How to change frequency interference range on AKG rs 40 wireless microphone?

I supect your best bet would be Ebay. be sure to check the frequency your receiver operates on and get a mic that matches it.

This headset uses a 900 MHz frequency for connection from the headset to the base.
You will always incur lots of interference in a busy office using that frequency band. Any antennas on the roof or close by?
Amateur radio users?
The other thing, you might have a faulty power supply or "dirty power" coming into the unit. You can try and isolate in a current regulating power bar and see if that helps.
Else, consider changing technologies and moving to, say a DECT band.
Avoid, 2.4 and 5 GHz bands as they are in the wireless devices range and likely will incur equal amounts of interference.

Channel 2 mic's receiver needs the Squelch adjusted. The squelch control mutes the receiver so that when the transmitter stops transmitting, erroneous noises are not picked up and amplified.

Make certain the transmitter and receiver are on the same frequency band. There are stickers on both that say what frequency range they can tune to.

I would suggest that you change your operating frequency. The antenna being removed suggests that the receiver is picking up interference on that frequency. This frequency is in the UHF TV band, and although analog TV no longer exists, digital TV still uses some of the frequencies.

Purchase a new user manual here http://www.owner-manuals.com/search-AKG%20PR40.html

I don't know a whole lot about microphones, but if it's wireless, then it has to accept interference according to the FCC. Wireless microphones normally connect using RF transmitters/receivers which can normally be tuned to specific short-range broadcast frequencies, which can be interfered with by passing waves of other frequencies. Even if the broadcasted radio waves aren't the same frequency, or within the same bandwidth, the harmonic distortion radiates at multiples of the fundamental (broadcasted) frequency.
If you can, try changing channels and see if that clears things up. If not, then perhaps contacting the manufacture can help.

Ebay lists them

No, when you buy multiple wireless mics you have to select different channels per unit if you want to use them on the same stage.

hope this helps
thanks for your rating

help me please akg sr60 , when torn on just mute