Ok, I'm going to lead you off into the world of radio crime.
A long time ago, I had trouble finding a frequency that was not busy. I went to the internet, and went looking for licenses, that others had. I found a channel, that was assigned to another surveyor, that was big on staying current, with all things. He had a slew of radios, and wanted his own private frequency, with a HIGH POWER communication, between crews, and office. Well, he has changed his methods, and now runs semi solo, and is no longer using this radio stuff. So, I borrowed his frequency. It is channel 11 in my old Legacy E RTK system. When I get into a noisy environment, almost ALWAYS this channel is clear.
Another comment. If ALL the available channels in the LS (the pre assigned channels) are busy, you probably are getting "Bleed Over" from other nearby channels. I did once set up on a hill, near a huge multi antenna cell tower. It was a big tall fenced tower, with loads of antennas. MISTAKE!
NO CHANNELS would work well. I finally made a long shot to a place in a cul de sac, (out in the middle of the cul de sac) and got a shot there. Moved my base. Ran with a deliberately LOWER antenna, (it was near my project) and it ran fine, with very little interference.
Sometimes UP ON THE HILL is counterproductive. Get low, where you are not going to pick up other signals, and near your site, and run less output power, and well, we can go back into the HAPPY HAPPY HAPPY zone!
I'm not telling you that these solutions are the BEST. I am telling you to "Get out of the box" and get productive.
Sometimes you have to make a trip through trouble, to discover it is not your equipment that is not working. It is your environment that is interfering. And, you will have to find creative solutions.
And, NEVER break the law.
N