[Antennas] Twin lead 450 Ohm
Chris BONDE
[email protected]
Wed, 11 Dec 2002 11:02:31 -0800
I donot know too much about transmission lines, I had started studying such
but a health problem came along. (So much for an intro)
One of the things that twiged my attention was the use of two parallel coax
lines as twin lead. The centres were used as the two twin lead lines, the
braid was joined at either end and grounded. The formula for calculating
the resultant characteristic impedance was not that difficult. Some people
have used short runs 10ft or so from the outside of the shack to the tuner
(of two coax lines) joined directly to the twin lead. The physical
placement of the two coax lines doesnot seem that onerous. So I think
that it should be looked at.
Any comments from those who have used and know?
Second point seems to me is that, yes, anything near the twin lead will set
up a disconuity hence a reflection hence changes. However, reading what
some pople have done, eg run the line over coax, over pipe, held down by a
tool box, it seems as if as long as the disconuity is equal on both sides
the reflection doesnot upset the ham stuff that much, ei can tune it out
and the conjugate match is great.
A minor point: donot the papers say that as long as the probable
interfering objects is 2 to 3 time the spacing between the wires away from
the centre of the wires there is little interference?
Again any comments?
Chris opr VE7HCB
At 09:22 AM 2002-12-11 -0500, Pastor-kc1di wrote:
>
>Many years ago In my novice days...
>A friend and I shared an antenna, 40 Meter dipole fed with 450 ohm open wire
>Line.. we buried my line underground in 8" sewer pipe.. PVC Green Stuff that
>seals at each joint.. the hard part was to pull the open wire.. (it was real
>open wire not ladder line) and keep it in the center of the pipe.. but as I
>remember it worked quite well. How ever I must emphasize that I had nothing
>else to compare it to at the time.. It got me on the air and that's all I
>cared about.. 73 Dave Kc1di P.S. Been thinking of doing something simlar
>here too.
>
>
>
>-------Original Message-------
>
>From: Jim Sutton
>Date: Wednesday, December 11, 2002 9:03:48 AM
>To: Mike J Maloney; [email protected]; van lincoln wd8aam
>Cc: [email protected]
>Subject: Re: [Antennas] Twin lead 450 Ohm
>
>In reply to ladder line in a pvc pipe - I ran my line in a 2 inch pvc pipe
>about 50 feet in my basement - through the wall of the house and then about
>25 feet underground to a center support for a triangular antenna. The
>horizontal portion was about 8 feet off the ground and the top point about
>25 feet in the air. I loaded the horizontal portion a bit and was able to
>operate over the top portion of 80 meters and on up in frequency.
>
>How much loss did I have -- don't know but all worked fine.
>
>73/Jim/AC4CZ
>----- Original Message -----
>From: "van lincoln wd8aam" <[email protected]>
>To: "Mike J Maloney" <[email protected]>; <[email protected]>
>Cc: <[email protected]>
>Sent: Wednesday, December 11, 2002 1:49 AM
>Subject: Re: [Antennas] Twin lead 450 Ohm
>
>
> > I have run 1.5" spacing ladder line thru my basement cinderblock
> > wall inside 2" pvc pipe, a couple of wood slats kept the ladder line
> > centered, and I used paper towels to stuff the ends up, and it
> > worked fine.
> >
> > wd8aam
> >
> > At 09:05 PM 12/10/2002 -0600, Mike J Maloney wrote:
> > >A very good question, one which I would bet very darn few(if any) have
> > >actually tested. This came up some months ago in a side thread about
> > >running ladder line into the shack. Most said any buried ladder line
> > >would have great loss. I dont see really why it should unless the pipe
> > >should become full of water which could be quite likely if care was not
> > >taken to prevent it. It would make for a good experiment, but before I
> > >went to 10 inch PVC with the line centered, I would try 2 inch centered
> > >and non-centered and work up to 4 and 6 inch to see if any detectable
> > >difference between this and loss in air. Even in 2 inch PVC it would
> > >seem to me that most of the dielectric between and surrounding the
> > >conductors would still be air and plastic? If the dielectric of the
> > >buried line in PVC is changed, it should be quickly detectable as a
> > >change in the electrical length at a given frequency as compared to being
> > >in open air. This is my speculation on the subject. It would be my
> > >thought that the most difficult part of making this practical would be
> > >keeping the inside of the PVC full of air or even better DRY air. What
> > >lower loss coaxial line is there than one with dry gas such as nitrogen
> > >under positive pressure being most of the dielectric? I cant see why
> > >coax of this type would be much different in attenuation or losses than
> > >that of open wire line, perhaps even better?
> > >73, Mike ac5p
> > >
> > >On Tue, 10 Dec 2002 07:15:38 -0800 (PST) Honest Charlie's Used Cars
> > ><[email protected]> writes:
> > >> Opinions Please...If 450 later line was suspended in
> > >> the center of a ten" PVC pipe and buried would it have
> > >> the properties of one suspended in Air?
> > >>
> > >> =====
> > >>
> > >> When I was a kid I was so naive, I would go
> > >> behind the barn and do nothing.
> > >>
> > >>
> > >>
> > >>
> > >> Twas a woman who drove me to drink, and I
> > >> never had the courtesy to thank her for it.
> > >> W. C. Fields ( 1880 - 1946 )
> > >>
> > >>
> > >> __________________________________________________
> > >> Do you Yahoo!?
> > >> Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
> > >> http://mailplus.yahoo.com
> > >> - - -
> > >>
> > >> Your moderator for this list is:
> > >> Larry Wilson KE1HZ [email protected]
> > >> _______________________________________________
> > >> Antennas mailing list
> > >> [email protected]
> > >> http://mailman.qth.net/mailman/listinfo/antennas
> > >>
> > >
> > >- - -
> > >
> > >Your moderator for this list is:
> > >Larry Wilson KE1HZ [email protected]
> > >_______________________________________________
> > >Antennas mailing list
> > >[email protected]
> > >http://mailman.qth.net/mailman/listinfo/antennas
> > >
> > - - -
> >
> > Your moderator for this list is:
> > Larry Wilson KE1HZ [email protected]
> > _______________________________________________
> > Antennas mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/antennas
>
>- - -
>
>Your moderator for this list is:
>Larry Wilson KE1HZ [email protected]
>_______________________________________________
>Antennas mailing list
>[email protected]
>http://mailman.qth.net/mailman/listinfo/antennas
>
>.
>- - -
>
>Your moderator for this list is:
>Larry Wilson KE1HZ [email protected]
>_______________________________________________
>Antennas mailing list
>[email protected]
>http://mailman.qth.net/mailman/listinfo/antennas
--- StripMime Report -- processed MIME parts ---
multipart/alternative
text/plain (text body -- kept)
text/html
The reason this message is shown is because the post was in HTML
or had an attachment. Attachments are not allowed.
Please post in Plain-Text only.---