You may not be the first Billy. This idea rings a bell. I believe VE2CV
(Jack Belrose) wrote an article about this very thing in QST just a few
years ago. I'll have to track down the article to be sure we're talking
about the same thing.
Phil
At 05:03 AM 12/17/2000 -0000, you wrote:
>
>Greetings Group,
>
>I would like to have this group's 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
>
>
>
>
>_________________________________________________________________
>Get your FREE download of MSN Explorer at http://explorer.msn.com
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
>
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|