clip wrote:Hey all,
Tried to add talkback to this PC76 by soldering a pot and on/off switch between the ext speaker and pa terminals. Should have gone smoothly but obviously I screwed something up
When I tried to TX, I got high SWRs by the meter on the radio and my ANT warning light came on. I went through and checked my cable/mount for shorts and the problem seemed to be when I had the power cord plugged in. I've checked the three prongs in the back of the radio with the center conductor of the antenna, and both the positive and negative posts show a connection to the center conductor. Should this be right?
With an external meter connected, I still got connection between the antenna and ground, but slightly lower SWRs and no ANT light. With an older CB connected, the antenna behaved like it should and stayed separated from the ground plane.
Should I have a connection between both the positive and negative terminals and my center antenna conductor?
Hi,
If you want an ON-OFF switch for a talk-back the easiest way is to put a 47 Ohm to 100 Ohm resistor from pin 4 of the mic jack to the Channel 9 switch. Disconnect the wires from the channel 9 switch and solder the wires that give you normal operation together; leave the other 2 disconnected. I would put some electrical tap on the wire leads and roll them up.
When you flick the switch that will turn the T-B on and off. To make it variable use a 250 Ohm pot and put a 33 ohm resistor in series with the potentiometer. One end goes to chassis ground and the other end goes to pin 4 of the Mic jack. Place the 250 ohm potentiometer where the Delta tune control is. I would just center the delta tune and tape up any exposed metal on the delta tune and tuck it inside the radio.
Keep in mind that the radio's case is part of the antenna system ground. The chassis ground is the Pin 1 of the Mic jack, an IF can or the input power lead ground. Putting a resistor on the case ground will affect the antenna system and give you a bad SWR. This is true for 99% of all CB radios. The Cobra 19 puts the case ground and the chassis ground at the same potential. Most Ham radios are like that as well, this includes the HR-2510. That is why the HR-2510 works so well with amps.
I bet you are using the case ground, which is the antenna ground,that is why your SWR indicator is lighting up.
Respectfully,
