Anyone have experience with HF antennas on short masts?
I’m hoping to do a few 1 to 2-day GM activations in the New Year and want to fly rather than drive (from the London area). My SOTAbeams 10-m Travel Mast is too long (67-cm travel length) for carry-on luggage. I realize I’m going to have to compromise a bit.
SOTAbeams do a mini telescopic fiberglass pole (51-cm travel length). I’m confident it will support a 2-m slim jim but what about HF antennas? It’s 4-m high but you can’t use the top 1 or 2 sections. So, is 3.5m too low for my SOTAbeams 20-30-40m linked dipole? I have a (LNR Precision) 20-30-40m EFHW – would that be better?
P.S. I’ve only seen discussion about higher masts on the reflector.
Andy, the lowest I have completed an activation had the dipole resting on the tops of some bushes at about 4-5ft above the ground… I made enough contacts for the activation… I generally hang my Dipole in a tree at a height I can easily reach the center… so IMO you’ll be fine at ~3.5m for the center… YMMV as they say… give it a go from home as a test with RBN…
If I remember my antenna theory correctly the closer the dipole to the ground the more radio energy is soaked up by the ground and the more vertical the takeoff. So skip distance will be shortened and I guess if you get low enough to the ground you may be in the situation where you can hear folk but not work them due to the difference in skip angle between the antennas and your reduced power.
I too have the 10 Metre Sotabeams mast and hardly use it since I got their Mini mast. I switch out between it and a 11mm diameter 13’8" tent pole. Both support an inverted V dipole. I have a KX2 and make numerous 20 metre SSB contacts while doing SOTA.
The antenna may be close to the ground on a short pole but the ground at the summit is usually very different to "normal’. It could be rocks or very thin soil. So in reality the ground that would absorb a lot of energy may be several tens or hundreds of metres below the antenna. This means the effect is often much less than you would expect.
My 5m pole has done 500+ activations, it’s about 1.5mm thick at the top and supports a dipole fine. I use 13/0.1 PVC wire and Rg-174. These poles are fine as long as you don’t use welding cables!
I’ve used a pole used for retrieving golf balls from lakes. 2-3 m in length extended. Coax into chock block. Home made “ladder line” ie radiating wir from chock block with plastic spacers then into about 10m of wire each leg and string to keep it just off ground. Did have it bungeed to a trig point but modified it to take a guy as well. Folds down to just a bit bigger than a sota wire winder.
I think a mast travel length of 51cm is the absolute limit for my large rucksack even when put inside diagonally (the budget airlines in the UK are very keen to make lots of passengers queuing at the departure gate check their carry-on bags into the hold, and I don’t want a conspicuous pole sticking out the top!). So, based on what many of you said, I’ll try the SOTAbeams mini poles.
Richard (G3CWI) just replied to my SOTAbeams website query and suggested the EFHW would be better than the linked dipole. But, given your shared experiences, I will experiment with both.
I’m keen to try SOTA on 60m and think the lower height isn’t a problem for NVIS activations and my KX2’s ATU (normally bypassed) gives good VSWR using the 40m setting on the linked dipole.
Andy, I use a pair of Black Diamond Distance FLZ Trekking Poles which collapse to just 40 cm (16 inches) for travel. After using the poles to hike to the summit, I extend the poles to their maximum length (140 cm or 55 inches each). I then lash the poles together with a length of reusable Gear Tie, forming a 280 cm / 110 inches long mast which supports my SOTABEAMS linked dipole or EFHW antenna. The lightweight trekking poles provide dual use and enable me to avoid the extra weight of a mast.
Whenever space permits, I carry the 6m version, because I feel without any systematic analysis that the additional 1m matters in terms of performance. I managed a 10,000km contact from SV8 to Japan two month ago when propagation was unusually good.
The downside is that the mast is 600+g and thus a bit too bulky for my taste.
I have now ordered the 5m version of this carbon pole: