Measure High Power Devices

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Volker
Newbie
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Joined: Thu Feb 28, 2019 11:59 am

Measure High Power Devices

Post by Volker » Mon May 20, 2019 6:36 am

I have an amplifier that can deliver maximum out power of about 36 dBm. It has a gain of about 45 dB.
I do ordinary VNA measurements with an input level of -17 dBm and an output attenuator of 20 dB. So it is on my side not to overload the receiver port...

What about the Gain Compression Utility ?

Max input power of the receiver port is +20dBm. Maximum Level for the utility +10 dBm. The users manual says that the power is swept from -20dBm to 0 dBm ( page 57 ). Marc stated in his youtube video "Pico VNA 106 Training Session 3" that the power ist swept from max ( 0 dBm) downto min ( -20dBm ) and demonstrated this with a slide.

If it works like Marc demonstrated the utility will immediatly overload the port and may damage ( ? ) it while the manual setup of the device is save.

Is there any protection or warning in the software that will stop this operation ?

Also I wonder how to stop the utility when using the option "Use existing sweep plan". Once started you can close the window but the sweep still seams to run. Waitcursor is visible and the field "12 Term Cal" in the bottom line is flickering until the time for the complete sweep plan has finished. After that the cursor turns to normal mode. I worry about this in combination with port overloading.

Volker

Gerry
PICO STAFF
PICO STAFF
Posts: 424
Joined: Mon Aug 11, 2014 11:14 am

Re: Measure High Power Devices

Post by Gerry » Thu May 30, 2019 11:09 am

Hi Volker,

Here is a response from Mark:

I will have to check back over my wording of the training video but I was using a lower power amplifier (15dBm) with more limited gain.

There are no protections against damage in our software so care does need to be exercised when using the P1dB and swept P1dB utilities.

The utility supports user definition of input and output attenuators either as user input attenuation values (assumed flat) or as an attenuation v frequency data files that are loaded to the input and output ports. In the case of 36dBm peak output power, a -16dB output pad would protect against damage to the VNA. A -26dB pad would ensure no overload of the receiver. A -20dB output pad might be the happy compromise, depending upon the expected or actual characteristic.

Say we have -20dB pad at the output and 45dB gain, that is 25dB of remaining gain, 24dB at the compression point.
If we pick a -20dB pad at the input too then we should be able to drive just past the -1dB compression point.

We can now either enter fixed 20dB attenuation at each port, or measure the attenuators to create loss characteristic files and then load them to their respective ports.

Once we have a measurement it may be necessary to more finely adjust pads at input and output to ensure that we are not overloading our receiver or that we are adequately establishing small signal gain and not wasting (limited) dynamic range by pushing too far into compression.

In general the PicoVNA will always complete a sweep before responding to user input. This is because sweeps are a fast hardware process, not soft interruptible.

Cheers

Mark.
Gerry
Technical Specialist

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