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[TowerTalk] W1JR Balun: choking impedance and power dissipation

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Subject: [TowerTalk] W1JR Balun: choking impedance and power dissipation
From: (Joe Reisert)
Date: Sat Jul 19 10:20:57 2003
Hi Tony,

You can surely do what you suggest. The 12 turn one on a 2.4" OD 61 
material toroid is very good from 40-10 (and even to 80 meters) meters with 
high impedance and no resonances.

To get to 160 meters with 61 material may pose a problem since more turns 
of coax (14-15 seems to be optimum maximum) may not fit easily on the 2.4" 
OD core. However, I did make a 2.4" OD 13 turn RG302 teflon coax W1JR type 
balun using 43 material and it was GREAT from 1-30 MHz with no resonances. 
Impedance at 160 meters was over 900 Ohms and typically 2,000 Ohms  over 
the range from 80-10 Meters. What I don't know is if the 43 material can 
withstand high power with a mismatch.


Joe, W1JR

At 02:09 PM 7/18/2003 -0400, N2TK, Tony wrote:
>Would there be a recommendation to have one design for the high bands
>(40-160M) and one for the high bands (10-30M)? If so, how many turns through
>the core would be recommended for each?
>N2TK, Tony
>-----Original Message-----
>[]On Behalf Of Chuck Counselman
>Sent: Friday, July 18, 2003 13:11
>Subject: [TowerTalk] W1JR Balun: choking impedance and power dissipation
>At 10:38 AM -0400 7/18/03, Joe Reisert W1JR wrote:
> >The "W1JR Balun" uses a 2.4" OD ferrite core. The winding consists
> >of 12 turns of RG141 or RG303 (the later recommended) teflon coax in
> >a "contra-wound" fashion....  The core used is the standard 2.4" OD
> >called the T240 by Amidon and others. The material used is Fair-Rite
> >type 61 (Indiana General Q-1) which has a initial permeability of
> >125.... If you use 12 turns, the impedance will be greater than 500
> >Ohms at 80 meters...and typically much greater than 1,000 Ohms from
> >7-30 MHz with no resonances.
> which I replied, "I'll measure one and report back."
>I just wound a "W1JR Balun" as specified, using an FT-240-61 toroid
>and RG-303; then I measured its common-mode impedance (between the
>ends of the coax shield).  The core that I used was the one that I
>had left on the shelf, out of a lot of ten bought earlier this year,
>which had the least permeability of the lot (which is why it was
>left).  Therefore I expected the impedance of this choke to be
>somewhat less than Joe had quoted at 3.5 MHz, and it is; but there's
>nothing to get upset about.  My measurement results:
>Freq.| |Z|  | Angle |
>(MHz)|(ohms)| (deg) |
>   3.5 | 408  |   90  |
>   7.0 | >1k  |       |
>14.0 | >1k  |       |if the
>21.0 | >1k  |       |
>28.0 | >1k  |       |
>30.0 | >1k  |       |
>33.3 | 610  |   29  |
>Basically, I confirm what Joe has written about his balun.  It _is_
>very good.  Like Joe, I have never seen a commercial balun so good.
>I have only one, _minor_, reservation about this balun, relating to
>its ability to handle high power with high SWR.  According to the
>back-of-the-envelope calculation that I just did (and which I invite
>anyone to check), nearly 10 W will be dissipated in this balun
>(mostly in the center conductor of the RG-303) if 1500 W is
>transmitted through it at a frequency of 28 MHz, and if the SWR in
>the coax is equal to one.  This (10 W) dissipation should do no harm
>to the balun, because the Teflon dielectric of the coax should take
>the heat, unless you do something foolish like potting the balun in
>My minor concern is that the dissipation _could_ be dangerous if the
>SWR were _high_.  If the SWR were equal to, say, 9, then for the same
>net (i.e., forward minus reverse) power transmitted, the current in
>the coax could be tripled and the power dissipated could be greater
>by a factor of nine.  Dissipating 90 W in such a small volume could
>cause trouble.
>All things considered, however, Joe's design has to be considered
>_excellent_.  Thanks, Joe, for sharing it with us.
>73 de Chuck, W1HIS
>73 -Chuck, W1HIS
>See:  for "Self Supporting Towers", "Wireless
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>questions and ask for Sherman, W2FLA.
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>See:  for "Self Supporting Towers", "Wireless 
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
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