C.b. is transmitting weak.
If it is low audio, it could be a problem with your mic or his speaker. If your signal is low, I suspect it is likely to be an issue with your antenna system.
The antenna systen consists of the feedline or coax cable and the antenna. The feedline should be inspected for evidence of damage from being pinched, cut or water entry over its entire length., Remove, replace or reposition to prevent the cable from becoming damaged in any way.
The antenna itself should ideally be located at the highest point on the vehicle. Further, it should be secured to firmly into the metal parts of vehicle - preferable to a large, flat surface. The surface should be grounded.
Matching the antenna system for lowest SWR to the transmitter is required. SWR is a ratio of "power out" of the transmitter to "power that is
reflected back" from the antenna. Ideal theoretical ratio or "match" is
1:1 (or one to one). Real-life is more like 1.1:1 (one point one to one). Most
transmitters are perfectly happy with a match (or mismatch as the case
may be) of 1.5:1 and some even up to 2.0:1. More than this is asking for trouble. A
mismatched antenna system can cause RFI and failure of the output final
Matching or lowering the SWR of a radio to an
antenna system requires that an SWR meter be installed between the
antenna coax or cable and the transmitter's antenna connection point.
There are two types of meters - dual needle and single needle. The dual
type is more expensive, but easier to work. The meter must be capable
of working on the frequency it is to used on. This means if it is
marked as a 400 - 512 Mhz or UHF type, it will probably not be accurate on 27
Mhz or HF.
Once the meter has been installed, transmit the highest
frequency or channel and take readings. Do the same at the lowest and a middle
frequencies and record findings. Physically adjust the length of the
antenna whip up or down in the antenna base - by no more than 1/4" inch (for 27MHz CB frequencies) and
check again. After a few tries in one direction, you should begin to see how shortening
or lengthening the whip changes the SWR of the system. Once set
correctly, the middle frequency will have the lowest SWR value while
the lowest and highest frequencies will have pretty close to equal, but higher SWR values.
It would look something like this: Ch1 = 1.6:1 Ch 20 = 1.2:1 Ch40= 1.6:1
Of course, if Ch1 = 1.7:1 and Ch 40 = 1.6:1 that would be fine, too. Once completed, the SWR meter can be removed from the antenna system.
A poorly matched antenna system can cause permanent damage to the transmitter, if not corrected.