Transmitting hot or just fine?

I wouldn't transmit w/o an antenna or a dummy load. Any CB shop can check it out w/o the manual or schematics. Will this help? http://www.radiomods.co.nz/unidenpc66pc66a.html

I have a dummy load. It's a quart paint can with an array of resistors inside equaling 50 ohms. I printed a picture of Red Fox and taped it on there ("You Big Dummy").

I've come across that page. L8-10 and L13 are part of the output network from the final transistor to the antenna. If I am reading the schematic right, it's a collector-modulated transmitter just like most CB radios I've seen. That means it achieves 100% modulation (and works the best) when the audio from the modulator makes the voltage on the final's collector peak at 24v and valley at 0v. That would mean the peak envelope power would be four times the idle carrier power, which should be 12 watts. I seem to remember reading that barefoot CBs are 4 watt radios, not sure if that's PEP or carrier.

Without a service manual having a detailed transmitter alignment procedure, I don't want to tweak these. The other option would be to get a new CB, measure the output of the rig, and then compare. It could be that I have a modulator problem.

I don't want to mess with the output network without a procedure because it could screw with the harmonic suppression. This is where you generate interference that gets you noticed. I'm going to see if there are CB shops in the area but they'll likely want more than I paid for the radio to look at it.

For now I'm not going to sweat it. I'll revisit the radio's performance when I have something to compare it to. Without an antenna it doesn't matter if the radio puts off 4 watts or 40.

Ed

 

Much appreciated. I suspected that this would be the case but I always try to gather information before just turning the tweak tool loose on the adjustment points.

 

So, good news.

I aligned the thing while watching the output on an oscope. It gets 3 watts of carrier, if my meter is to be trusted. When I whistle into it, I can see the modulation envelope does exactly what I'd expect from an AM transmitter. The radio has an automatic drive limiter so it reduces AF drive if it's seeing over-modulation. I can see this in action on the scope.

Although I'm only seeing 3w carrier, that is not as big a problem, as the difference between 3 and 4 watts in radio is hardly anything.

As far as I'm concerned, it's time to make an antenna.

Ed