[TenTec] 450 Ohm feedline

[NJ0IP]

The balun Bob has describes is super but huge.
It is described in detail ub Bill Orr's (W6SAI) BEAM ANTENNA HANDBOOK in the
chapter on Matching Devices.

I have always used the rule of thumb to use ballans at 1/10 of their
manufacturer's rated power level.  Using them at 1/5 has occasionally burned
several of them out.  However I usually have used a 4:1 balun so maybe Bob
has a good point here.

The very best place to put the balun is on the transmitter (50 ohm) side of
the matchbox, but then you have to "float" the entire matchbox above ground.
However this extra effort enables the balun to see its design impedance on
both its input and output side and you don't get any unballances due to high
SWR on it.

Someone spoke about a new Palostar coupler with "Link" coupling.  I didn't
know any of them had that.  I think they all have roller inductors and use
the trick of floating the matchbox to a balun on the TX side.  Can anyone
confirm I'm right or if I'm wrong, then update me please?

73
Rick

-----Original Message-----
From: tentec-bounces at contesting.com
[mailto:tentec-bounces at contesting.com]On Behalf Of Robert & Linda McGraw
K4TAX
Sent: Thursday, April 15, 2004 6:57 PM
To: tentec at contesting.com
Subject: Re: [TenTec] 450 Ohm feedline


Regarding twisting the feed-line, why do you suppose the phone company
called it "a twisted pair"?  Answer: because that what it was and it was
used to maintain symmetry and thus reduce induced voltage from overhead
power lines.  Same applies here.

As to tuners, the general run of tuners, your choice of brand, used with an
adequate external current balun of 1:1 characteristic will work quite well.
I know there are those that poo poo baluns, however I have found that most
internal baluns being 4:1 devices do get strange in terms of balance with
highly reactive loads.  On the other hand, 1:1 baluns rated at high power
seem to work well on HF in most all reactive configurations.  I suggest
using a minimum 5KW rated current balun for those that run "legal limit".
If you run the "DX legal limit" then perhaps one should consider a 10KW
balun.

And the best balun I've tested is a coil of coax on a form.  I use some 26
ft of RG-213 wound snug on the outside of a piece of 4" PVC.  I space the
turns with 1/4" nylon sash cord.  It handles the power and maintains balance
to 30 MHz and works well down to 1.8 MHz.  Cheap but ugly.

73
Bob, K4TAX

----- Original Message -----
From: <ac5e at comcast.net>
To: <tentec at contesting.com>
Sent: Thursday, April 15, 2004 2:52 PM
Subject: Re: [TenTec] 450 Ohm feedline


>
> Well, you learn something every day. But I 'spect my first Elmer, Old
Hardman, would have a good belly laugh about twisting the line to keep it
balanced. Back in '47 we were told that the two halves of a doublet antenna
could not be exactly identical in length and siting so doublets were
inherently unbalanced. And of course, since the load must be unbalanced the
transmission must also be unbalanced.
>
> According to then established doctrine, open wire line, and later TV
twinlead, was to be twisted to reduce automobile ignition noise and other
impulse noise pickup. Radio Craft had a big illustrated writeup showing
Kukla, Fran, and Ollie eaten up with ignition noise that went away when the
twinlead was twisted at a one turn in three feet rate.
>
> Of ocurse, at that time the closest TV station was in Chicago so that
didn't make much of an impression on us. Later, when the idiot boxes became
common I found twisting the line sometimes made a difference - but not when
the source of the noise was close to the transmission line.
>
> 73  Pete Allen  AC5E
> --
> Never squat with your spurs on
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
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>


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