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Re: [TowerTalk] Just set up a long mast Screwdriver Antenna - was 43 ft

Subject: Re: [TowerTalk] Just set up a long mast Screwdriver Antenna - was 43 ft
From: (Trevor Smithers)
Date: Fri, 28 Nov 2008 12:30 +0000 (GMT Standard Time)
List-post: <">>
Mike, AD6AA said:
>I've been thinking off and on about a stationary Screwdriver Antenna for the 
>low bands.
I've just set up something similar based on the HiQ 5/160 antenna here

I have a 5/160 set up as a ground mounted base station antenna. Feed point is 
about 6" 
above 30 buried radials of various lengths and fed via a 4:1 balun to an 
MFJ-927 remote 
tuner - main interest 160, 80 and 40.

>You can put a much larger Cap Hat on it than if you were going down the road
The HiQ site mentions how effective the EB8 cap hat is so I thought I'd check 
it out for 

(a) Using just the 102" whip I obtain resonance on 1.836 with a coil setting of 
(MFJ-1924 controller) which is nearly maximum inductance.

(b) Adding a 1ft extn rod, and an EB8 with whip on top moves the coil setting 
to 145

(c) Adding another 1ft rod gives further improvement to 154

(d) Adding another EB8 1ft above the first together with the whip gives even 
improvement to 193 on the controller.

So, all in all, there is a reduction of 163 turns (and corresponding 
inductance) in the 
number required to maintain resonance on 1.836 between the whip on its own and 
adding two EB8 cap hats.

In theory this improvement should translate into improved radiation efficiency 
(quoted as 
1.3% for 160 using just the whip) but I'm not sure how to go about checking 
this. I tried 
taking reading using an untuned field strength meter with a short whip but 
couldn't see 
any difference.

The quoted radiation efficiency for the standard 5/160 with 102" whip is 1.3% 
12% (80m), 43% (40m) and 77% (20m). It would be nice to know what the revised 
figures would be with the addition of the two capacity hats. 

I appreciate that my arrangement using two EB8's might not be suitable for 
operations (unless you're feeling very brave) but, for base station use its 
quite feasible, 
and gets me onto top band from an otherwise unsuitable qth.

73 to all
Trevor  G0KTN 

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