Thanks David for the advice. I was looking at Stewart of Reading stuff after recommendation from Ed Dinning. No doubt HP makes the best RF test equipment in the world. A budget of £750+2500 = £3500 seems out of my league. It would be like firing a NLAW and then a Javelin into my savings against the backdrop of costs of living crisis. I had many hobbies, i probably spent significantly more than £3.5K on other hobbies in my younger years. The older i get , the more prudent i become with disposable income. I have a big mortgage to repay. Probably it is a question of how justifiable to spend that amount on a serious hobby and how many more years i will stick to this hobby before i get bored of it. I am not that crazy about Ham radio and restoration of antique radios. I just read about RF stuff and make homebrew radios to take my mind off from stress at work and the pandemic.
Realistically I would go for the entry-level offerings by Rigol or Siglent. I have been eyeing for the Siglent SSA3015X PLUS with tracking generator (resolution bandwidth of 1Hz, -161 dBm/Hz Displayed Average Noise Level ) at about £1265, and the Rigol DSA815-TG with trackng generator at £1000 ((DANL) <-155dBm/Hz,RBW = 10Hz. I don't have a bench, any HP or Macroni beasts would be too bulky and heavy for my small PC desk. The modern spectrum analyzers are very light and compact.
The more I read about the IP3 measurement, the more I realize it needs very good equipment. The TinySa video gave the over-simplistic illusion that it is a simple measurement. This Texas Instrument article is probably the best explanation why the slopes of the two straight lines (fundamental and IMD3) in the power log-log graph are 1 and 3 respectively:
https://www.ti.com/lit/an/slyt090/sl...oogle.com%252F