Tuesday, March 13, 2012

Further work on the 30 Meter Vertical

Over the weekend I did some more work on the 30 meter vertical. Being slightly na├»ve with regard to verticals as I have had little experience in building them I thought that it would be fairly quick and easy, which to be honest it can be, but reading up on the web suddenly opens up a whole new can of worms with regard to ground radials and SWR.

Initially I thought my SWR reading of 1:4:1 was out and I was certain I could get a better result, but with a little bit of investigation via the web 1:4:1 is pretty well spot on for a vertical. However ground radials are a separate issue, in that for optimum performance according to many experts you need at least 120! And there was I with my paltry 12 pieces of telephone cable consisting of 4 wires per cable, a grand total of 48 wires.

So armed with this new knowledge I rechecked the SWR and also the resistance; 1:4:1 with a resistance of 40 ohms, actually not bad but in a perfect world R should really read 36 ohms. So I added some more ground radials to see if it would have any further effect. I had been given some old overhead telephone cabling which consisted of 7 wires per cable and since I had a spare 8 connections left in my choc connector, I did a bit of fidling and wired up two more cables giving me a further 14 radials.

With the connection box opened I could add a load more radials

The actual length of the extra radials is much longer than the 30 meter quarter wave (23ft), but since I had the room to fit them I thought what the hell and buried them a few inches below the ground. So I now have varying lengths of radials, 48 at 23ft and 14 at approximately 40ft.

Initial tests show little difference, but I suppose that’s not surprising, interestingly though the SWR remained at 1:4:1 but the resistance at the base of the antenna was now 38 ohms which was certainly better, however connecting the MFJ at the shack showed the resistance back at 40 ohms, obviously the 30 metres of coax from antenna to radio had come in to play, ( I do have a 1:1 balun), but no real surprises. I guess this is where your surrounds and ground come in to play. 

The old “dipole versus vertical” is an interesting topic to read up on and of course there are pros and cons to both, with the general outcome being that the vertical is better for DX. But it all depends on your own situation; whether you are surrounded by buildings or trees or have the right ground etc. I think as an experiment I will re hoist the old inverted V and do a weeks comparison testing just to see how my particular surrounds effect each antenna. Certainly I’ve never had an issue when using the inverted V and the vertical is more of a fun build, but since I have gone to the trouble of burying all those blasted radials I’m not packing it away just yet!

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