On 12/30/2011 12:28 PM, Jim Brown wrote:
> This doesn't matter much on TX, but it can on RX -- you may hear more
> noise or QRM that the Yagi rejects but your feedline picks up. And
> THAT'S a big part of why a common mode choke with greater choking
> impedance is a good thing.
Thanks for the informative reply. I have an M2 mono band Yagi and I'm
using the 1:1 balun that M2 supplied with the antenna. I'm told there
are better baluns available and was wondering if you could recommend one
that has greater isolation capabilities -- or at least one that's known
to work well.
> On 12/30/2011 6:44 AM, Tony wrote:
>> Would there be any noticeable pattern changes while receiving on a Yagi
>> antenna i.e., reduced f/b f/s if it's balun became faulty?
> It depends on what you mean by noticeable, and what you mean by
> "balun" and what you mean "fail." If you mean a common mode choke
> that is coax wound around or passing through ferrite cores, the coax
> might have shorted or the core might have cracked. The shorted
> condition will result in no signal at all. The cracking, if it happens
> to all of the cores in the choke, will render the choke completely
> The primary effect of a common mode choke on the antenna is to
> decouple the antenna from the transmission line, so that the line does
> not become part of the antenna. When the line becomes part of the
> antenna, it both radiates and receives, filling in the nulls that the
> antenna creates. This doesn't matter much on TX, but it can on RX --
> you may hear more noise or QRM that the Yagi rejects but your feedline
> picks up. And THAT'S a big part of why a common mode choke with
> greater choking impedance is a good thing.
> 73, Jim Brown K9YC
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