[TowerTalk] Doublet for 80/40M using ladder line

[Jack Brindle]

With a good ATU, an open-wire fed short dipole can perform quite well. There are many advantages over using coax - first the losses in the line will be much lower than with coax.
Noting that he wants to use a shortened dipole and not one cut for 80 meters, the antenna will not provide a good match on any of the bands. This means that the coax will also
not be matched and will provide a large amount of loss resulting in heating of the line. Open-wire will also not be matched, but it will also not suffer from dielectric heating the way
coax does. Ladder line will provide a bit more dielectric to be heated, but it will also be much better than coax. The low loss in the line means that the antenna will essentially be
transported to the tuner, where the match can be properly made to make the transmitter happy. In general, as N6BV has shown, the loss in coax really can’t be overstated. At
the same time, the loss in open-wire, while still significant, is no where near as high.

Now I will also add that I far prefer tank-circuit tuners over L or T style ATUs (with the necessary balun). However it is far more difficult to build an Auto-tuner in the form of
a tank circuit (but certainly not impossible). In using an L style ATU the losses from the ATU to the balun will also be significant, but not nearly as high as a lengthy run of coax
to the center feed.

The biggest thing I would suggest is to try both. Put one up and try it for a while (months), keeping very good records of stations worked and heard, or even better using the
RBN to track your signal, then take it down and try the other. Ham radio has traditionally been a great place for experimentation, and this is a perfect place to do some.
Along the way, you will learn a lot about both types of antennas.

73,

Jack, W6FB


> On Sep 29, 2017, at 11:10 AM, Bert Almemo <balmemo at sympatico.ca> wrote:
> 
> Hi guys,
> 
> A friend of mine told me the other day
> he's putting up a doublet for 80/40M
> feeding it with a ladder line. He also
> wants to use the doublet as a T-antenna
> on 160.
> The doublet will be put up in an Inv.-V
> configuration. He has a small city lot
> and is exposed to the usual interference
> sources you'll find in an urban area.
> 
> Considering the latter, how about making
> a fan dipole for 80/40M fed with coax
> and using that for a T-antenna on 160 -
> would that work?
> 
> 73 Bert, VE3NR
> 
> 
> 
> 
> 
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