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On Sat, 21 Sep 2019 at 10:07, Andy G0FTD via Groups.Io <punkbiscuit=
[email protected]> wrote:

On Sat, Sep 21, 2019 at 01:20 AM, <qrp.ddc@...> wrote:

Yes, limiter diode will ruin measurement. There are two issues with

diode:

- it add parasitic reactance
- it add non-linear distortions of the signal

100% agree.

There is no simple way to protect RF device with no deterioration of it's
dynamic range.

Seems to be that way.

I had a brief research period last yesterday just to look up how others
deal with this issue.

It seems they don't, and simply practice safe procedure.

Spectrum Analysers on the other hand have much higher input levels, and do
have some
solutions, but are cannot be used in the case of a network analyser.

It obviously depends on individual instruments, but a quick check of mine
shows that the HP 8720D 20 GHz VNA I have, is *much* more tolerant of high
power & DC than my 22 GHz spectrum analyzer.

*8720D 50 MHz-20 GHz VNA*
* 40 V DC
* +30 dBm max
* No electrostatic discharge

*HP 70905A RF section of spectrum analyzer, 50 kHz to 22 GHz.*
* 0 V DC
* 15 to 30 dBm depending on the value of an internal attenuator.

Given that the attenuator in the SA is set by the the user from the
interface, I would say assuming it’s set to 0 dB is sensible, so the
maximum power is 15 dBm. That makes the power handling of the VNA 32 times
higher than the SA, and the VNA tolerating 40 V DC compared to 0 V of the
SA.

I remember my favourite instrument, a Hewlett Packard HP8594 SA having a
blown front end and getting a quote for repair.

73 de Andy

--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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