SSB and over modulation?

aphil138 · #1 (**permalink**) 07-04-2006

I was finally able to call in to Cruiseheimers this morning on my SSB radio. It was explained to me that I could be heard loud and clear, I was over-modulating. Can anyone explain that to me?Alan

gc · #2 (**permalink**) 07-04-2006

Over modulation is a distortion of the audio being transmitted. The audio (your voice) is mixed with radio waves to form the transmitted signal. It is then unscrambled on the receiving end. This mixing is done by modifying the radio waves strength according to the audio wave. When you overmodulate it is trying to reduce the radio waves strength below zero. Obviously this does not work and generates distortion by the time it is de-modulated on the other end. The fix is to lower your voice or move the microphone further away from your mouth. This reduces the audio volume going into the mixing process and gets things working the way they are designed to work.
Find someone to work with and try several transmissions with different voice levels to find which gives the clearest reception.

aphil138 · #3 (**permalink**) 07-05-2006

Thank you.. so the problem is with me rather than with the gear. Comforting, at least I know the installation is working.
alan

k1vsk · #4 (**permalink**) 07-05-2006

Not to get too technical but it's not actually over-modulation which is a term commonly used on FM and AM but is distortion of the audio. You can't over-modulate an SSB signal as the signal is essentially all voice audio, i.e., the signal level rises and falls with the level of your voice.
Long story short - rather than figure out how loud/soft near.far away to speak, just pick a comfortable voice and distance from the mic and adjust the mike gain control such that the audio is clear. Obviously, it helps to have someone listening...

aphil138 · #5 (**permalink**) 07-06-2006

OK, This is a SGC2000 with an auto tuner. It has no mic gain that I know of. Is there a good frequency to use to find someone to test things out with?
alan

k1vsk · #6 (**permalink**) 07-06-2006

If you are at a marina, what I'd do is walk the dock looking for someone who has an antenna (other than ther typical VHF) and ask them to monitor your transmission. Their close proximity will help ensure that they are hearing your signal without any interference. The goal is to "modulate" the signal at the strongest level without causing distortion as SSB transmitted power is a function of audio level. Any frequency will suffice.
Don