What is the best/easiest way to link a series of UHF analog repeaters in both clear (with PL) and DES-XL mode? Something along the lines of 3 local-coverage UHF MSF5000's.
I don't see this discussion come up much, and I did a search that didn't immediately come up with anything.
Securenet Repeater Linking
Moderator: Queue Moderator
Re: Securenet Repeater Linking
It was done with leased lines. In the clear is pretty straight forward, but coded mode required the line be clean enough and fast enough for the built in modems to sync up. They had to be very low latency circuits. Trying to do it by any other means will require experimentation.
Re: Securenet Repeater Linking
From Wikipedia: http://en.wikipedia.org/wiki/Continuous ... modulation
"12 kbit/s CVSD is used by Motorola's SECURENET line of digitally encrypted two-way radio products."
So those modems will have to be either CVSD or already up and running and able to deal with "fast" data. A telephone-grade phone line won't cut it unless it's going into a channel-bank on site.
Does anyone know if Securenet used MSK or FSK or another form of FSK?
"12 kbit/s CVSD is used by Motorola's SECURENET line of digitally encrypted two-way radio products."
So those modems will have to be either CVSD or already up and running and able to deal with "fast" data. A telephone-grade phone line won't cut it unless it's going into a channel-bank on site.
Does anyone know if Securenet used MSK or FSK or another form of FSK?
Re: Securenet Repeater Linking
Motorola trunking used MSK, so knowing Motorola, I'd say it's probably MSK -- especially since the bandwidth is pretty pinched there. 9600 BPS through a standard FM modulator uses a LOT more spectrum than you think it might. We're talking 12Kbps, so Motorola was likely either using C4FM/4FSK or MSK. Some of those are easier to decode than others using minimal radio hardware. Hence why Motorola trunking often used these protocols; you only need a level-slicer to "clean up" the output of the discriminator before feeding it into the UART.
I just busted out the googles and found what a lot of you already know: The modulation for Securenet should be set to -/+4KHz. So now we know we've got a 12KHz data stream in 8KHz of total deviation. Also, the note mentions that the signal is low-passed before modulation. This looks more like GMSK or 4FSK processing.
"How Does it Work?
Speech is digitized using the CVSD method and then combined with a "random" stream of data
generated by the secret key and the DVP encryption algorithm. The reverse process is applied
to the receiving radio."
Knowing a few things about encryption and compression, this results in a larger data stream than is necessary for a given mode. In effect, the random bit stream may actually be causing errors to the CVSD stream, resulting in the audio sounding more robotic.
Coming backwards around, it appears that Securenet is a two-level FSK format... somehow that information came out of here, but I haven't found it yet. So Securenet has more in common with FLEX paging than first thought. DVP is mentioned as a self-synchronizing cipher, and the 4FSK method of FLEX allows for a several virtual data streams in the four phases (braddye.com, former Motorola Sales).
I just busted out the googles and found what a lot of you already know: The modulation for Securenet should be set to -/+4KHz. So now we know we've got a 12KHz data stream in 8KHz of total deviation. Also, the note mentions that the signal is low-passed before modulation. This looks more like GMSK or 4FSK processing.
"How Does it Work?
Speech is digitized using the CVSD method and then combined with a "random" stream of data
generated by the secret key and the DVP encryption algorithm. The reverse process is applied
to the receiving radio."
Knowing a few things about encryption and compression, this results in a larger data stream than is necessary for a given mode. In effect, the random bit stream may actually be causing errors to the CVSD stream, resulting in the audio sounding more robotic.
Coming backwards around, it appears that Securenet is a two-level FSK format... somehow that information came out of here, but I haven't found it yet. So Securenet has more in common with FLEX paging than first thought. DVP is mentioned as a self-synchronizing cipher, and the 4FSK method of FLEX allows for a several virtual data streams in the four phases (braddye.com, former Motorola Sales).