yaesufanatic wrote:
I am trying to understand the features and limitations of D-STAR. I
have viewed every D-STAR video on YouTube (Especially good were KN4AQ
Gary Pearce's videos) plus I have read the articles/manuals on the
Icom site and DSTARusers.org.
How can D-STAR radios communicate without a repeater or the Internet?
Yes, simplex.
Can D-STAR radios communicate with each other without a repeater as in
a simplex mode, as long as they are on the same frequency?
Yes.
Can a DVDongle be directly connected to a radio for DVDongle to radio
to radio to DVDongle communication?
No.
Thank you for explain this exciting new digital technology to an old
analog guy.
\\\
Well, welcome to the world of D-STAR. Your first two questions revolve
around understanding what happens in a D-STAR radio. A D-STAR radio is
fundamentally an FM radio that is tapped at the discriminator on receive
and directly at the modulator for transmit, these two points are
connected to a GMSK modem which demodulates the signal to 1s and 0s
(digital) and modulates 1s and 0s to the transmitted signal. If in DD
mode (128kbits on 23cm) it basically provides a half duplex Ethernet
bridge between radios. If in DV mode (4.8kbps on all supported bands),
a voice signal is de/en-coded via the use of an AMBE chip at 2400 bps +
1200 bps forward error correction + 1200 bps for data and overhead.
Whether DD mode or DV mode, once it goes through the GMSK modem it is
just radio like you are used to, you can use it on simplex, or through a
repeater.
The nice thihng about it is that it is digital from end-to-end. A
D-STAR repeater merely repeats the digital signal (GMSK modulated FM
[actually there is an additional modulation scheme, but GMSK is what is
in use]) from one frequency to another, just like an analog FM
repeater. Because it is already digital (and the conversion to/from
audio and data happens at the end radios), a D-STAR repeater controller
can transfer the digital signal across the Internet with no further
encoding or decoding where it can be relayed to its destination with no
degradation of the signal (other than lost signal or bit errors) and the
receiver anywhere in the world receives with the same fidelity as a
simple, local simplex signal.
The DV-Dongle is a computer attachment that has an AMBE chip in it and
thus can encode/decode analog (and the assoicate data) voice. Some
folks have written applications on the computer to talk to a GMSK modem
attached to a radio, but you cannot hook the usb port of the DV-Dongle
directly into the radio. (It would be kind of like hooking a microphone
directly to a dipole, there has to be a little bit more in between in
order to create radio.)
Keep asking questions, there's a lot to learn.
--
John D. Hays
Amateur Radio Station K7VE <http://k7ve.org>
PO Box 1223
Edmonds, WA 98020-1223
VOIP/SIP: [email protected] <sip:[email protected]>
Email: [email protected] <mailto:[email protected]>
