[TowerTalk] Pattern Distortion caused by faulty balun?

[Tony]

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. 

Hi Jim,

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.

Thanks,

Tony


> 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 
> ineffective.
>
> 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
>