Measure High Power Devices

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Volker
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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
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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
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Volker
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Re: Measure High Power Devices

Post by Volker » Tue Jul 02, 2019 9:11 am

Hi Gerry,

I can understand that one sweep is not interruptible. But I cannot understand that a sweep plan that consists of many single sweeps cannot be interrupted. It lokks like that this is still running even when you close the window.

Best

Volker

Gerry
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Re: Measure High Power Devices

Post by Gerry » Thu Jul 11, 2019 12:04 pm

Hi Volker,

Sorry for the delay in responding (I have been out of the office).

The P1dB sweep of power and frequency is indeed a single sweep plan of the whole test space. The whole plan runs on the hardware and is not uninterruptible until it completes. This would include closure of the P1dB window.

Could you tell me if what you are saying is that a new sweep starts after Utility window closure?

Regards,

Gerry
Gerry
Technical Specialist

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

Re: Measure High Power Devices

Post by Volker » Fri Jul 12, 2019 6:34 am

HI Gerry,

this is not a time critical discussion...

I just mentioned that if you close the utility window a sweep plan will not stop. It looks like it continues even so the data cannot be used since the utility window was closed.

I can imagine technical reasons that it is not possible to interrupt a single sweep, but none why it should not be possible to interrupt a sweep plan.

I think this could be a point on the feature list.

Still one question is open:
Will you start a power sweep from high to low power or from low to high ?

Volker

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