[Elecraft] Re: MFJ259

[Jack Smith]

Don:

I've been  giving the subject a bit of thought as well and a noise 
bridge came to mind rather quickly. I have an old MFJ 202 noise bridge I 
bought 25 years ago.

However, I believe a broad band detector such as the AD8307 will fail. 
The null condition is rather narrow frequency wise, and the noise 
generator detector output is broad, so the different in total power at n 
AD8307 detector between no null and perfect null will be tiny, 
particularly if the bridge is constructed to have good balance, which 
is, of course, the objective.

This is a case where one needs a narrow band tuned detector, I believe. 
Or, a narrow band source.

Jack K8ZOA
www.cliftonlaboratories.com


Don Wilhelm wrote:
> Those who have both an Elecraft N-Gen and a KX1 have everything needed
> except the bridge elements to construct and use a relatively compact version
> of that Improved Noise Bridge described by John Grebenkemper in that August
> 1989 QST article.
>
> The N-gen is the noise source and the KX1 can serve as the detector - listen
> for the null.  Of course, it is easy to construct the noise generator, so
> those with only a portable receiver like the KX1 can have an accurate
> impedance meter once it is calibrated.
>
> Detectors other than a receiver can also be used - an AD8307 based power
> meter should work just fine and fit into a small case.
>
> The 'disadvantage' of the noise bridge is there are two knobs to deal with,
> but when a deep null is achieved one can read both the resistive and the
> reactive component of the unknown impedance.
>
> 73,
> Don W3FPR
>
>   
>> -----Original Message-----
>>     
>
>   
>> Dave G3YMC wrote:
>>
>>     
>>> I would also make a plug for a noise bridge. I built the one by KI6WX
>>> which appeared in QST in August 1989 (available to download from the
>>> ARRL site). If you have a suitable portable rig to couple to it does
>>> most of what the fancy analysers can do at a fraction of the cost.
>>>       
>> It should not be too difficult to design a fairly simple receiver
>> drawing a
>> small amount of current to be enclosed with a noise bridge to
>> make an 'easy
>> to carry' instrument. Top of head thinking.
>>
>> 73,
>> Geoff
>> GM4ESD
>>
>>
>>     
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