[Elecraft] BL2 choking Impedence measurements?

[David Cutter]

This brings me nicely to the final bit of the puzzle:  say, in a given 
location, you want to set up your own personal outdoor lab to make these 
measurements comparing various solutions.  How do you create a constant 
noise source *which will most effectively demonstrate* the performance of 
one choke against another?

I suspect that, at the end of the day, this is probably going to be the 
cheapest and most conclusive of all tests.

David
G3UNA

>
>>Equally silly (and applicable here) is measuring a device in a 50-ohm
>>environment and trying to determine attenuation, when in actual operation,
>>neither the source or load impedance is known.
>
> Exactly. It is the 50 ohm environment that is the source of much of the
> measurement error. Measuring S21, by one means or another, is an effective
> solution, and the one I've used.
>
> Measuring shield current, as David has suggested, is an indication of the
> effectiveness of a choke IN A PARTICULAR CIRCUIT -- for example, a 
> feedline
> onto which it is inserted, the antenna to which the feedline is connected,
> and the termination of the feedline at the receiver. The effectiveness of 
> a
> choke in any given application depends upon the common mode impedances
> within that particular circuit.
>
> These are two VERY different problems, and two very different 
> measurements.
> Both are useful. Measuring the choke on the bench tells us about the
> properties of the choke. Knowing that, we can optimize the choke for a
> given frequency range and use, AND we can insert the properties of a choke
> into a model and, if the model knows enough about the circuit of interest,
> predict the effectiveness of the choke in reducing common mode current.
>
> There is, of course, another set of unknowns. They relate to the source(s)
> of the noise, their location, polarization, directivity, proximity to the
> feedline and to the antenna, the directivity of the antenna, etc. The 
> choke
> will have little effect on the component of noise picked up on the antenna
> -- it can suppress noise picked up only on the feedline. In general, the
> choke will be most effective in suppressing noise that is much closer to
> the feedline than to the antenna, and/or is rejected by antenna
> directivity.
>
> 73, Jim K9YC
>
>