[ARC5] Making Stable VFO for 2 MHz

[J. Forster]

> I agree with Ken 100%. Those coils were never intended to be used as
> frequency determining inductors, especially near 2 MHz. What is the self
> resonant frequency? I bet it also varies from unit to unit.

I used it because I had it on hand. If I thought it was a permanent
solution, why would I ask about stable inductors?

I now have the thing working nicely with a just-made air core coil. It has
stayed w/in 500 Hz in the last couple of hours. It's not a forever design,
because my core is cardboard.

-John

================


 This reminds
> me
> of a young engineer with an MSEE who worked for me about 30 years ago. He
> needed a BPF in his design project at work so I gave him Saal's book on
> normalized filter element values. He managed to get all of the math right,
> but, the filter did not work. When he showed it to me I could not believe
> it. His air wound inductors were wound as multi layered solenoids with a
> very low self resonant frequency due to all of the distributed
> capacitance.
> Once I pointed that out, and he re wound his inductors, everything was
> fine.
> Regards - Mike
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net]
> On
> Behalf Of Kenneth G. Gordon
> Sent: Wednesday, June 29, 2011 7:40 PM
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Making Stable VFO for 2 MHz
>
> On 29 Jun 2011 at 15:21, J. Forster wrote:
>
>> A Vishay RF choke from Mouser, about the size of a 1 Watt resistor.
>> I'm working on the keying at the moment.
>
> I know those things quite well. In my experience, they are VERY
> unstable inductors. They are horribly temperature sensitive and were
> never designed to be part of a frequency-determining network. They
> work OK as an RF choke in certain circuits, but I would never attempt
> to use one in a VFO.
>
> What is the value of the inductance which you need?
>
> Ken
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