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Hi Martin,

You are absolutely correct. I thought about it a bit more pretty much as soon as I pressed "send'.
I have now extracted my foot from my mouth and have put my teeth back in:-)

Firstly, there are two modes:
1. SA Mode where probe is used on the input to the TinySA. I believe the -52dB is pretty close in this case. But I will check.
Again, you are correct that the compensation capacitor will make the probe attenuation frequency dependant, depending on the input capacitance of the TinySA.

2. Sig Gen Mode where the probe is used to inject a signal into a circuit.
Here the impedance at the injection point will most likely be much higher than 50 ohms and therefore the attenuation will be less, probably much closer to your 20-30dB.
I can't argue with you practical experience here. I have also used a probe in similar circumstances but never measured the results.

I recently purchased a handheld digital oscilloscope and had intended doing some frequency response measurements on it using a TinySA as a generator and the TinySA Ultra to measure the level with the CRO bridged across the Ultra input.

I had also intended to check a few discrete frequencies using the x10 probe on the input to the Ultra. 455KHz, 10.7MHz for peaking IFs and 147MHz. The CRO is supposed to be good to 180MHz. I have already checked that I can see 147MHz from the TinySA in generator mode and I can. I did not have an SMA "T" at the time, so I could not do the 3 way test.

The use of the oscilloscope probe is a very convenient means of connecting to a circuit under investigation, both in probing and injecting a signal.

Still a work in progress.

Cheers...Bob VK2ZRE