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Thread: Astro Saber Repeater?

  1. #1
    tim No Longer Registered

    Default Astro Saber Repeater?

    Hi Folks,

    We currently have a 'portable' repeater made from a Kenwood TKR-720. Since this used for public safety, obviously we have to change it out before January.

    Also, it looks that we will be using some P25 in the future, I was thinking of some ways to make a portable P25 capable repeater.

    Using a couple of Astro Sabers we could do either analog or digital (just change the channel on the radios), and the ID number of the user would not be re-transmitted, but are there any other things that I would need to consider?

    Are the Sabers shielded enough to use 2 of them in a repeater application, or should I plan on putting each one in some kind of shielded box? Our frequencies are about 5mHz apart, and there is a pancake type repeater in the base of the 720 that I would use.

    Just looking for ideas.

    Thanks!

    Tim


  2. #2
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    I realize you're looking for a portable, tactical repeater. Not a full-time implementation, so I won't rag on you for using back-to-back radios for public safety communications

    This is something Motorola never really addressed, in the sense of creating a product or accessory to handle the job. They did come up with a special cable which interconnects two XTS5000s (or 2500s) to make a portable tactical repeater, but they refuse to sell it to the general public. I'm happy to post the details if you're interested, and wish to pursue it. Double-vocoding is involved, so yes: It would sound like ass.

    For a portable *tactical* repeater, I might even suggest you use two back-to-back Maxtracs, modified to pass flat audio (discriminator--->modulator), set up for narrowband (if you consider 2.83 KHz ASTRO to be narrowband) operation. This would pass ASTRO communications AND narrowband analog communications.

    The plans for the Maxtrac repeater are on Batboard, inside the ASTRO sub-forum. Unfortunately Alex has set it up so you must be logged in to the forum to read the ASTRO posts (I guess it's a secret?), otherwise I'd be happy to post a direct URL.

    Also be aware of some complications with the Maxtracs, which you'll need to overcome/correct before putting the repeater into operation:

    - There's a DUTY CYCLE monitor built into the firmware. It will fold back the TXPO to nearly zero, if you do not bypass this. There are instructions on repeater-builder.
    - Cooling fans are a must.
    - Turn the TXPO of the transmitting radio down to about 2-5W or so. No reason for 25-45W on a tactical repeater. It'll just burn out sooner. To get the TXPO down this low, you'll need to bypass the microcontroller and install a manual potentiometer. Again, instructions are on repeater-builder. Very simple to bypass/install.
    - You might want to build a simple repeater controller and throw a large cap across the PTT line, so it stays biased for a few seconds after losing the COR/COS. You can accomplish this with a transistor (or relay). Very simple.

    The benefit of this configuration is it WILL pass radio IDs and other signalling data, as you're not double-vocoding the digital transmissions.

    But I have to stress, this is NOT the ideal setup for PUBLIC SAFETY communications. But as you said, it's a portable, tactical, repeater. I see no reason why this wouldn't be acceptable, so long as you do not rely on it as a piece of critical infrastructure, and you construct it in a way which is highly unlikely to fail as a result of mechanical or heat-related stress.

    There's lots to talk about in terms of optimizing the Maxtrac back-to-back repeater, so if you do go this route, please continue the conversation here. I'll walk you through some of the technical challenges and adjustments. Been there, done that.

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    And for all the non-believers, here's the SP "Federal Only" Portable Tactical Repeater option for the ASTRO25-series portables.

    I did attempt to solicit more information on this from Motorola, and was transferred to their Federal Sales division. I was told it's not available to the public and they refused to provide any further details on it. I was also told they haven't sold many. Another example of Moto wasting their money making a product which isn't selling, and group comes along (us hobbyist geeks) wanting to purchase what will likely get tossed into the garbage at some point, and they refuse to play nice.

    Anyway, enjoy the reading.
    Attached Images Attached Images
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  4. #4
    tim No Longer Registered

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    Hey Mars, thanks for the info.i thought about the maxtracs, but didn't think they were narrowband compliant.i've seen the portable repeater made from the old MX series, and the suitcase Spectrastim

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    I've seen one of those at a Hamfest. Someone Ray-Ray was sittng with had it.

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    Quote Originally Posted by tim View Post
    Hey Mars, thanks for the info.i thought about the maxtracs, but didn't think they were narrowband compliant.i've seen the portable repeater made from the old MX series, and the suitcase Spectrastim
    Hey, anytime.

    Correct me if I'm wrong, as I'm a Canuck (no narrowbanding up here) but in order to be narrowband compliant, I would think you would only have to adjust your TX deviation to ensure you're within the conditions outlined in your FCC license. 2.5 KHz is what narrowband FM is, however I do believe there is something written (I have no idea where) that recognizes P25 as narrowband equivalent. P25 deviation is approximately 2.83 KHz. Analog service monitors may show 2.9 - 3.4 KHz. This is caused by the rapid FSK data.

    The receiver in a potential Maxtrac configuration doesn't care about narrowbanding. The IF filter is just a "window" for passing a 5 KHz (approximately) wide signal. The narrowband FM or P25 signal will pass without clipping or distortion just fine.

