Date: Fri, 21 May 2010 09:45:25 -0700
From: "Jim Brown" <jim@audiosystemsgroup.com>
Subject: Re: [TowerTalk] Baluns/tutorial/notes.
On Fri, 21 May 2010 08:06:59 -0700, Jim Thomson wrote:
>Do we really require 5 k choking Z ??
Considerable experience has shown that this is a good target for
noise pickup. In my analysis, I also showed that a very high value
has the additional benefit of minimizing dissipation. Since I first
published my recommendations about three years ago, I've received
MANY reports from guys who have built and installed chokes like this
and experienced considerable noise reduction. Many of them are
serious contesters like me, who spend entire weekends on the air
trying to pull weak signals out of the noise.
## Interesting. Since abt 1980.. I have been running all coax down the
Inside of the tower, since the tower's were wide enough to climb up
the inside, and it was easy to bring coax up. Dunno if that would help
the noise pick up issue..or not? With this new crank up, coax will
be on the outside. OK, if the ants are say down low to start with,
say 30'-50', why wouldn't any noise be directly induced/picked up by
the 'low' ants?
Last winter, I gave an in-person tutorial for several engineers from
the CIA. A few months ago, the lead engineer from that group sent me
a DOD engineering report from 1966 that assumed the 5K ohm value as a
target, came up with the same parallel equivalent circuit that I did,
and came up with a design with three chokes in series that provided
5K from 2 MHz to 30 MHz. The ancients have again stolen our
inventions.
## after parasitic arcing with too many turns of RG-400 coax on
torroids... I wondered if they could be fed nose to tail instead,
to increase the total choking effect. Each torroid could also be wound
slightly differently, and/or with different mix torroids, to create
a broadband [or at least broader] effect. Then I saw the german
kellerman baluns.. which use what appears to be RG-400/303... with
2-3 turns on a large ferrite bead.[1" x 1'].... and a lot of such beads,
strung nose to tail. I'm just re-inventing the wheel.
I did not conceive of 5K as the target -- W1HIS did, and published
about 2006 saying so. I read his paper and agreed that he was right.
After reading it, I added something like 3K to an antenna near my
house that already had a conventional 500 ohm choke, and was picking
up QRN from some noisy power supplies. It reduced the noise
significantly.
## this is amazing info. But the 3-5 k has to go at the feedpoint,
and not in the form of a line isolator at the entrance to the shack?
These line isolator's appear to be just a bead balun..but with coax
connector's on both ends. Put another way, is their any benefit to
installing a 5 K choke balun at the entrance to shack... [for noise
elimination] ? I think a line isolator would solve residual problems,
mainly from TX being induced into the feed line, if ant pointed at the
station. I have never used one...so don't know.
>Has anybody actually toggled between 2 x identical yagi's
Not an easy test setup. :)
### plenty of folks out there with stacks., multiple ants,
anything that has the DE close to the tower, to swap out a
balun, would be the easiest to do a A/B test.
>will they handle 2.5 to 3 kw...with high SWR ??? After line loss,
>I want to see at least 2250 w at the ant feed point.
I'm an honest and honorable ham who plays by the rules. I have zero
respect for those who don't. That said, the big coaxial chokes I've
described have considerable headroom for dissipation above 1.5kW ham
power limits.
## maybe the limit is 1.5 kw in the usa...but it's 2250 w pep...
after feedline loss... in Canada. 750w on cw / fm... and 800w
CXR on AM [4 kw pep with 125% pos mod] .. and 750w on 30m
band. There are several countries who have even higher limits.
If you want ther balun to be reliable.. and handle 1.5 kw.... then
build it to handle double that.
>A simple clamp on ammeter will tell you just abt all you want to
>know.
Nope. It tells you about that current AT THE POINT WHERE YOU INSERT
IT. Common mode current on the feedline varies with the position on
the line, just as with any other antenna. To get meaningful data, you
would need to insert it at the feedpoint of a wire dipole (because
that's where the noise is being coupled) that's 100 ft in the air,
and you would need a great pair of binoculars to read it. And, of
course, if the choke was working well, you would be at the bottom of
the meter scale.
## I'm referring to running it down the coax..from top to bottom
of the tower.
## I will try one of these 5K baluns this fall. I have enough spare vac
relays, I might be able to toggle between the outputs of 2 x baluns..
with just a pair of spdt vac relays.... and also use 2 coax feedlines. I would
like to be able to do a A/B test on it.
Tnx.... Jim VE7RF
73,
Jim Brown K9YC
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