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Thread: All about the P1821AX UHF Spectra Suitcase Repeater

  1. #1
    williamray507 No Longer Registered

    Default All about the P1821AX UHF Spectra Suitcase Repeater

    Hello everyone, I have a question about a P1821AX UHF Repeater. I just picked this up and in the RSS it shows the band split as 403-433 MHz, my question is what would it take to change it over to 440-470 MHz? And if so what all is going to be required.


  2. #2
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    2 Higher split low power spectra decks (neither needs the power amp deck) and the separate higher split amp module specific to the P1821AX which I have not seen. Usually easier to find one in the correct split then the work to change it over. Also the radios will have to be bitbanged into the right configuration. I started to do one a while back and it wasn't worth the effort.
    Keith Dobbins N8KLD
    Mainframe Network Engineer/
    Managed File Transfer Engineer
    W8TAP Repeater Engineer
    Parkersburg, WV 26104

  3. #3
    4n6inv No Longer Registered

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    Welcome to my parlor said the spider to the fly.

    I just finished doing exactly that. So; here's my low-down. First; search the forum for the P1821AX manual, RSS manual, and PR2 software. It's on here and offers a great deal of information. I could have never done this without those resources.

    First thing you do is BACKUP the files from the radios - although they should be identical. Ditto for the repeater codeplug.

    The PA is a standard UHF R-3 from a mid-power Spectra. I found one NOS on eBay for $20.00. dissect it and install the PA board onto the anvil sized heat sink assembly inside the chassis. Clean off the crappy white lithium grease heat sink compound and use Artic Silver for better and more reliable heat transfer from the PA transistors.

    I bought two old, crappy UHF Spectra's on eBay that were bare bones radio only that would power up, read and write for next to nothing. This served two purposes. First; I was able to remove the MLM's from the repeater radios and bit bang an R-2 band split into each one. It took me about 5 minutes each and only involved changing one number in the address, programming it, then re-reading the codeplug and writing it back in to clear the checksum error. I then harvested the R-3 front ends and installed them into the repeater radios. Next, I installed the Spectra UHF preamp option in the receive radio.

    Remarkably; I already found two NOS UHF R-2 VCO's and installed them.

    So; now I have a Spectra P1821AX suitcase repeater with 19.1 watts out of the PA, 17.9 out of the internal duplexer - oh, yeah; you'll need to have the internal duplexer retuned. No biggie.

    You can also define in the repeater software whether the mode is for internal or external duplexer. I coordinated a pair of ham freqs using the internal duplexer, and have a cellwave 6 cavity external duplexer with patch cables that I keep in the sleeve inside the top of the duplexer that is tuned to the "unofficial" GRMS emergency channel.

    It's a very cool setup. What sounds like a lot of work, really wasn't. The greatest challenge was finding the NOS parts. The miracle was finding actual R-2 UHF VCO's that were NOS.

    The end result is one super, badass rapid deployment repeater that works great and is a true rarity in like new working condition.

  4. #4
    4n6inv No Longer Registered

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    So begins the long, shaggy-haired dog story:

    I picked up what appeared to be a NOS Spectra suitcase repeater at a hamfest in Plano for $50.00. Still had the delivery cards, cal sheets, and delivery information still in the plastic bag. Not to mention, all of the original accessories still new in their plastic bags. Never had been programmed. Born on date was June 2002.

    After I read it; I realized why I got it for $50.00. It was an R-1. Bummer. It sat, untouched for about 5 years until I found John's post and decided to give it a crack.

    I recapped both Spectras and the control head. I did the white backlight mod for the control head (my avatar). After reading the manual that he so generously posted; I realized that this wasn't going to be such a PITA.

    First thing you do is BACKUP the files from the radios - although they should be identical. Ditto for the repeater codeplug.

    The PA is a standard UHF R-3 from a mid-power Spectra. I found one NOS on eBay for $20.00. Dissect it and install the PA board onto the anvil sized heat sink assembly inside the chassis. Clean off the crappy white lithium grease heat sink compound and use Artic Silver for better and more reliable heat transfer from the PA transistors.

