The RF Power Amplifier output level is set by detector CR1 at the input of the attenuator on board A3.? The ALC action reduces the output impedance of the PA to almost zero ohms, i.e. a constant voltage source. The attenuator input/output impedance is almost certainly 50 Ohms, as the input impedance of the Impedance Converter board A4 is also close to 50 Ohms aided by R2 (56.2 Ohms).? The accuracy of the Q measurement would be affected by serious mismatches or attenuation uncertainty in the chain after the ALC detector to the injection transformer, because the high impedance voltmeter has no information about the level at the injection transformer.? HP never seemed to be afraid to go for precision or selected components to achieve excellence with simplicity.?
PeterS??? ??? ??? G8EZE
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On Mon, 19 Sep 2022 12:33? John KN5L wrote:
John, 50 ohm series input may be built into R2 attenuator input series resistor. Don't know, as attenuator resistor values are not marked.
In "30 3" switch position, connection is straight through, impedance matching is not required, as long as load is near 5o ohm, using A4 Assy R1 parallel with Q1 Base.
On 9/18/22 8:58 PM, John Kolb wrote: > Q3 & Q4 of the power amp are identical circuitry to the impedance > already analyzed to have a very lot output Z, so I would expect to see a > 50 ¦¸ resistor between the emitter of Q4 and J1 to make the power amp > output match the input Z of the attenuator. > > John? KK6IL
