[Elecraft] Monitoring RF Outout

[Mike Walkington]

Hi Bob,

Thanks for getting back to me with the info.  I appreciated the fast
response.

Cheers

Mike
AC7MZ
K2 - 2599



----- Original Message -----
From: "Bob - AG5Q" <AG5Q@attbi.com>
To: "Mike Walkington" <walkingtons@attbi.com>; "Elecraft Reflector"
<elecraft@mailman.qth.net>
Sent: Saturday, January 04, 2003 9:04 AM
Subject: Re: [Elecraft] Monitoring RF Outout


>
> ----- Original Message -----
> From: "Mike Walkington" <walkingtons@attbi.com>
> To: "Elecraft Reflector" <elecraft@mailman.qth.net>
> Sent: Saturday, January 04, 2003 3:27 AM
> Subject: [Elecraft] Monitoring RF Outout
>
>
> Hi Mike,
>
> If  the K2 is driving a 50 ohm load, the power output can be calculated
> using the voltage at R66 with this formula:
>
> Power into 50 ohms = 0.58*(VRFDET+0.3)^2
>
> Where ^2 means "Squared"
>
> That is:
>             Power into 50 ohms =  0.58*(VRFDET + 0.3)*(VRFDET+0.3)
>
> The 0.3 term takes into account the voltage drop across the Schottky diode
> D9.
>
> A quick approximation is:
>
> Power = 0.5*VRFDET^2
>
> If you have an unused connector on the back of the K2 you could bring out
> the voltage at R69/C77  for easier connection. It would be a good idea to
> put another resistor near R69/C77 to isolate this external line from stray
> pickup inside the K2 and also protect the K2 circuit from an accidental
> short on the output.  If you're using a DMM for monitoring, the isolation
> resistor could be in the range of 10K to 20K without affecting the
accuracy.
>
> If you know the input impedance of the DMM (say, 10 megohms) then the
> isolation resistor could be used to scale the DMM reading to make
> calculating power a bit easier. If the isolation resistor is 3Megohms,
then
> the formula for power becomes:
>
>   Power = (Vdmm)^2  ( this neglects the diode drop of D9)
>
> Even if you don't want to use an external connector to make contact to
this
> point, you could solder one end of a resistor to the pad and leave the
other
> end sticking up to make a test point to hook on to.
>
> 73/ Bob - AG5Q
>
>
>
> > Some time ago when tuning my Rev A K2 for the first time, a friend
> suggested
> > that in addition to using the K2s internal wattmeter, I could monitor
the
> > output of the RF Output Detector (R66) with the analogue display on my
> Fluke
> > DMM.  I did this, and found that I seemed to have a bit more sensitivity
> in
> > making tuning adjustments.  So, my questions are:
> >
> > 1)  Is there general agreement that this is another valid way of getting
a
> > tuning indicator?
> > 2) What would be the formula to convert the voltage measured at R66 into
> > Watts?
> >
> > 73s
> >
> > Mike
> > AC7MZ
> > VK1KCK
> > K2 2599
> >
> >
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