The NTIA manual that Harry provided the link to has some interesting things to say. First, it shows the frequencies 163.100 and 168.350, that we have been so used to listening to being used as tactical frequencies by the Forest Service and, especially, the National Park Service, are to only be used for repeaters. 163.100 is the repeater output and 168.350 is the input. The two new wide area federal itinerant frequencies that may be used as simplex are 168.6125 and 163.7125. I'm going to program those into my scanners right away.
It is stated on page 4-182, item 6a, that the output of repeaters using the 406-420 MHz pairs shall be the lower of the two and the input shall be the higher. What that means when the pairs are used as links is that the down link will be on the lower frequency of the two and the upper will be the up link. All the up links, as we previously knew, are 9 MHz higher than the downlink. This will be easy to remember as we can say "down low, and up high" meaning the downlink will be on the lower frequency and the uplink will be on the higher frequency.
The manual refers to a due date of 12/31/07. That would explain why the upper frequency isn't being heard anymore by so many of us in the last 6-8 months. For those reporting that they are still hearing down links on the upper frequency, these would be non-conforming to the plan and will probably have to be switched out as soon as possible. As with any deadline, not everyone is always on board when the due date is reached and passed, especially considering the situation with radio system management that I outlined above.
The only down link I'm hearing on the upper frequency is for the Silver Peak National Air Guard remote. The down link is on 415.550 MHz. Using this frequency for the down link on a National Forest's National Air Guard remote base is very common around California (Region 5 of the Forest Service). Most Forests only have one remote base for Air Guard as aircraft don't need lots of repeaters or remote bases to reach the dispatcher on a Forest unless they are flying quite low. You might try this frequency out if you are close to the "hub" electronic site of a nearby National Forest. I would bet some folks in the Central Valley would have no difficulty monitoring this downlink. The switch may have been made on some Forests so you should try listening to 406.550 MHz in addition.
OK, this brings up another topic and I think I will start another thread for it so it gets the visibility it needs. That topic would be the use of 168.650 for flight following. Watch for another thread in the California forum for this.
