Introducing the SV1428 - 14 & 28 MHz Short Vertical Antenna.

 

 

Since I've been using my EFHW antenna, I haven't really felt the need for another one. Problem is that this antenna is horizontally polarised. I wonder sometimes if a decent vertical antenna might perform better on those days when contacts are hard to come by. The reason I think this is because of the disparity in signal reports I receive, when I know full well that the signal should be better. The reverse is also true - I might get a high signal report only to send a poor one back.

The main reason for not having a vertical antenna erected is because of its appearance. I try to be as inconspicuous as possible. As a compromise, I came up with this short 14 MHz vertical. After all, I was really surprised at the performance of my shortened dipole which uses the same principles. I did attempt this antenna before using a centre loading but the frequency response was way out. I must have miscalculated somewhere. It seemed to be resonating at about 9 MHz no matter what I changed - so no use for anything really!

The overall height of this antenna is 3.5m. Doesn't look too obvious if mounted a couple of metres below the apex of the roof. I didn't want to top load the antenna because it would make it top-heavy and unstable in high winds. I also wanted the loading to be above the centre mainly because, I'm led to believe by so called experts, that the first couple of metres of an antenna is where the work is done. I also needed it to be calculated properly if it was to have a chance of working on 28 MHz too. Finally, after checking, tweaking and double-checking my calculations, I came up with this design. 

To limit the number of turns required on the coil to a sensible size, I had to increase the diameter of the former to 42mm, allowing me to use only 16 turns, which also keeps the weight down. The wire I used is 2.5mm2 solid insulated household wiring cable. Hopefully this will minimise any resistive losses. All of the antenna is built using an old fishing pole for the main part. I stripped down an empty silicon sealer tube to make the reducers to match the coil tube down to the diameter of the pole, and glued in place. I also left about 1 foot of extra wire sticking out of the top to give me some trim capacity.

On to the testing. Any 1/4 wave vertical needs a good ground plane to perform. I found that two pieces of wire about 2m long stretched out in opposite directions at about 45 degrees and connected to an 8 foot aluminium ladder on top of the garage did the trick. I will add more radials later as I see fit. There may be some experimentation needed here because it can be quite finicky to get the right result into a small space. If there is enough room, you can fit full 1/4 wavelength radials which would probably be better. This antenna may also benefit from an additional ground connection. The antenna was fed by Mini RG8 coaxial lead. So first of all I connected the analyser and did a sweep from 13MHz to 15MHz to see where the sweet spot is. The excess wire at the top had to be removed as it happens.

As you can see there is a good dip of low SWR from about 13.5 to 14.8. Perfect! Any mismatch can be sorted with the ATU. A quick call on FT4 and 10 Watts got two instant responses from Germany and the Netherlands, both with positive signal reports. The SWR reading on the rig was even better than the analyser suggested. I put this down to the length of coax that was now being used. Moving on to check at 28Mhz I was pleased to see a good SWR here too, as can be seen below.

An operating range of 27.7 to about 33MHz - very useful! Once again, operational SWR was better with the rig. An even better ground plane would allow this antenna to perform to its full potential. I find it extremely difficult to compare one antenna with another. I still seem to get more contacts with the EFHW, but it does work extremely well. 

Here we can see the spot reports from Gridtracker.

More operational trials may be required under different conditions. I am going to name this antenna the SV1428. This will be my vertical option for the present time. Here it is just above the edge of the roof line.