Message-ID: <4E6F73C7.6090605@iup.uni-heidelberg.de>
Date: Tue, 13 Sep 2011 17:16:23 +0200
From: =?UTF-8?B?U3RlZmFuIFNjaMOkZmVy?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Simple yet reliable method for measuring Q?
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Hi Daniele,

It is not OT!

Am 13.09.2011 17:07, schrieb Daniele Tincani:
> I'm looking for a (reasonably) reliable method for measuring Q of a 
> parallel LC resonator at LF frequencies (ferrite-cored coil + variable 
> air cap).
> I have a spectrum analyser (without tracking capability), oscilloscope 
> with 10x probes, RF generator with built-in attenuator and sweep 
> function, frequency counter. I'm doubtful in particular about how to 
> avoid loading the LC with either the output Z of the generator or the 
> input Z of the meter (or both). Any tips?
Just make a small turn of wire and connect it to the VFO, say 30 cm 
diameter. Then couple a signal into the ferrite core, by adjusting the 
distance. Take the 1:10 probe (10 MOhm input resistance and some 10 pF) 
and measure the voltage across the LF circuit with the scope.
For example adjust the distance to measure +- 4 div at resonance. Then 
increase and decrease the frequency until you get 2.83 div. (4/sqrt(2)). 
Note these values.

If fres is 137 kHz, flow=136.7 kHz and fhigh is137.4 kHz, your Q is 
137/(137,4-136,7)= 196.


73, Stefan/DK7FC





> Best regards
> Daniele

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Hi Daniele,<br>
<br>
It is not OT!<br>
<br>
Am 13.09.2011 17:07, schrieb Daniele Tincani:
<blockquote
 cite=3D"mid:1315926429.28889.YahooMailNeo@web29518.mail.ird.yahoo.com"
 type=3D"cite">
  <div
 style=3D"color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font=
-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div style=3D"font-size: 10pt; font-family: arial,helvetica,sans-serif;=
">I'm
looking for a (reasonably) reliable method for measuring Q of a
parallel LC resonator at LF frequencies (ferrite-cored coil + variable
air cap).
  <div
 style=3D"font-size: 12pt; font-family: times new roman,new york,times,se=
rif;">I
have a spectrum analyser (without tracking capability), oscilloscope
with 10x probes, RF generator with built-in attenuator and sweep
function, frequency counter. I'm doubtful in particular about how to
avoid loading the LC with either the output Z of the generator or the
input Z of the meter (or both). Any tips?</div>
  </div>
  </div>
</blockquote>
Just make a small turn of wire and connect it to the VFO, say 30 cm
diameter. Then couple a signal into the ferrite core, by adjusting the
distance. Take the 1:10 probe (10 MOhm input resistance and some 10 pF)
and measure the voltage across the LF circuit with the scope.<br>
For example adjust the distance to measure +- 4 div at resonance. Then
increase and decrease the frequency until you get 2.83 div.
(4/sqrt(2)). Note these values.<br>
<br>
If fres is 137 kHz, flow=3D136.7 kHz and fhigh is137.4 kHz, your Q is
137/(137,4-136,7)=3D 196.<br>
<br>
<br>
73, Stefan/DK7FC<br>
<br>
<br>
<br>
<br>
<br>
<blockquote
 cite=3D"mid:1315926429.28889.YahooMailNeo@web29518.mail.ird.yahoo.com"
 type=3D"cite">
  <div
 style=3D"color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font=
-family: arial,helvetica,sans-serif; font-size: 10pt;">
  <div style=3D"font-size: 10pt; font-family: arial,helvetica,sans-serif;=
">
  <div
 style=3D"font-size: 12pt; font-family: times new roman,new york,times,se=
rif;">=C2=A0</div>
  <div
 style=3D"font-size: 12pt; font-family: times new roman,new york,times,se=
rif;">Best
regards</div>
  <div
 style=3D"font-size: 12pt; font-family: times new roman,new york,times,se=
rif;">Daniele</div>
  <div
 style=3D"font-size: 12pt; font-family: times new roman,new york,times,se=
rif;"><var
 id=3D"yui-ie-cursor"></var>=C2=A0</div>
  </div>
  </div>
</blockquote>
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