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K3: LPA power level accuracy?

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K2QI

K3: LPA power level accuracy?

Hello fellow Elecrafters,

Quick question - I've noticed that when using the LPA, output power is
always slightly off compared to the reading given off by two fairly accurate
meters. For example, a constant carrier output of 5 watts always reads
about a half-watt less on the external meters. The output power from the
KPA3 however has always been on the dot - 80 watts drive reads 80 on the
meter, 100 watts output reads 100W on the meter, etc. etc.

I'm not really concerned, but was wondering if this was typical? I've
calibrated several times in the past using the K3 utility, but the results
are usually the same.

--
73 de James K2QI
President UNARC/4U1UN
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--... ...-- -.. . .--- .- -- . ...

The Smiths

Re: K3: LPA power level accuracy?

There's also an adjustment that you can make manually to move the power up or down from what the meter is reflecting on the K3, have you tried that too?

> Date: Fri, 29 Oct 2010 17:00:21 -0400
> From: [hidden email]
> To: [hidden email]
> Subject: [Elecraft] K3: LPA power level accuracy?
>
> Hello fellow Elecrafters,
>
> Quick question - I've noticed that when using the LPA, output power is
> always slightly off compared to the reading given off by two fairly accurate
> meters. For example, a constant carrier output of 5 watts always reads
> about a half-watt less on the external meters. The output power from the
> KPA3 however has always been on the dot - 80 watts drive reads 80 on the
> meter, 100 watts output reads 100W on the meter, etc. etc.
>
> I'm not really concerned, but was wondering if this was typical? I've
> calibrated several times in the past using the K3 utility, but the results
> are usually the same.
>
> --
> 73 de James K2QI
> President UNARC/4U1UN
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
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K2QI

Re: K3: LPA power level accuracy?

No, wasn't aware of that. It's been a while since I've delved into the K3's
menus. Do you know what that option is called, or where to find it in the
manual?

Also, just to make sure I'm understanding you correctly - do you mean to
suggest that if the K3's watt meter reads 5W, but actual output power is
4.5W, you can adjust output power to match the K3's meter? As it is, the
K3's meter and LPA power settings do not match the readings displayed on my
outboard analog and digital forward power meters. When the LPA is in use,
displayed power is always a .5 to 1 watt lower on the external meters.

73 de James K2QI

On Fri, Oct 29, 2010 at 5:04 PM, The Smiths <[hidden email]> wrote:

> There's also an adjustment that you can make manually to move the power up
> or down from what the meter is reflecting on the K3, have you tried that
> too?
>
> > Date: Fri, 29 Oct 2010 17:00:21 -0400
> > From: [hidden email]
> > To: [hidden email]
> > Subject: [Elecraft] K3: LPA power level accuracy?
>
> >
> > Hello fellow Elecrafters,
> >
> > Quick question - I've noticed that when using the LPA, output power is
> > always slightly off compared to the reading given off by two fairly
> accurate
> > meters. For example, a constant carrier output of 5 watts always reads
> > about a half-watt less on the external meters. The output power from the
> > KPA3 however has always been on the dot - 80 watts drive reads 80 on the
> > meter, 100 watts output reads 100W on the meter, etc. etc.
> >
> > I'm not really concerned, but was wondering if this was typical? I've
> > calibrated several times in the past using the K3 utility, but the
> results
> > are usually the same.
> >
> > --
> > 73 de James K2QI
> > President UNARC/4U1UN
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>

--... ...-- -.. . .--- .- -- . ...

Chester Alderman

Re: K3: LPA power level accuracy?

James,

You are beginning to venture on a losing battle!! What used to be the 'old
reliable' Bird watt meters had an accuracy of +/- 5%. Typical ham watt
meters, especially the ones that use diodes to produce forward and reflected
power, typically never mention an accuracy specification. You will also
notice that for a given constant load, the same watt meter will change the
SWR reading as you change your power. As you know, SWR is not a function of
RF output power! 4.5 watts is 10% of 5 watts and if you change watt meters
you are going to get a completely different answer. Very few watt meters are
calibrated to any standard and if they are, they most likely are not
recalibrated once a year.

The only solution to the answer you are seeking is $$$$$$$$$$! 'Close
enough' will have to do with watt meters.

Tom - W4BQF

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of James Sarte
Sent: Friday, October 29, 2010 5:18 PM
To: The Smiths
Cc: Elecraft Reflector
Subject: Re: [Elecraft] K3: LPA power level accuracy?

No, wasn't aware of that. It's been a while since I've delved into the K3's
menus. Do you know what that option is called, or where to find it in the
manual?

Also, just to make sure I'm understanding you correctly - do you mean to
suggest that if the K3's watt meter reads 5W, but actual output power is
4.5W, you can adjust output power to match the K3's meter? As it is, the
K3's meter and LPA power settings do not match the readings displayed on my
outboard analog and digital forward power meters. When the LPA is in use,
displayed power is always a .5 to 1 watt lower on the external meters.

