Frequently I hear one ham tell another, while talking through an FM repeater, “your audio is low but maybe when you get closer it will come up.” That statement shows a lack of understanding about how FM works.
FM is short for Frequency Modulation. That means the intelligence, voice or other information, volume level is increased by increasing the deviation (the shift in frequency plus and minus from the un-modulated carrier frequency). One of the reasons FM is such a good mode of modulation when using a repeater is because the level of audio output remains constant after full capture (full quieting) of the repeaters receiver is achieved. So if the received signal is sufficient for full capture of the signal by the repeater’s receiver the audio will not increase or decrease with an increase or decrease of power reaching the receiver.
So if your audio is low and you have full quieting on the repeater output and you have not experienced that problem in the past using that repeater make the following checks.
Check the mike connector and mike cable. If possible change mikes to see if there is a change.
Check antenna connector, cable, and SWR to make sure no RF is getting into the audio stages and deteriorating their operation.
If your transmitter is capable of the new narrow band FM check to be sure the narrow band switch has not been toggled.
The deviation level of most modern transceivers can be adjusted by programming the desired deviation level. If your transceiver has such a programming feature then check to be sure it is correct. If deviation is set by an internal potentiometer it might be wise not to try to set the level without a deviation-meter.
If your transmitted audio is reported to be distorted and low check to be sure you are equipment is set to the proper frequency. It is easy to set the transmit frequency 5 KHz high or low in frequency and while the signal may still open up the repeater it will be distorted.