I used a 44ft doublet with my KX3 in the 2014 QRPTTF event and took first place. It’s an excellent antenna 40-10M. Feeding with 300-ohm twinlead works fine. I fed mine with twisted pair wire harvested from CAT-5e network cable, which is lightweight and cheap.
73, Barry N1EU
Barry, I cheched CAT5e cable and it seems to consists of twisted pair cables with plastic mantle. If and yes the antenna works well with that cable type, it is not necessary that the cables of the landing part of antenna have not constant difference like in web page picture NorCal QRP Club - NorCal Doublet Antenna. Have I understood it correct manner?
73, Saku
The antenna is simply a 44ft doublet fed by balanced line. The configuration of the balanced line feeder is not important as long as it’s reasonably low-loss.
The use of 4-conductor ribbon cable in the original was just a cute gimmick to make a very inexpensive, lightweight antenna. I suspect twinlead or CAT5e twisted pair will perform much better (lower loss) than the original.
73, Barry
Thank’s Barry, now I know what is my next project! ;-D
The significance of the 44ft length is that it is the longest length that will maintain two-lobe broadside radiation pattern through 10M. The lobes get progressively narrower (higher gain) as you go up in frequency from 7MHz to 28MHz. 88-ft doublet works in a similar manner for 3.5MHz to 14MHz (but loses the 2-lobe broadside radiation pattern above 14MHz)
I use a doublet made entirely out of CAT5e. The hardest part is too remove the outer insulation and the shielding foil. After this you have material for four antennas. Just measure your desired feedline length and untwist the rest. Cheap and lightweight. (Idea found here). With the right technique you do not need any winder to put it on.
I must admit I don’t care about the exact length. The ATU of the KX3 does not seem to do so either.
Works great for me.
73, Felix
The CAT5e cable installed in buildings has solid conductors, which aren’t ideal for portable antennas, as they tend to fracture eventually. If you can get hold of the type of CAT5e used for patch leads, that has stranded conductors, which are much more flexible.
(Both types also come in shielded and unshielded versions)
Adrian
G4AZS
I have one, they work very well in my experience - an effective multiband solution.
I use it with a 10m pole…
73 Angel
I generally use a 88 ft doublet on my activations. I have found it performs very well, and is extremely packable. I don’t have a 44ft setup but I bet it would perform very well.
Here is a setup vid of my antenna (Not The Greatest!)
And a few pics of the setup
thanks everyone for the great replies to my question. I posted quite late last night and I just got home from work to find all the answers to my question. So thanks again I will check out all the links as well over coffee.
I have MFJ 300 ohm twin lead like the SOTA Rangers set up and I would need to do a quick tune up test with my kx 3 as the first job. The slotted 300 ohm ribbon like Steve used with his guitar pick centre insulator is quite hard to find around here and I have some tangled old tv type 300 ohm feeder we used for tv before coax was used on tv antennas. I like the MFJ feeder because it rolls up in a respectable manner and is very light weight… Something to work on, mni tnx agn
73 de Ian vk5cz …
If you’re rig/tuner can’t find a match on all bands, you might try a 4:1 balun between feedline and rig/tuner as KQ2RP mentioned.
Barry N1EU
Thanks
Barry I made up the antenna last night and will test it after work Thursday and my friend and I will do a 4 summit weekend on Saturday/Sunday and give it a try. I have a couple baluns by ldg a 1t1 and a 2t1 I made. Will see what the kx3 can handle later today. checked out the links on everyone’s comments all good.
73 de Ian vk5cz …
I made one my self after using VK6MB’s to activate VK6/SW-061, 7 qso’s in under half an hour with 3 VK3 and 1 VK5. Mostly on 40M. No problem tuning with the KX3.
Thanks Michael for your report and success with the antenna.
I did not take the 44 footer this time out activating but will on my next one, possibly Saturday depends if the cold wx sticks around. I still have not had a chance to test it properly apart from tuning it in the passage of the house because its been raining here a lot. Yes the passage in my house is 16 m long 3 floor tiles per metre ideal for measuring out antennas in out of the elements. cheers de Ian vk5cz …
Here ís my brand new 44 Foot Doublet for heavy use! 
Virgin test will be May 31st or a week later!
73, Saku OH2NOS
Where can I buy that plastic center-feed connector, please? It looks well-made.
Thank you for the video.
Gives good ideas that can be shared and can see hows its done.
Good demonstration quite enjoyed that thanks again.
karl
Product name for center feed connector is WDC-300 Watson 300 Ohm Dipole Centre. I bought it from local supplier, but for example you can find it there: http://wsplc.com/watson-wdc-300.html
73, Saku OH2NOS
Thank you for helping me, Saku. I just ordered a couple of the connectors from the UK.
73 de David VK2DMH