On Dec 27, 2007, at 11:46 AM, [email protected] wrote: > > Hello, > > This email message is a notification to let you know that > a file has been uploaded to the Files area of the Repeater-Builder > group. > > File : /Simple P25 Repeater / > ASTROCapableRepeaterUtilizing2UHFMotorolaMaxtracRadios.pdf > Uploaded by : efj44 <[EMAIL PROTECTED]> > Description : Simple P25 Repeater using 2 Motorola Maxtrac Mobiles . > > You can access this file at the URL: > http://groups.yahoo.com/group/Repeater-Builder/files/Simple%20P25%20Repeater%20/ASTROCapableRepeaterUtilizing2UHFMotorolaMaxtracRadios.pdf
This has already been done in a number of places with various rigs. The disadvantages are many, but the main one is in that the digital signal is converted to analog and then back to digital, and the resulting "double-vocoded" audio which has been put through two lossy CODEC's will sound really bad. We have a similar setup here on a VHF machine in Denver. It's copyable, but the audio at the end-user radio will NOT be an accurate representation of what was originally transmitted. Comparing the Amateur P25 system that's double-VOCODed vs. a real P25 repeater is like night and day. There's no such thing as a free lunch -- for P25 (or any other digital real-time audio stream of bits) to sound as good as it can sound, you have to stay digital at the repeater. You should post information on your website or however you communicate with your users that the system's audio will never quite sound right. Otherwise, they may think that P25 always sounds that bad. Other disadvantages are that the repeater won't pass Unit ID's properly, and most of the features of P25 will be lost. Unit to unit calling, etc. Anything included in the data stream beyond the audio is lost. It also won't be ID'ed legally without the assistance of the end-users in that configuration unless you switch back to analog mode for ID's under the watchful eye of an intelligent repeater controller. (Putting MCW through the IMBE VOCODER sounds like the CW is coming from underwater, but it's copyable if you have to go that route.) It's a quick-and-dirty way to set up a P25 capable repeater, but it'd be wise to start shopping for a digital-capable Quantar or similar from any other manufacturer if you want P25. -- Nate Duehr, WY0X [EMAIL PROTECTED]
