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  • Frequency converter

    Hello, I'm wondering if the following technology exists:

    Some mobile phones only support the 3G networks of certain carriers, e.g. from what I understand, the T-mobile G1 supports WCDMA at 1700/2100 MHz but AT&T's UMTS network is at 850/1900. Unlocked phones, e.g. ADP1, can't receive 3G on AT&T's network. Is there a technology that would act as a middle-man, e.g. receiving signals on 2100 and re-broadcasting on 1900 (and doing the reverse)?

    I'm thinking it might be something like a signal booster, (like your CL801241), but with frequency conversion.

    Thanks

  • #2
    Hi,
    Unfortunately not. That would be nice!

    What you have to realize is that it's not simply a matter of frequency translation which would be pretty straighforward. Also not only is the center frequency different but the channel bandwidths are different as are the number of channels and there's no one-to-one mapping between the channels in different bands. So you cannot easily map for example an UMTS Band IV (AWS band) to an UMTS Band II (PCS band). This is different from the cellular repeaters that operate in a single band at a time since all what these do is amplify the signal and re-radiate and just use tower control packets to determine the amount of transmit power.

    Just a little bit of background:

    There are two main components in a radio modem and by radio we just mean a device that transmits and received RF waves such as cellphones or datacards. The Analog Front End (AFE) and the Digital Baseband. The latter is quite straightforward to implement since it can use digital CMOS processes and can shrink with technology and become very complex with each technology evolution (which is why microprocessors have become very cheap and very complex every year). The Analog Front End which has stuff like the frequency generator, upconverters/downconverter mixers, low noise amplifiers, power amplifiers, etc is much more complicated and is what contributes the most to the cost of radios. The AFE doesnt shrink well and normally cannot use cheap CMOS processes. Bottom line it's costly.

    Now different radio technologies utilize different AFE architectures. A 850/1900MHz WCDMA (UMTS/HSxPA) is very different from a 1700/2100 WCDMA which is very different from 850/1900 CDMA2000 (EVD0). So a device that can work on both would necessarily have to have both radio technologies and different basebands to decode the different spectrums. Which is what happens for "quadband" radios. We actually do have a radio that is spec'd to support T-Mobiles AWS band as well as AT&T's 850/1900 but we havent tested that. Check out Option Globesurfer III but see this post on a discussion about this.

    So while it theoretically can be done it hasnt been done and it's not as trivial to do. There are also practial motivations against this since these are licensed bands and carriers typically either own a specific band in a certain geographic area or if they have both utilize one.
    KF7RCQ

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    • #3
      Got it. Thanks very much for that answer thuor.

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