73 de James K2QI

On Fri, Oct 29, 2010 at 5:04 PM, The Smiths <[hidden email]> wrote:

> There's also an adjustment that you can make manually to move the power
up

> or down from what the meter is reflecting on the K3, have you tried that
> too?
>
> > Date: Fri, 29 Oct 2010 17:00:21 -0400
> > From: [hidden email]
> > To: [hidden email]
> > Subject: [Elecraft] K3: LPA power level accuracy?
>
> >
> > Hello fellow Elecrafters,
> >
> > Quick question - I've noticed that when using the LPA, output power is
> > always slightly off compared to the reading given off by two fairly
> accurate
> > meters. For example, a constant carrier output of 5 watts always reads
> > about a half-watt less on the external meters. The output power from the
> > KPA3 however has always been on the dot - 80 watts drive reads 80 on the
> > meter, 100 watts output reads 100W on the meter, etc. etc.
> >
> > I'm not really concerned, but was wondering if this was typical? I've
> > calibrated several times in the past using the K3 utility, but the
> results
> > are usually the same.
> >
> > --
> > 73 de James K2QI
> > President UNARC/4U1UN
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>

--
73 de James K2QI
President UNARC/4U1UN
______________________________________________________________
Elecraft mailing list
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html

______________________________________________________________
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Ken Kopp-3

K3: LPA power level accuracy?

In reply to this post by K2QI

Hi James,

You're chasing your tail, me thinks ...

I'm a retired career two-way radio tech and a
fan of Bird meters, thought by many to be the
best in their price class, and they're rated at
+/- 5% of full scale ... if they're calibrated to a
lab standard ... which in itself isn't likely to be
much better. Even two "identical" elements will
differ in the readings they produce.

Accurate RF power measurement is difficult
under the best of circumstances.

I have several Birds, a Bird dummy load, a W1
and a W2 and I'm satisfied that the W1 and W2
are pretty good. "Pretty good" is about as good
as it gets for us ordinary folks. (:-)

73!

Ken Kopp - K0PP
[hidden email]

______________________________________________________________
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Tony Scesny

[ELECRAFT]K3:LPA power level accuracy?

In reply to this post by K2QI

Hi James:

Use the DL1 dummy load from Elecraft. Its a great diagnostic
tool. It has low inductive resistors 20 watts but will take 90 watts
for short periods. Its greatest feature IMHO is the terminals to
measure the RF voltage. It has much greater accuracy. Hook it
directly to the coax connector on the back of K3. For power settings
from 0-12 LP CONFIG:WTMTR will show LP and all power above that it
will show HP. Now [disp] will show the defaults of 70 for LP and 30
for HP. Set power for LP at 10 watts and the voltage reading should
be around 15.4 volts and 90 watts at 35.65 volts. Adjust LP or HP to
correct the voltage. The change won't be linear so watch it. After
changing the LP and HP re-run the 5 and 50 watt calibrations. As the 5
and 50 watt cals are running you can watch the resulting voltages as
each band changes. (5 watts is 10.9v and 50 watts is 35.65 v) for
reference. There may be a particular band you want greater accuracy, so
you may want to interpolate to get the best average, since it is NOT PER
BAND. My K3 showed LP of 70 was OK but I changed HP to 40 to get
greater accuracy at 90 watts.

Don Wilhelm corrected the formula listed in the DL1 sheet. Watts
= (Vdmm + Vdiode} ^2 / 25 where Vdiode is assumed to be 0.3 v.

73 and have fun Tony K2ZLS at optonline dot net
______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
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Don Wilhelm-4

Re: K3: LPA power level accuracy?

In reply to this post by K2QI

James,

There are too many variables to give you a good answer.
Are you using the lowest scale on your wattmeter? Is the difference
between the K3 power setting and your wattmeter reading less than 10% of
the wattmeter's full scale reading? If so, you can likely blame the
difference on your wattmeter at low power levels.

You can calibrate the K3 internal wattmeter - at both the 5 watt and the
50 watt points. The procedure is in the Calibration section of the
manual. However, I would strongly suggest obtaining a measurement tool
that is better than the typical analog wattmeter. A calibrated Telepost
LP-100 wattmeter is one solution, a calibrated Elecraft W2 is another
good solution, and an inexpensive solution that will work well for the 5
watt calibration is the Elecraft DL1 with its built-in diode detector.
The latter solution will be quite accurate if you read the voltage with
your DMM and compute the power as indicated in the DL1 manual.

Accurate low power measurement (error less than 5%) is not an easy task
- it ranks right up there with making MDS measurements.

You may look in the archives to see my occasional "rant" about wattmeter
accuracy.

