For many years I tried with little success using random dimension dipoles fed with balanced – ladder line or twin lead as described in in antenna books as the ultimate solution for a poor ham wanting to work multiple bands with one antenna. From what was said one essentially would put up as long a wire as your space allows for feeding it with whatever length of balanced line needed to connect to the tuner in the shack.
One day I was fortunate enough to find W5DXP’s website that gives a detailed explanation of using determined feed line lengths to make the match from the rig to the antenna easily done without a tuner by varying the lengths of the line for the band that one wants to work – No Tuner All Band HF dipole. I also learned that the length of the doublet plays a factor in getting an easy to obtain match using an outboard antenna tuner, since doublet length isn’t that critical when using balanced line so the length can be adjusted to make an easier to use system. Making the doublet as long as possible is not always best and an approximate 3/8 wavelength on the lowest frequency of operation is as short as one wants to cut the dipole – essentially 100 ft for 80 meter and above usage and a minimum of 50 ft for 40 – 10 meter operation. BTW A G5RV or 102 ft dipole works pretty well when properly used. That got me thinking on how to apply that theory to my limited space QTH to have one wire for at least 80 – 30 meters.
I have had optimized G5RV style doublets before but now I wanted open wire feed line for two reasons – 1) it is much less affected by moisture and rain than it’s more solid cousin “window line” and 2) open wire has less line loss due to a poor mismatch than window line does. A G5RV dipole in it’s typical installation is a poor SWR match on 30 meters making it lossy.
So I ordered a 100 ft dipole with a 50 ft feed line from True Ladder Line and Wire Antennas because that is all that there is room for on our city lot. Questions to their customer service were quickly and accurately answered as was my request for a doublet of a different length than the ones listed on the company website, order to shipping time was outstanding.
Since having put up my last doublet, the optimized G5RV I acquired a Heathkit SA-2060 antenna tuner that is well designed with robust components and is known for easily handling a wide range of antenna loads. With that in mind after hanging the new doublet in it’s new home I ran the open (ladder line) wire to in a straight line to my Balun Design 1:1 remote balun that connects to the tuner via 10 ft LMR 400 coax – about 25 foot run of the open wire.
Loading the doublet on the low end of 80 meters was acceptable, however on 40 meters only a mediocre match could be had that was very sensitive as in don’t sneeze in the direction of the tuner. So much for this situation as I want an antenna for 80 – 40 -30 especially 40 meters where I spend a lot of time so I decided to add additional open wire to the approximate 25 ft run. After putting pencil to paper I spliced in a 9 ft length of line then found a way to route the excess line which in this particular case was a bit harder to use than window line or twin lead because it can not make certain bends due to it being open wire. After some trimming of the transmission line length I found a “sweet spot” where 80 – 20 meters was easy to get a match with approximately 32 ft of the ladder line.
The doublet isn’t as good as a 40 meter 3 element Yagi at 70, then again no everyone is able or willing to have antenna and tower of that magnitude in their yard. It does make contacts on multiple bands with a minimal effort. The short length 10 ft of low loss LMR400 coax and open wire make the losses on 30 meters acceptable when one considers the ability to work multiple bands on one wire when space is limited.
I give True Ladder Line a 10 for a quality product and would definitely buy another one. The one thing I might would do differently on the feed line install would be were a certain length of line needed that entailed bends or turns would be to splice in a section of 450 ohm ladder line because it can be manipulated in tight spots easier. Doing this might create a small impedance “:bump” but it would be negligible so long as the line balance were maintained. That is not a True Ladder Line quality issue but one of making the most of the space available.