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Thread: ASTRO TAC receiver to comparator conversion

  1. #1
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    Default ASTRO TAC receiver to comparator conversion

    A couple of weekends ago, a good friend and I were brainstorming ideas to build a more easily deployable alternative to the ASTRO TAC 3000 comparator.

    For an upcoming (low-budget) project we need two comparators, but we only really need to two channels on each (one for a Quantar, another for a satellite receiver.)

    Rather than buying (and shipping) a pair of rare, heavy and expensive ASTRO TAC 3000 comparators, I figured we could build a lower footprint version of the same thing fairly inexpensively.

    Buy a cheap 800MHz or UHF R1 ASTRO TAC receiver. Throw the receiver module in the trash. Add a 68040 coprocessor, appropriate firmware SIMMs, new codeplug EEPROM etc, and you've got yourself a two-port ASTRO TAC 3000 in a package half the size and a third of the weight.

    I have never seen inside an ASTRO TAC receiver and I have only a general familiarity with Quantar hardware, so my question is: Does this sound feasible?


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    Since you are talking about deployable, have you considered space diversity? Place one transmitter and two receivers on same tower and use a comparator to select best BER . The antennas would need to be separated vertically by about 15 to 20 feet. The duplexes antenna on top, the RX only below with bandpass/ reject filtering.

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    The backplane (TRN7737A) is the only unique part to an AstroTAC comparator. The power supply (12V/265W), wireline/V.24 cards, the cage, and the controller card (with mods as documented here and elsewhere) are all interchangeable with Quantar parts.
    "The Girl Scouts found several hungry REACT members at the finish line..."

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    The backplane is the only thing that might cause the ATAC SCM to get confused, or refuse to co-operate.

    Bryan Fields, W9CR has done some excellent work and documented how to modify a Quantar into an ASTROtac 3000 on his wiki.

    Thankfully, he has published the details here --> http://wiki.w9cr.net/index.php/ASTRO-TAC

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    Quote Originally Posted by RFI-EMI-GUY View Post
    Since you are talking about deployable, have you considered space diversity?
    That's pretty much the plan. Urban environment with lots of steel and concrete, so it's multipath hell. No tower space so it'll be horizontal separation, but I planned to try a circular polarised antenna on the second receiver to see how well that mitigates some of the multipath pain.

    Quote Originally Posted by MattSR View Post
    The backplane is the only thing that might cause the ATAC SCM to get confused, or refuse to co-operate.
    That's the bit that I was worried about. I took a look at Bryan's page and his mods just seem to be extra connectors for wireline cards, so if the ASTRO TAC receiver backplane is otherwise functionally identical I shouldn't need to do anything.

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    What you are describing is the situation of RT/RT

    The condition is though you have different channels and your set, if you can live without the "voter"

    Channel 1 - Quantar with a 293 NAC
    Channel 2 - Astro-Tac RX with a 351 NAC

    Or anything to your liking

    Configure RT/RT in the RSS and ensure you have good links on Astro Modems or V.24 between your stations

    You would then direct cable the Astro Modems or V.24 links between the stations. (quantar to quantar, quantar to Astro-tac, etc.)

    Mandatory to enable INTERNAL timing on the modem page under Wireline or the links will not sync

    Also will need to wire the V.24 cables for cross over

    Installs I have done skipped the crossover cables and went back to back with Telenetics modems resolving the timing and cabling

    Have run this as a solution for multiband users as a crossband solution

    CoD

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