    I bought two old, crappy UHF Spectra's on eBay that were bare bones radio only that would power up, read and write for next to nothing. This served two purposes. First; I was able to remove the MLM's from the repeater radios and bit bang an R-2 band split into each one. It took me about 5 minutes each and only involved changing one number in the address, programming it, then re-reading the codeplug and writing it back in to clear the checksum error. I then harvested the R-3 front ends and installed them into the repeater radios. Next, I installed the Spectra UHF preamp option in the receive radio.

    Remarkably; I already found two NOS UHF R-2 VCO's and installed them.

    Naturally; I had to take the whole rig to a friend with a service monitor and re-tune / align the radios using the Spectra RSS Service software. Not to mention the internal and external duplexers. Now; credit where credit is due: The one thing that my rig didn't come with was an internal duplexer. So; John and I traded favors and he was good enough to trade a UHF internal duplexer for that specific repeater in exchange for a little work on a couple of his Spectras. Thanks, again, John! You're a God!

    So; now I have a Spectra P1821AX suitcase repeater with 19.1 watts out of the PA, 17.9 out of the internal duplexer. 2uV receive sensitivity.

    You can also define in the repeater software whether the mode is for internal or external duplexer. I coordinated a pair of ham freqs using the internal duplexer, and have a Cellwave 6 cavity external duplexer with patch cables that I keep in the sleeve inside the top of the lid that is tuned to the "unofficial" GRMS emergency channel.

    It's a very cool setup. What sounds like a lot of work, really wasn't. The greatest challenge was finding the NOS parts. The miracle was finding actual R-2 UHF VCO's that were NOS.

    The end result is one super, badass rapid deployment repeater that works great and is a true rarity in like new working condition.

    Was it worth the work? Hell yes! Can just anybody do it? Probably not. But; if you've done any appreciable work on any of the Spectra series radios, it's a no-brainer.

    And; if you want to do it, but need some help; I'd be more than happy to assist. I can't speak for John; but having had the pleasure to meet him in person recently; I'd wager that he'd be happy to help - as his time permits - as well. The man's a genius. And, a damn nice guy.
    Last edited by Alpha; Jun 19, 2014 at 06:40 AM. Reason: Moved from P1350 thread

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    2 MICROVOLTS of sensitivity? or .2uV?

    I sure the hell hope it's not 2uV!

  6. #6
    4n6inv No Longer Registered

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    Damn tiny laptop! Yes; .2uV. I thought that was pretty good.

    I know that there are those that will argue that is too hot of a receiver, but I'm in the middle of BFE west Texas, and no one except hams use UHF. And; with it being a portable repeater, using a mag mount; I figure that I can use all the help I can get.

    Another cool thing that I forgot to mention is; in the repeater SW, when you are defining modes - yes, you name the display mode names in the repeater SW - NOT the RSS and define whether the mode is "Local" - meaning a standard tx / rx pair, or repeat with the option of "Internal Duplexer", or "External Duplexer". It has two RF ports, so you can attach a separate external duplexer, like mine, and an internal RF switch automatically switches the RF ports accordingly. Way cool. So; for the "Local" option, or "Internal Duplexer", you have one antenna port. If your using an external duplexer, there are two RF ports - one for the high side of the external duplexer and the other for the low. Based on how you defined the mode, the controller automatically switches the RF lines.

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    If that "white lithium grease" was Dow Corning 340 Heat Sink Compound, Arctic Silver may not have been an improvement.
    Last edited by Slimbob; Jun 25, 2014 at 11:12 PM.

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  9. #8
    4n6inv No Longer Registered

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    Quote Originally Posted by Slimbob View Post
    If that "white lithium grease" was Dow Chemical 340, Arctic Silver may not have been an improvement.
    Going with experience with radio PA's and high power CPU's, my experience has been that Artic Silver doesn't dry out and harden like Dow. Everyone else's mileage may vary. And; I've only been using Artic Silver for about 5-6 years. 5-6 years from now; I may well be eating my words.

    But; point taken. Thanks.