40m 20m 15m Multiband Inverted-V (5th HF Antenna project)
This antenna started life as a 40m inverted-V. It has now been converted to cover 20m as well as 40m (with 15m on third harmonic of 40m). Click here to jump to latest news on this antenna
40m inverted-V origins
My two earlier 40m dipoles were both about 12′ off the ground and although some surprisingly good DX had been worked with them, these contacts were probably highly reliant upon the far end’s antenna system doing all the work. To make matters a little more balanced, I decided the antenna needed to be significantly higher.
The new antenna is a compromise. I wanted a higher feed-point, Pam (my XYL) wanted a stealthy solution. The available free space meant that the antenna would be sited east-west. I also wanted to be able to get at the feed-point without hiring a cherry picker so a pulley arrangement would have to be used. The result was a 10′ pole mounted just below the roof gutter at the back of the house where there are 3 floors. The top of the pole is about 35′ off the ground so allowing for pulley etc the new feed-point height will be at 33′.
Plan A was to use 75-ohm twin feeder which I had no experience of. After finding some strange SWR effects as I was trimming the dipole legs, I decided to revert to Plan B – old faithful RG58U coax and was then quickly able to tune it for 40m. Kevlar is used to support the pulley and to support the legs. Whilst working on the antenna an elderly neighbour dropped by. I was half wondering whether he’d come to report some previously unknown TVI problem which I was now advertising with this bigger antenna! As it happened he came bearing gifts, in the form of WW2 porcelain egg insulators and dipole centre – very welcome indeed. In fact my Plan B has incorporated these to good effect.
Initial Performance First trials indicate it’s hearing is much improved from its predecessor – the morning after installation, 20m was full of VK, ZL and JA with signals between 53 and 58 – alas they couldn’t hear me! My first QSO however was still extremely welcome, it being the WACRAL net with G2UG/MM in it (G0PFH Geoff using the Halifax ARS call from Marseilles) – both reports at 55.
Two EMC issues had arisen, both involving lighting based on PIR sensors being activated by my transmission. I was also aware of significant RF in the shack. I decided these were likely to be caused by feed-line radiation (difficult to measure with any accuracy in this situation). My first solution was to put a ‘lasso’ style common-mode coax balun at the feed-point and a spare T200 iron core on the coax just below the pole – this didn’t seem to make any difference! My second solution was to replace the ‘lasso’ with a ferrite ring at the feed-point, winding the coax through it (forward and reverse). RF is now low in the shack even on mismatch bands and I can now easily tune up the Inverted-V on 160m (using my z-match ATU) so it must be doing some good!
A note about moisture penetration: despite taking what I thought were good measures to prevent water getting into the connectors, I kept finding them wet. I tried a combination of glue gun sealing, petroleum jelly, self-amalgamating tape and even a shrink sleeve with that covered in petroleum jelly too. The fact is that water always wins, even when you’ve put shrink collars on and ended up with something like this…
Ultimately the best approach has to be to eliminate connectors and work on the principle of removing the water and not trying too hard to stop it getting in. So since then I have taken out all of the PL259s. The balun is in a plastic bag with a silica gel pouch in it!
On a whim I extended the legs and formed a loop (rhombus more like). This had interesting results – I could tune up easily on all bands except 40m! I also tried it as an end-fed on 160m and 80m. In general noise levels were higher (perhaps because part of the antenna was now lower) but performance hadn’t improved. The balun remained as a 1:1 which undoubtedly wasn’t ideal as the impedance would now be rather different. The experiment was abandoned and the antenna is now back as an inv-V with one change – it is now resonant on 7.170, a little high in frequency but this brings the swr down on 15m nicely; don’t believe that a 40m dipole will give a 1:1 on 15m, 3:1 is more likely and over imperfect ground with changing levels etc the points of resonance won’t be exactly on odd harmonics of the fundamental either – c’est la vie!
Over the May Day weekend 2006, I’ve worked great DX on 40m all quality QSOs at typically 57-59 :- Tasmania (VK7GK), Venezuela (YY1RDX), Oregon W.coast US (W7EJ) and Mid West US (W0YWT). I did some tests with Gerry VK7GK. We started on 100w from my end and 300w from his and found 5w from me and 50w from him (to get above my local noise level) was still workable.
6th May 2006 – I’ve attached a 20m inverted-V dipole to the same feed-point. Initial reception comparisons suggest this has had a 10-15dB gain on 20m over use of the 40m dipole on the band. On 20m leg has been hung about 6-12″ below the 40m leg. On the garden side, 20m and 40m legs are 45 degrees apart and in a similar plane dropping to about 15-20′ above the ground. My first QSO was interesting – JX9NOA, Ole on Jan Mayen Island above the Arctic Cirle in the North Atlantic.. The island is part of the Kingdom of Norway but it’s closest major land mass is Greenland.
Last updated: 6th May 2006