Sunday, August 23, 2020

The humble dipole is really a great antenna

Because my hexbeam is still down and awaiting repair, I have been using wire dipoles and my Antron 99 to make QSOs. But I had no resonant antenna on 20 metres and was badly missing the action on that "bread and butter" band.

The apex of my inverted vees. The short one is the new 20m dipole, with homebrew insulators made from PVC chopping board!

So I recently added a 20m dipole to my nest of inverted vees. Previously, I had three vees, one for 80m, one for 40m and one for 30m. When I added the 20m dipole, I was surprised and perhaps a little annoyed to find that it was not resonant. Its inclusion in the nest did not seem to upset the VSWR on the other bands too much, thankfully, but with an SWR of 7:1 on 14Mhz, it simply was not effective and not radiating efficiently at all.

Astonishingly, I did not have an antenna analyzer. It's a piece of equipment that every shack should have but it's something I had never invested in. During a conversation with some fellow DXers on a WhatsApp group, I got chatting with John EI3ISB, who kindly offered not only to give me a MINI60S analyzer which was surplus to his requirements, but also to come to my home and help me analyze the 20m dipole and either extend it or trim it to resonance.

A wider view of the inverted vee dipoles. 

Yesterday morning, Saturday, John arrived and within a short time we found that my 20m inverted vee dipole was resonant on 15.67Mhz – way above where it needed to be. I still do not know how this happened, except that I must have been using the wrong online dipole calculator or else I made a mistake in trimming the two legs. Either way, the antenna needed to be LENGTHENED. And not just by a few centimetres, but actually by about 50cm.

I lowered the dipoles down using the pulley rope and we quickly got to work on adding a piece to each leg before hoisting the whole lot back into the air again.

A quick check with the analyzer revealed that resonance was achieved towards the top of the 20 metre band, at around 14.300Mhz. I lowered the pulley rope again and added another 5cm or so (a couple of inches) on each leg and raised the dipoles again.

This time, resonance was around 14.100Mhz, which is pretty good. I do a lot of digital modes, and prefer CW to SSB, so this was a more than acceptable point of resonance.

John left and I was grateful for all his help. I was finally operating properly on 20 metres! I had a very rewarding day on the band, working DX on FT8 in most parts of the world.

A screenshot from showing where my 20m signal has been heard during the past 24 hours.

I hope you can see from the above screenshot that the dipole has been very effective in carrying my signal to various parts of the world. I see that I was heard in the Falkland Islands, in Alaska and in Kenya. In fact, I worked 5Z4VJ in Kenya using FT4 yesterday evening. Other DX stations worked included several JA ops, YB0MWM in Indonesia, BG0BBB and BD7BS in China, ZP9MCE in Paraguay, A45XR in Oman, LU8EKC in Argentina, 9Y4DG in Trinidad and Tobago, YV5JLO in Venezuela, along with several stations in the United States and Canada.

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