Re: Power Meter

Nick Kennedy
 

Most people do a power calibration on their PHSNA system at a "mid-range"
frequency like 10 MHz but do not do one over the expected frequency range
of the detector. A well calibrated scope is adequate for that (mid-range)
purpose.

The high end of the complete system is about 30 or 60 MHz depending on
which DDS is used.

If well constructed, the detector used alone can be reasonably flat up to
about 500 MHz, per Hayward and Larkin. I haven't had the equipment to
validate that, however. I expect it's OK up through 2 meters. without much
doubt.

I recently bought a used Fluke 6060A/AN signal generator at a great price.
It's 1980s technology and not at all state of the art. But I used it to
check the response of my AD8307 detector yesterday, from 10 MHz though 300
MHz at -10 dBm input. Referred to the reading at 10 MHz, it was down 0.8 dB
at 100 MHz and 1.8 dB at 300 MHz. Again, the signal generator itself isn't
super accurate, but I felt that this was a good validation that the
detector is working as it should.

73-

Nick, WA5BDU



On Tue, May 8, 2018 at 3:02 PM Philippe CREIS <Philippe.Creis@...>
wrote:

Hi all,

i think using a scope is not a good solution at all. Measuring a voltage
with an oscilloscope is a good idea. Provided you know the subtleties of
this device. An oscilloscope becomes very quickly false, even very false in
the measurement of a voltage. Look at this excerpt from an article
published by Yokogawa, and this is true for all the scopes:
"The analogue bandwidth is defined as the frequency at which the amplitude
measured by the oscilloscope has reduced by 3dB (-3dB point). This is
approximately 70.9% of the actual signal amplitude (Figure 1). This means,
for example, if a 200MHz pure sine wave with 10 Volts peak to peak is
measured with an oscilloscope with a bandwidth of 200MHz, the amplitude of
the displayed signal will be approximately 7 Volts peak to peak."

So, if you want to calibrate your wattmeter based on an AD8307 with an
oscilloscope on 430MHz, you will have to find a very, very expensive
oscilloscope !!!! Look rather on the side of the references of power, to
realize yourself, it will be much more precise.

--
73... Philippe - F4GRT




Message du 08/05/18 00:19
De : "Pravin via Groups.Io"
A : PHSNA@groups.io
Copie à :
Objet : Re: [PHSNA] Power Meter

Hi Alfredo,
It will be a over kill to purchase a power enter for calibration of
AD8307 chip meter . If you have an access for an Oscilloscope and having a
carbon resistor for 51 Ohms you can simply measure the voltage across the
resistor and compare it with your Ad8307 chip values .
Power = Square of Vrms/50 . Nothing will be more precise than that and
no need of sending power meters to be calibrated in US every now and then .

--------------------------------------------
On Mon, 5/7/18, Alfredo Mendiola Loyola via Groups.Io wrote:

Subject: [PHSNA] Power Meter
To: PHSNA@groups.io
Date: Monday, May 7, 2018, 5:51 PM

Hello,

I would like to buy a power meter to
calibrate my AD8307

Is there a power meter that doens't
require anual Calibration.

I line in Peru and it is expensive to
send the power meter to US just for anual calibration like
the Power Meter 6G of Minicircuits.

73
Alfredo.








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