Frequency Agile Antennas

[Brian - K3ES]

I use wire antennas for my portable activations. Over time I moved from dipole to 49:1 EFHW and 9:1 random wire, because of ease in changing bands. I'm still experimenting, and would be interested to hear about others' experiences and preferences.

How important are quick band changes to your field operations? How has that influenced your antenna choices?

73 de Brian - K3ES

[KO4AWH]

I almost always activate QRP on 20m with an EFHW. I want to start running a random wire, an inverted V 35 or 41 foot likely. I love the efficiency of the half wave but having the flexibility of bands is nice. Anyway I go has to be highly portable hence the end fed wire…not to mention I make them (tufteln antennas). Weird but here lately I seem to be catching more QSOs on 40 vs 20m at the QTH (40m EFHW). I typically have digital operation capabilities with me for portable as well, propagation testing on the bands is something I like to do and a 9:1 fits that for me.

Joshua
KO4AWH

[SkipRD]

Yes, I'd say that having at least one other band you can switch to is very important for many reasons, but the most common is that propagation is often vastly different on different bands. My 10-15-20-40m EFHW is more than adequate (I know a random wire with a tuner would give me more options, but I don't have a portable tuner.) I occasionally will do 30m CW QRP, which necessitates carrying another little setup, but, for example, over the past year I've had 1725 HF POTA contacts, of which all but 3 were on 20m (578 contacts) and 40m (1144 contacts). I almost always start on 40m, and then run until either I have to go home or I'm persuaded that 40m isn't cooperating, at which point I switch to 20m (hence the disparity in my 40m/20m stats).

73 Skip K4EAK

[KK4Z]

I use several different antennas while activating. Some of my favorites are Sparkplug (49:1). 29.5' random wire with a 17' counterpoise (fed directly into a tuner), 40 meter OCF dipole, an 80 meter dipole, an 80 meter doublet, and my Buddipole-Chameleon Frankentenna https://youtu.be/0AlifLvOH[url]https:// ... AlifLvOH6w[/url]w. Most of the time I am bringing a vertical or an end fed. It just depends on space.

Of the antennas I mentioned, my random wire always goes with me. I run QRP in the field and this antenna fits in a small zip lock bag. I like to put up he biggest antenna I can but sometimes space can be an issue. That being said, I like to bring at least two antennas with me.

I find most of my activity on 40-30-20; I mostly do CW with a little FT8. Frequency agility depends on how impatient you are. If you are a leisurely activator, then stopping to readjust the antenna shouldn't be an issue. If you like to be able to quickly hop around than a multiband antenna or an antenna with a tuner would work. I like the convenience of being able to hop around without too much fuss.

I hope this helps de KK4Z

[Brian - K3ES]

Thanks to all for their thoughts on the subject.

I started my QRP journey with a homebrew linked dipole set up for 40, 20, 17, and 15. It works great, but has two drawbacks. It takes longer to set up than an end-fed antenna, and requires lowering, fiddling with multiple links, and rehoisting for any band change.

At the moment my go-to antennas are EFHWs. I took one to a park today with my TR-35. The antenna is cut for 40, and gets 20 as a harmonic (it will also do 15 and 10, but the TR-35 will not). I built this antenna with links for 30 and 17, because the TR-35 supports those bands. I've been pleased with its performance running QRP CW. While changing to or from 30 or 17 requires lowering, fiddling and rehoisting, there is less of it than with the linked dipole.

My latest project was another EFHW cut for 40 and built with small switches that set radiator length for resonance on 30, 17,and 12. It still requires lowering and rehoisting for the WARC bands, but links are a snap (pun intended). So far, so good, but I'm still testing.

I also have a Packtenna 9:1 4andom wire set up with a 71' radiator. I am using it with a KX2 with built-in tuner. All in all, a good pairing.

I guess I should mention that I use all the above in inverted V configuration, typically supported by an arborist throw line overall tree branch.

One thing I have not tried is an OCFD. Anyone have thoughts on that for field use?

