Results 1 to 18 of 18

Thread: Tait TM8100's for P25 Crossbanding

  1. #1
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default Tait TM8100's for P25 Crossbanding

    Hey, after a bit of messing around with the TM8100 programming application settings and by use of the data crossbanding cable, I am able to reproduce the C4FM signal through two linked TM8100's.


    The P25 signal is repeated with little loss, averaging at around 98% QoS as displayed by the TP9100 receiving the signal. Of course there is no error correction but this setup will have it benefits when established on elevation providing the extra signal coverage.

    All signals are re-broadcasted transparently!! Encryption, Individual calls and Call alerts (pages) can be made through this repeater.

    This is a good interim/alternative to the costly quantar/TB9100 option(s).

    Here are the screen shots of the PTT and I/O pages of the programming app which must be modified for P25 re-broadcast.

    ptt.png


    io2.pngio1.png

    Other than two TM8000's, the programming app, a duplexer for in-band repeating, all you need is the cable.

    If anyone wants to buy a cable, PM me and we will sort something out.
    Last edited by Motorobber; Oct 05, 2012 at 07:06 PM.


  2. #2
    mtp850 No Longer Registered

    Default

    Looks good motorobber, I'll give this a test next weekend. have you tried having one radio receive with 1 crypto key and having the second radio TX using a different key ?.

  3. #3
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    Are you talking about two digital radios talking thru the TM8100 repeater setup with mismatched encryption keys?

    If so, yes and all you get is the usual garble.

    Is this what you mean?

  4. #4
    mtp850 No Longer Registered

    Default

    No what i am saying is are you able to set the first radio up to receive with key1, then pass audio to radio 2 that is set to tx with a different key?

    I would love to be able to setup a portable tactical repeater that could do an in band conventional patch between different frequencies that are using different crypto keys.(on the cheap of course )

  5. #5
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    That's with the digital radios linked rather than the analogue. No I haven't tried that. Good idea, let me know how you go.

  6. #6
    Alpha's Avatar
    Alpha is offline T S - Moderator
    CS Forums $upporter
    Join Date
    Feb 12, 2012
    Location
    Directly above the center of the earth.
    Posts
    2,689
    Thanks
    844
    Thanked 1,362 Times in 671 Posts
    Country: Christmas Island

    Default

    I'm guessing if they are truly transparent, then no.

    The concept of a transparent repeater (non double vocoded) is that exactly what comes in goes out, it might be re-clocked or error- or time-corrected but essentially no attempt is made at decoding the stream. That's why there's no DSP in a Quantar that does vocoding, for example. If you want that, you need a DIU to do it (for say, a console or dispatch access to the repeater). The station by itself has no digital audio decoding capability, all it does is clean up the digital stream and remodulate a TX with it.

    In order to make a "key translator" device like you are describing you need one to decode with key1 and just pass decoded audio and PTT to radio with key2. That is what they call a double-vocoded repeater because it decodes the audio then re-encodes it on the second radio, and the net effect is the audio quality sucks, that's why real P25 repeaters are transparent.

    So far all the "field portable" or "tactical" repeater solutions of hooking 2 mobiles up back-to-back have the problem of being a double-vocoded setup. If these 2 will pass the true digital stream without messing with it they will be the first solution to do this transparently! All the other schemes short of buying a Quantar will get you a double-vocoded solution so this is very cool if it in fact works as it is said to.

  7. #7
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    Yes to do what mtp850 is talking about you would need two digital radios to carry out the "key translator" method which would hence be double vocoded. An example of this would be two linked TM9100's linked by the crossbanding cable passing the demodulated (and decrypted) signal from the receiver to the early stages of the transmitting radio.

    The method that I am using to repeat P25 is definitely with two Analogue TM8100's, extracting the rxed signal from the early stages of the receiver, passing to the transmitting radio via the data cable, injecting the signal into the latter stages of the transmitting radio. All subscriber unit ID's and paging techniques are passed with ease. Is this what you call transparent operation?

  8. #8
    Join Date
    Dec 21, 2011
    Posts
    4,514
    Thanks
    3,790
    Thanked 6,654 Times in 1,898 Posts
    Country: Canada

    Default

    Repeating transmissions without double-vocoding is possible, but sure would require a lot of specialized hardware.

    When analog audio goes into the vocoder, it becomes digitized. From there, it goes through the encryption hardware. If one were to design a circuit which takes the encrypted signal, decrypts it, then takes the CLEAR vocoder stream and puts it through a second hardware encryption circuit -- reencrypting the digital audio with a new key, it would not affect audio quality. Signalling information such as RID, NAC, etc. would also be preserved.

