CW filter design using analog components

[kf4hcw]

On 3/20/21 11:22 PM, samudra.haque at gmail.com wrote:
>
> Would a  VNA gadget you showed plot the curve of this filter board? If
> I only had a signal generator (455 kHz, to simulate CW carrier 2^nd IF
> stage) and a spectrum analyzer, that couldn’t be used to generate a
> filter curve right because it wouldn’t sweep? Any poor mans way of
> sweeping  (e.g., manual and then plotting the level?)
>
>  
>
> Is there a software VNA that can plot the filter curve?
>
A VNA working at those frequencies could do it.

RC filters are also well understood so that most RC filter tools will
also show you a curve given your component selections.

If you want to do this in RC filtering-- I recommend you grab some op
amps that are happy at those frequencies and build a salen-key filter
with enough poles to do what you want... that will eliminate your
injection losses.

If you want a poor-man's solution and you have a scope that does FFT you
could build a noise generator (I presented a project for that:
http://www.lifeatwarp9.com/2017/05/curiously-strong-junk-box-noise-source/)
and use the noise source on the input to your filter-- then measure the
output... the result on your FFT will be the curve of the filter. This
also works if you have an SA that doesn't have a tracking generator.

Even more low end way of doing it is with an ordinary variable
oscillator, or if you're lucky a sweep generator:

https://www.youtube.com/watch?v=-A_DxsxPdeI

Hope this helps,

_M


-- 
kf4hcw
Pete McNeil
lifeatwarp9.com/kf4hcw

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