[Elecraft] KPA1500 on AM

[Grant Youngman]

Precise calibration of a monitor scope isn’t that terribly essential. An SB-610 or equivalent is hardly a precision instrument, but more than adequate.  The point of the scope is primarily to observe and prevent negative peak clipping, ensure you’re not out of headroom and starting to flattop on positive peaks, and adjust mic gain for something approaching 100% modulation.

Grant NQ5T

> On Feb 4, 2021, at 3:26 PM, Joe Subich, W4TV <lists at subich.com> wrote:
> 
> 
> On 2021-02-04 3:12 PM, Grant Youngman wrote:
>> Actually, that assumes that peak to avg is exactly 4.  Which it rarely (never?) is with a real human voice.
> It also assumes the modulation is symmetrical and that the mic is
> wired with the correct polarity.
> 
> > A monitor scope on the output is essential …
> 
> ... and that the deflection on the scope is accurately calibrated
> to PEP level (peak voltage across 50 Ohms).
> 
> 73,
> 
>   ... Joe, W4TV
> 
> 
> On 2021-02-04 3:12 PM, Grant Youngman wrote:
>> Actually, that assumes that peak to avg is exactly 4.  Which it rarely (never?) is with a real human voice.
>> Aside from the legal (and oft disputed) aspects of AM power limits, you’re better off being conservative and setting drive levels for something under 375W carrier from the amp.  Maybe 250-300W.  That will ensure you have some headroom for voice peaks (especially if you have a good bit of positive voice asymmetry), keep the amp cooler, etc.  And no one on the receiving end will know the difference, anyway.  The referenced article is a good place to start.
>> A monitor scope on the output is essential …
>> Grant NQ5T