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#1 2012-03-28 14:24:40
- einreb
- Member
- Registered: 2011-12-01
- Posts: 12
Toroid Temperature Stability figure
I want to build a variable Cap. type VFO (5Mhz) and noticed that there are several mixes of toroids that I can use which will give me the inductance I need. To make a choice, what does the spec "Temperature Stability (ppm/*C)" of a toroid actually indicate? Is a lower figure better than a higher one and how do I compensate for it with capacitors? (The kind of capacitor, NPO, etc.)
Any suggestions?
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#2 2012-03-29 05:51:51
- W8DIZ
- Administrator
- Registered: 2008-08-12
- Posts: 317
Re: Toroid Temperature Stability figure
einreb wrote:
I want to build a variable Cap. type VFO (5Mhz) and noticed that there are several mixes of toroids that I can use which will give me the inductance I need. To make a choice, what does the spec "Temperature Stability (ppm/*C)" of a toroid actually indicate? Is a lower figure better than a higher one and how do I compensate for it with capacitors? (The kind of capacitor, NPO, etc.)
Any suggestions?
There are books written on this subject and there is no simple answer to the questions.
Generally speaking, the lower the (ppm/*C)", the better but that may not be so, depending upon the rest of the VFO circuit.
Sometimes you can use a toroid that is not the most stable, but would compensate the temperature/freq drift from the rest of the vfo circuit.
I have used -2 toroids instead of -7 toroids, because their use made my VFO more stable.
Here is some text from my VFO circuit: http://kitsandparts.com/vfo.php
The "main" tune toroid (L1) is a T68-2 with 69 turns of #28 wire.
Some of you may suggest that this toroid should be a -7 material
which has better temperature stability +30 ppm /°C but
the -2 material at 95 ppm /°C better compensates the negative
drift from other circuit components.
Sorry I can not give a better answer.
73, Diz, W8DIZ
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#3 2012-03-29 08:28:10
- einreb
- Member
- Registered: 2011-12-01
- Posts: 12
Re: Toroid Temperature Stability figure
Thank you for your reply. Your answered essentially my question, the lower the figure the more stable the material. From your answer I can see that other components in the circuit may actually determine the final choice of the material. As a hobbyist without extensive knowledge in designing circuits, it seems that I can start with a suitable toroid which I have in my parts box and see how the circuit behaves with it. If it does not, I can try to do better by changing the toroid material. This may or may not help, but it is worth a try. (This method of designing is generally called politely "the empirical way of doing things" :
)
Since I have several components in my circuit of which I have no idea how they behave at different temperatures, I might start with a -2 material as you did and see what happens.
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