> NO NO NO NO. You only need to know the RATIO between the output
> and input power. That's what a dB is... A RATIO .. That's what
> GAIN > is.... A RATIO.... Even an uncalibrated watt meter will
> give you that information as long as it is linear.
NO! You have to know what the two values are in order to know
what the ratio is, Even if you're using a two channel scope,
it is necessary to measure the specific RF voltages. Then, IF
you know the impedances accurately (or your can guarantee they
are identical) you can calculate the radio.
> What are you talking about? How does measured power applied to
> the input jack have anything at all to do with what's going on
> in the exciter?
Many amplifiers do not have properly designed inputs and the
solid state exciters operate at significant SWR. Add to that
the changes in tuning based on power level which will change
the input SWR, and simple wattmeters with insufficient
directionality will mis-state the true input power.
Of course, you could use a 6 dB pad between the exciter and
the amplifier to isolate the exciter from the amplifier tuning
- but then most users would not know anything about that either.
73,
... Joe, W4TV
On 5/23/2010 8:28 PM, Larry wrote:
>
> On 23-May-10 4:06 PM, Joe Subich, W4TV wrote:
>>
>> > The beauty of 1 dB compression power is that unlike two tone testing,
>> > absolute accuracy is not required to achieve proper operation of the
>> > amp.
>>
>> Sure, if you end up reducing the drive by 3 dB because the user
>> can't tell the difference between 1 dB compression in the amplifier
>> and 1 dB of foldback in the drive due increased input SWR.
>
> What are you talking about? How does measured power applied to the input
> jack have anything at all to do with what's going on in the exciter? I
> don't understand your point. 100 Watt carrier doesn't care if the
> exciter is in compression or folded back or standing on it's head. 100
> watt carrier is 100 watt carrier period.
>>
>> > You DO NOT need to know what the actual power output is, you
>> > only need to know at what point you should be adjusting the
>> > drive to when running a linear mode.
>>
>> You do need to know both the drive and output accurately. That
>> is the only possible way to accurately determine the gain of the
>> amplifier and thus determine when the gain has dropped by 1 dB.
>
> NO NO NO NO. You only need to know the RATIO between the output and
> input power. That's what a dB is... A RATIO .. That's what GAIN is....
> A RATIO.... Even an uncalibrated watt meter will give you that
> information as long as it is linear. Why do want to make this harder
> than it really is?
>
> Larry
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>
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