"Jeff Liebermann" wrote in message
news
On Fri, 13 Nov 2009 07:28:34 -0600, "amdx" wrote:

My original thread seems to have died, still wondering how the folded loop
is matched to 50 ohms. (probably isn't? cheap, but works?)
I've added a dimensional drawing and some more pics.
If more info is needed let me know.


I need an overall length, measured from the CENTER of the driven
element (the plastic screw hole) to the CENTER of the last director.
That's because a tiny error in the spacing between elements at 1.060"
(2.69cm) grows rather rapidly when multiplied by 14 elements.

The CENTER of the driven element (the plastic screw hole) to the
CENTER of the last director is 36.7cm (14-7/16")


Please check the length of the first and 2nd directors. I don't
believe MFJ would make them the same length as the other directors.

ALL directors or the same length (within .003")
They are 46.6mm in length.

Also, measure the coax balun cable dimensions. Mostly, I'm interested
in the:

1. Shield to shield length.

54.2mm (2.134")

2. Center pin to start of folded dipole length. (i.e. exposed center wire
length).

61.75mm (2.431)

3. OD of center conductor wire.

0.94mm (0.037")

4. ID of shield.

3.3mm (.130)


5. A good guess as to the type of dielectric (foam, solid, or PTFE).

My guess is solid poyethylene, if you have a test other than poking it
with a pin to get feel of it, which I did.

6. Any markings that might identify the coax.

No help there.


That thing doesn't look anything like a
4:1 balun (unless there's something we missed under all that shrink tube).

Looks like 4 toroids that slide over the coax, you can see the outline of
the edges of each toroid.

Mike