12-11-2023, 12:30 PM
Hi Steve
I had recollections that pre-emphasis had to be applied to one of them. As I am not paid to think anymore I looked it up.
PM has inherent 6 dB/octave whereas FM does not.
To make FM the same as PM, 6 dB pre-emphasis needs to be applied to the FM modulating signal.
The 6 dB/octave improves the S/N radio at the higher modulating frequencies.
On receive, de-emphasis need to be applied to restore the incoming signal to the original source signal.
This is separate to any signal/frequency processing that may have been applied to the original source signal transmitted.
If the early Japanese radios used FM this would explain why they sounded different.
I had always assumed that maybe they sounded different because they had been set up to better suit the Japanese language.
But it looks like the radios just did not include any pre-emphasis. Overlooked during design maybe?
With crystal looked radios, PM is easier to implement on multi channel radios as it provides for consistent deviation between channels where as this is difficult to achieve with FM. In addition FM can reduce transmit frequency stability due to the means used to achieve the FM.
73
Igor
I had recollections that pre-emphasis had to be applied to one of them. As I am not paid to think anymore I looked it up.
PM has inherent 6 dB/octave whereas FM does not.
To make FM the same as PM, 6 dB pre-emphasis needs to be applied to the FM modulating signal.
The 6 dB/octave improves the S/N radio at the higher modulating frequencies.
On receive, de-emphasis need to be applied to restore the incoming signal to the original source signal.
This is separate to any signal/frequency processing that may have been applied to the original source signal transmitted.
If the early Japanese radios used FM this would explain why they sounded different.
I had always assumed that maybe they sounded different because they had been set up to better suit the Japanese language.
But it looks like the radios just did not include any pre-emphasis. Overlooked during design maybe?
With crystal looked radios, PM is easier to implement on multi channel radios as it provides for consistent deviation between channels where as this is difficult to achieve with FM. In addition FM can reduce transmit frequency stability due to the means used to achieve the FM.
73
Igor