Hey there, trainwreck...
Actually, Parkview EMS and Tuttle PD aren't quite on the same frequency. Parkview EMS's repeater output is on 155.94 MHz, and Tuttle PD's repeater output is on 155.9325 MHz.
BUT, because these two frequencies are very close, they may at times be heard on a radio programmed to either of these frequencies if the radio doesn't have high selectivity specs... like many scanners. In fact, I tune my base scanner, a lowly BC145XL, which isn't capable of accepting 12.5 kHz channel-spacing frequencies, to 155.94 just to listen to Tuttle PD. If the radio has better selectivity and is operating in the proper mode for each channel (NFM in the case of Tuttle PD, FM in the case of Parkview EMS), they may not experience this interference most times.
Programming PL tones may help to reduce interference, as KD5WLX advised. Keep in mind that once the squelch is broken on the repeater in question (or on your scanner), it will continue to remain open until all signals sufficiently strong enough to keep that squelch open have subsided, regardless of the PL tone they are transmitting, and this may still allow interference to reach your scanner, albeit in smaller amounts.
Generally speaking, the FCC doesn't do a whole lot in coordinating the frequencies that they assign. Public safety frequency coordination in Oklahoma is handled by APCO for police, and IMSA for fire/EMS. Since the consolidation of the public safety VHF pool (now the "PW" license pool) a few years ago, it is easy to see that a police department could be coordinated by APCO on a frequency very close to that of a neighboring fire department coordinated by IMSA.
What is not as easy to understand is how several neighboring fire departments could be coordinated by IMSA on the same frequency. El Reno Fire, Tuttle Fire, Duncan Fire, and Wadley EMS all use 150.790 as a repeater input. Tuttle and Duncan have some separation, but Tuttle and El Reno are 20-25 miles apart... Tuttle and Wadley's are 25 miles apart, etc. The same holds true for 154.340... Bridge Creek FD and Elmore City FD are around 25 miles apart. APCO's guilty of this, too... Yukon PD runs animal control and other police-allied activities on 155.715. Yukon's 15 miles away from Tuttle, who used to use 155.715 for police dispatch before abandoning it for their new 12.5 kHz repeater pair because of all the interference.
These are all examples of very poor coordination, and have all demonstrated severe cases of interference at times. In the case of Parkview EMS vs. Tuttle PD issue, if there are complaints, my understanding is that the FCC will require Parkview EMS to take care of their own issue, as Tuttle is licensed on a repeater pair that is compliant with the implementation of narrowband regulations. This, of course, assumes that Tuttle PD's equipment is operating properly and within specs and regs.
Anyways... sorry to ramble on this... hope it helps.
