[Elecraft] Stupid electronics question re: K2 transmitter alignment

Sat Dec 21 12:53:06 2002

Hi

You are close but to change from Pk to Pk to RMS you need to divide by 2 to
get peak then multiply by .707 to get RMS or you can multiply PK to PK by
.3535 to go directly. To get to watts
square the RMS voltage and divide by the dummy load resistance (50 ohms) An
example would be if you measured 63 volts PK to PK on your scope across the
dummy load (remember to take into account the X10 probe) then multiply by
.3535 = 22.3 volts RMS squared = 496 divides by 50 ohms = 9.92 watts

Don Brown
KD5NDB

----- Original Message -----
From: "Gil Bishop" <[email protected]>
To: <[email protected]>
Sent: Friday, December 20, 2002 8:46 AM
Subject: [Elecraft] Stupid electronics question re: K2 transmitter alignment

> Remember, you were warned - even to a neophyte like me this sounds like it
> must be  a really dumb question! :)
>
> Alignment and test part III states, "To align the transmitter you'll need
> some means for monitoring power output as you adjust the band-pass
filters.
> An analog wattmeter or oscilloscope is ideal."  Ok, I've got a decent (so
> I've been told) Hitachi 50Mhz dual-trace scope than I can use pretty
> effectively for  basic signal tracing and troubleshooting but I'm reaching
> as to how to use it for the task of monitoring the transmitter power
output.
> Is it as simple as connecting the 10X probe across my dummy load and doing
> the alignment for maximum peak-to-peak amplitude, then reverting to basic
> Ohms law math for the power calculation?  If so, then I'm assuming that I
> need to find RMS voltage from the peak (not peak-to-peak, right?) reading
on
> the scope.  For that I would use E(rms)=E(peak) x ~.707, correct?  Then
> I=E(rms)/50ohms and finally P=IE(rms).  Oh, that basic electronics course
> was SEVERAL lifetimes ago - wish I'd stayed awake....my brain hurts!
>
> Am I on the right track?  Any shortcuts?
>
> Thanks muchly and 73
> Gil
> k1gil
>
>
>
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