[TowerTalk] Any BN-86 Balun Replacement Suggestions?

[Joe Subich, W4TV]

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 at contesting.com 
> [mailto:towertalk-bounces at 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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