Tom Rauch wrote:
>
To: <towertalk@contesting.com>
> > Date: Mon, 15 Jun 1998 13:34:19 -0400
>
> Hi Guy,
>
> > I have the same MFJ unit. I got one of those cheap bead choke balun kits
> > from The Wireman, and always have it on the MFJ analyzer. All the wierd
> > problems disappeared. Guess it was unbalance: My hand attached to the
> > case, therefore one side of the feedline and not the other. I also have
> > the other analyzer (RF-1? It's at home...) and don't use it without the
> > bead choke either.
>
> What antenna type were you measuring? If you add the beads and it
> changes something, you have a balance problem somewhere.
>
> If adding the beads fixes the analyzer, it indicates a need to fix
> things elsewhere in the system.
>
Depending on *exactly* what you mean by the above, not always.
Consider a system, Trancievo Deluxe, choke isolator, SuperSplat linear,
choke isolator, el buncho coax, random length out to tower, a break for
ManiFaze lightning widget, up tower to 1:1 balun, to Smokem multiband
yagi. Not a bad setup. Would even get LXC stamp of approval.
One day, swr in shack goes way up. First impulse is to go out to tower
base, disconnect tower coax from Manifaze and attach Lilbox Z-analyzer.
Lilbox is in plastic case, no shielding at all. Lilbox sees two things
in parallel: 1) screwed up impedance from Smokem due to fried impaled
buzzard on the driven element shorting to 1st 10 meter director, and the
impedance of the shield of the 5/4 physical wavelength coax from lilbox
up to the balun.
Operator-man doesn't notice the impaled buzzard, because he has buzzards
on antenna all the time, the paralleled impedances just happen to equal
50 ohms. He proceeds to tear up feedline back to the shack, jumpers in
the shack, etc, with no improvement in results, and growing frustration.
A few days later, his wife points out that one of the buzzards is stuck
on his antenna, hasn't moved in a week, and is starting to smell.
So, to remove the oderiferous obtrusion, Operator-man climbs the tower
and removes the buzzard. Now he goes back to the coax at base of the
tower, hooks up Lilbox, and reads 2:1 because he's now measuring a
correct Smokem in parallel with the coax shield up to the balun.
In utter frustration, Operator-man takes down the antenna, pruning
lengths on the Smokem, reinstalling, taking down, etc, until he gets 1:1
on Lilbox at the bottom of the tower. He goes back in the shack, fires
up Trancievo, and gets 3:1. Thereupon, he stomps out the Lilbox in rage,
pulls down the Smokem, and posts a tirade on Towertalk about how bad the
Smokem is. He takes out a 2nd mortgage on the house to purchase and
professionally install an inferior Spitfire multiband, which now
measures 1.3:1 in the shack because the coax shield is taken out of the
picture by the balun at the antenna, the ground at the Manifaze and the
choke isolator in the shack.
***
The coax running up to the balun from the bottom of the tower isn't what
I, personally, would consider "something to be fixed in the system".
Much easier to put a Wireman 833 or equivalent bead choke on the RF1 or
MFJ.
73, y'all
Guy.
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