My spell checker sold me on the use of Feebleness instead of Feed Lines.
Please excuse my feebleness.
Jay Terleski wrote:
> Hi, you have rediscovered an old trick.
> If you look at ON4UN's book "Low-Band Dxing" you will see some arrays of
> verticals using an element fed with parallel coaxial feebleness. To
> match, and also create the magnitude of current needed for the array.
> The triangle array is one such example. Of course in reality when you
> try to build this array it creates a complex relay matrix, since we wish
> to "steer" the array, but it works. Three towers in line is another
> There are other ways to feed this type of array using single coaxial
> feed lines too.
> But the point is that it is a common practice with phased arrays to use
> parallel coaxial cables.
> Reducing loss in the cable is not usually the concern, but I guess a
> little less IR drop in an antenna feed line that has say 6 ohms of
> impedance would be good. Say a mobile whip used on 160 meters. Here an
> ohm of IR RF loss would be worth the effort to reduce.
> Or guys on the 1750 meter band. These antennas probably can have a
> fraction of an ohm of radiation impedance.
> Jay, WX0B
> Billy Ward wrote:
> > Greetings Group,
> > I would like to have this groups input on something that I have been working
> > on today.
> > Today was not the first time that I've toyed with this idea but I performed
> > the experiments again that I have done a few times with the same results as
> > before. There was a question posted on another forum about some ideas for
> > low-loss coaxial cable and I offered some information as a POSSIBLE
> > solution.
> > This is it:
> > The Idea was to use two 72-Ohm Belden cables in parallel to obtain 36-Ohms
> > to match a 32-Ohm 1/4 wave ground-plane antenna. In doing this, the I
> > squared R losses would also be 1/2 unless there is something that I am not
> > seeing. Since the tests show that it works, if I qualified the tests
> > properly, I would have no doubts except that I have been a Ham and a RF
> > engineer for almost 40 years and have never heard of running two cables in
> > parallel.
> > I used an MFJ-259-B and measured the Characteristic Impedance of three
> > lengths of Belden 72 ohm cable.
> > One of them was Three Feet, one was 12 Feet and the other one was 18 Feet.
> > They measured 71.2-, 71.3 -and 71.2-Ohms. I then measured the velocity
> > factor using the "Distance to Fault Mode" to determine the electrical length
> > of the cable in inches and and then divided that figure by the actual length
> > in inches.
> > The Velocity Factor measured at .80, .80 and .79 blinking to .80
> > After making up 3 parallel cables by fitting both cables into a single
> > Pl-259 at each end just as you would to make a co-phasing cable for CB
> > radios, I made the measurements again. The impedances were almost exactly
> > what I expected at 35.7, 35,7 and 35.4.
> > The Velocity Factors were a little further from the single cable figures
> > than were the impedances, measuring at 82.3, 82,4 and 82.0. I figured that
> > this was because the losses from the insulation was divided among the two
> > cables causing the Velocity to be just a little faster than one cable.
> > I am familiar with Conjugate Matching and realize that there is really no
> > practical reason for using this cable arrangement in order to radiate 100%
> > of the power delivered by the transmitter less the power dissipated by the
> > cable losses.. Also the amount of power saved by halving the losses of
> > cable that is already low enough is not worth the time it takes and the
> > extra cost of the cable to bother with it. However, to stir up a discussion
> > on the other forum, I offered this idea. So please NO preaching about why I
> > do not need to bother with this idea. It is just a fun thing for
> > discussion.
> > In your opinions, are there any flaws in this being a viable feed line.
> > Billy
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> Jay Terleski
> WX0B - Array Solutions
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