Sunday, 15 June 2014

Shorty and Stealth

The 'Selby Shorty' mobile antenna has been analyzed, and found to, as expected, not be very good! Although it does have a resonance just below the 20m band, the radiation resistance is so low its really not much use, and the SWR on 20m is just beyond whats really usable with the FT-857D. Adjusting the whip was no help. I will look at changing the mast for a taller section later, but first I might, just for fun, rejig it to a design frequency of 21MHz and see how it does.

The license application for the St Mary's church activation is filled in and ready to post tomorrow. Ive spent some of today checking coax patch leads to see what I have and ensuring they are all marked with their length, this is invaluable in the field as knowing which coil is the right length for the job saves a lot of hassle! I have three lengths of RG-213/214 salvaged from work which need testing. One has N-types on it already, that just needs a check over to make sure the sheath is in good order, and a quick check of losses to make sure the conductors are sound. The other two, one of which is 50ft long, are unterminated at present and also rather dirty!

Im also just 1m short of 300 ohm ladder line for the ZS6BKW! So i'll have to order a pack of that, and the minimum is 5m!

Yesterday evening, I installed eight ground radials for the flag pole antenna. These are in slots cut in the turf of the lawn and then stomped shut. Actually, Tom did much of the stomping! Most of the radials go in a reasonably straight line, but the three to the east didnt have enough space. Two curve somewhat to fit them in, whilst one actually has to zigzag a bit!

I now have to find time to analyze the flagpole antenna to find its resonant frequency, which im expecting to be a bit below 20m, and then work out the necessary loading and matching.

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