How to verify the amplitude of a basic 100MHz module

[enut11]

I want to verify the high frequency amplitude response of my Tek 2445 CRO to 1% or better, if possible.
I have a 100MHz module specified as 13dBm (no tolerance) which I understand is 2.8Vpp. The module is powered from a regulated 5v supply.
The 2445 shows 2.34Vpp on the 50 ohm input which looks to be a bit low for a 150MHz instrument so I want to be able to verify the output of the 100MHz module before I draw any conclusions.
I do not have an RF power meter but I do have a Nano VNA and an accurate DMM.
Question: is there a simple way to verify the 100MHz module amplitude using basic equipment and/or perhaps a DIY circuit?
enut11

[moffy]

Found this: https://techlib.com/files/detect.pdf
while looking through this: https://www.eevblog.com/forum/projects/idea-for-super-peak-detector/
For the 'detect.pdf' circuit if you used a dual schottky diode it might be possible to use one as a temperature compensated reference for the offset.

[enut11]

Hi @edavid
The module outputs a sine wave.

[radiolistener]

You can use some chinese module with logarithmic-detector. They usually have about 60-90 dB usable dynamic range. But you're needs some reference source to calibrate it.

Something like this one: https://www.aliexpress.com/item/1005007116984716.html
Or this one: https://www.aliexpress.com/item/1005007221165402.html

If you want more professional equipment, then look for RF voltmeter.

[enut11]

Thanks. What type of 'reference source' do you have in mind?

[radiolistener]

Thanks. What type of 'reference source' do you have in mind?

It can be some oscillator with stable and known amplitude. For example you can use some TCXO powered from REF voltage source and ask someone who own calibrated RF voltmeter to measure it, then you can use it as reference source.

Another but less reliable and less precise way is to measure some low frequency oscillator (about 10 MHz) with 200-300 MHz bandwidth oscilloscope, it should give you result within about 5-10% error. Then use it to calibrate logarithmic detector module from such 10 MHz reference and then use logarithmic detector module to measure 100 MHz signal.

The logarithmic detector allows you to use low frequency (about 5-10 MHz) source for calibration and then measure much higher frequency.

If you have oscilloscope with >= 400 MHz bandwidth, then you can measure 100 MHz signal amplitude directly with oscilloscope. But oscilloscope measurement is not so precise, the error will be about 5-10% or even worse if frequency is more than 1/3 oscilloscope bandwidth.


Another option is to use tinySA Ultra, it can measure signal level, show signal spectrum and can be used as reference source, but its cost about 100 USD.

If you decide to use tinySA Ultra or logarithmic-detector, then also buy 20 dB attenuator and connect it through attenuator, because 2.34Vpp (which is +11.4 dBm at 50Ω) is pretty high level. With attenuator you will need to add attenuator value to measured signal power in dBm.

So, it depends on your budget.

[David Hess]

I want to verify the high frequency amplitude response of my Tek 2445 CRO to 1% or better, if possible.
I have a 100MHz module specified as 13dBm (no tolerance) which I understand is 2.8Vpp. The module is powered from a regulated 5v supply.
The 2445 shows 2.34Vpp on the 50 ohm input which looks to be a bit low for a 150MHz instrument so I want to be able to verify the output of the 100MHz module before I draw any conclusions.

Gaussian response for a 150 MHz oscilloscope should be down to about 84% at 100 MHz, or 2.32 volts peak-to-peak, so your measurement is consistent with likely errors.

As far as accurately measuring the output of your 100 MHz source, a sampling oscilloscope or sampling voltmeter would be my first choice.  Analog Devices makes some logarithmic RF detectors which should be accurate.  A compensated peak detector using microwave diodes should also work well.

[Postal2]

vacuum temperature converter.

http://lampes-et-tubes.info/sp/sp059.php?l=d

[enut11]

Thanks everyone. Some interesting replies, especially the last one!
The logarithmic detector solution proposed by @radiolistener does not appear to meet the 1% error requirement. However, the TinySA Ultra sounds like a wonderful tool to be explored at a later date.
@David Hess points out that my 2445 may already be in spec but it might be fun to verify that in some way.

As a first approximation for a viable solution I am going to build the circuit based on an article proposed by @moffy in Reply #1, dectect.pdf.
The response is shown as linear for RF signals greater than about 200mV.
enut11

[jonpaul]

see Tektronix serv man 2445, on testing, spec and repair of input mod.

Read 1980s Tektronox Circuits Concepts book


Oscilloscope vertical amplifiers

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