Topband: Transformer isolation vs common mode choke was: Re: T Vertical feed

[Julius Fazekas]

I had been using an isolation transformer with my system for a number of years. It is HB and works reasonably well. I had not been using a common mode choke.

After reading Jim's document, and having the parts on hand, I constructed a choke and added it to the installation. It definitely was worth the effort.

My coax/heliax feedlines are either on or under ground. The antennas in question are close to the house/shack (25' to 50'). 

The common mode choke also cleared up some issues with the Tee transmitting antenna. It was easy enough to build and well worth the effort. I'd recommend it to anyone who may have a less than optimum antenna situation.

73,
Julius

Julius Fazekas

N2WN



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--- On Fri, 1/27/12, Pete Smith N4ZR <n4zr at contesting.com> wrote:

From: Pete Smith N4ZR <n4zr at contesting.com>
Subject: Topband: Transformer isolation vs common mode choke was: Re: T Vertical feed
To: topband at contesting.com
Date: Friday, January 27, 2012, 2:33 PM

Someone recently commented in favor of using transformer isolation in 
lieu of a common mode choke in a receiving application.  I presume this 
would be a 1:1 transformer using a binocular core, or at least 
completely separate primary and secondary windings.  What are the pros 
and cons of this idea?  Does capacitive coupling between primary and 
secondary, or some other factor, limit how much isolation can be 
achieved this way?

73, Pete N4ZR
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On 1/27/2012 1:07 PM, Jim Brown wrote:
> On 1/27/2012 8:40 AM, Charles Moizeau wrote:
>> I am willing to insert a common-mode choke, but don't know what to measure beforehand to learn if one is needed.
> There is NO DOWNSIDE to using a good common mode choke other than cost
> and weight, and as W4TV has noted, there are downsides to NOT using one.
>
> As it turns out, there was a typo in the link I posted to my RFI
> tutorial, which includes Cookbook guidelines for winding effective
> ferrite chokes.  The correct link is
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> 73, Jim K9YC
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK