I fully agree with Stuart. Curt must have made some strange experience to
cause him to feel that way.
Ladderline does not radiate like crazy - hardly at all - if the load at both
ends are symmetrical. Stuart's tip about twisting it is highly recommended.
I've used openwire for over 40 years and the ladderline since about 20 years
now. I have often had cases of it radiating. Specifically, nearly every
time I tried to feed it thru a balun in front of an asymmetrical matchbox.
I don't care which side of the matchbox you place the balun, it still did
not eliminate this radiation - especially when running a linear.
I have also had at a truly symmetrical matchbox (Annecke) for the past 25
years and each time I had the problem above, I solved it by using my
symmetrical matchbox instead of the jerry-rigged solution described above
(and still sold by many vendors as "a symmetrical solution"). Lesson
learned. There are no shortcuts in life and quality costs money.
In the meantime I have 4 symmetrical matchboxes with various power ratings
and I run legal power here and don't have any problems with feedline
radiation.
Coax radiates too if it has high SWR on it (everybody knows that and knows
how to fix it).
Open wire feedline radiates when either of its ends are not in balance (keep
it in balance and it won't radiate).
These are rules of thumb.
Of course there are rare exceptions to every rule, but the statement that
ladderline radiates like crazy is blatantly wrong!
Using ladderline or homebrew openwire is an excellent way to build a simple,
effective wire antenna which will operate all (or most) bands.
If anyone is interested in using openwire / ladderline feedline but wasn't
sure how to feed it, here is some useful information:
In the meantime there are good symmetrical matchboxes available for all
sorts of power level. The are at least 5 or 6 vendors offering excellent
products for a reasonable price. A recent ARRL (QST) article described some
of these, but only focused on the U.S. vendors (MFJ, Palstar). There are
alse several European vendors with great products too (e.g., U.K. Amp,
Hamware, Christian (DL3LAC), and DL1SWR). Just be sure the box you are
interested in is truly symmetrical. MFJ and Palstar both make good and bad
products advertised as suitable for symmetrical.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Curt
Sent: Friday, July 08, 2005 11:45 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] "Radiates like Crazy"???? No
I don't care if you do or don't...you're
wrong!!!!!!!!!!
--- Stuart Rohre <rohre@arlut.utexas.edu> wrote:
> I must respectfully disagree that ladder line
> "radiates like crazy".
>
> It is BALANCED line, that means if it is fed from a
> balanced source and goes
> to a balanced antenna, the currents are equal and
> opposite in each wire and
> their fields cancel within a few diameters of the
> line. See the theory of
> transmission lines in the ARRL Handbooks.
>
> It should cross conductors at right angles, and
> should be twisted every 18
> inches or so, to minimize effects from nearby
> conductors that could
> unbalance it.
>
> If you ever have ladder line "radiating" you are mis
> applying it in some way
> at one end or the other. Balanced antennas are
> center fed beams, dipoles,
> etc. with line brought off at 90 degrees to the
> antenna wires.
>
> Let's bury these old wive's tales about balanced
> parallel transmission
> lines.
>
> Stuart
> K5KVH
>
>
>
> _______________________________________________
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> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
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