apu said:
IMHO, an equally serious problem (if not worse) is having the right frequency without a standardized PL/DPL.
You're right, it is a serious problem.
Especially since newer equipment seems to have monitor features that are harder to find and less functional than the old speaker - speaker with a slash through it, or "PL"/ "CSQ." When I was working in two-way radio, we would get requests to have a 'private channel' (like there really was any privacy in being on the same frequency but having a different tone...) and would get out of it by showing the SPEN or JEMS plan and stressing how important it was (16 years ago) to have some standardization to speak with other agencies. My biggest concern was that other shops - and even other technicians where I worked - may not have have had that concern. What's the difference? I used to work in EMS and was on a volunteer fire department for a while, so I actually used the stuff at one point and have found myself standing next to someone who thought they couldn't talk to me because their channels were out of order and called something different. You stand next to each other, key one radio and twist the channel knob on the other and stop when you hear feedback; a totally jack*ss way of determining 'who's on what' (but it works).
In the ISPERN/ SPEN 2 case, IF the SPEN radio were programmed correctly, they could talk because it is a carrier squelch system. But I've seen many SPEN radios programmed with 131.8 on every channel. It depended on whoever was doing the programming; the plans were never sent to the radio shops and technicians mostly guessed. The Illinois plan has an agreement with many pages and a programming sheet that could be handed to the technician. Still, in most metropolitan areas and RF dense sites, it is impossible to monitor anything in carrier squelch without some noise, even with RF filtering in place. Think SPEN 1 and MTAC. The NJ guy and the MO guy are on the same frequency, but one is using 131.8 and the other 156.7 Hz. The potential of standing at the same (big incident) scene, waving at each other and then using cellular phones or other similar means is greater than both of them figuring out how to drop to CSQ in different radios, particularly when those radios have programmable options with many features and the same button can do different things, or the same feature can either drop to carrier squelch or open the squelch to a wide open position.
There is a movement in NPSTC and the professional organizations promoting interoperability to use 156.7 Hz as the default CTCSS tone and $293 as the default Network Access Code (most, if not all P25 equipment comes 'out of the box' with $293 programmed as the default NAC - this IS NOT the "digital carrier squelch" NAC). It was hoped that the Commission would embrace at least a tone/ NAC and mnemonic, but they are mostly lawyers and a lesser number are engineers, and they didn't want to compell anything. 156.7 Hz was selected because it was previously used in 800 MHz on ICALL/ITACs. $293 was the path of least resistance, as the test mode was usually configured with it.
I'll see if I can export that file to an acceptable format.
