Roland wrote:I really should go and buy a CRT oscilloscope - as I'm sure anything I buy will be considerable better than anything I can build
Roland.
Once you've had access to an oscilloscope, it's almost impossible to do anything in electronics without one! Can you imagine life now without mobile phones or the Internet? It's like that!
I had to send my old Goldstar scope away some years ago for a repair and re-calibration, it was away for three weeks. It was like having my right arm cut off.
Everything I wanted to do I would reach for the probes...but they weren't there! It was so frustrating! Now the Goldstar has been retired and only re-awakened if its replacement is unavailable. (I had to send the new one back under warranty repair one time).
An oscilloscope is the best investment as far as test equipment goes that you can ever make in electronics, perhaps next to a multi-meter. Within the requirements of NBTV there are new models you can buy for just over 100 pounds, they're not super-duper, but they're good enough for NBTV unless you want to get into digital standards convertors and the like.
Put off that new PC, buy a scope! Even a second-hand one, you won't regret it!
However, if you don't mind mucking around with a few hundred volts, building your own is not that hard.
There are also PC based scopes, I have one I sometimes use with the laptop when 'on the road'...
http://www.picotech.com/
Steve A.