Jack_Crow
Enlightened
Re: Old, Old panel meters, discovered in a box tod
Zel,
Answers interlaced.......
(Jack_Crow: Afraid that I know very little about radio systems, so can't tell you why the systems used differnece impedances. Only indication on the meters to do with impedences is Res <0.7?, though the word res there tends to make me think it's somehow referring to the resolution of the meter rather than anything to do with the system it's to be connected to.)
Meter movements internal impedience are usually on the low side that's what the .7 number is most likely showing.
The whole bit with dividing up the RF spectrum into 'bands' came out of WWII as a short hand (and somewhat classified) way of ID'ing different frequencies. P band, C band, Ku, ect.
As for the transmitter impidence, it works out this way. The Britt RF guys use 75 ohms, at 75 ohms, you get maximum RV voltage transfer.
At 50 ohms you get maximum RF current transfer.
Generally speaking it works out to a VSWR difference of 1.2 and if your smart, you won't get worked up about it.
That's why instruments made for the Euro market are set up with 75 ohm I/O.
Enjoy your old toys and use them with care.
Zel,
Answers interlaced.......
(Jack_Crow: Afraid that I know very little about radio systems, so can't tell you why the systems used differnece impedances. Only indication on the meters to do with impedences is Res <0.7?, though the word res there tends to make me think it's somehow referring to the resolution of the meter rather than anything to do with the system it's to be connected to.)
Meter movements internal impedience are usually on the low side that's what the .7 number is most likely showing.
The whole bit with dividing up the RF spectrum into 'bands' came out of WWII as a short hand (and somewhat classified) way of ID'ing different frequencies. P band, C band, Ku, ect.
As for the transmitter impidence, it works out this way. The Britt RF guys use 75 ohms, at 75 ohms, you get maximum RV voltage transfer.
At 50 ohms you get maximum RF current transfer.
Generally speaking it works out to a VSWR difference of 1.2 and if your smart, you won't get worked up about it.
That's why instruments made for the Euro market are set up with 75 ohm I/O.
Enjoy your old toys and use them with care.
