You are talking about a radio band which, by
Finally, FINALLY, the voice of reason. What he says is the absolute truth. You will NEVER get better than telephone quality audio from an aviation AM COM radio. Never. Worse, under some conditions, yes. But never better. But then again, we've all been flying with AM radio since the 1920s and nobody seems to mind that we can all get good communications with it (albeit sometimes tinny). And the man is correct, your audio panel isn't all that shabby. Outdated? Yes. Bells and whistles? Yes. But extremely functional until you decide you want more "hi-i" from your audio system.
Now, if you want to upgrade to the latest PS or Garmin panel with all the bells and whistles and slide that 197 out for the latest and greatest comm...you will still be limited by the FCC bandwidth/rejection/response parameters set for the aeronautical radio service. Will it be better? Perhaps. Will YOU hear what you sound like on the other end? Not unless they play the skimmer tape back for you. Can you plug in your smart device, call for clearances, and listen to tunes while committing aviation and have it sound good with the new stuff? Sure. If you have the AMUs to spend...it's your ride.
Is true. But fix your radio first. Then, if you want the bells and whistles and are willing to spend the money, go for it.
Full disclosure: hold a general radiotelephone license after my 1st Phone expired in '83, 15 years in radio station engineering, and partner for 5 years in an avionics shop (and an extra class amateur license).
Full disclosure: Hold the same general FCC radiotelephone paper after mine expired. Started fixing Narco Omingators when I was 14 with a neighbor who was an avionics tech back in the day when you could do it from the back of your pickup truck (1957) and my local airport dirt strip. Worked my way through college as an avionics technician for a major airline, and graduated with a degree in Semiconductor Physics. Was immediately employed on the Surveyor, Apollo, and Viking space programs as a radar engineer. Got my MSEE at night. Founded an avionics manufacturing company in 1973 that is going today. Invited author monthly column on avionics in Kitplanes Magazine. Amateur Radio Extra and Qualified FCC Examiner. Qualified FCC Type Acceptance Engineer. I ain't got nuthin' more, other than A&P IA.
My suggestion? Have your local shop go through the chain from the mic input to the antenna, get the 197 aligned (there are still shops who know how, despite King's pulling back of the tech manuals), have them run an SWR check on the antenna system and get what you have working at its best and go fly. Yeah, it may cost you half an AMU. But that's a lot cheaper than a new panel, radio, etc without knowing whether what you have now can be/is working correctly.
I'll modify the suggestion, if you don't mind. Three major parts to the problem. Radio. Cable. Antenna. First, test the airplane radio IN THE AIRCRAFT for power output and modulation. Then, use the aircraft radio power output to drive a VSWR detector on the cable-antenna combination. Then, load the cable with a dummy load and see what happens. If all this check out, you've got an audio problem, but from what you've given us to date, it sounds like an RF problem.
Just my $.02; for the record, no financial interest in any of the manufacturers mentioned, any avionics shop, or provide equivalent services...just talking from personal experience and observation.
$0.02 Isn't that 8% of two bits 
Mine too. Let see if we can solve this problem between us.
Jim
