Use the pa function and plug an external speaker into it. It can give you a rough indication of how loud you are and how you sound.
No worries man. It works, not a real talkback, but at least you can see what you sound like and how loud it really is. I do it with my PC122xl, used it to check my 2018 extreme mic. You will be happy with the cr-577. They are good mic's, I love my 2018 extreme. Anyway glad to have helped and hope you get everything situated. God bless.
I would adjust the pot, or have a pro tune up your radio. Probably won't even need a power mic once it's tuned right. If you stick a power mic on it, and the modulation pot is halfway open, you're just trying to shove more through it and it will probably just squeal.
73,
RT307
How did you know it squeals? With a PA speaker plugged in?
Do you have the mic wired for a Royce?
Did they wire it up for you ?
I found the literature that comes with the CR577
http://www.servicedocs.com/ARTIKELEN/7200247450001.PDF
Pin 1(red)
I'm thinking the PTT ground and the audio shield should go to pin 2(black&shield)
Pin 3(white)
Pin 4(blue)