20M VERTICAL GROUND PLANE FOR PORTABLE USE

 

With the CQWW SSB 2008 getting ever closer in fact a week away i made my mind up to try something different this year. Last year was a vertical 20m dipole taped to one of those Maxi poles that Richard (G3CWI) sell's on his site SOTABEAMS and i found it to work very well except the pole was not mine and had to go back.

This hobby has so many different things to go at it certainly keeps me busy and once again i have found myself enjoying something different and its SOTA which stands for SUMMITS ON THE AIR . I live within a few miles of three SOTA summits and around here in the North West part of the UK its become popular, even though these three summits are easy to walk up i see challenges as many others do.

I recently went up the summit Gun and for the first time tried a vertical which happens to be the same one i use for the drive on mast support i built out of wood. Tested by myself with Tom (M1EYP ) and his son Jimmy (M3EYP) we soon found the advantage of the low angle offered by a vertical making several easy contacts into the States and Europe. There was a slight problem with the dipole and that was ground effect detuning it and me taking a slightly over sized ATU with me to correct the mismatch. I was using one of the smaller SOTA poles ... then i had an idea!

Buy a Maxi pole from Richard and build a full size mono band vertical and while im at it have a min of three radials that droop 45 degrees ( this angle is supposed to give a better 50ohm match ) and also act as guy lines but not coming into contact with the ground. I was talking to a work colleague about radio and he was interested in what i was up to so he offered me the use of his workshop and any skills he might be able to offer in building this new aerial Although i knew what i was going to do to build the aerial i took Clives invite up. So over to a gusty Buxton me and my son Daniel travelled.............

Where do we start asked Clive? We will be needing a Set square with the vertical and horizontal lengths at least 3ft and that was it my wish was granted. Yes there is probably a way to work angles and lengths out with formula but i decided this way was as good as any. Once this page was uploaded i got a reply from Tom (M1EYP) who happens to be head of Mathematics at a secondary school and here is his reply ...

BTW, yes there is indeed a mathematical way to calculate the length of your 45 deg radials. It is whatever the height is where they attach to the pole, multiplied by 1.414.

Cheers, Tom M1EYP

So thats the alternative to building wooden triangles HI! Next time i need formula i will ask Tom.

Minutes later it was almost finished oh and that bike is a little 125cc pitt bike and yes i had a go on a nearby field....great fun!

Daniel was eager to try a saw out so under supervision we showed him how to cut a piece of wood, maybe he could help me in future projects too?

There were some sharp nasty screws protruding through the joints on the set square so clive chopped them off with his angle grinder.

Time to cut 4 lengths of wire one for the vertical element and three others for the 45 degree guy/radials.

They were cut 1/4 wave length each using THIS ONLINE CALCULATOR at 14.200mhz. The three radials were soldered together for strength as they are going to be the guy lines as well. The wire was multi stranded PVC coated so well up to taking the strain of guying a 10m fibre glass pole.

With all wires now cut it was time to get some angles, here we used a long straight fence and placed the pole fully pulled out to 10m lay it on the ground and place at 90 degrees to the fence...so far?

This is just the way i saw on how to do the angles for the radials but no doubt theres plenty of other ways.

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With the vertical wire element in place the set square was placed at the feedpoint where the radials attach, here you can see the set sqaure has moved slightly and Clive running the radial along the 45 degree slope. Nylon tent/awning guying line was attached to the end of the radial by using a knot. Look into knots it will make things a lot easier as i found out. The nylon line was pulled taught then cut when it was touching the fence with an inch over to allow for the loop.

Back from the field with the long fence and we cut the two remainding guy lines to the same length as the original.

Time was not on my side so instead of a local hill to test the vertical Clives garden became the place it would make its maiden voyage. With the three guy wires/radials soldered together i used velcro cable ties and these were used for each wire under the joint so the radials could not slip off and the whole thing fall down! An idea of Clives so worth building at his QTH. I might just take another look at maybe a collar or something else but i found the velcro ties amazingly strong.

 

There she is with 45 degree radials in gusting winds.

As can be seen it was windy with the upper sections bending.

Not where i wanted to test this aerial but either way i had the FT817 in the car and hooked it up using an external SWR meter i smiled at 1.3:1 with no adjustment and i felt why fix something that aint broke? Yes i left it alone had a tune round and worked straight away first call 59 into Spain shortly followed by a contact into Italy with what sounded like some doubt as to me using 5w! Down it came and WX depending up to a local SOTA summit for the CQWW SSB.

On uneven ground the radials will not all be 45 degrees this shouldnt be a big problem but could be over come by using adjusters on the nylon guy lines and developing an eye for the angle. 73's Sean

 

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