Rough Calibration of Attenuators When Used on 10GHz.

 

A bit of activity in the lab today:

While I have two SMA attenuators capable of working at 10W with 10dB nominal on 10GHz, I wanted to test some lower cost attenuators specified up to 6GHz. How to test that without a true, calibrated 10GHz signal generator. Some thinking was needed. Here is what I did:

Using my calibrated (well enough for me) RF generator on 70MHz entering the signal into the up-converter described a few days ago, except omitting the output (2-stage) amplifier, just using the DRO/Mixer and the first (buffer) stage module.

This got me an output on 10GHz close to the output on 70MHz, e.g. 0dBm on 70MHz -> 0dBm +/- 1dB on 10GHz. It looks like the buffer on 10GHz essentially compensated for the loss in the (passive) mixer. OK, now I have a reference signal, showing -1.5dBm on the HP432 power meter.

Here are the values measured with the HP432:

10W/10GHz/10dB:-10.5dBm   ->9dB

2W/6GHz/10dB:    -11dBm      ->9.5dB

2W/6GHz/6dB:      - 7.5dBm    ->6dB

Non-brand

6Ghz/6dB:             - 9.5dBm    ->8dB

Return loss has not been tested, so the impedances are not well known, but given  the values I got from the brand attenuators I used, those are probably close enough for my purposes.

So now I have a good set of SMA attenuators capable of handling up to 10W, and with sufficient attenuation to avoid destroying the thermistor mount of my HP432 power meter.

Before anyone aks: Yes, I did terminate the input and output of the 200mW output stage, to avoid those stages oscillating. They might be unconditionally stable, but I do not know. With components/modules like this, better safe than sorry.

All this took some time because I removed +12V DC power from the unit every time I changed attenuators etc.

I do have 2 more attenuators capable of operating on 10GHz, those have N-connectors. They will be tested together later, as one of them is mounted in my 2.4GHz up-link transmitter system. Now, at least I know that I can safely measure power with sufficient accuracy on 10GHz.

Why do all this? Today I received a 2W amplifier from another seller in Italy, and I do want to test that one.