By Ross Glover ZL1BGB
“NOT ANOTHER AERIAL!” was the wife’s comment.
“The fence looking like a Porky Pine” was the comment by another ham.
With four antennas already mounted on fence posts, there were still plenty of posts for more verticals!
October 2007 had me retrieving a 5m length of 32mm ali’ pipe from the rear of the garage. A length of coil of 48 turns, 2.5mm was wound onto a length of 2-inch plastic pipe at one end of which were inserted two brazing rods 3 ft long, at right angles to each other and soldered together. (HOLD IT! You will need 79 or 80 turns.)
Above these, a ¼ inch bolt with nut was inserted. Then another locking nut, then two washers and another nut. All stainless steel. The coil was “screwed” onto the pipe and secured at the ¼ inch bolt.
A “jumper” wire was secured between the two washers at the inside of the pipe and the nuts locked. Solder the free end of the “jumper” to the capacity hat rods.
Make sure no dry joints. The jumper wire could be wrapped around where the rods cross.
The other end of the coil – form a loop to go around a one inch stainless steel self tapper screw. Pass a drill bit through the loop and drill a hole a snug fit into the plastic pipe. Hold the coil/rod unit alongside the ali’ pipe with the unit slightly clear of the ali’ pipe. With a felt tip pen, put a mark where the self tapper screw will secure to the ali’ pipe. Drill the Ali’ pipe.
Now slide the unit on to the ali’ pipe and secure with the self tapper and at least two stainless washers. This should hold the unit in place but you may want to add another ¾ inch self tapper farther along the plastic pipe, below the coil.
I started out with the 48 turns/rods unit on the work bench and used an MFJ annalyser with a 3-turn link of slightly larger diameter than the coil.
I was getting dips between 16 & 45 mhz! Geez! Even a borrowed GDO sez I was no where near 7mhz!
So I went and bought 15 ft of 2mm wire from a ham who winds transformers as a job and used the before-mentioned former to make up 31 turns. So now the total is 79 turns! The soldered joint of the two coils sections doesn’t look very flash.
Ah ha! Now the MFJ says 10 MHz and even 4 MHz.
I fitted the coil/rod unit onto the ali’ pipe, fastened to the fence post, attached a foot of coax to the base of the ali’ pipe – braid to two radials 60 ft long and then plugged into the MFJ with 6.8 MHz.
I had the antenna up and down like raising the flag on Iwo Jima over the next few days trying different taps on the coil and adding 200mm lengths of wire to the end of the rods to add capacitance.
The result on November 8th 2007 with a tap at eight turns from the bottom of coil was: 7.130mhz 2.5:1 @ 100 ohms.
Then 7 turns: 7.080mhz 2.5:1 @ 100 ohms.
Different lengths of coax will give you different readings at the transmitter end. I found 8m the best with the MFJ saying 6.640 1:1 @ 50 ohms. So used tuner.
A 20 ft length and the result was horrible.
It is often said that the length of coax doesn’t matter. Sorry, but I don’t agree! Get the antenna on frequency and use the tuner to make sure of low SWR at the shack.
Tuned radials: I hooked the radials onto an egg insulator and a foot of coax to the MFJ. I pruned both ends of the radials to show 3.650.
Was all the hair pulling/frustration worth it? Well so far not enough contacts to prove that this new 5m 40metre vertical is any better than the 2.5m 40m vertical.
The 2.5m (of 19mm pipe) 40metre vertical is a lot easier to handle with the coil wound onto 19mm conduit, with an insert that plugs into the 19mm ali’ pipe.
Switching between both 40metre verticals there seemed to be no difference in the incoming signal strengths. With 5m of ali pipe being twice that of 2.5m, I hoped for another 6db! Hi!
If you have a 2.5m length of 32mm ali pipe, a piece of plastic pipe 38mm diameter would make a neater job. I used what I had.
Listening on 40m at 9pm on 3rd November, the Europeans and JAss were booming in.
On November 4th at 4pm I ran a check with Jim ZL1JW at Papatoetoe. On the small vertical S9. On this new one S7!
On November 8th 2007: the noise level on the 2.5 antenna was S8+. The noise level on the 5m antenna was S6. I tuned onto a signal (possibly ZL3) who vanished into the noise with the 2.5m vertical but was quite readable on the 5m vertical.
On 9th November 07, I listened to VK7AC who dropped 2 S units when I switched to this new antenna!
Nov 10th: I decided to check the antenna out at the bottom of it, with MFJ. No bloody dip on 7MHhz! But at 4.95, 9, 14.180, 15.5 and 21 MHz.
Dropped the antenna, cleaned bird shit off coil, checked soldered joints and erected. Now see 14.173, 15.4 and 21.1.
Nov 13th: Bugger me! Today the MFJ sees 4.65MHz!
I moved the tap back to 7 turns from bottom and saw 4.685 1:1 where before I saw 7.080 MHz!
I give up! Looks like this project is gunna be dumped behind the shed!