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Author Topic: a 34ft doublet, ladder line, a balun & remote tuner  (Read 2053 times)

Offline KO7I

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a 34ft doublet, ladder line, a balun & remote tuner
« on: August 04, 2014, 05:35:36 UTC »
I call my antenna a doublet because it is non-resonant, fed with ladder line and used on multiple bands above 20M.
Today i did some more playing with my antenna and had a ball. 15M was open, where was everyone?
Normally I feed this antenna with 100 ft of RG-213 which connects to a DX Engineering 4:1 balun rated at 10kw peak. from the balun I use 100ft of ladder line to the antenna that is 35 ft high. With this setup I have a lot of transmission line loss.
Today I moved my MFJ 929 auto tuner out to the 4:1 balun and installed a bias tee inside the shack. It worked very nicely. I was able to make multiple QSO's answered several CQ's on SSB on the east coast running 5W. I also made a couple contacts on CW. I played around on 20M too and I was working very well too.
It has really paid off to reduce the coaxial cable losses across the 100 ft run.
Basically I went from struggling to making qso's on the higher HF bands with ease, I was able to work almost everyone I could hear - except for the VK9EX dx-pedition to Christmas Island. HI HI.
Chasing the SOTA activations has been a hoot. Doing QRP to QRP is fun.
I think I will begin looking for a ammo can to put the MFJ 929 auto tuner inside for this winter.

Vy 73, Don KO7i

Don KO7i
Arlington, WA

QRP Rig: Elecraft KX3

Home Station Ant's:
Verticals 80 & 40M, with 36 radials.
Center Fed Dipole 34 ft long, 40 ft high, fed with ladder line and remote antenna tuner.

Offline G0BVZ

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #1 on: August 07, 2014, 00:20:42 UTC »
Hi Don, sorry I was so slow in coming back with my two penn'orth.

One day I dispensed with coax and balun and obtained an MFJ-974HB. I ran 300ohm slotted feeder from the shack all the way to the feed point of the longest inverted V doublet I could fit into my plot. It was a BIG improvement for both tx & rx. I can operate on all hf bands and the brutal simplicity of the balanced setup really appeals to me.  Why 300ohm slotted? -Because it catches the wind less than 450ohm twin, which is an important consideration when the antenna support is a 12m Spiderpole. ;D
(I've reached that stage in life where going aloft ain't so smart: those light glass fibre masts are a real game changer for me.)

Three observations:-
1) There is great merit in simplicity
2) Those old time hams knew a thing or two about antennas!!
3) Not using a balanced tuner is a compromise. Just sayin'.

73,

Vic /Ship's Cat


Offline sm5mek

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #2 on: August 07, 2014, 07:54:26 UTC »
As i can see it is an double Zepp, dipole with random lenght and feeded with ladder. See more here.  :D

Best regards, 72 de SM5MEK, Jenny.

Offline G0BVZ

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #3 on: August 07, 2014, 09:47:41 UTC »
The good people at Sotabeams  (a local company for me) have an info page at url

http://www.sotabeams.co.uk/a-simple-multi-band-doublet-for-portable-operating/

The venerable multiband doublet is described there: it also mentions that the doublet is one of Cebik's "Top Five Backyard Multi-band Wire HF Antennas" which is good enough for me!!    ;D

True open wire feed is most efficient, but I prefer the advantages of good slotted 300ohm feeder for taping to glassfibre fishing poles and I'm prepared to accept the slightly worse losses for that convenience.

Offline KO7I

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #4 on: August 09, 2014, 05:22:13 UTC »
Hi Jenny & Vic,
I've tried a 20M double zepp, center fed with ladder line for a winter DX season once before.  It worked very well.  By shortening the antenna to that of a 20M dipole, the entire element is now a minimum of 35 ft high.  This has helped my situation out a lot.  I think this antenna, with the tuner located remotely is going to be winner. 
Now I am working on procuring a military surplus ammo can, for water proof storage of the auto tuner.  Looks like the local Cabela's store has them in stock.
I am an professional EMC engineer and I can not bring myself to operate with ladder line in my ham shack. I perform Hi Intensity RF fields compliance testing on a daily basis. There are times I run QRO power and I need to be careful of cumulative RF exposure.
I do everything I can to keep RF out of my shack.
For the average ham running 5W there is nothing to worry about.
73, Don KO7i

Don KO7i
Arlington, WA

QRP Rig: Elecraft KX3

Home Station Ant's:
Verticals 80 & 40M, with 36 radials.
Center Fed Dipole 34 ft long, 40 ft high, fed with ladder line and remote antenna tuner.

Offline G0BVZ

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #5 on: August 09, 2014, 20:37:17 UTC »
Better safe than sorry, Don. I'm with you 100% on RF exposure: 20 years ago I went QRT when my son was born because I was reluctant to expose him to any sort of rf. Now he's at uni and I'm back on he air!  Wasn't much hard info back then so I went with safety first.

Your project should be a winner so be sure to tell us how it works out!!  ;D

Offline KO7I

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Re: a 34ft doublet, ladder line, a balun & remote tuner
« Reply #6 on: March 28, 2015, 17:17:38 UTC »
I thought I would post some follow-up experiences of my doublet experiment. For me it has been a winner in ways I never imagined. Each element is 17ft long. It is fed with 100ft of commercial 300ohm window line. I did find that switching to a 1:1 balun and then a 4 ft length of RG-213 coax to the auto tuner has worked out best. The 4:1 balun created tuning challenges on 20M.
This past winter I had the honor of getting to be a host station for W1AW/7 (WA) on 30 & 17 meters. I was able to log just shy of 1,000 qso's for 10 hrs of operations.
I used a 1/4 wave vertical tuned to resonance on 30M (with 60 radials). On 30M I ran 100W out - the pile up was that crazy.
On 30M (& 40M too) I found that I had high local QRN levels on the vertical - s6 to s7. On a whim I "auto-tuned" the doublet to 30M. The 30M received signals were down 1 s unit, but the QRN levels dropped to s2 to s3. This made working the weaker callers so much easier. The chatter on the DX node while was operating on 30M the guys were reporting that they thought I had a beam. This because I would forget to switch back to the vertical for transmit at times.  ;D
On 17M I ran with my KX3 and the doublet during the W1AW/7 op, I did run split freq ops to maintain control of the pile-up. The doublet performed very well and I was quit pleased.
This past winter DX season, I found myself drawn to 17M the most. I did get several of the DX-expeditions into the log using the KX3 and the doublet. I had difficulty with 10M and the MFJ tuner not wanting to load that band. No biggie, most of the time when 10M was open, I was at work anyways. So no worries.
Sorry for not doing a technical review, sometimes it is nice to share a "hamming it up" message. This summer I will putting up a 52ft tower with a 20 - 6M 2 element 6 band quad. The doublet will not be taken down - I like it that much!
73 es vy gud dx, Don KO7i



Don KO7i
Arlington, WA

QRP Rig: Elecraft KX3

Home Station Ant's:
Verticals 80 & 40M, with 36 radials.
Center Fed Dipole 34 ft long, 40 ft high, fed with ladder line and remote antenna tuner.