On Thu, 26 Oct 2000 12:31:43 -0700 measures <2@vc.net> writes:
>> If the DAF is built per the original design, with a time constant in
>>the screen circuit that will allow the screen voltage to follow the
>>envelope of the SSB signal, then a two-tone test will give valid
>results.
>>
>What time constant? A two tone signal produces constant output in DAF
>amplifiers, therefore the screen potential can not be following
>anything.
>
Hi RIch,
The effective screen resistance of the 4-125A is going to vary quite a
bit in the DAF as the voltage is going to wander. Let's assume a typical
value, for the moment, in the range of 10K-15K ohms plus there is an
additional 27K, if I recall correctly, resistor to ground in some DAF
implementations. Since there is a .005 uF capacitor in the DAF screen
circuit, and neglecting the impedance of the charging circuit for the
moment, the time constant of the screen "supply" is around 25-50 uS
(considering the two screens plus maybe the resistor). This will be a
little faster at higher drive levels and somewhat slower a lower drive
levels
In any case, it is quick enough to follow the envelope of a typical two
tone test signal or voice generated SSB.
73,
Marv WC6W
*
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