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Thread: FM/DAB digital radio - THAT WORKS!!

  1. #721
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    Join Date
    Dec 2009
    Posts
    33
    coool ill be buying one then.... thanks....my car PC is just missing radio...now will be complete...

    ill keep an eye out, do post up if that tri-plexer works...

    should have said, running windows 7 and CF 3.1....so it should just work?

    now to figure out how to remove roof lining to fit that aerial before i buy it...

  2. #722
    Constant Bitrate
    Join Date
    Jun 2006
    Posts
    188
    the venice requires 50R impedence. IN all honesty, the missmatch between 75R and 50R isn't going to make that much difference.

    I've frigged up a passive multiplex unit but you end up losing some signal. An active multiplexer would be better but in its current state it will not run from the USB any more. I have made a smaller more power efficient unit but I am unsure if Craig will sell this or not.

    I have used both the venice 5, 5.1 and 7. There is not much to choose between the three. Through london i had no problems with the 5 or 7. The serial control is better on the 5.
    The epitome of Function over form and is probably the best Car PC in Europe.
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  3. #723
    Newbie
    Join Date
    May 2009
    Posts
    53
    Hi

    The tripplexer does work - I have been using one (different make) since May. The tripplexer will need powering (up the output coax). You'll get nowt from it without the juice. That complicates things since you have to get the power up the cable (but not back into the DAB unit), and you'll want to maintain a good screen. There are DC injectors for this purpose. Also, note that the supply fed to the tripplexer needs to be clean - feed it a noisy supply, and it wont work as well - I have noticed this on mine when powering the tripplexer from a PP3 vs USB.

    I like the passive dipplexer idea the most (this is what I was actually searching for and failed to find when I went the tripplexer route!). It may well be possible to gut this and solder the cables directly to it and to expose a couple of f-types on the side of a nice, grounded metal box containing radio and dipplexer. It might be ideal (with mods) for what Craig intends to market as an fm/dab add on dippliexer for the radio board.

    Cheers for posting, I think i'll order one!

    Nigel

  4. #724
    Constant Bitrate
    Join Date
    Aug 2009
    Location
    UK
    Posts
    178
    How much signal did you loose with the passive multiplexer, nrgizerbunny?

  5. #725
    Constant Bitrate
    Join Date
    Jun 2006
    Posts
    188
    on DAB the error rate went up from 3 to 12ish
    The epitome of Function over form and is probably the best Car PC in Europe.
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  6. #726
    Newbie
    Join Date
    May 2009
    Posts
    53
    Hi

    I have just performed this same test on my setup, and see a slight improvement from an error rate of 7-8 direct and 4-5 when routed via the tripplexer.

    Unfortunately, its not that simple... If I force a poor signal (my removing the mast from the aerial), then I have error rates of 20 direct, and 30 when routed via the tripplexer - i.e the tripplexer makes the signal worse.

    This is a simple case of the RF amp within the tripplexer amplifying everything (signal and noise) equally. If the SnR at the input is good, then the tripplexer will amplify the signal more relative to the noise, while if the SnR is bad then it will amplify the noise more relative to the signal.

    The results are plain to see in the error rates above.

    So, with an amplified tripplexer, you *will* loose some signal (in poor signal area's), while you might gain in better signal area's. Arguably you will only gain when signal strengths are such that you don't really need to gain anyway!

    For me, the benefits of having FM without swapping cables outweigh this problem, and with error rates of 20, DAB is beginning to get a touch warbely anyway.

    It would be interesting to know at what SnR the tripplexer provides a unity gain. If that SnR gives error rates of say 15 (on the verge of being unlistenable to anyway), then the tripplexer will not really be doing any harm.

    Running this on a test bench indoors, I am amazed at the signal gains that a buiscuit tin lid can provide when its placed under a magi mount dab aerial - Ground planes are important! Probably one of the reasons why magi-mounts and through roof dab aerials work so much better than on glass aerials (with their half-arsed ground plane). Additionally, if you are using a magi-mount, play around with its positioning on the roof while looking at the DAB error rate. Moving mine away from the sunroof hole (thus providing a uniform ground plane) halved the error rate that I had!

    I don't pretend to understand much about RF but the whole subject appears to be far from an exact science!

    Looking forward to the next version of that CF plugin!

    Nigel

  7. #727
    Constant Bitrate
    Join Date
    Aug 2009
    Location
    UK
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    178
    Nigel, could you please post details of the triplexer that you are using?

  8. #728
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    May 2009
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  9. #729
    Newbie
    Join Date
    Feb 2007
    Location
    Macclesfield, UK
    Posts
    39

    Dead?

    My Venice 5 module has just died...
    Andy Whittaker
    Macclesfield, UK

  10. #730
    Constant Bitrate
    Join Date
    Jun 2006
    Posts
    188
    oh dear what happened.
    The epitome of Function over form and is probably the best Car PC in Europe.
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