[Test-Equipment] Q Meter?

[Richard Knoppow]

----- Original Message ----- 
From: "Ray, W4BYG" <w4byg at att.net>
To: "'Discussion of Electronic Test Equipment'" 
<test-equipment at mailman.qth.net>
Sent: Friday, June 20, 2014 4:38 PM
Subject: Re: [Test-Equipment] Q Meter?


> When one does not have one, is there a reasonable way to 
> homebrew a
> "Q-Standard" reference inductor?
>
> In other words, are there known specs for fabricating one?
>
>
> Ray, W4BYG
>
     You can always get a reasonable Q measurement from the 
bandwidth over center frequency. The bandwidth is measured 
where the voltage is 0.707 of the peak value. This is also 
the half-power point.  By definition this is the Q of the 
_tuned circuit_.  The assumption is that the capacitor has 
much higher Q than the coil so the Q is pretty much that of 
the coil.
     I do not know how Boonton calibrated the Q of the Q 
standard coils but it may be in one of the BRC Notebooks. In 
any case the bandwidth method is also a good check on 
measurement made by the resonant rise method used by the 
Q-Meter.
     If you are fairly comfortable with math the tutorial in 
the 260-A handbook is good plus the articles in the BRC 
Notebook.
     The Q-meter will also measure distributed capacity of 
coils and some other stuff although the measurements are not 
always elegant.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com