> Oh now I understand. You are assuming that everything possible
> is going to be worst case. Broken amplifier, broken load, broken
> exciter and broken operator. Given that assumption, I have to agree.
It may or may not be "broken" as you put it. However, given the
number of amplifiers with untuned inputs and the number of solid
state transceivers that fold back unpredictably with such amplifiers
or have alc/power controls that are unstable, it takes more than a
little skill and test equipment well beyond the "CB Special" wattmeter
to make accurate 1 dB compression measurements.
A semi-competent individual is just as likely to achieve results
that are just as good by tuning an amplifier for maximum smoke
and backing off the drive until the output is 80% of that maximum
level (down 1 dB). Unfortunately, the prevailing attitude is to
hit an amplifier with the maximum possible drive level and tune
for maximum smoke ... who cares about maximum plate current
ratings, plate dissipation ratings, or grid current ratings?
73,
... Joe, W4TV
On 5/23/2010 10:22 PM, Larry wrote:
>
> On 23-May-10 6:15 PM, Joe Subich, W4TV wrote:
>>
>> > 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.
>
> Oh now I understand. You are assuming that everything possible is going
> to be worst case. Broken amplifier, broken load, broken exciter and
> broken operator. Given that assumption, I have to agree.
>
> Silly me, I assumed that if something was not right, it would get fixed
> before trying to measure it.... But then given the posts that appear on
> this list I guess yours is the more correct assumption.
>
>
>>
>> > 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.
>
> Again, it boggles my mind that any intelligent person would try to do
> anything under those conditions. Again, apparently a wrong assumption.
> But given those conditions, you could not do a two tone test or anything
> else that made sense.
>
>
>>
>> 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.
>
> I agree.
>
> However, I still maintain that given a reasonably technically competent
> operator with equipment that is in reasonably good condition, the 1 dB
> PO compression test will quickly establish the best linear operating
> conditions for any given amplifier within acceptable ham radio
> tolerances. It works for QRP, QRO, and mega-QRO; BJT's, FET's, triodes,
> tetrodes, and even TWT's, anything that is supposed to be linear. If you
> look across the industry P1dB is a standard, only in ham radio is it
> ignored.
>
> 73, Larry
>
>>
>> 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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