The easy standard I know:?? 2x(max audio freq + max dev) = bandwidth.? Although this isn't 100% accurate, it is the approximation the
FCC accepts for determining occupied bandwidth for narrow FM.? I beleive this method accounts for 90% of the energy, but there
is still occasional low level feculence outside this bandwidth approximation.? Maybe not a problem if stations are widely seperated
geographically, but should be looked out for.? There are more detailed formula, but not necessary.
So: 2x(3k+5k)=2x(8k)=16khz
and: 2x(6k+5k)=2x(11k)=22k??
and: 2x(5k+5k)=20khz
and: 2x(5k+4.2K)=18.4k
and: 2x(3k+4.2k)=14.4k?? I beleive this is what the 2meter coordinators specify in Southern California as they use 15khz spacing.
If only there was still room for 30khz channel spacing.
So the question, what is the max audio frequency and how much do you have to reduce the dev to accommodate the 15Khz
spacing and any drift?? Does anyone out there have a audio spectrum analyzer to find out the maximum frequency of the program
content after improvements are made with a good sounding mic and audio stages?? Human speech above 4k is uneccessary, but
harmonics from singing or screaming can go on up to 17K?.? Most of what you need for hard consonants is 1k to 3k.? Do you need
to sacrifice dev for hearing a baby scream?? Maybe you want to roll that off.? There is a lot of conflicting information out there from
people who equalize as they are often mixing many different musical sources and seeking a subjective "feel".?
Where the problem is: So. Cal specifies 4.2 max dev but radios shake out of the box with 4.5-6kc dev and almost no one will admit
that they ever check their radios, let alone performed Mic gain, Freq and Dev adjustments or even know what that is.? After bringing
a service monitor to club meetings for years, only 2 or 3 people were ever interested in keying their portable for a quick check.?
I noticed that OQKs website showed some compression and/or auto-leveling.? I don't much care for compression because it can only
make clipped stations sound worse, but maybe 3db of auto-levelling might help, as we see people who are modulating anywhere between
1kc and 6kc dev and varying mic levels, from timid to listening to the car stereo in the next lane on the freeway.? It is important to try to
"minimally" get people between 2 and 4kc dev at the repeater TX in order to avoid wearing out volume controls and still avoid pushing
the level into dev clipping that will increase intermodulation and harmonics that will require a post filter to avoid scratching the repeater users
15kc and 60miles away, because they can do the same to you just by tweeking their IDC pot.?
The other problem is having all this bandwidth available so that some users can abuse it and make a bad name for you.
If you want broadcast quality, maybe start by mortgaging the house to buy a broadcast station and frequency and actually have the room
to improve the audio quality of that broadcast station and maybe make some money from it as well.? I have heard some poor FM stereo
stations out there and a couple of really clean ones, so there is room out there for some purists with the desire.?
