Jim,
> OK, I just took a look at the manual for the BN-86. It appears to be
> a simple common mode choke. My guess is that it fails because the
> common mode impedance is not sufficiently high over the range of
> operating frequencies in use. Not unusual.
The BN-86 is a standard voltage balun; trifilar winding on a
ferrite rod. Common failure mode is due to excessive voltage
and arc over at high SWR. If I recall correctly the worst case
is using a tuner on phone (high end of the band) with an antenna
tuned for CW.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Brown
> Sent: Tuesday, April 08, 2008 2:45 PM
> To: Tower Talk List
> Subject: Re: [TowerTalk] Any BN-86 Balun Replacement Suggestions?
>
>
> OK, I just took a look at the manual for the BN-86. It appears to be
> a simple common mode choke. My guess is that it fails because the
> common mode impedance is not sufficiently high over the range of
> operating frequencies in use. Not unusual.
>
> When I've attempted to stress a choke by putting it at a very high
> voltage point and shove a lot of power to it, it will typically fail
> by melting the coax. If the heat source (the transmitter power) is
> removed soon enough, the melting may not do permanent damage.
>
> I suggest that you build one of the coaxial ferrite chokes listed in
> the "cookbook" section of my tutorial. If you run the antenna only
> between 14 and 29 MHz, four widely spaced turns through 5 #31 or #43
> 2.4 inch o.d. toroids would be a good design. That choke will start
> running out of gas below 20M. If you run the antenna down to 40M,
> you'll want more impedance. Simply add a second choke in series of 5
> turns on 5 cores to add some impedance on 40M.
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> What you'll observe when you're done is that the antenna hears a lot
> less noise, because it is more effectively decoupled from the
> feedline.
>
> 73,
>
> Jim K9YC
>
>
>
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