On Thu, 17 Jul 2003 10:58:16 -0700, Frank Gilliland
wrote:

In , Swan Radioman
wrote:

On Thu, 17 Jul 2003 09:58:13 -0700, Frank Gilliland
wrote:

In , Swan Radioman wrote:

On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland
wrote:

In , Swan Radioman
wrote:

Why is 12 watts the limit for a legal SSB radio?

Because the FCC says so.


Why?

I can only speculate. Any CB radio capable of both AM and SSB would probably use
the same final, which must be linear to allow SSB operation, and be capable of
16 watts PEP (4 watts AM, 100% mod). But the -average- power of SSB, if limited
to 16 watts PEP, would be higher than that of AM with a carrier of 4 watts RMS
(assuming a peak-to-average modulation ratio of 3 to 1), and could require a
final with higher power dissipation. So my guess would be that the FCC adopted
the lower limit of 12 watts PEP to put the average RF power of SSB -below- that
of AM, therefore preventing the need for a CB design that would allow AM power
greater than 4 watts carrier RMS.

If you have a better explanation, please share it.

The only one that I have seen is, they just took the 16 watts PEP for
AM, subtracted the 4 watts for the carrier.

Thats why I asked you earlier about PEP power for an AM radio.

The problem here is that AM PEP is not a simple sum. For example, if you start
with 16 watts PEP (100% mod) and subtract the 4 watt carrier then you are left
with 12 watts that must be split between two sidebands. So each sideband should
have 6 watts, but that's wrong because we already know that each sideband has
only 1 watt. That is also the reason why carrier and modulation must be measured
seperately with AM power -- because it's not simple addition.


So what do you think power output of a average legal SSB CB is? 12
Watts?