    When a Maxtrac repeater is calibrated, there are two adjustments to make:

    - A pot should be inline between the discriminator (RX) and modulator (TX). It must be set just under the clipping threshold. This is accomplished with a service monitor.
    - The master deviation adjustment in the TX Maxtrac must be set for a minimum of 2.83 KHz, to pass P25 without packet loss. (And remain within the conditions of your license.)

    The repeater must be optimized for P25. If analog is slightly overdeviated (maybe by 0.5 KHz?) it will not be noticeable. If underdeviated, you may have problems passing PL/DPL, or MDC PTT-ID data.

    Personally, I would set it up for P25 and not run any analog

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    From the looks of the picture there, the actual interface is just a straight cable from one radio to the next (straight as in, no interface box). Is it really as simple as just matching a few pins between each? If so, it wouldn't be hard at all to replicate one of these.

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    Quote Originally Posted by Durchschnitt View Post
    From the looks of the picture there, the actual interface is just a straight cable from one radio to the next (straight as in, no interface box). Is it really as simple as just matching a few pins between each? If so, it wouldn't be hard at all to replicate one of these.
    If only it were this easy

    The cable uses a Dallas Semiconductor 1-wire chip. When connected (radio to radio), the radio(s) are put into PTR mode. The chip is programmed with a certain code. It would take some reverse engineering to figure out, but it's not impossible.

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    Well colour me surprised...heh. I guess the custom software on the RX radio sends some sort of COR-like output on one of the pins when put into PTR mode.

    Shame Motorola wouldn't sell these suckers, they'd be good for ARES. Or at least, they could swing it that way.

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    The only thing good for ARES are barricades, with them on the other side.

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    LoL, no kidding.

    Anyway, for those interested and can't get to the BL thread, here's a diagram of what Mars is talking about Re back-to-back Maxtracs.

    http://img34.echo.cx/img34/3465/astromaxtrac5zr.jpg

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    Thanks for posting the link. I see The Pager Geek (author of diagram) came up with a newer revision since I built one about 7 1/2 years ago. He has added the pot between the discriminator/modulator. This is good.

    All the Maxtrac info one could ever ask for is here:

    http://www.repeater-builder.com/maxt...rac-index.html

    And the manual power control mod is here:

    http://www.repeater-builder.com/maxt...r-control.html

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    I know Wireless Pacific made a portable repeater which utilized two XTS3000 connected together. I believe it was a double vocoded setup as well. The original model is off their site now, but I found the page through archive:

    http://web.archive.org/web/200308080...om/RDXprod.htm

    Brochure PDF: http://web.archive.org/web/200308080...m/brochure.pdf

    Powerpoint presentation: http://web.archive.org/web/200308080...ProdOV0203.ppt


    Here's one of their current products, which appears to be totally transparent: http://www.pwcau.com/p25-solutions/p...ment-repeaters

  14. #14
    tim No Longer Registered

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    Hi All,

    Thanks for the info - I'll be looking through the various areas.

    Unfortunately, down here, if the transmitter isn't certified by the FCC for narrowband, then it won't be legal come 2013. You can't use any kits to narrowband stuff, although I've seen some for sale. Shame to pitch all of those good MII & Micor repeaters that are working just fine. Ugh, let's not go there!!

    Tim

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    You can use kits, if they are from the oem and the radios were also type accepted with the kit installed. The only ones I can think of are the GM/GP300 and kenwood tkbx20 series.
    Quote Originally Posted by tim View Post
    Hi All,

    Thanks for the info - I'll be looking through the various areas.

    Unfortunately, down here, if the transmitter isn't certified by the FCC for narrowband, then it won't be legal come 2013. You can't use any kits to narrowband stuff, although I've seen some for sale. Shame to pitch all of those good MII & Micor repeaters that are working just fine. Ugh, let's not go there!!

    Tim

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    I have used the PDR3500's in VHF and they work really well for NB and P25 both on the ground and airborne. I highly recommend them for mission critical tactical use. Yes you will pay thru the nose for them...

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    If you're already willing to pay through the nose for PDR3500's, then the DVRS from Futurecom should be considered as well:

    http://www.motorola.com/web/Business...chure-Fire.pdf

    It's also available in a transportable Pelican case with optional external 12V battery.

    http://www.futurecom.com/uploaded/ti...0X03-Rev-3.pdf

    Canada Border Services uses these on the East Coast when searching large container ships to get the coverage they need. They can plunk it down anywhere in the ship, or operate it from a vehicle parked alongside the ships, whatever works best in a particular situation. It really is a slick piece of gear. Requires the use of an XTL2500/5000 in order to power & operate.

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    Oh man, that PTR would be great for the SAR community if they sold it! Our SAR group uses a RICK between two CDM1550s for a crossband repeater and that works great but I'm right now looking right now to MacGyver a better in-band solution.

    Doesn't also either EFJ or Bendix King offer a "tactical briefcase" that lets you interconnect two radios with Jedi connectors?