[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: R: QFH modification

>Hi Mak,SV1BSX and Dom,
>Wondering if has significant difference in the behavior of a QFH antenna
>if we replace the UT-141 section or the "hard line" by wich is made the
>half-turn bifilar loop changing it with a soft copper tube wich has inside
>a piece of coaxial cable having smaller diameter of the copper tube diameter
>it is necessary to understand how the infinite balun feed works as described
>by Walter Maxell W2DU in the ARRL Antenna Book 15 th Edition Chapter
>20 Page 20-5  "The Infinite or Inherent Balun"
>In operation, current flowing on the inner conductor of the first half
>bifilar loop made with coax emerges at the feed point to flow onto
>the second half of the bifilar loop wich is made of solid wire.
>For current flowing on the inside surface of the outer conductor of the
>coax, on its arrival at the end, the only path for current flow is around
>the end of the braid and than fold onto the outside of the outer conductor
>of the coax and such external feed line current is the desired antenna
>current so that the outside portion of coax extending from the feed point to
>the antipodal point became part of radiator.
>If we replace the UT-141 or the "hard line" using a piece of coaxial cable
>in to a soft copper tubing it works provided that the braid end of the
>coax cable is carefully soldered all around to the open end of the copper
>Fail to solder the end of the braid with the end of the copper tube the
>current will tend to flow over the outside surface of the braid and not
>over the outside surface of the tube as requested by it to work as a

Exactly what I did, Dom... I was very careful to read Maxwell's theory.
I soldered both ends very carefully to insure 360 degrees periphial 
electrical continuity as well as making the tube water proof..

UT-141 with it's insulation is of course has very good water tight 
integrity, and didn't want to upset that end of the equation...

I'm really "plumbing" along with most of this stuff, so very reluctant to 
take ANY departure....!!

All, please keep the info flowing...this is the prod that I can certainly use..

            73, Dave wb6llo@amsat.org
                    Disagree: I learn....

               Pulling for P3E... 
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org