I think you've misread the chart, at 50 MHz it shows
the input resistance to be 55K ohms.
Ken g8beq.
The VTVM is connected across the variable capacitor
and the input of the VTVM is way
up there impedance wise, up until around 50 MHz were
Boonton designers decided the
accuracy was no longer sufficient.? The graph below
displays the input resistance of the
Q Meter VTVM as a function of resistance. At the low
end, it is nearly 100 MegOhms. By
50 MHz the input resistance drops to about 55
MegOhms. Still pretty darn respectable.
<Graph.PNG>
The circuit of the Q Meter VTVM is displayed below:
<Q%20Meter%20VTVM.PNG>
The area circled in red is where the inductor is
connected during test
and captures the resonating variable capacitor.
Obviously the inductor and variable capacitor are in
series. But initially
I thought the 0.02 Ohm precision resistor was in
series with the inductor
and variable. Actually the precision resistor is in
parallel with the series
tuned inductor and variable cap. The circuit from
the manual was
redrawn to make it easier to recognize what is
happening.
<Q%20Meter%20lashup.PNG>
The meter measuring the voltage across the variable
capacitor is scaled to
read Q despite it being a single range voltmeter.
The scale on the meter
is a fixed slide rule of sorts in that the scaling
is based on the ratio of the
measured voltage to the 20 milliVolts across the
0.02 Ohm resistor. The
premise of the measurement is that the numeric value
of the ratio of either
the voltage across the inductor or the capacitor at
resonance, is the Q. If
the voltage appearing across the variable capacitor
is 2 Volts then:
??????? 2 volts/0.02 volts =100.
Professional draftsmen generally drew the formal
published schematics
using hand drawings/sketches provided by engineers.
The draftsman's
focus when drawing the schematic was to get all the
pieces on a sheet
of paper in compact of a space as possible. Not
being trained to organize
the pieces in an order that logically lumps the
individual pieces according
to function, the draftsman would readily place an
audio amp adjacent to
and RF Amp on a schematic if it allowed a smaller
space to be used.
Unless the engineer hovered over the draftsman's
shoulder, the draftsman
filled the page with symbols and connected them with
lines that matched
the connections provided in the rough hand sketch
from the engineer.
The assumption was the service tech would be savvy
enough to deduce
the circuit topology.
Regards
Chuck WD4HXG
