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. N7BKV

    N7BKV Ham Member QRZ Page

    Yeah, I don't need a "radio" just to do VOIP. Already do that with my computer and cell phone. But I understand the competitors wanting to stay in the game with futurist technologists that like radio and internet together. OK.

    FT7900 is hardly in the pipeline anymore. Most retailers are sold out. But since the real radio part of it is nearly 10 years old, would a FT7250 be a better "radio", and just ignore the digi capability it has?

    Price of the FT7250 is lower than the few remaining FT7900's out there. Is that a reflection of poor quality newer radio? Or a failing to gain a foothold in the digi FM space, so they have to nearly give them away?

    B
     
  2. K7JEM

    K7JEM Ham Member QRZ Page

    They are totally different approaches to radio. The 7900 will run both bands at the same time, do cross band repeat, and has remote mounting capability. I don't think the 7250 does any of those things, plus a lot of other features dealing with display modes, etc.
     
    N7BKV likes this.
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Never ever said it was new, and amateur VHF 2-meter is 20 and 15 Khz channel spacing depending on state of operation and everything higher is is still 25 Khz.

    That is not accurate. the uplink communications where lower peak-to-average power ratio (PAPR) greatly benefits the mobile terminal in terms of transmit power efficiency. As for the RX side today I do not know of any modern radio today that does not use frequency DSP so that is a moot point.

    The issue with D-Star and Yeasu flavor of C4FM is they are licensed technologies like MS Windows or Qualcom CDMA. Whereas DMR and P25 are open standards. Amateur radio use to lead in technology, today sadly lags far behind.
     
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Duplicate post removed.
     
  5. K7JEM

    K7JEM Ham Member QRZ Page


    Right. But hams could switch to "narrow" analog FM and use the same 12.5KHz channels that commercial people use. IOW, the problem is not with the mode, it is with the deviation being used. Analog operations currently are authorized on 12.5KHz channels, and work well there. Digital starts to get a real advantage when the channel spacing is reduced to less than 12.5KHz.


    Are you saying that a C4FM transmitter has a better efficiency than a common FM transmitter? That a handheld voice radio using that format consumes less power than a similar FM radio? I'm trying to figure out where the longer battery life comes from.


    This is true.
     
  6. KV6O

    KV6O Ham Member QRZ Page

    C4FM and the Internet have nothing to do with each other. C4FM stands for Continuous 4 level FM, which is a type of FDMA (Frequency Division Multiple Access) modulation scheme. The Internet is a huge, global computer network - you're using it right now if you're reading this.

    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, which is important when you want to build a network of repeaters, or link networks. To route an analog signal across 5 links and have it sound acceptable is almost impossible. Digital does that easily. Ma Bell figured that out 60 years ago.

    The Internet comes into this as the ubiquitous digital network. It's way easier and cheaper to leverage what has been built, than to build it from scratch. That said, there are many radio networks that don't use the Internet, we have one here in Colorado run by the Rocky Mountain Ham Radio Club that interconnects DMR repeaters across the state largely on a private microwave backhaul. I run a government funded radio network (P25) that interconnects with the the larger State network - over 200 sites - no Internet backhaul.

    So, while you can link hundreds of repeaters together, and you can use the Internet, you can also have a standalone digital repeater with no interconnectivity. This might not buy you much in the ham world over FM, but in a digital world it's easier to control access, carry data in the transmission stream (position info, for example), etc. But the killer app for digital modes is the routing and transport capability.
     
    WE4E, NL7W, WD4IGX and 1 other person like this.
  7. K6CLS

    K6CLS Ham Member QRZ Page

    Ok lotsa of Sunday pedantry... We've lost the point.

    OP wants to know, if the FT7250 a good rig?

    What do you think about the Alinco DR735?
     
  8. KD4UPL

    KD4UPL Ham Member QRZ Page

    Simply not true. The FT-7900 is not both bands at the same time and will not do cross band repeat.

    Fusion is the dominate digital VHF mode in my area. I have two Fusion rigs that I bought for their APRS capabilities. Operators here are generally in agreement that the Fusion audio quality is not as good as standard FM. Also, the useful range when in C4FM mode is significantly less than in analog mode. For someone who simply wants to "talk on the radio" this makes Fusion inferior to FM. However, the Fusion system does allow for the transmission of text messages, pictures, and GPS location data along with the voice traffic. This can be useful in some situations I guess but in my mind does not really make up for the audio quality and range issues.
    As for linking repeaters, I agree, let's keep ham radio on RF, not the commercial internet. But, these digital repeaters can be linked via digital data links very simillar to Wifi, even using "off the shelf" Wifi routers, radios, and antennas. Some of those channels, being in the ham bands, will even allow the use of gain antennas and amplifiers.
    The 7250 does not have a remote face. It does not have a built in GPS and is therefore useless for sending position information in the data stream. I don't think it works with the camera mic to send pictures either. It will allow digital voice if you really want to do that.
     
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Conventional digital signals like DS1 and DS0 can and are carried over the internet for legacy systems.
     
  10. K7JEM

    K7JEM Ham Member QRZ Page

    Yes, you are right. I was thinking of the 8900 when I posted that, it is about $100 more than the 8250 and is quad band and cross band repeat, etc. The old 8800 was the dual band version that was very similar to the 8900, but somewhat cheaper. But they don't make that one any more.

    I don't think the sound quality of any current digital voice mode is very good. I think they have caught on because they are the "in thing" and offer some options that regular FM doesn't have. But "great sound quality" is not an advantage to any of these modes.
     
    WD4IGX likes this.

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