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.
QRO?
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.
Figure 9-4a shows voltage for full wave and current for half wave. b is correct. both are half-wave.
And yes for half wave voltage at the end is very high and the reason one does not find high power baluns for end fed unless you get something large that can handle the voltage. Also due to voltage high at the end and no matter where you feed it any install must be done to protect against this voltage including not bringing close to metal that can arc over and become part of the antenna.
73, ron, n9ee
I think you hit on the high points here. The short answer is, there’s no way to avoid it, so live with it. Like everybody I like to hoist in the clear when possible, but in many locations it just isn’t, so I suck it up.
The point about insulated wire is good, too. It’s amazing how persistent the old myth about having to use bare wire is. We’re talking about radiation, not electricity. The same radio waves that easily reach your FM radio through the walls of your house will eat that thin layer of plastic for breakfast. Leave it on, for protection from the elements, added strength, and… insulation. (Against tree branches.)
Good post, Thomas!
Great article!
I usually add a plastic ring(PVC) over the wire and tie my throw line to the ring and pull it up at the apex.
Similar to Chameleon antennas.
72,
N8RQJ
I have used high strength fishing line (40-60lb) attached directly to the radiator pulling it back away from tree branches. Fishing line is a great insulator but also very strong and can work well.
I agree completely, Thomas; I always use insulated wire, I will allow my wire to touch branches as required by the location, and perhaps most important I find the effect (if any) to be negligible.
Good article! There are probably others out there asking this question.
http://driftlessqrp.com
just signed up to your blog. I’m in the process of studying for my license here in Canada and had the pleasure of sitting in on your presentation to the Charlottetown club last night. That was a very interesting and informative presentation, although much over my head. Much to learn.
Hi, Mike,
It was so much fun to present to the Charlottetown club!
This can all seem a little overwhelming at first, but we have a great community here who can help.
Also, make sure to check out our discussion board at http://qrper.net It’s a great place to ask questions along with the comments sections of our posts on QRPer.
Good luck with your exam! No doubt, you’ll soon have a VY2 call and on the air! Hope to log you sometime this year!
Best & 73/72,
Thomas (K4SWL / VY2SW)
We do this often, including with 100W FT-8 during Field Day for 24 hours straight, and branches are never an issue on multiple antennas touching branches. Many decades have caused no fires.
We do watch out for excessive leaves, since if it rains the wet foliage screws things up.
One thing I love about this blog is that every question is answered without judgement. “No question too ‘small’.”
I believe many seasoned operators don’t remember not knowing this stuff and lots of details are simply overlooked. Newbies appreciate your efforts to address every nuance of QRP field operations. Thank you.
This makes my day. Thank you for the kind words, Susan.
I’d like to read some discussion regarding wire gage, and what works best given the electrical vs mechanical characteristics, and the ability to loft different weights of cable.
When running QRPp (quarter watt RockMite ( I’ve seen tree branches gang a large adverse effect, so I try to avoid them whenever possible.
In the 100 W front, I once managed to RF burn my finger several layers of skin down, so yup, that’s an actual concern☺️
On a side note, I am noticing that many people are using the word “antenna” and “radiator”. I’m old school and we never used the word “radiator” to refer to any elements. I’m a little confused here. Can I safely say that my antenna “radiates and receives” so we can just use the term “antenna”? Or is there another meaning that you folks are trying to get across?
Hi, Joe,
Great question! So I typically say “radiator” when I’m speaking about the main radiating element/s of the antenna, and counterpoise when I’m speaking about the side of the antenna that is acting as ground or (as is often the case with antennas I use) the wire portion of the antenna coupled with the ground.
To me the “antenna” is the complete system and the radiator and counterpoise are elements of the antenna.
In my videos and field reports I often speak about the counterpoise and radiator because I describe how the antenna is deployed. For example, “My radiator is in a vertical orientation in this tree.” or “The radiator is in an inverted vee configuration and the counterpoise is elevated 1 foot off the ground.”
When I’m just speaking about antennas in general, I just say antenna (or aerial when I’m writing for the RSGB). 🙂
Cheers,
Thomas
K4SWL
I finally came across this article! Thanks so much for answering my question so thoroughly. I’ll be letting my inverted V’s drape over branches all summer! Qrp cw is the best. Cheers. AE9XT (keysrawk)