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.
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!
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........
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