Topband: Chokes - ferrite vs air

[Jay E Ostrem]

AA1K: 
> Without these chokes, all the feedlines going up the tower would
> effectively make it a grounded tower. With the chokes, it is like the
> feedlines aren't even there and works just like a series-fed tower should.

I had a similar experience on my series fed tower.  It was a 130ft tower
made of Rohn 25G.  The insulating section was 10ft up.  The tower was
inductive (too long) due to the leaky power line insulators,  and an 8
element log on top.  It resonated at 1400 kc.

I initially tried to "choke" the feedline to the log periodic with 8 large
ferrite cores (1.25" long X  1" diameter) with no result.

I then wrapped 100ft of RG-58 around a 5 gal pickle bucket, and that did the
trick.  I started taking wraps off in increments and found around 60 ft of
coax did the trick.

I then went back to the ferrite, realizing I needed more cores.  I put 36 of
them on the line, and they just started to show a positive effect.

The tower was very reactive on 160, if it was resonant, I would assume
fewer cores or less coax would be needed.

At the time I didn't want to go to the expense of extra line for coils,  so
I built a switch that opened all the lines across the insulating joint, when
I was on 160.

Jay W7CW in Wyoming





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