posted on May, 12 2010 @ 03:08 PM
Conventional radio systems put the user on a specific frequency. For instance the ground units at Nellis are on 148.1MHz NFM (narrow FM). An agency
would have several of these conventional radio repeater systems. In order to save spectrum and squander money, trunk radio was created. In a trunk
radio system, one of the frequencies is assigned to a control channel. The remaining frequencies are allocated to the "trunk", and are assigned by
the computer running the control channel. The control channel is digital, while the remaining channels could be voice (NFM) or digital (APCO-25 for
The trunk users no longer have a specific frequency to use, but rather they use frequencies in the trunk. The user participates in a "talk group".
For instance, there would be a talk group for security. Each radio had a unique ID, so when some idiot steals the radio, the site administrator can
lock it out. This also makes it harder for some outsider to spoof on the system. (On a conventional radio system, you could declare yourself Adam-12
and the dispatcher might fall for it!)
There Nevada Test Site set up a networked trunk radio system with several sites, where a site is a simple trunk system with the ability to talk to the
other sites. Nellis AFB became a user of this system, having a range of talk groups assigned to it. The NTS system is P-16, which without going into
much detail uses a slow data channel and APCO P-25 on the voice channel (also called Astro). Some of the users on the system have encryption.
[Technically a P-25 system has a 9600bps data channel, while the P-16 data channel is 3600bps IIRC.) Nellis just ordered new radios for the NTS system
with AES-256 encryption.
In addition to the NTS trunk radio system, there is a multi-site EDACS trunk radio system on the Nellis range. It uses DES encryption based on the
opinion of a radio dealer I contacted, though most of the websites say it is ProVoice. This EDACS system also has one site at Nellis AFB, and a site
at Basecamp. IIRC, the TTR has both systems available to it, though the NTS system is coming from a repeater at the radar site in Tonopah rather than
being on-site. The Groom system can't be monitored, presuming it really is DES encrypted. The NTS system can be monitored on several scanners from
either Radio Shack or Uniden.
Both trunk systems are in the federal 400MHZ band (roughly 406 to 420 MHz).
Most "visitors" to the range monitor the VHF and UHF aviation bands. These signals are mostly in the clear, but some planes use "Have Quick", a
type of encryption. The list I provided in the other message covers the radio capable of UHF aviation, a band left out of many scanners.
Digital trunking scanners are expensive ($400 or so, maybe $250 used). Military UHF capable scanners are easy to find used for $60 to $100. While some
people try to use one scanner to cover everything, you really should have several scanners that cover conventional VHF/UHF frequencies. There is simpy
too much activity in the range. During Red Flag, you would park one scanner on the AWACS, run another on air to air frequencies, a third on the ground
frequencies, etc. There is talk of the ground units going to the NTS system, which might be related to the Nellis request for a few new radios.