--
Yeah, but it was irrelevant in context; just more of your smoke and
mirrors.
here's the original "dicourse":
>>A good signal generator should be a 50 ohm source at all frequencies.
>>
>>John
>
>---
>Yes, of course.
>
>We all know that, but a signal generator with an attenuator designed
>and legended to drive a resistive load will only be accurate at the
>frequency where the capacitor's reactance is such that the voltage
>across it will be half that of the open-circuit voltage of the
>generator.
Gibberish.
>
>And, even at that, the attenuator will only be useful in determining
>the voltage across the load, not the power into it, as displayed,
>since the load is reactive.
Ditto.
John
Why Gibberish?
Not at all. You just have to apply any corrections as needed. Into a Hi-Z load, the output voltage is 2x compared to driving a 50 ohm load. It's just a voltage divider. Any reasonable amount of 50r coax between the generator and the load has no effect.
The OP needed exactly that 2x correction. Or a termination.
I explained the OP's situation long ago: RF generators are usually calibrated assuming a 50 ohm load, and his load is a small capacitance. You and Phil explained the error in terms of standing waves, with Himilayan mountains of dips and peaks, which is wrong. His voltage is twice what he expected because he has a hi-Z load. It's a simple case of a 50 ohm source making more voltage unloaded than it does loaded. It's just a voltage divider.
As noted, that was settled long ago. It's bog simple. Why you want to keep clucking about it, I can't imagine.
I also noted that function (not RF) generators are usually specified, for output voltage, unloaded. The ones I sell sure are. We usually seed a lot of notes into our specs (like "+-10 volts max, +-5 max into
50 ohms") in lots of places, because many people don't understand this.
If you've got a 50 MHz 'scope that may be enough to see your PMT pulses. There will be some broadening of the pulse, but still visible. I assume there is a discriminator in part of your ortec equiment? (comparator with variable refernce level) That should be all you need to get some nice big pulses for your counter.
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