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Accuracy of Wattmeter W2 under 2 Watt

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Hajo Dezelski

Accuracy of Wattmeter W2 under 2 Watt

Hello,

I have been using a wattmeter from Fox for powers under 1 Watt, but
the display is too nervous and hard to read. So I stumbled over the
Elecraft W2 and read that with the 200 W sensor, you can read also
power levels under 2 Watt. This would be really helpful for I
experiment with power levels down to 0.5 mW.

So before I invest, let me just ask some questions:

1. Has someone compared the power indicatores for the levels of 100 -
1000 mW with a precise wattmeter? As far as I understood each led
signifies 100 mW.

2. If I would use the computer readout: How precise is the output?
Just 100 mW or ist it e.g. 147 mW?

3. I am working max. 10 Watt with the Kx3, but normally use only
between 100 mW and 5 W max. Could I adjust with the calibration of
active sensor down to let's say 1 Watt instead of 2 Watt?

4. Is it possible to modify the transformer T1 and T2 of the sensor so
that the range would be (20W - 2 W and 200 mW. Or is there a sensor
like this available on request from Elecraft.

I know a lot of questions, but as far as I can see this meter would be
a real champion for QRPP and could be used with a WSPR TRX.

73 de
Hajo (DL1SDZ)

---
Cela est bien dit, mais il faut cultiver notre jardin.
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Rick Robinson

Re: Accuracy of Wattmeter W2 under 2 Watt

I don't have the paperwork in front of me but the Elecraft DL 1 dummy load
has provisions to measure power up to 20 watts with a 10% accuracy. Just
use a dvm. They also make a WM1 that handles more power with a .5 dbm
accuracy.

On Sunday, October 25, 2015, Hajo Dezelski <[hidden email]> wrote:

> Hello,
>
> I have been using a wattmeter from Fox for powers under 1 Watt, but
> the display is too nervous and hard to read. So I stumbled over the
> Elecraft W2 and read that with the 200 W sensor, you can read also
> power levels under 2 Watt. This would be really helpful for I
> experiment with power levels down to 0.5 mW.
>
> So before I invest, let me just ask some questions:
>
> 1. Has someone compared the power indicatores for the levels of 100 -
> 1000 mW with a precise wattmeter? As far as I understood each led
> signifies 100 mW.
>
> 2. If I would use the computer readout: How precise is the output?
> Just 100 mW or ist it e.g. 147 mW?
>
> 3. I am working max. 10 Watt with the Kx3, but normally use only
> between 100 mW and 5 W max. Could I adjust with the calibration of
> active sensor down to let's say 1 Watt instead of 2 Watt?
>
> 4. Is it possible to modify the transformer T1 and T2 of the sensor so
> that the range would be (20W - 2 W and 200 mW. Or is there a sensor
> like this available on request from Elecraft.
>
> I know a lot of questions, but as far as I can see this meter would be
> a real champion for QRPP and could be used with a WSPR TRX.
>
> 73 de
> Hajo (DL1SDZ)
>
> ---
> Cela est bien dit, mais il faut cultiver notre jardin.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email] <javascript:;>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email] <javascript:;>
>

--
Rick, W8ZT

Sent from Gmail Mobile
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John Oppenheimer

Re: Accuracy of Wattmeter W2 under 2 Watt

Hi All,

I agree with Ron, the DL1 can be very accurate with a good DVM.

I have computed diode voltage loss using an attenuator. The results are
here:

http://www.kn5l.net/DL1-diode/

John KN5L

On 10/25/2015 05:36 PM, Ron D'Eau Claire wrote:
> The DL1 can be very accurate.
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Don Wilhelm-4

Re: Accuracy of Wattmeter W2 under 2 Watt

In reply to this post by Rick Robinson

All,

Keep in mind that if you use the excellent method Ron describes, there
is a huge dependency on the precision of the dummy load - just any old
resistor will not do unless it is characterized first. It must be
characterized for not only resistance, but the resistance and any
possible reactance over the frequency range for which it is to be used.

With the resistance and reactance (hopefully zero) known for the
frequency of measurement, and the forward voltage drop of the diode also
known, the power can be calculated with a very small error.

I typically use the RF voltage observed on an oscilloscope connected
directly across a known dummy load - that voltage allows the power to be
calculated within 5% if your eyes are good at determining the 'scope
trace deflection.

73,
Don W3FPR

On 10/25/2015 6:36 PM, Ron D'Eau Claire wrote:

> The DL1 can be very accurate. As a QRP and QRPp enthusiast I have a homebrew
> version that goes back decades before Elecraft, Hi!
>
> A simple RF voltmeter is a common way and inexpensive to measure very small
> power levels. (For the more exotic measurements a bolometer or, optionally,
> an accurate well calibrated oscilloscope is often used.)
>
> The RF voltmeter system (which the DL1 uses) gets inaccurate as you get down
> into the barrier voltage range of the diode. In that range the response of
> the diode is no longer linear. My homebrew version uses a 1N34A Germanium
> diode which is darn near "unobtainium" these days but a good PIN diode such
> as Elecraft supplies in the DL1 is just as good. Both have a barrier voltage
> of about 0.2V.
>
> But you can make very accurate measurements even at very low levels where
> the barrier voltage makes the system non-linear with a little more effort.
> Instead of applying RF to the device, connect an adjustable dc power source
> of about a 1 watt. Use your accurate DMM to measure the voltage and current
> applied to determine the output as you vary the d-c power applied. The d-c
> power reading is the same as the RF power reading from such a device. So, by
> creating a calibration chart using accurate d-c power levels, you can now
> measure similar RF power levels with excellent accuracy.
>
> 73, Ron AC7AC
>
>
>

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kk5na

Re: Accuracy of Wattmeter W2 under 2 Watt

In reply to this post by Rick Robinson

I use the NORTEX Accuprobe. Nice inexpensive, versitile and very sensitive.

