[sdiy] Oscilloscope recommendation(s).

[harry bissell]

I was going to say "Bullshit, old man" but it appears that it is 
possible that I am
actually ~older~ than Mr. Schrieber, so "Bullshit, young 
whipper-snapper"   :^P

If the scope is capable of x-y inputs you CAN calibrate V-oct if you 
have a good
stable frequency generator (that can hold a frequency for more than a 
few minutes).

I use this method, and also use a high-quality guitar tuner.

Use the guitar tuner to set your reference oscillator to a midrange 
frequency for your VCO
and send it into the Y input

Send your unknown frequency into the X input.   If you have a triangle 
or sine wave output
you should use it.

If the input and reference frequencies match (and you have sine waves) 
you will see a static
or slowly moving display of between a circle, ellipse, or 45 degree 
angle line.

2x or 1/2x frequencies will be a rotating figure eight.

Set your voltages and adjust to 'freeze' the display.

I have never been happy with a frequency counter for VCO calibration. I 
have only own3d
cheap, crappy ones  (ok Paul ???   :^)

I can use the guitar tuner in other places, like tuning my guitar...

If you do not do a LOT of calibrations, the frequency counter will 
probably never pay off.
I assume that I do as many cals in my lifetime as Paul does in one week 
!!!   So if you can find
a good frequency counter its a viable method.  But you ~can~ do it with 
a scope

H^) harry



Paul Schreiber wrote:
> You *cannot* tune a 1V/Oct input (VCO, etc) with a scope. You need a 
> frequency counter.
>
> Now, the problem is, *most* frequency counters are designed for 
> counting *MHz* signals, not Hz.
>
> You need a frequency counter that has what is called 'reciprical 
> counting': instead of measuring the frequency, it measures the 
> *period* and calculates the frequency. This is if you want realy good 
> accuracy. The MOTM-standard is the Philips-Fluke PM6666 which can 
> accurately count down to 0.001Hz resolution no problem and it's 2 
> channels. I have seen these on eBay for ~$200. When new, they were 
> around $1600. Not a bad deal!
>
> If you get an older HP counter (HP53xx series) you have to use the 
> 1sec or 10 sec (gack!) gating times to read audio, then it's not 
> nearly as accurate as a recip counter (the PM666x series. There is 
> 'new in box' unit on eBay now for $250).
>
> Paul S.
>
>
>