Best 73, and thanks again for the input.

de Brian - K3ES

[Rob-W4ZNG]

My favorite field design is this hybrid W3EDP-Zepp, ah, thing. It does require a 4:1 unun as well as a tuner to tame it, but it is definitely frequency agile. The original designs are here:
https://thewakesileave.wordpress.com/20 ... own-south/
and here:
https://thewakesileave.wordpress.com/20 ... -w3edp-jr/

The one mod from the original design is to use 450 ohm window line, rather than the suggested 300 ohm TV line. Window line is more rugged, and is way easier to work with.

I've used both directly from a manual tuner's 4:1 balun output, but now I'm finding it easier to use a 4:1 unun (one of those little green LDG matchboxes) and 50' of coax, just to be able to find a better tree near a campsite. With either, hook a 17' ground/counterpoise to the tuner. I've never gotten any RF bite from these antenna systems, in any configuration I've tried so far.

The 21' mini is very easy to throw up in a tree, so that's a plus. It easily tunes down to 20m, and with some effort I've gotten it to tune down to 80m. Down that low, it has a very narrow bandwidth and requires frequent re-tuning. But it will make contacts, even at QRP levels.

The 42 footer is a bit harder to get up in a tree, though I'm getting better with the arborist throw bag. It's a beast on 60m, does 80m well, and I have yet to try it on 160m but it'll probably work there too.

I also have an 84' full-size in the camping antenna bin, which I'm hoping to try out next fall when the weather cools and the bugs abate here in N FL. I'm thinking to rig it horizontally & low for NVIS. We shall see.

[Jim72Upson]

Best of both?

I operate SOTA in Pennsylvania, and on occasions I find stringing up 65’ EFHW antennas a challenge with so many tree branches snagging even an S-clip….thankfully the copper clad steel 26 AWG wire has yet to break…but I prefer not to look for trouble when driving to summits often require 200+ miles one-way…

So….my EFHW will have no links.

My current antenna is a 65’ 40m EFHW…which gives me 20m. It is set up as inverted-V.

I PLAN to also string up, at the same time and not too far away from the 40/20 EFHW (feedpoints ~20’ or so apart), a Packtenna 29’ random wire (EFRW + 17’ counterpoise) for 30m and higher…but in a pinch it’ll work well on 40m too. This will be vertical…

Both only use a short 6’ coax to the radio (KX2)…

So…my plan…is that I will need to take a short “hike” (20’ or so) to get to one or the other feed-point…but no links etc. to fiddle with.

I expect efficiency as well set-up time and frequency-agility to be above average.

Crazy? What are your thoughts ?

73,
Jim /AC3B

[Brian - K3ES]

Hi Jim,

My operations are POTA in the Pennsylvania woods, so I know exactly what you mean about tree branch snagging. My preferred setup is to avoid putting wire over branches. I use inverted V and pull the wire up with the throw line over the branch. Lately, I leave the throw bag attached to the line, because it helps to drag the line and wire back down again.

By not pulling the wire over a branch, I can get away with links or switches in the line. I am firmly with you on the Cu-clad steel wire. I have never broken my poly stealth wire.

I also use a Packtenna 9:1, but I replaced the radiator with 71' of poly stealth, so 40, 60, and 80 tune easily.

Best 73 de Brian - K3ES

[w4mkh]

My mobile setup is based around hamsticks. I have tuned them mounted on both a tripod and a stake mount using three 33' radials. I marked the steel whip part with a permanent marker to show the resonant point of the whips for each hamstick. So when portable I setup the band I want to use and adjust the other hamsticks to the marked resonant point and lay them on the ground so that they are ready. If I want to change bands it is a quick task to unscrew one hamstick and screw the desired one onto the tripod.

For transport I simply loosen the set screw and slide the whip all the way into the coil base then attach a velcro loop.

This may be cumbersome for hiking into your activation site but for short hauls it works okay.

[Jim72Upson]

Hi Brian….yeah…..I need to spent some time to master the throw-line approach…..

I keep putting it off (even though I own the same set-up Thomas (K4SWL) currently uses…brand new…still in the bags they came in.. )

I started with a SotaBeans 33’ telescoping fiberglass pole to hang my 40/20 EFHW….and never tried any other approach.

So….between Thomas regularly referring to his throw-line set-up on his POTA videos, and your response….I plan to head out to my local park and see how I do with it…

Jim /AC3B