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Now, I wonder if someone here, with more accurate test equipment, can test the changes as above with a BNC âTâ , and report back here in terms of both SWR and Return Loss.
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If you just want to measure VSWR then I'm not sure it's necessary to do any extensive tests... A typical x10 scope probe will probably have an Rp of several thousand ohms at 29MHz in parallel with maybe 12pF. I think there could be some variation here though because a x10 scope probe usually has very lossy coax and I'm not sure the Zo of the coax is the same from probe to probe.
But the VSWR should remain quite low with the x10 probe even at 29MHz and it will be dominated by the influence of the 12pF.
Forgive me for posting up yet more simple models but I think you can model a x10 scope probe based on the Zo of its (deliberately) lossy coax. The crudest broadband model for maybe 10-50MHz would be 12pF in series with the Zo of the lossy cable.
So some x10 probes might look like 12pF in series with 50R (across a huge RF bandwidth) others might look like 12pF in series with 100R.
If the probe looks like 12pF in series with 50R then at 29MHz this would mean Rp would be about 4000ohms. So the VSWR of a 50R load in parallel with 4000R and 12pF at 29MHz would be about 1.1:1.
Maybe someone with more experience of playing with x10 scope probes can comment. I don't see them as precision devices and care is required to compensate them correctly and old/tired probes can often have unstable compensation as the probe is handled.