    As far as I know, there's nothing currently in existence which accomplishes this. But there's certainly no reason why it could not work. As long as the original digital signal is kept intact and does not go through a D-->A --> D conversion stage, all is good.

  9. #9
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    I think it's best I post a video to show what's been done. Stay tuned....

  10. #10
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    I suck at making videos, but take a look at this!


  11. #11
    Alpha's Avatar
    Alpha is offline T S - Moderator
    CS Forums $upporter
    Join Date
    Feb 12, 2012
    Location
    Directly above the center of the earth.
    Posts
    2,689
    Thanks
    844
    Thanked 1,362 Times in 671 Posts
    Country: Christmas Island

    Default

    I understand completely what was done, I was trying to explain the concept of a transparent repeater to the crowd, because MTP immediately came up with a completely incorrect usage and non-feature of what you had done, so I felt some clarification of what "transparent repeater" meant was in order.

    As I said, this is a very cool thing - but is basically the same as cross-wiring 2 MaxTracs together. If you have a wide-band connection between the discriminator on one radio to the direct modulation of the other, you can do what you have done. All the other solutions would use the recovered audio and would be the equivalent of wiring 2 Astro Spectras together back to back, in which case what MTP suggested would be possible, BUT would be a sub-standard solution due to the problems I mentioned with double vocoding.

    What Mars is talking about sounds neat too, but again is outside the scope of what was done here, good idea, but even a Quantar doesn't do that yet!

  12. #12
    mtp850 No Longer Registered

    Default

    All good guys, I understand how it has been done. I was clutching at straws in hope something different had been found.... I already have a couple of Simoco SRM9000's setup with the link cable that does the same thing as motorobber has done with the Tait's. it passes everything transparent just like maxtrax/CDM's. I live in really low spot and have a transparent repeater setup to receive a distant repeater and repeat it so I can use a portable to listen in the house.

    The back to back astro spectra setup that Alpha mentioned sounds interesting, does anyone have a wiring diagram/cps settings on how to wire this up ?


    Quote Originally Posted by Alpha View Post
    I understand completely what was done, I was trying to explain the concept of a transparent repeater to the crowd, because MTP immediately came up with a completely incorrect usage and non-feature of what you had done, so I felt some clarification of what "transparent repeater" meant was in order.

    As I said, this is a very cool thing - but is basically the same as cross-wiring 2 MaxTracs together. If you have a wide-band connection between the discriminator on one radio to the direct modulation of the other, you can do what you have done. All the other solutions would use the recovered audio and would be the equivalent of wiring 2 Astro Spectras together back to back, in which case what MTP suggested would be possible, BUT would be a sub-standard solution due to the problems I mentioned with double vocoding.

    What Mars is talking about sounds neat too, but again is outside the scope of what was done here, good idea, but even a Quantar doesn't do that yet!

  13. #13
    Dm3600 No Longer Registered

    Default

    Motorobber can you please post the video again, I would be interested to see how it works.

    Thanks DM3600

  14. #14
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    Here is the link
    http://youtu.be/4-TEBy-ZveI

  15. #15
    Join Date
    May 07, 2012
    Posts
    78
    Thanks
    4
    Thanked 2 Times in 2 Posts

    Default

    Nice. How does it go at lower signal strengths?

  16. #16
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    I use it for cross banding from the VHF to a UHF unit in my vehicle. I can then use use my 5 watt UHF portables thru the crossband setup (2 TM9155's on analogue frequencies) in the car in order to link to the VHF network (powered by quantar) when at distance further than the 5watt portables can reach by using the 25watts in which the car VHF unit puts out. This is great for when I'm out in rural areas. I have not done a lot of strength testing by use of attenuators etc. It would be nice for someone with some test gear to measure the effectiveness of this method.

  17. #17
    Join Date
    Sep 07, 2012
    Posts
    27
    Thanks
    18
    Thanked 0 Times in 0 Posts
    Country: United States

    Default

    Old thread I know, but a couple questions:

    Does this setup work with the TM9100 series P25 capable radios as well? (per the last post it appears so)

    Does this programming still allow conventional FM channels to be repeated, or only P25 transmissions?

    Thanks,
    -Dan

  18. #18
    Join Date
    May 16, 2012
    Location
    New Zealand
    Posts
    98
    Thanks
    4
    Thanked 19 Times in 10 Posts
    Country: New Zealand

    Default

    The answer is yes to both of your questions.