09-06-2016, 11:12 AM
I should point out that the analyser I've given to the museum, like the one I still have, is designed to scan the spectrum. This shows up problems such as spurii and ingress that a single channel measurement would miss.
My own meter will show the levels of up to four channels simultaneously, which is even better!
The point is that, because of the scanning process, each channel is only sampled for a brief period which is fine with negative modulation because there is a 100% modulation sync pulse every 64µS whereas, on normal programme material, a positive modulation signal might have 100% peak white signals once in a while. Even a test card has very little peak white in it, if you look closely.
My own meter will show the levels of up to four channels simultaneously, which is even better!
The point is that, because of the scanning process, each channel is only sampled for a brief period which is fine with negative modulation because there is a 100% modulation sync pulse every 64µS whereas, on normal programme material, a positive modulation signal might have 100% peak white signals once in a while. Even a test card has very little peak white in it, if you look closely.
