The QRPer Board

Hi all,
The ARRL 10 Meter contest is in a few weeks.
I am thinking about entering as QRP Portable/POTA.
Usually I run a vertical ant, but wonder how easy/hard it would be to build a portable 10M Yagi for the CW bands - to use with my KX2?
Would it be worth it...this is for a POTA and not SOTA.
Does anyone have some plans they could point me towards ?
Thanks in advance for any suggestions.
Best,
Bob K4RLC

You might take a look at building or buying a 10m Moxon. There are a number of websites with information and plans, and MFJ sells one that gets a couple of good reviews on eHam.

Jim - K0RGI

Jim - Tnx, will check it out. That's a new antenna to me.
73 de K4RLC Bob

Why not a G4ZU (SK) "Jungle Job" antenna ?

https://www.essexham.co.uk/images/g4zu-junglejob-01.jpg

it's a 2 elements yagi with a decent gain and the size is still manageable, plus it just needs a simple 1:1 balun at the feedpoint; a note, the formulas given are for metric units

with a bit of reasoning it shouldn't be difficult to make the boom and reflector "telescopic" and the reflector arms foldable, that would result in an antenna which is quick and easy to deploy and can be easily carried around

for further infos and a NEC model, see here

https://qrper.net/viewtopic.php?t=84

notice that according to the NEC model, the antenna placed at 0.6 Lambda from ground offers a quite nice radiation pattern and a gain above 10dBi, not bad

couple notes, first of all, it will be easy to optimize the "jungle job" for CW, just calculate it for the middle of the CW slice and then prune the dipole to bring it to resonance

Then... a contest like the one you named is somewhat "a different kind of beast" and in that case you'll want to bag as many contacts as you can, now, for such a purpose a bi-directional antenna (e.g. a delta loop, corner down or an h-doublebay) may fit better, since it will allow you to make contacts w/o the need to turn the antenna (too much) and, at the end of the day, this may result in a "fatter" station log (and with a unidirectional you may miss stations calling you "from the backside"), yet, if hunting DX, the "Jungle Job" may be the "tool of trade"

Andrew - Couple of things: Have never worked a contest QRP....so wanted to maximize the gain.
For POTA 20M CW with 50 watts, I use a Chameleon 17ft whip on a "magic carpet" AL screen wire ground (no coil)...and have great results. Sometimes put the same whip on a MagMount on the 4Runner, and it radiates well.
I've read that a 102" whip will be good for 10M CW...
Also, have a 40-20 Trap Inverted V - So I can try that one, I guess ?
If the Trap dipole wouldn't work, I can easily build a 10M dipole/Inverted V.
-For this contest, will also be POTA and battery operated at Kerr Lake K-3845, on the NC Virginia border.
What do you think ?
73 de K4RLC Bob

Bob, I understand your wish to try maximizing the little power you use, but...

If it was a matter of chasing DX or to contact some "rare" call, then I'd absolutely go for a "Jungle Job", since it's easy to put together so that it will be easily portable/deployable and since it will offer 10dBi of gain and a nice front-back ratio which would allow to "null out" undesired signals coming from the "back", but...

If the aim of the contest is to make as much contacts as possible, then in my very humble opinion, a "bi-directional" antenna would be a better choice, since it would allow to hear/contact stations on both "sides" and since it would be fast/easy to turn the antenna of 90° (at max) to improve the signal from/to some given station

Now, probably some people here may (and will) disagree, but again, it's just my take

Anyhow, if you want to follow my suggestion, here's an antenna for you

(click here https://postimg.cc/sGggkhtw to see the image full size)



it's a so-called "oblong loop" or "narrow loop", basically the antenna is a full wave loop whose horizontal sides are 1/3 of the long ones (you start by calculating the perimeter as 1 Lambda and then calculate (perimeter/2)*0.33 to obtain the short sides length), the antenna, built as for the image, offers a gain of almost 9dBi, a bidirectional lobe with pretty low takeoff angle and a quite wide bandwidth (SWR<2), plus its feedpoint impedance is near 50 Ohms (48.7 -j 2.89) so it can be fed using a "standard" Guanella 1:1 BalUn and won't need a tuner

The sizes in the pic are for the 10m band (centered around 28.120 MHz), to build it you'll need a fiberglass telescoping rod (or fiberglass pole, the ones in sections), if going for the fishing rod, pick a 10 meters one and remove the top, thinner, sections to obtain an (about) 8 meters rod, then use a pair of PVC pipes for the horizontal supports (upper and lower) and 1.5mm diameter insulated wire for the radiator, to tune the antenna just shorten the wires at the feedpoint a bit at a time and raise the bottom PVC pipe, once completed the tuning the bottom pipe may then be fixed in place, for a portable version, use nylon tiers (or the like) to fix the top and bottom horizontal pipes, that will ease deploying the antenna, just fix the top pipe and pass the radiator wire, extend the rod, fix the bottom pipe and connect the wire to the 1:1 BalUn at the bottom, to hold up the antenna, use a "surfcasting" fishing rod stake, that's all

And by the way, if you'll try it, let me (ok, us, the forum) know how it went; anyhow ... fair winds and following seas !

Forgot, if you'll go on and build it, please, post some pics !

[edit]

further infos and a video here

https://ei7gl.blogspot.com/2020/01/oblo ... 0-mhz.html

I'm most of the way done building a Moxon (basically a folder 2el yagi) based on this article:

https://www.jpole-antenna.com/2023/09/2 ... a-project/

I bought poles that were a little longer, in case I want to try using it on 17m, but you could also use shorter poles for 10m.

I'm actually hoping to have several sets of wires that I can use to set it up for different bands.

Mike, KL7MJ

A moxon may be a nice antenna, but... please see my observations; and then, a "Jungle Job" is really easier to build and deploy in almost half the time needed to deploy a moxon and is much simpler than the mox if you think at it for a second, plus ... well want we talk about performance of an U shaped dipole vs a V shaped one ? And then we may also deal with impedance matching

Andrew,
How would you go about constructing the jungle job? For 28MHz, you'd need about a 16 foot reflector. Do you make it out of aluminum pipe or PVC with wire inside (or outside)? To me, it sounds a lot more difficult than a Moxon with a 3D printed hub - maybe because I've already printed the hub!

73,
Mike, KL7MJ