Many thanks to Keysrawk on my YouTube channel, who asks:
Do you usually try to use an isolator or do you often let your wires touch branches by just pulling them over? When you deploy 20m EFHWs, for example, do you try to avoid having an end touch a branch and only have the throw line going over the branch? I tried to go through your videos and look but you don’t often mention how far you pull the wire up and possibly over. Thanks!
This is a great question!
Before I answer, I’d like to add a little context:
- I am a QRP operator. The maximum amount of power I use in the field is 10 watts, but 99.5% of the time, it’s actually 5 watts or even much less.
- I am answering this as a field operator, meaning I’ll be referring to temporary antenna deployments.
That said, the quick answer is no, during park and summit activations, I do not worry about my antenna radiator wire touching tree branches.
I do isolate the end of my wire antennas from tree branches and leaves, but I don’t worry about other parts of the radiator touching.
Also, all of my antenna wire has some sort of jacket–I don’t run bare wire in the field.
More often than not, when I deploy a longer wire antenna–say, a 40M EFHW–I simply use a tree branch to support the apex of the antenna if I deploy it in an inverted vee configuration.
Indeed, when I’m under a heavy, dense canopy and I deploy a wire antenna vertically (say, a 31′ 9:1 EFRW or a 20M EFHW), the wire will often touch multiple branches.
Ideally, of course, it’s best not to allow your line to touch branches because it can have an adverse effect on antenna performance. When I deploy an antenna for a permanent station–say, at my QTH–I will not allow branches to touch my antenna wire if it can possibly be avoided.
I find that during POTA, WWFF, and SOTA activations, it’s more important that I simply get the antenna deployed and get on the air in short order rather than worry about an “ideal” deployment where my wire antenna/radiator is hanging in free space.
I find that even if branches have a negative impact on antenna performance, it’s negligible and has no meaningful impact on my activation.
That said, if I were to operate higher power–say, 100+ watts–I would be cautious at least about the end of my wire antenna touching tree branches or leaves.
I’ve no experience doing this personally, but I have to assume under the right conditions (say, if you’re running a high duty cycle mode like FT8 and pushing a few hundred watts) the voltage at the end of your radiator would be quite high and possibly burn the tree.
Because I’ve so little experience running QRO in the field, I reached out to my friends on the Ham Radio Workbench crew and asked for their advice. Consensus was that for most of us, the main point of the antenna we need to isolate from tree branches and leaves is the end of the radiator.
George (KJ6VU) noted that when operating 100W or higher:
Make sure you have a good high voltage insulator and the wire does not come in contact with anything at the end. See [Figure 9-4]:
Voltages are highest at the ends of a dipole.
From a practical point of view 100 watts is pretty low risk but 1kW can burn a piece of wood. I have seen it happen.
So there you go! Exercise caution when running QRO and stick with good amateur radio operating practices. For a really deep dive into the world antennas, check out the ARRL Antenna Book.
I’d like to thank George, Mark, Vince, and Mike for sharing their input!
In a nutshell, though, as a QRPer, I don’t worry about my wire antennas touching tree branches or leaves in the field. I do keep the end of my antenna isolated, though.