13-11-2012, 11:46 PM
Perhaps I'm missing something, (not unusual), but that 'Advance' pad / dummy aerial combo. confuses the hell out of me. 
Why is the input terminal, that is connected to a generator whose source impedance is 75 Ω, labelled 37 Ω? I did some sums: assuming that the load on the DA and E output terminals is a very high impedance (which, itself, may not necessarily be so), the impedance that the generator 'sees' looking into the "37 Ω" socket is 75 Ω - as it should be, to match the generator's source impedance.* On that basis, that "37 Ω" input socket should be labelled "S.G. input: 75 Ω". Then everyone will understand that that socket should be joined to a generator of that impedance through a co-ax. cable whose impedance is also 75 Ω . . . . which is what is required and what 'Advance' clearly state is necessary and what their 'box' is designed to do.
* Moreover, that calculation of 75 Ω justifies the assumption that the load on the DA and E terminals is a very high impedance, otherwise that 75 Ω figure would be smaller).
Anyone care to enlighten my darkness, please?
Al.
Why is the input terminal, that is connected to a generator whose source impedance is 75 Ω, labelled 37 Ω? I did some sums: assuming that the load on the DA and E output terminals is a very high impedance (which, itself, may not necessarily be so), the impedance that the generator 'sees' looking into the "37 Ω" socket is 75 Ω - as it should be, to match the generator's source impedance.* On that basis, that "37 Ω" input socket should be labelled "S.G. input: 75 Ω". Then everyone will understand that that socket should be joined to a generator of that impedance through a co-ax. cable whose impedance is also 75 Ω . . . . which is what is required and what 'Advance' clearly state is necessary and what their 'box' is designed to do.
* Moreover, that calculation of 75 Ω justifies the assumption that the load on the DA and E terminals is a very high impedance, otherwise that 75 Ω figure would be smaller).
Anyone care to enlighten my darkness, please?
Al.
