[TowerTalk] HY-GAIN BN86

[ersmar at verizon.net]

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 at charter.net>
Date: 2007/04/21 Sat AM 10:34:36 CDT
To: towertalk at 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 
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