Noel:
When I installed my HF Yagi in 2001 I followed the advice on the URL
below. But after I had wound the solenoid for 20-10M use, I used my MFJ-259
analyzer to measure the impedance of the balun's shield.
After I had wound the balun and temporarily taped the windings in place, I
removed it from the five-inch diameter paintcan form (no PVC of that size
available.) I connected my analyzer's leads to opposite ends OF THE BALUN
SHIELD, essentially ignoring the center conductor. I ran the analyzer through
the Yagi's frequency range, from 14 - 29 MHz, and recorded the impedance I saw.
My objective was to show a total impedance of 5-10X the nominal fifty Ohm
impedance of the RG-213 coax at the highest freq.
IIRC, six turns of coax showed an impedance less than 250 Ohms at 29 MHz.
I settled on five turns for a total impedance of about 300 Ohms at 29 MHz.
(The lower freqs showed greater impedance at all windings, as I had expected.)
Winding twelve turns for use at, I assume, 20-10M would give too low a
choking impedance; too much turn-to-turn capacitance would short out the
choking effect of the shield. As the URL states, that number of turns would be
more appropriate for use at lowband freqs such as 40 and 80M.
One last thing: Don't wind your solenoid too tightly, especially if
you're planning on running QRO. The heat will soften the center insulator a
bit and the tightly-wound coil's center conductor may migrate to the outside of
the windings and short to the shield.
73 de
Gene Smar AD3F
From: K4SAV <RadioIR@charter.net>
Date: 2007/04/21 Sat AM 10:34:36 CDT
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HY-GAIN BN86
Read this.
http://www.k1ttt.net/technote/airbalun.html
VE2RYY wrote:
>I want to replace a BN86 by choke.
>Hy-Gain says 12 turns or RG13/U coax, 6" diameter.
>I was told that 12 turns is too much.
>Cushcraft says.....8 turns on 6" diameter...
>What is the best one???
>Thanks
>NOEL
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|