trisquare eXRS
Ok,
I'm pretty savvy on this stuff having worked on digital modulation using PI/4DQPSK and a TDMA multiplexing format in the past but I admit to being a tad "corn-fused" by what I am reading about these TriSquare radios. On the one hand, yes the "narrowband FM" seems to indicate an analog FM variant yet on the other hand you read this from the March, 2008 issue of Popular Communications - the article reviewing these units (and reprinted on the TriSquare website):
"The transmitter’s microphone audio is digitized,
modified by a DSP algorithm to
extract only the most useful information,
summed with a digital timing and position
signal, and time-compressed to allow
proper hop framing and provisioning of
the control data (caller ID, private call,
etc.) within each frame. The receiver’s
DSP extracts the modified audio, performs
digital noise reduction, and expands it
back to the original voice signal timing
(slightly delayed after processing)."
Also, from the same article, the specs read as follows:
"Transmission protocol: Half-duplex TDMA
• 4.0 kHz FM RF deviation (nominal)
• 3.0 kHz compressed audio bandwidth (nominal)"
Ok, I guess you could apply TDMA in an analog fashion (is the hopping considered "time domain"?; I hadn't thought of it like that as to me it is more like frequency domain - I guess the timing of the hopping sequence is "time domain"...?), technically, but the description in the article is confusing to me (just me - I admit ignorance here, ok - just asking - feeble brain syndrome, etc.). Am I to infer, here, that the audio is digitized simply to allow it to be processed in the digital domain, compressed, noise reduced, etc., and then converted back into analog narrowband FM to be transmitted and then is re-digitized in the receiver so that the receiver's DSP can expand the audio, clean it up, and strip off the hop frame timing signaling and spits out the analog audio? So, the DSP, in this case is merely acting like a trumped up compressor/decompressor? So if so, and one were to actually demodulate the FM using a normal narrowband FM receiver (disregard the hopping issue - lets say the hop is stopped) then you would hear the audio but, well, highly compressed and with, what, some, I guess, audible signalling, what, tones, subaudible data bursts,...???
Anyway, I wish someone would get one of these and "stop the hop" and park it on a spectrum analyzer and see what it is - I would imagine there is a testing mode they could be put in to do this but it would be, of course, proprietary. Of course the article could be misleading, lack detail, or even be completely incorrect. And marketing being able to essentially change the laws of the physical universe (I know, I've seen them do it, to my utter amazement, but, then again, I'm just an idiot tech type so what do I know!) the info can be, well, um, highly compressed, massaged, recoded, and packetized in the "marketing domain" ("marketized"?).
-Mike
(just admitting my extreme ignorance here, nothing to see, move along, move along...)
