KXB3080 power questions

[David Toepfer]

I just finished installing my KXB3080, which seems to work fine.  Using my DL-1
dummy load I noted the following power ratings?

When I first tested it I got the following power readings with R4 fully
clockwise:

full power:
20m: 2.8w
40m: 3.5w
30m: 3.7w
80m: 6.3w

Since 80m power out seems too far out of spec, so I backed off R4:

reduced power:
20m: 2.3w
40m: 3.0w
30m: 3.2w
80m: 4.8w

QUESTIONS:

1) If I ran 6.3w out on 80m is that too much (ie. I risk letting all the smoke
out?)?

2) Is there a way to reduce the power /only/ on 80m, so I can get the full
power out for all of the other bands (non-80m) seen in the top list?

3) How accurate is the DL-1?  Does it tend to read hi (optamistic) or lo
(pessamistic)?

Thanks,
David, K3TUE
.

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[David Toepfer]

> 3) How accurate is the DL-1?  Does it tend to read hi (optamistic) or lo
> (pessamistic)?

I asked this because the the KXAT1 reads higher than the calculation I get from
the DL-1.  The DL-1 matches the KXAT1 if I use the following calculation
(instead of the one supplied in the DL-1 manual):

P=(((E*sqrt(2))+0.75)^2)/50

Of course, this could be miscallibration of my volt meter.

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[Don Wilhelm-3]

David,

Spreading the turns of the low pass filter toroids may give you a better
spread of power across all the bands.  With a 13.8 volt supply, I typically
expcet close to 4 watts on 80, 40 and 30, and about 3.5 to 3.8 watts on 20
meters using a 14 volt power suppy.  Yes, the major contributor to power
output deviations from these values is the L1 and L2 toroid inductors.  The
transformer T1 is a secondary candidate for power output vsriation.

Proper caslibration of the KXAT1 wattmeter is essential to determining the
actual power output, but the difference between bands is likely a function
of the Low pass filter inductance.

73,
Don W3FPR


> -----Original Message-----

>
> I just finished installing my KXB3080, which seems to work fine.
> Using my DL-1
> dummy load I noted the following power ratings?
>
> When I first tested it I got the following power readings with R4 fully
> clockwise:
>
> full power:
> 20m: 2.8w
> 40m: 3.5w
> 30m: 3.7w
> 80m: 6.3w
>

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[Don Wilhelm-3]

David,

The DL-1 wattmeter is likely quite accurate.  If you are using a slow DVM,
be certain that you allow enough time for the readings to settle down.

The formula in the DL1 manual should be correct with the exception of the
diode drop (the 0.15 constant in the voltage could vary a bit from diode to
diode).  Remember that the diode detector reads peak voltage, but only
across half of the load.  If the RF voltage is 2 volts or higher, the diode
drop becomes insignificant - 0.15 volts divided by 2 volts is 0.075 meaning
less than a 7.5 percent error if the diode drop is ignored.  This error
becomes less as the voltage reading increases.  It is quite possible that
your particular diode has a lower voltage drop than the formula's 1.5 volt
average drop.

The diode drop and the actual value of the dummy load resistance should be
the only quantities that would vary in the formula.  The accuracy will be
directly proportional to the actual resistance, and the actual power will be
dependent on the square of the voltage, so the voltage is the most
significant factor.

I will have to give it some more thought, but I believe the formula may be
better stated as;
((V+1.5)SQRT2)^2/50 because the diode drop should modify the peak voltage
rather than the RMS, but I will have to give it some study to be sure (I
could be wrong and it is late at night).  As I said, if your voltage
readings are in excess of 2 volts (about 0.05 watts), the diode drop becomes
less and less significant as the measured voltage increases, so only at QRPp
levels is the diode drop a significant factor.  Drawing conclusions for a
difference of less than 10% is risky and can have other variables involved
such as the actual resistance ot the dummy load - the resistors are 5%
tolerance and can account for a part of the discrepancies that you are
seeing.  Measuring the dummy load with an antenna analyzer can be
informative.


73,
Don W3FPR


> -----Original Message-----

> > 3) How accurate is the DL-1?  Does it tend to read hi (optamistic) or lo
> > (pessamistic)?
>
> I asked this because the the KXAT1 reads higher than the
> calculation I get from
> the DL-1.  The DL-1 matches the KXAT1 if I use the following calculation
> (instead of the one supplied in the DL-1 manual):
>
> P=(((E*sqrt(2))+0.75)^2)/50
>
> Of course, this could be miscallibration of my volt meter.
>
>

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[David Toepfer]

After some pushing the LPF turns back and forth I was able to get all bands
between 3 and 4W with a gel cell supply.  Which I guess means it's time to get
out and throw some wire in a tree.  Thanks for all the help.

David, k3tue
.


--- Don Wilhelm <[hidden email]> wrote:

> David,
>
> Spreading the turns of the low pass filter toroids may give you a better
> spread of power across all the bands.  With a 13.8 volt supply, I typically
> expcet close to 4 watts on 80, 40 and 30, and about 3.5 to 3.8 watts on 20
> meters using a 14 volt power suppy.  Yes, the major contributor to power
> output deviations from these values is the L1 and L2 toroid inductors.  The
> transformer T1 is a secondary candidate for power output vsriation.
>
> Proper caslibration of the KXAT1 wattmeter is essential to determining the
> actual power output, but the difference between bands is likely a function
> of the Low pass filter inductance.
>
> 73,
> Don W3FPR
>
>
> > -----Original Message-----
>
> >
> > I just finished installing my KXB3080, which seems to work fine.
> > Using my DL-1
> > dummy load I noted the following power ratings?
> >
> > When I first tested it I got the following power readings with R4 fully
> > clockwise:
> >
> > full power:
> > 20m: 2.8w
> > 40m: 3.5w
> > 30m: 3.7w
> > 80m: 6.3w
> >
>
>

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