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File /LP.pdf uploaded #file-notice


ajparent1/KB1GMX
 

RE: Q

First there is unloaded Q, for most iron powder toroids with a single layer winding
a good working value is 200. It can be higher, I've see 275.  Its not all that critical.
Test for various values and you will see.

Loaded Q is a internal design feature and hard to bound and interacts with the
filter equations.  Easy answer you don't get to choose.

There is a yabut... and untested in that example.  Assume correct +-5% on
inductors and go +- 10% on caps.  Then play with the Q of caps as the possible
range is 500 to 3000.   Unlike the inductor you do get to pick higher Q over lower.

Allison
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Bob Benedict, KD8CGH
 

Bill

I didn't say only QRP Labs. Why would you say that?
--
  73
    KD8CGH


Alan G4ZFQ
 

Why would the winding of toroids be a problem only for QRP Labs filter kits and not for *any* project that has toroids to wind?
Bill,

Yes, The QRP Labs LPFs and BPF use standard designs.
It seems to me that very often that when I have wound toroid coils for any project the inductance is a little high. Possibly due to the ferrites being at the high end of their spec.
A tested-accurate inductance meter may help otherwise it is trial and error as detailed in the assembly instructions.

73 Alan G4ZFQ


Bill Cromwell
 

Hi Bob,

Why would the winding of toroids be a problem only for QRP Labs filter kits and not for *any* project that has toroids to wind?

73,

Bill KU8H

bark less - wag more

On 7/15/20 8:19 AM, Bob Benedict, KD8CGH wrote:
geoff
  Thanks
  No, I didn't examine Q. I took the default values. I was focused on inductance values in the model to try to determine from my measured S21 gain trace why one of my filters didn't perform well. For the QRP Labs filter kits winding torroids appears to be a source of problems.
--
  73
    KD8CGH


Bob Benedict, KD8CGH
 

geoff
  Thanks
  No, I didn't examine Q. I took the default values. I was focused on inductance values in the model to try to determine from my measured S21 gain trace why one of my filters didn't perform well. For the QRP Labs filter kits winding torroids appears to be a source of problems.
--
  73
    KD8CGH


geoff M0ORE
 

Nice work Bob, one quick question. How did you arrive at the values of Q?  Sorry, two questions. Did you try some plots with different values of Q?

Many years ago in my college days we learnt how to calculate Q and then measure in a practical situation but long forgotten now.

On 15/07/2020 01:13, QRPLabs@groups.io Notification wrote:

The following files have been uploaded to the Files area of the QRPLabs@groups.io group.

By: Bob Benedict, KD8CGH

Description:
LP filter models SimSmith model of a 20 m LP filter and results with varied inductor values. This might be useful in diagnosing as built filter problems


QRPLabs@groups.io Notification <QRPLabs@...>
 

The following files have been uploaded to the Files area of the QRPLabs@groups.io group.

By: Bob Benedict, KD8CGH

Description:
LP filter models SimSmith model of a 20 m LP filter and results with varied inductor values. This might be useful in diagnosing as built filter problems