[Elecraft] Can I measure antenna impedance with K2?

[Don Wilhelm]

P-T,

If one uses the voltage divider example, yes the maximum efficiency is 50%,
But the output of a PA stage is not a resistor, and the collector load 
"resistance" is set by the designer to produce the output power desired.

The 'resistor' assumption is a simplification that can be used when 
constructing equivalent circuits to analyze the voltages and currents in 
the network that follows the perfect generator.

The theory of large signal amplifiers is too great for detailed 
discussion on this reflector, so we usually have to settle for 
simplifications.  An equivalent circuit is not a full representation of 
the workings of an actual PA stage.  I believe that is where the 
misunderstanding comes from.

73,
Don W3FPR

On 7/31/2014 6:57 PM, Per-Tore Aasestrand wrote:
> Would not this imply a maximum efficiency of 50% ?
>
> P-T
>
>
>
> On 1 August 2014 00:40, Matt VK2RQ <matt.vk2rq at gmail.com> wrote:
>
>> I think we have hit the posting limit for this topic, so I'll just finish
>> with this remark: the maximum power transfer between a power amplifier and
>> its load will occur when the source and load impedances are complex
>> conjugates (this can be seen using the voltage divider equation and some
>> differential calculus). In the case of a purely resistive load, this
>> reduces down to the source and load resistances being equal.
>>
>> 73,
>> Matt VK2RQ
>>
>>> On 1 Aug 2014, at 8:24 am, Per-Tore Aasestrand <ptaa at ieee.org> wrote:
>>>
>>> Hi list,
>>>
>>> Isn't an RF transmitter or PA actually more like a current generator? Its
>>> internal resistance is kept low in order to reduce internally dissipated
>>> power, with consequent reduction in efficiency. It is usually designed to
>>> work efficiently into 50 ohms.
>>>
>>> It is important to know the difference between these two statements:
>>> (A) The transmitter has a 50 ohm output impedance.
>>> (B) The transmitter is designed to work into a 50 ohm load
>>>
>>> A transmitter will be able to put its rated power into a 50 ohm load, but
>>> this says nothing about its output impedance. That is why I don't think
>>> conjugate matching will be appropriate.
>>>
>>> (Hope this is not getting too much OT now)
>>>
>>> Per-Tore / LA7NO
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