Topband: Use of CAT 5 cable to feed a Beverage

[Herb Schoenbohm]

I have just been given a 1000' roll of shielded CAT 5 cable of seemingly 
high grade.  I would like to feed a far away start point to a 900 foot 
Beverage but not exactly sure on how this will work.  Do I tie all cross 
pairs together? I understand there will be a need to have a small toroid 
to match the Beverage itself and see the advisability of floating the 
shield there.   But do I ground the shield at the station end to try and 
create a Faraday shield to reduce common mode pick up or does this only 
work at AC and not at RF?


Just curious


Herb Schoenbohm, KV4FZ




On 8/13/2013 3:16 AM, Jim Brown wrote:
> On 8/12/2013 2:10 PM, JC N4IS wrote:
>> 50/75 BALUN
>
> Thanks for the detailed post, Carlos. BUT -- please let's use the 
> right words to describe things so that people understand what you're 
> describing and how it works. I strongly suspect that at least some of 
> those things you are calling a "balun" are really a simple transformer 
> -- that is, a primary and a secondary with magnetic coupling between 
> them, and probably on a ferrite or powdered iron core. If it's a 
> transformer, let's call it a transformer. Likewise, if we have a 
> common mode choke formed by winding a coil of the transmission line, 
> it is a common mode choke, not a "balun."  Using the word "balun" 
> confuses things, because that word is used to describe at least a 
> dozen very different things that I know of.
>
> When we use the word "balun," it's a magic box that few hams really 
> understand. When we use the right word, most hams have a chance of 
> understanding what it does in a circuit. :)
>
> Yes, there are arrays of common mode chokes that can be used to 
> transform impedance, and there are transmission line transformers of 
> various sorts that can do that as well.
>
> BTW -- your discussion of phasing between elements of an RX array 
> causes me to add an important post script to my advice that a perfect 
> match is not required. When ANY passive network is used to produce 
> phase shift, the source and termination impedances DO matter. The 
> tricky part, though, is knowing what the input Z of the RX is, and if 
> you're doing something like a phased array using phasing lines that 
> end at the RX input, it might be a good idea to actually measure input 
> Z and the antenna Zs with a VNA.
>
> 73, Jim K9YC
> _________________
> Topband Reflector