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40 80 Meter GP Vertical

from James R Hilt II, N8NSN on March 10, 2013
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40 80 Meter GP Vertical
By James "Jimmie" R Hilt II, N8NSN

Having a small lot was fuel for coming up with a good 40 and 80 meter vertical plan. I also wanted easy maintenance for the antenna and the ability to quickly let it down in foul weather conditions or for portable operations. I didn't want a lot of overall height due to the limitations of supports (few trees and the ones we have are not large).

I designed the following ground plane vertical to cover the 40 & 80 meter bands with no antenna tuner needed on either band. The platform for this antenna is a used telescopic fiberglass mast of 48 feet when fully extended. There is an issue of too much flexibility with it at 48 feet so I only used 33 feet of length, with the bottom section not being used at all (stored away).

The feed point is eight (8) feet from ground level for easy reach access to the variable capacitor used in the 80 meter mode. Here is a schematic of the 80 meter matching L Network section, a little larger to show detail.

An on hand enclosure has been used for many past antenna projects. This is evident from the patches of neoprene, nut, & bolt plugs where previously used holes reside. It serves as a great housing, though anything to keep the weather off could be used. During 40 meter ops the inductor and parallel cap are not in the line. This is achieved with a simple DPDT contact switch rated for full legal limit applications. In 40 meter mode a 0.75 uH shunt inductor is used for DC grounding and serves, as well, as a matching transformer for the 50 ohm feed line. In 80 meter mode, an “L network” consisting of a 12.1 uH inductor with a 150 uF variable air capacitor (2.5KV rated) in parallel is engaged. A shunt inductor in base of the load inductor is also switched in at approximately 0.9 uH to achieve the 50 ohms. Varying the cap between 50 and 90 pF makes the entire 75 and 80 meter band workable with no antenna tuner used.

The "T" section at the top of the antenna, for the cap hat, was a driven element from of a salvaged 2 meter yagi antenna. The vertical wires have terminal ends crimped and soldered on. Stainless hardware attaches this vertical wire to the "T" section at the top.

As shown the original saddle for the 2 meter element was used to keep the element level. This all attaches to the top of the vertical mast by means of a home brew compression/expansion connection. This was done with a long SS 10x32 bolt and hardware, with a drilled rubber stopper over the long bolt. The stopper compresses/expands by means of a SS flat washer preceding the lock-washer and nut.

Stainless steel hardware and wire terminals attach the end-drop wires to the "T" cap. The bottom ends of the drop-wires have terminals and stainless hardware to attach to the fiberglass truss at the base of the cap hat. The fiberglass truss is reinforced with cyanoacrylate (super glue) and clear heat-shrink tubing, post drilling (drill slowly with a very sharp bit to prevent fracturing of the fiberglass). The truss was made from a section of 3/8 inch fiberglass rod from an old mobile antenna mast. This truss is fastened to the fiberglass mast via an appropriately sized saddle clamp.

Here is an over-all shot of the cap hat assembly. You can just barely see one of the ground counterpoise wires lying on the ground under the laid-over antenna.

Nestled away, secured from any impending storm damages, in just over 60 seconds.

Also a simple fold over set up was made with a scrap piece of 2.5 i.d. gas pipe. Some aluminum one quarter by two inch bar stock and aluminum one quarter by two by two inch L-Channel served well as the shackle set. Not a necessary component to this system, but it sure made the initial “tune it up process” a lot easier.

Laying the whole sh-bang over is easy by well placed quick disconnects on one of the counterpoise wires and the pair of Dacron ropes used to add support for the feed line and reduce antenna sway. Notice where the mounting board is C clamped to the fiberglass mast, I added sections of scrap rubber hose to the home brew, all thread, C clamps. This prevents an over torque thus mashing and splintering the fiberglass and/or the threads chafing the mast. The spring used on release one was a spare screen door spring I picked up at a garage sale for a quarter J Frugal…

This was another fun and productive project to share. Many would say that at only 8 eight feet up for the feed point it's somewhat of a compromise in ground losses and all those other gremlins that deter so many from trying things with antennas. It is worthy to state that even as a compromised situation for an antenna; Regular early morning contacts to Australia, New Zealand, and such make for a great accolade to the efforts in this project. Many European contacts in the evenings... All on 40 meter CW. On 80 I'm having a ball and so far working South American countries' stations, and still in frame of mind to keep seeing what comes next. I'm excited to see what it does with portable ops, as well.

S.W. Ohio - USA

Member Comments:
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40 80 Meter GP Vertical  
by WX4O on March 10, 2013 Mail this to a friend!
Great idea! It's easy to see that a lot of thought went into this project. Good work!
RE: 40 80 Meter GP Vertical  
by N8BOA on March 11, 2013 Mail this to a friend!
I like it You could see that this would be easy to control remotely
Would make a great FD project
40 80 Meter GP Vertical  
by G0VKT on March 11, 2013 Mail this to a friend!
33' radials do seem to be very short!(I think that is what they are, I can't quite read what it says in the picture) But if it works then there is hope for my small garden.
RE: 40 80 Meter GP Vertical  
by N4JTE on March 11, 2013 Mail this to a friend!
Wow can't ask for a better detailed construction article. I am guessing also that it would be a fine antenna on 40 as it is a full size vertical with, I am guessing, some raised radials at 8ft.
Also guessing that your matching circuit is designed to accomodate 50 ohms on an extremely short cap hat loaded 80 vertical.
No small endeavor !
I would be interested with your further results on 80 with the design.
Nice job and tnx for sharing.
40 80 Meter GP Vertical  
by NA4IT on March 12, 2013 Mail this to a friend!
It's hard to see the numbers in the pictures. Could you post a link to the full size pics, or better yet a pdf file of the dimensions?
40 80 Meter GP Vertical  
by G0MGX on March 12, 2013 Mail this to a friend!
I too would like to see the pictures in more detail; can we have a link to them posted somewhere please?

40 80 Meter GP Vertical  
by VE3XQQ on March 12, 2013 Mail this to a friend!

Nice project... this may fall into the make it before field day catagory!!

For those who want cleaner images enter N8NSN into the eHam Call Search box and resultant page has a better copy of the image detailing the dimensions.
40 80 Meter GP Vertical  
by N2DY on March 13, 2013 Mail this to a friend!
Great article. Nicely done do-it-yourself project. Thanks for sharing it with us.
40 80 Meter GP Vertical  
by N8NSN on March 13, 2013 Mail this to a friend!
Clinton has informed me that the server is making a mess of things. Yes, better pictures are needed and the files were large enough, but the server only has limited bandwidth for such non-sense :-D
QRZ my call. The prints (i call them such,loosely) are big as life and clear to read. Enjoy !
Thanks Clinton and all the staff at eHam for a great site and keeping it "free".
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