C4FM Thing of the past or of the future?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N7BKV, Jun 22, 2019.

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  1. AD7VB

    AD7VB Ham Member QRZ Page

    All these systems (D-star, DMR, P25, NXDN and Fusion) use AMBE's codec for voice encoding and decoding.

    The only part of D-star that is closed is the AMBE codec which all the other systems use in one version or another.

    I tend to think that the only reason DMR is popular now is the number of cheaper Chinese radios on the market.
    VE1DDD, WD4IGX, W4POT and 2 others like this.
  2. AA5CT

    AA5CT Ham Member QRZ Page

    re: "What C4FM (and other digital modulation systems) have going for them is they are are transmitted and received digitally, which is easier route and transport"

    Except, and I don't know this for a fact, but, isn't the over-the-air bit-saving protocol 'expanded' back to normal PCM (pulse code modulation) audio THEN routed on the internet?

    The reason digital is preferred is, the NAC (or whatever DMR uses) accompanying the digitized, processed speech selects the 'net' or network the radio intends to be part of ... with analog, DTMF in-band signalling would have to be used, and, there is no 2nd time-slot to use with analog (compared to Phase-II P25 for instance).
  3. W4EAE

    W4EAE Premium Subscriber QRZ Page

    No. This can be verified by the fact a an AMBE chip is necessary to decode the audio stream at any step along the way. For the most part it is never decoded in internet transit, simply passed along.

    This brings me to another thing. While D-Star, YSF, DMR, etc. continue to use AMBE, none of them are anything less than proprietary. Maybe back in the last century when D-Star was developed, this was the best they could do; but now there are free and open codecs which could achieve the same or better comms audio with potentially lower bandwidth.
    WD4IGX and PY2RAF like this.
  4. K2CQW

    K2CQW Ham Member QRZ Page

    Our club has had a fusion capable repeater for two+ years but our techie dragged his feet getting into wires-x. Now he has a massive hard on for dmr. I finally set up my Personal Digital Node. I like it. Screw the techie, our club leadership is getting thoroughly disgusted with him. I will be presenting my PDN experience at our club meeting. Screw the techie.
  5. W4EAE

    W4EAE Premium Subscriber QRZ Page

    If you guys want DRM, then your will need a second repeater anyway. Let the DMR guy have his fun, and you volunteer to connect the Fusion repeater to Wires-X. If you have already setup a PDN, you have the skill and experience.
  6. K2CQW

    K2CQW Ham Member QRZ Page

    The goddam thing is hooked up. He says he's run of ports whatever The $#@% that means. It's been two #$@%ing years and now, this Saturday he will present his new excuses.
  7. VE1DDD

    VE1DDD Ham Member QRZ Page

    Not D-Star. D-Star was created by the Japanese national radio association (forget their name) not a commercial company.
  8. SM0AOM

    SM0AOM Ham Member QRZ Page

    It is somewhat more complicated than that.

    D-Star was conceived in mid-90s as a Government funded grant to the
    JARL and Japanese radio industry (Icom was the only taker) to develop an amateur radio digital standard, primarily to alleviate a perceived scarcity of repeater spectrum in Japan.

    The standard is open, but Icom currently owns the trademark "D-Star".
    But to implement it, you at least formally, are required to buy the AMBE codec. A property D-Star shares with many other digital voice implementations.

    KB0MNM and NL7W like this.
  9. W4EAE

    W4EAE Premium Subscriber QRZ Page

    How about reverse-engineering the AMBE codec? This has been done time and again with other proprietary audio codecs. I am unaware of any codec commonly used for consumer A/V that is proprietary. The market simply won't bear it.

    Amateur Radio is small, and a lot of its number focused mainly on 20th Century technology; so I really do not see this happening soon unless I take up the banner myself.
  10. SM0AOM

    SM0AOM Ham Member QRZ Page

    It has been done.

    Years ago, I saw on a Brazilian web-site a description of a project with this aim, "SDS" and mbelib, and apparently they succeeded.

    However, the documentation contained a stern warning of that you might be paid a visit by lawyers from DVSI if the AMBE reverse-engineered codec was actually used.


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