Ground mounted helical wound vertical HF antenna

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Ian Bardell:
Hi All
At present I have a home made helical ground mounted antenna with approx 22.6 Meters of 14 gauge copper wire on a 4 Meter glass fibre rod, with a 2 meter copper earth and two 5 Meters insulated ground radials which are buried about 2 inches below ground.

I would like to make this antenna multi band, mainly for 80M, 40M and 20M I am not too worried about gain but some gain would be nice as I am restricted to only 10 Watts, so could anyone please give me any ideas on how to improve this antenna, there are a few restrictions, mainly local council and neighbours so the antenna can not be raised and it must be able to laid down flat at ground level when not in use, Thats england and our red tape!! HI HI

Regards
Ian Bardell
M3GXX

Steve Katz:
Where'd you come up with that design?

The problem with using helically loaded antennas like this is it's inconvenient to change the inductance and above resonance the antenna becomes very inductive very fast.  It can be an RF choke on higher bands, and not much of a radiator.

It's only 13 feet tall or so, which is awfully short for 80 meters.  It would normally need a much better radial system than you describe to prevent enormous ground losses that will eat up most of your signal.

Get hold of the ARRL Antenna Book and look at section 6-28.  It describes a helically loaded vertical antenna having an adjustable matching network at its feedpoint and provides all winding and tuning information on the following pages.  The same section also shows a typical radial system for such an antenna in "Figure 51," and that photographically shows a base plate to which 60 (sixty) radial wires are connected.  That's usually about the quantity required for short verticals to achieve reasonable performance.  

Thankfully, if you can bury the radials you never have to work with them again so this is definitely the place to put the major effort.  And your neighbors won't know!

WB2WIK/6

Ian Bardell:
Hi WB2WIK
Thank you for your reply.

I purchased the antenna from EBay for a very cheap price, even if I could get the antenna to work well on 40M and 20M that would be great.

I have had some good contacts on 20&40M, I have worked a W1 on 40M and I2,YU,UE,9A, to name a few, all on 20M, all contacts using only 10 Watts but I'd still like to improve the antenna if I can.

I will get a copy of the formentioned book and have a good read.
Apart from the height restrictions I also have a very small garden it is only 25ft long by 15 foot wide which restricts me with respects to dipoles and quads!

Yet again many thanks for the information sir
Regards and best 73's
Ian
M3GXX

Steve Katz:
Hi Ian,

1.  Get the Queen to give up half her real estate.  Then, divide that amongst every landowner in the U.K. and you'd have plenty of space for all sorts of antennas.

2.  Put up big antennas.

Okay, it's a joke.  But I know I'm not far off...

25' x 15' is a small area for radials, true.  But if you made that entire area solid aluminum or copper, it would probably work fairly well.  A *lot* of radials are sure to work better than only a few, even if they're all too short.

Good luck & catch you on the bands!  U.K. is easy for me on 17m, Saturday or Sunday mornings about 1600-1700 UTC.

Steve WB2WIK/6

Bob Lewis:
The general rule is that burried radials don't need to be any longer than the vertical is high BUT you need lots of them. Twenty or thirty at a minimum. Three is surely not enough.

Even with a proper radial system the antenna will not be too efficient on 80M and 40M, although you will certainly make contacts with it. It should be a little better than a good mobile setup.

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