days and very much by luck I found a broken jubilee clip (Read hose clamp) in the garden yesterday. Looking up I could see it was off the 4M and 6M beam antenna I installed back here:

http://g0mgx.blogspot.co.uk/2013/05/thatll-never-work-will-it.html

So I have had the antennas down again today, it's surprising how big my "mini beam" is when it's on the ground:


You can see that I have to remove the outer parts of the one element to get it past the fence next to the raised border in the garden! But I have replaced the clip and also altered the resonant point of the 4M section to be exactly at the Meteor Scatter frequency of 70.110MHz.

After adjustment the "dip" is now ~70.12MHz with a return loss of > 32dB ; the SWR at 70.11 (my target) is 1.05:1 and across the band is no more than 1.7:1.


and at 50.23MHz the SWR is a respectable 1.2:1:


Looks pretty damn fine to me!

Cat's been next to useless:



Fun, egh?

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