New Frequency, Old Problems
I have a personal example of problems with bleedover on 121.775. During a nice clear winter day back in North Central Region (my second stint there), we had recently made the conversion for our aircraft, L-Per, and Pointer Practice Beacon to 121.775 MHz. A new crop of cadets had just been taught how to use the venerable L-Per and were itching to try it out. I was more than happy to oblige! Our airport had an FSS on the field--to be extra nice, we not only let them know that we'd be conducting training, but showed them just what an ELT looks like! The Practice Beacon is called such because a PELT is a PERSONAL ELT, and its a much calmer thing to hear "practice beacon" on the radio than "ELT."
The Practice Beacon was "hidden" in plain sight on a wooden post near the FSS's weather monitoring equipment. It was about 100 feet from their front door. This was the cadets' first time using an L-Per so we wanted a simple and positive learning experience with nothing tricky.
The tower-controlled field we were practicing at had a ground control frequency of 121.750. 25 kHz spacing, see? Our so-called "safe" frequency overloaded the ground controller's radio so badly that he called the FSS. The FSS was located about 100 yards from the tower. The briefers there calmly took note of the problem, and when we showed up a half hour later or so, they let us know. Why they didn't go outside and shut the thing off themselves was completely beyond me. Since we were terminating practice for the day anyway, we shut off the beacon and elected not to re-hide it.
In any case, it only goes to show that the new frequency is not without its problems. The moral of the story? 1) Hide the practice beacon more than 400 feet from the tower--a LOT more. The other side of the airport is a safe bet. Be nice and responsible and let the locals know you're conducting training, and tell them how they can get in touch with you. By "locals" I mean the FSS at 1-800-WX-BRIEF, your local tower, RAPCON, airfield manager, and/or whoever else you think might be important.
On another subject, changing to 121.775 MHz for our Practice Beacon frequency does not necessarily negate our capability to train with other organizations who are using 121.6 MHz. Your L-Per should be able to receive 121.5, 121.6, 121.775, and more frequencies depending upon your model. Naturally, you need one receive crystal per frequency. I hope you didn't throw away that 121.6 Rock, because it would be better to keep it in there. I don't have personal experience with other organizations that hunt ELTs, but I still think that CAP can play along.
To clarify: just about anybody can add crystals to an L-Per. To swap TRANSMIT crystals on a Pointer or other practice beacon requires a professional. This is due, in part, to the type-acceptance of ELTs by the FCC.