73, Joe KK5NA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On 10/25/2015 4:35 PM, Rick Robinson wrote:

> I don't have the paperwork in front of me but the Elecraft DL 1 dummy load
> has provisions to measure power up to 20 watts with a 10% accuracy. Just
> use a dvm. They also make a WM1 that handles more power with a .5 dbm
> accuracy.
>
> On Sunday, October 25, 2015, Hajo Dezelski <[hidden email]> wrote:
>
>> Hello,
>>
>> I have been using a wattmeter from Fox for powers under 1 Watt, but
>> the display is too nervous and hard to read. So I stumbled over the
>> Elecraft W2 and read that with the 200 W sensor, you can read also
>> power levels under 2 Watt. This would be really helpful for I
>> experiment with power levels down to 0.5 mW.
>>
>> So before I invest, let me just ask some questions:
>>
>> 1. Has someone compared the power indicatores for the levels of 100 -
>> 1000 mW with a precise wattmeter? As far as I understood each led
>> signifies 100 mW.
>>
>> 2. If I would use the computer readout: How precise is the output?
>> Just 100 mW or ist it e.g. 147 mW?
>>
>> 3. I am working max. 10 Watt with the Kx3, but normally use only
>> between 100 mW and 5 W max. Could I adjust with the calibration of
>> active sensor down to let's say 1 Watt instead of 2 Watt?
>>
>> 4. Is it possible to modify the transformer T1 and T2 of the sensor so
>> that the range would be (20W - 2 W and 200 mW. Or is there a sensor
>> like this available on request from Elecraft.
>>
>> I know a lot of questions, but as far as I can see this meter would be
>> a real champion for QRPP and could be used with a WSPR TRX.
>>
>> 73 de
>> Hajo (DL1SDZ)
>>
>> ---
>> Cela est bien dit, mais il faut cultiver notre jardin.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email] <javascript:;>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email] <javascript:;>
>>
>

Hajo Dezelski

Re: Accuracy of Wattmeter W2 under 2 Watt

In reply to this post by Hajo Dezelski

Hello,

Thanks for your suggestions. It seems that the owners of the W2 use it for
higher power settings than qrpp. So it is natural that nobody could answer
my questions.

So I will continue to use my Pm2 http://www.foxdelta.com/products/pm2.htm .
But in a private discussion I was pointed to a solution of the irritating
numbers shown on the display. I have no cabinet and the cable from the
RS232 was too long and not shielded. So there was some hf going direct into
the circuits. So I will build a box and take some ferrits and hopefully
will be happy.

Thanks for the advice and your time.

73 de Hajo DL1SDZ

Gruss
Hajo

---
Cela est bien dit, ...,mais il fault cultiver notre jardin.
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Hajo Dezelski

Re: Accuracy of Wattmeter W2 under 2 Watt

Hi Ron,

I bought the unit from a ham, who finds pleasure and has the equipment to
calibrate. And he did it to the unit and the sensors. This is all
documented and well done. So I could measure my wspr output of 500 uW
were I reached the 1 Mio km per Watt goal.
But I had the troubles described above, so although I hate tinkering I will
change my profession and will become a box maker ;-) and will report ...
after I have done my homework.

73 de Hajo
Am 26.10.2015 8:52 nachm. schrieb "Ron D'Eau Claire" <[hidden email]>:

> Hajo:
>
> A power meter based on the AD8307, such as the PM2 uses, can be very
> accurate and sensitive but requires calibration. The AD3807 takes RF in and
> produces a dc output proportional to the logarithm of the input signal
> amplitude.
>
> I have a homebrew version based on a design by W7ZOI that works FB down to
> below -90 dbM. That's the native sensitivity of the AD8307. You are quite
> right that shielding is needed otherwise any local source of RF can upset
> the readings. I presume the PM2 has an input attenuator but any RF getting
> to the AD8307 chip can cause errors. If you have a steady source of RF
> nearby (i.e. a broadcast station) it can introduce a fixed error in
> addition
> to the jigger you saw from the RS232 bus. That will depend upon how they
> have terminated the input to the AD8307.
>
> I suggested a solution that is not dependent upon specialized test
> equipment
> most Hams don't have handy or depending upon the manufacturer's calibration
> data. If that is not an issue, by all means the PM2 is suitable.
>
> 73 and have fun!
>
> Ron AC7AC
>
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Hajo
> Dezelski
> Sent: Monday, October 26, 2015 11:47 AM
> To: [hidden email]
> Subject: Re: [Elecraft] Accuracy of Wattmeter W2 under 2 Watt
>
> Hello,
>
> Thanks for your suggestions. It seems that the owners of the W2 use it for
> higher power settings than qrpp. So it is natural that nobody could answer
> my questions.
>
> So I will continue to use my Pm2 http://www.foxdelta.com/products/pm2.htm
> .
> But in a private discussion I was pointed to a solution of the irritating
> numbers shown on the display. I have no cabinet and the cable from the
> RS232 was too long and not shielded. So there was some hf going direct into
> the circuits. So I will build a box and take some ferrits and hopefully
> will
> be happy.
>
> Thanks for the advice and your time.
>
> 73 de Hajo DL1SDZ
>
> Gruss
> Hajo
>
> ---
> Cela est bien dit, ...,mais il fault cultiver notre jardin.
>
>

Hajo Dezelski

Re: Accuracy of Wattmeter W2 under 2 Watt

Silly me,

I was just told, that I even have a newer version PMA3
http://www.foxdelta.com/products/pm3.htm

It is sometimes a pain getting older.

73 de Hajo
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