The 17-5 HF Vertical Antenna

This is the next project to be undertaken. Named the 17-5 because the top vertical element measures 17.5 feet in length. A short counterpoise wire of 3 feet completes the antenna when connected to the feed point via a 9:1 unun. The installation will be terminated with a 1:1 balun to deal with any common-mode current issues. I am reliably informed that the antenna will match up on 40m down to 10m, maybe even more.

I decided to model the antenna first to give me an idea of the radiation patterns. As you can see below, the take-off angle looks quite impressive - very similar to a ground plane antenna.

The far field plots show good gain figures at low angles with the antenna mounted at a height of 3m above ground. The 3D plot shows the highest energy radiation in pink / purple which is perfect for DX.

I have some fishing pole sections which I keep using and re-using for my antenna projects that can be utilised once again here. I slotted some sections together to give me a total of about 22 feet. I intend to feed the wires along the inside of the pole. The unun will be fixed at just over 3 feet from the bottom of the pole.

Completed Antenna

To test the antenna before erecting, I put it together and then stood it up in the washing line receptacle in the lawn. This is the temporary fixing of the 9:1 unun on the pole.

The antenna is 20.5 feet in total, which is still quite long.  A quick scan with the Nano-VNA showed reasonable SWR readings across the bands. So up it goes!

I decided to fit a waterproof box onto the pole to house the unun and partially cover the PL239 connection. Final position is above the garage on the gable end of the house, not ideal, but the most practical for my situation.

When permanently installed, I found that I could not get a decent match on 7 MHz and below. Also 18 and 28 MHz were a no-go. Proximity to buildings, metal brackets or other antennas? Who knows, probably all of the above. However, it did match up on 50 MHz which was a bonus, however, this may be outside of the efficient operating frequency of the unun, and consequently, I haven't made any contacts on this frequency yet with it.

Performance

It does work well, outperforming the 58ft wire sometimes. The long wire does work better on the lower frequencies though. I find antenna comparisons really difficult. Any tests you might perform are always against a backdrop of constantly changing conditions. I test using WSPR and comparing spot reports and also FT8 reports, but there are many variables to factor in. A good way I find to test the reception performance is to tune into a morse beacon and switch between your antennas to compare the S Meter readings. My wire antenna is horizontal while this is one is vertical. The long wire is in free space, while this one is quite enclosed between buildings. Despite all this I have made contacts in the USA and Brazil and across Europe, which is quite impressive. I will continue to try to improve the band coverage by firstly doubling the counterpoise to 6 feet. I have modelled this and it shows an improvement in SWR so let's see what happens. More to follow........

 

Simple Remote Antenna Switch

 I'm getting a bit bored with having to go to the airing cupboard to switch my antenna over. That's where the switch is located. My plan is to switch the three antennas I have installed by remote control. There are many ways to do this - just take a look online.  I intend to build a relay box to house the connections to the SO239s and Schrack miniature relays with contacts rated at 250VAC 8A. (see images below) 

Each antenna will have its own relay that will connect or disconnect as required. The coils of the relays will be operated by a 12 volt DC signal from a rotary switch, located in the shack. This arrangement also allows me to move all of the cables and switch box into the loft out of the way. Protection diodes were included along with some indication LEDs on the control box. The circuit diagram can be seen below:

Some designs use the normally closed contacts on the relays to ground the antennas not in use, while others just leave them open. I decided to go with non-grounded. I don't want to create a lightning magnet! I don't think there is any down-side to this. After all, my manual switch doesn't ground any outputs / inputs so it should be fine.

Testing:

I connected the Nano-VNA to the common input to the box and a dummy load to each of the outputs in turn. A sweep at different frequencies didn't show any adverse SWR readings compared to the manual switch. (in fact there is a slight increase in SWR with the manual switch and an identical increase with the relay box, so I'm guessing we're all good to go!) This is probably due to the extra connections being used. I think using coax to wire to the relays is a good idea here. I previously made a box, expecting the metal enclosure to provide adequate screening. Using coax makes for a reduced loss in the circuit.

I tested the unit live and made several contacts with no apparent problems. This is a project that has really been worth doing.