Re: OT; Feedline question

Posted by Matt Zilmer-3 on Apr 15, 2017; 5:16pm
URL: http://elecraft.85.s1.nabble.com/OT-Feedline-question-tp7629317p7629318.html

This is an amateur topic, so there's no reason to take it offline, imho.

If you run the impedance vs spacing calculations, you'll see the spacing
doesn't make a whale of a lot of difference.  I don't have the numbers
here, but I switched from 1/2 of a BIC pen  body (hole centers about 2"
apart) to some ceramic spacers another ham gave me a box full of.  The
new spacers had centers about 3.2" apart.  I had to re-tune the ATU on
most bands, but everything continued to work fine.  From (a tired old)
memory, the impedance varied from about 450 ohms to something like 600
ohms, but let someone on a computer run the calcs for this.  It just
didn't make enough difference to worry about, but did change the ladder
feed's impedance.

This antenna is a doublet about 180' long at 45 feet height, fed with
the ladder line (61' of it, from memory).  The ladder line terminates
into a 1:1 balun (Elecraft BL2) and the last 20 feet is LMR400 low-loss
coax back to the station's antenna switch.  It continues to work just as
well as with the earlier ladder spacers.

73,

matt W6NIA


On 04/15/2017 09:39 AM, Richard Fjeld wrote:

> Forgive me for the OT, but there are many antenna people here above my
> pay-grade.
>
> I need to replace the spacers on my ladder line.  If I deviate from the
> standard spacer length for impedance
> (separation between conductors), are there problems I'm not thinking
> of?  I use a quality manual tuner, and
> an 80 meter delta loop.
>
> Perhaps it would be best to reply off line for this.  Thank you in advance.
>
> Dick, n0ce
>

--
"Always store beer in a dark place." -- R. Heinlein

Matt Zilmer, W6NIA
[Voignier]

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