Re: Power Meter


Steven Dick
 

Quite correct. If you need the amplitude to be accurate to ~1%, you need to
derate your scope by a factor of 0.1x, meaning that on your 100MHz scope you
can only capture 10MHz with a 1% error in amplitude. If you reduce this
reqquirement to 3% accuracy, you need to derate it by a factor of ~0.3x, so
a 100MHz scope can accurately measure 30MHz to 3%.

-----Original Message-----
From: Philippe CREIS
Sent: Tuesday, May 08, 2018 4:02 PM
To: PHSNA@groups.io
Subject: Re: [PHSNA] Power Meter

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.






Join PHSNA@groups.io to automatically receive all group messages.