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Old May 12th 06, 09:57 PM posted to rec.radio.amateur.antenna
Reg Edwards
 
Posts: n/a
Default 2 Meter Choke Baluns


"Darrell Bellerive" wrote in message
oups.com...
From what I have read there seem to be two common types of choke

baluns
employed at 146 MHz, the coiled coax balun and the W2DU type with
ferrite beads over the coax. Looks like other types of baluns such

as
the sleeve balun or a Guanella toroidal balun could also be used.

Other than the obvious restrictions imposed by physical mounting
arrangements, what are the advantages and disadvantages of each

type.

There seems to be considerable variation in the design of coiled

coax
baluns, with most designers advocating a few turns of coax with a
diameter of 3 to 8 inches. One designer was convinced that anything
over 3/4 of an inch would not be functional at VHF frequencies.

Others
maintain that the coil of coax should be wound on a core keeping the
turns aligned, while others simply coil the coax up and tape it
together. Some recommend one coax width of air between turns.

With regard to ferrite beads on the coax type of balun, how many
ferrite beads of what type are most effective? Some advocate that
another set of ferrite beads be placed at a point below the

feedpoint.

Seems there is lots of latitude in construction of these types of
baluns. Are they really this forgiving, or are there a lot of less

than
full effective balun designs?

I'm trying to decide what is the best option for me, and am confused

at
all the variations.

Darrell
VA7TO

=======================================

A choke balun made from RG-58 coax cable, centred on 145 MHz and
having a high impedance over the 2 meter band has the following
dimensions -

6 turns of RG-58
Length = 30 mm = 1.2"
Diameter = 37.5 mm = 1.5"

Measurements are between centers of turns.

Make it neatly.
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Reg, G4FGQ