Brett,
All that sounds like you have a significant amount of reactance
connected to the K2s antenna jack. If you have an antenna analyzer,
remove the coax from the K2 and check the entire load that your dummy
load, wattmeter and coax combination is presenting to the K2.
Since you have a 'scope there - put on a 10X probe and measure the RF
voltage directly at the BNC antenna connector on the K2 while feeding
your load. Read the peak to peak voltage and calculate the power
directly from the peak to peak voltage as V^2/400 and you should find it
agrees with the internal indicated power - if it does not, there is a
problem with the internal detector. If it does agree, you have a
problem with the setup that you have connected to the K2.
Again, the K2 will control power according to the RF voltage it measures
with the RF Detector. If you have the amount of RF voltage that
calculates to the requested power output, then the K2 is controlling the
power output as designed.
Yes, the basic K2 is very sensitive to loads that are reactive or not
exactly 50 ohms due to the simple diode detector used. That changes
when the KAT2 or KPA100 or KAT100 is installed because those units
include a real wattmeter which reports power rather than RF voltage to
the microprocessor.
On the 'harmonic' situation - yes, what you observe is true if you are
probing with a spectrum analyzer inside the K2 circuits. The Low Pass
Filter will reduce the harmonics significantly before they reach the
output jack. To properly use a Spectrum Analyzer to measure internal
stages, the transmitter circuit must be opened, transformed to 50 ohms
and then fed to the spectrum analyzer. A spectrum analyzer has a 50 ohm
input impedance and cannot be properly used for in-situ measurements
like a high impedance oscilloscope can be used.
73,
Don W3FPR
Brett gazdzinski wrote:
I am not certain what you mean by the phrase "the RF watt meter built
into the rig reads correct on 80 and 40, but does not reflect
the lower
power output on the higher bands, its still pegged". What do
you mean
by "pegged"?
The watt meter in the rig indicates 10 plus watts out
even though the power out is 5 watts at full power.
The RF sense circuit does reflect the lower power, with say
2 point something volts out of the RF pickup instead of the
4 plus volts when the rig puts out 12 watts.
Below about 2 volts the RF sense voltage falls off like it should
and the watt meter on the front panel starts going down.
Is the internal RF meter indicating a high RF voltage? If so, you
should believe that the RF voltage is really high and
something is wrong
with your test setup. The detector used in the basic K2 is a simple
diode detector and does accurately reflect the RF voltage, and the
microprocessor calculates that value to watts with the
assumption that
the load is 50 ohms resistive.
The voltage reads something like 4 point something volts
on 80 and 40 at 12 to 14 watts out, and as I go up in bands
and the power falls off, the output voltage drops to something
like 2 volts (from memory).
I tried an experiment by loading this voltage down with
a 10k to ground at the DMM leads and did not see any change
except on the watt meter reading on the rig, which went down
a bit.
I do not suspect a problem with the RF sense circuit.
Is your load at the time of these measurements a good 50 ohm
resistive
dummy load?
Yes.
If you do have a good 50 ohm dummy load on the K2, then I
would strongly
suggest that you check your connecting coax link before doing
anything else.
I tried 2 cables, both are likely 75 ohm as I don't have any
rg8x to bnc cables, but the cables are short, like 2 feet long.
I will try some rg8x into bnc to 259 adaptors just to be sure.
What kind of power meter are you using? How has its accuracy
been verified?
2 different ones, and yes, they are in the ballpark.
We need to know exactly what your setup is before we can provide
informed answers to your questions.
How are you measuring the current draw? Is this the
indication on the
K2 or are you using some other measuring device?
Only by the K2 readout. I suppose its just a rough
reading.
All in all, what I can say at the moment is that the base K2 will
control its power output according to the RF voltage indicated at the
internal diode detector. That detector is not a wattmeter
and needs a
good 50 ohm resistive load in order for the K2 to control the
power output.
This does not seem to work past 80 and 40 meters, it does seem
to be close on 80 and 40 meters, set the rig for 2 watts out and I
get close to 2 watts out and the bar graph power meter indicates
2 watts out. Above 40 meters, the power out is low, the rf sense
voltage is lower, but the power is lower then the bar graph indicates.
As far as adjusting C21 - adjust any of the bandpass filter
elements at
a power of 2 watts or lower. Attempting to adjust them at
higher power
levels can lead to incorrect alignment due to several other factors.
I tried it both ways, at 2 watts and full power, and at as low a power
I could read on the watt meter, does the same thing, but I think
its just some sort of resonance...
How are you determining that the harmonic content "goes way
up"? That
is unusual and indicates that you have a problem with soldering or
incorrect components somewhere.
While I was probing T1, T2, and T3.
Its not a valid test of the output of the rig, but under say half power,
the signals look clean and normal, as you turn the power up, the harmonics
go WAY up past the fundamental frequency.
The reason I noticed this is because my O scope was doing a poor
job at measuring the signal levels at the various transformer ins and outs.
I don't know if this is valid at all, as even at the 2 watt level, power
is down on the bands above 40 meters.
The usual cause of high current draw coupled with low power output is
the Low Pass Filters and/or the T4 circuitry. Do you have T4
properly
wound?
I think so.
It looks like figure 6-30 on page69 of the book.
2 turns of green wire, 3 turns of white wire, and the two
bare wire links, all pulled tight to the board.
73,
Don W3FPR
Thanks,
Brett
N2DTS
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