Aloha, and to continue:
> >Jim's VSWR of the antenna itself is much worse than that.
>>The 2.5% mismatch is the mismatch BETWEEN the tuner
>>and the PA when the tuner is tuned for min SWR.
Yes, true; however.........
have now removed the tuner and the Hofi switch from the set up,
and the result is.... the true behavior of my particular C4 at 28055,
where I find phone "interlopers" from the Western Pacific area
this AM, so did the following measurements right where they
did not belong, hi.
Using the P-3000 Digital RF Power/VSWR Indicator
Indicated Forward Power = 1.82 kW
Indicated Reflected Power = 305 watts
Calculated Voltage Reflection Coefficient = 0.39, or 39%
Indicated True Forward Power = 1.51 kW
Indicated Forward Peak Voltage = 310 volts
Indicated Operating VSWR = 2.3 : 1
First Question: Is it correct to assume that these conditions would
be "legal" for operation, within the stated accuracy of the P-3000
indicator, which is, per the manual, +/- 10% +/- the analog to digital
converter resolution (whatever that might be) ? Probably should back
the drive off so that True indicates more like 1.4+, would guess.
This assumes that the final circuits, Pi-L of the tube linear, are
in fact reflecting back up the coax all of the reflected power
originally reflected from the antenna/line mismatch. This seems
to me to be the only way you can have a constant VSWR on the
line, which is a steady-state condition. The amplifier continuing
to deliver sufficient power to generate True forward power, overcoming
real line I-square-R loss and "reflection loss" with the standing
peaks/nulls of voltage on the coax line of about 417 volts
(from Peak voltage is the square root of the product of the
power delivered to the line by the linear, 1510 watts in this case,
multiplied by the line Zzero, or 50 ohm, multiplied by the
vswr on the line, here 2.3 to equal 417 v.)
Second Question: Problem with the above is that the 39%
reflection, or 300 approximate watts reflected, seems to
indicate that the linear is delivering 1820 watts to the line
input (reflected power is equal to the square of the reflection
voltage coefficient, or about 0.15 in this case which is around
280 watts approaching the P-3000 indicated 300 watts).
In this case then, the peak voltage on the transmission line
becomes about 460 volts, still OK.
So, the linear seems to be supplying sufficient power to
generate the radiated, or true forward indicated power
plus the 300 reflected watts. In this case then, the linear
output circuit's apparent output real resistance is, in fact,
dissipating the entire reflected 300 watts as heat !
In either case, the radiated peak power is at the legal limit, I
presume. If the first supposition is true, the output circuit
does what a tuner would do; that is, re-reflect the power
originally reflected at the line/antenna terminal; and in the
second, the linear dissipates the reflected power as heat.
Which do you suppose is true, or is neither ?? And, of course
the above numbers are presumed to be within the accuracy
of the indicator, even thought the impedances on the line,
where the meter is inserted, are obviously not 50 ohms, which
is where the meter is designed to operate ! So how can any
meter/indicator designed to work in a 50 ohm "environment"
indicated accurately, or to within it's given accuracy anyway,
when in a situation that is neither sourced, nor loaded by
50 ohms ? (Always questions, hi.)
73, Jim, KH7M
PS: Would rather be on 10 CW just now, 2100z, but the band
seems dead from here, and I got intrigued by this topic, hi.
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