73,
Don W3FPR

On 10/29/2010 5:00 PM, James Sarte wrote:

> Hello fellow Elecrafters,
>
> Quick question - I've noticed that when using the LPA, output power is
> always slightly off compared to the reading given off by two fairly accurate
> meters. For example, a constant carrier output of 5 watts always reads
> about a half-watt less on the external meters. The output power from the
> KPA3 however has always been on the dot - 80 watts drive reads 80 on the
> meter, 100 watts output reads 100W on the meter, etc. etc.
>
> I'm not really concerned, but was wondering if this was typical? I've
> calibrated several times in the past using the K3 utility, but the results
> are usually the same.
>

Ken Kopp-3

K3: LPA power level accuracy?

In reply to this post by K2QI

Hi James,

You're chasing your tail, me thinks ...

I'm a retired career two-way radio tech and a
fan of Bird meters, thought by many to be the
best in their price class, and they're rated at
+/- 5% of full scale ... if they're calibrated to a
lab standard ... which in itself isn't likely to be
much better. Even two "identical" elements will
differ in the readings they produce.

Accurate RF power measurement is difficult
under the best of circumstances.

I have several Birds, a Bird dummy load, a W1
and a W2 and I'm satisfied that the W1 and W2
are pretty good. "Pretty good" is about as good
as it gets for us ordinary folks. (:-)

73!

Ken Kopp - K0PP
[hidden email]
>
>
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

K2QI

Re: K3: LPA power level accuracy?

Hi Ken,

You're probably right; my analog Bird meter and my digital MFJ-828 were
calibrated to "lab standard" or so I believe. I had a buddy of mine who
happens to be a communications officer for UNICEF take my meters and
calibrate them against their lab-grade equipment a couple of years ago.
They used some fancy signal generators and what-not to do the
work. According to him if memory serves me right is that the margin of
error should be around 5-7%. Not being a complete techo-geek, I took what
he said at face value. So, with all things being equal, my two outboard
meters should be quite accurate.

Anyway, if my K3's LPA output falls withing both meter's margins of error,
then I guess I really shouldn't be concerned.

73 de James K2QI

On Fri, Oct 29, 2010 at 8:16 PM, Ken Kopp <[hidden email]> wrote:

>
>
>
> Hi James,
>
> You're chasing your tail, me thinks ...
>
> I'm a retired career two-way radio tech and a
> fan of Bird meters, thought by many to be the
> best in their price class, and they're rated at
> +/- 5% of full scale ... if they're calibrated to a
> lab standard ... which in itself isn't likely to be
> much better. Even two "identical" elements will
> differ in the readings they produce.
>
> Accurate RF power measurement is difficult
> under the best of circumstances.
>
> I have several Birds, a Bird dummy load, a W1
> and a W2 and I'm satisfied that the W1 and W2
> are pretty good. "Pretty good" is about as good
> as it gets for us ordinary folks. (:-)
>
> 73!
>
> Ken Kopp - K0PP
> [hidden email]
> >
> >
> >
> >
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

--... ...-- -.. . .--- .- -- . ...

K2QI

Re: K3: LPA power level accuracy?

In reply to this post by Don Wilhelm-4

Hi Don,

My Bird analog meter and MFJ-828 digital meter were previously calibrated by
a friend and colleague with the proper tools. According to him, both should
have had a margin of error of about 5-7%. - perhaps 10% now given the time
that has elapsed. Regardless how accurate his claim was, I can't be sure -
so I take what he's stated at face value.

Anyway, you're absolutely correct in stating that there are too many
variables at play. With my poor ground plane, even rain water saturating
the balcony has an affect on SWR and forward power. I suppose I should be
satisfied that at least my LPA output measurements fall within a 10% bracket
of error. I was simply curious if others have experienced similar when
using the LPA.

73 de James K2QI

On Fri, Oct 29, 2010 at 8:10 PM, Don Wilhelm <[hidden email]> wrote:

> James,
>
> There are too many variables to give you a good answer.
> Are you using the lowest scale on your wattmeter? Is the difference
> between the K3 power setting and your wattmeter reading less than 10% of the
> wattmeter's full scale reading? If so, you can likely blame the difference
> on your wattmeter at low power levels.
>
> You can calibrate the K3 internal wattmeter - at both the 5 watt and the 50
> watt points. The procedure is in the Calibration section of the manual.
> However, I would strongly suggest obtaining a measurement tool that is
> better than the typical analog wattmeter. A calibrated Telepost LP-100
> wattmeter is one solution, a calibrated Elecraft W2 is another good
> solution, and an inexpensive solution that will work well for the 5 watt
> calibration is the Elecraft DL1 with its built-in diode detector. The
> latter solution will be quite accurate if you read the voltage with your DMM
> and compute the power as indicated in the DL1 manual.
>
> Accurate low power measurement (error less than 5%) is not an easy task -
> it ranks right up there with making MDS measurements.
>
> You may look in the archives to see my occasional "rant" about wattmeter
> accuracy.
>
> 73,
> Don W3FPR
>
>
>

--... ...-- -.. . .--- .- -- . ...