On Tue, 30 Aug 2011 09:03:33 +0200, Helmut Wabnig [email protected] ---
-.dotat wrote:

I wonder how important matching is for a pure
direction finding antenna, methinks rather it should not.

You are right, not at all.

Only the coax cable currents are not considered
in the simulator diagrams, there might be an influence.
Therefore matching is important :-)

You should have stopped writing at the first thought. CHOKING is
supremely important, and is a benefit found in good matching design.
Choking can be achieved without matching, however. And choking will
be needed at least at the feed point, and again a quarterwave down the
line.

73's
Richard Clark, KB7QHC

On Aug 30, 11:17*am, Richard Clark wrote that :
On Tue, 30 Aug 2011 09:03:33 +0200, Helmut Wabnig [email protected] --- wrote:
I wonder how important matching is for a pure
direction finding antenna, methinks rather it should not.

You are right, not at all. ...
73's Richard Clark, KB7QHC

Matching, perhaps not so much, HOWEVER, the antenna pattern/phase/
characteristics are *THE* most important aspect of a DF antenna/
system. The DF antenna characteristics must be as close to ideal as
possible. I've been involved in DF since my stint in the Navy and they
went to great lengths to get the antenna sites ideal, for that reason.
Also...

But why I re-posted.... Thanks to Richard's post...
I forgot to mention a bead choke that I used with success on one of
these beams.
They also significantly improved the performance of a four dipole
Doppler type DF antenna
that one of the locals had and knew it was not right, but couldn't
decide what to do to fix it..

We used two cores on the coax to get well above the coax 50 ohms.

The following cores will fit inside the PVC pipe and around RG-58 size
coax.

Mouser: 623-2643540002
Fair-Rite (Mfr) # 2643540002
O.D. 0.562"
I.D. 0.25"
Len. 1.125
250 ohms @ 100MHz. [specs. I did not measure them as I recall]
171 ohms @ 25 MHz.

Finally,

Helmut,
You have quite a bit of reading there with that sliding element.
Can't wait to dig into it.

73, Steve, K9DCI Haven't read this group in ages.