Uniden Mystery Board - ARX 800EB (MRS 804 LTR Repeater board) - Page 1
Forum section: electronics / general

author: Stonent
author_rank: Super Contributor
timestamp: July 09, 2013, 03:00:58 am
content: My recent visit to Tanner Electonics (https://www.eevblog.com/forum/reviews/store-review-tanner-electronics-carrollton-tx/) netted me an interesting board for $5.00.The board is made by Uniden and has part number ARX 800EB marked on it. Seaching the net got me nothing.It has a few Mitel chips on it and references to DTMF and Token Ring, so I'm gathering this is some kind of phone system board or some part of a modem system that dials into a Token Ring network. (Sorry, I know the audio is low, I forgot to take the cover off my phone which someone impeads camera audio.)

author: PuterGeek
author_rank: Regular Contributor
timestamp: July 09, 2013, 06:27:43 am
content: Seeing that board caused a little bit of a flashback. After searching a little I believe that is the control board for a MRS 804 LTR Repeater.LTR is/was E.F. Johnson's version of trunked dispatch radio (also known a land mobile radio) and the MRS 804 was for the 800 MHz band. LTR used sub-audible signaling for trunk control and DTMF/call progress tones to patch telephone connections.My second engineering job was a startup developing LTR compatible systems and we worked with Uniden. There were discussions of Uniden buying the startup I had worked for but E.F. Johnson executives interfered. Their interference cost the CEO and controller their jobs and E.F. Johnson was forced to buy the company for what Uniden had offered the investors.Couldn't find any free schematics or manuals online for the MRS 804 but there were some for sale.Hope that helps!-Joe

author: Stonent
author_rank: Super Contributor
timestamp: July 09, 2013, 06:59:46 am
content: http://www.ebay.com/itm/UNIDEN-MRS804-LTR-REPEATER-CONTROL-BOARD-ARX800BZ-NEW-/190456679837Looks a little different but I see a lot of similarities. I thought there may be something RF involved because of the small coax plug on the board.

author: Stonent
author_rank: Super Contributor
timestamp: July 09, 2013, 07:20:18 am
content: Ok, I've found a near perfect match.http://www.ebay.com/itm/Uniden-ARX801E-Revision-1-ESAS-Logic-Board-New-Old-Stock-For-Uniden-Repeater-/171068878047?pt=2_Way_Radios_FRS&hash=item27d47fecdf

author: Stonent
author_rank: Super Contributor
timestamp: January 06, 2015, 05:57:35 am
content: It's been a while but I did manage to power the Uniden board up. There was a 13.8v test point on it so I fed in 12V to a connector marked power and the LED graph lit up with some flashing lights. I connected a small speaker to the speaker pins on the board and just heard a click or two every so often. Playing with the squelch pot would make the squelch light come on and go out. If I touched my finger to the test point near the squelch pot I could hear a 60Hz buzz that sort of had a doppler effect sound to it.I guess that means the board at least works in some way. I've been debating harvesting parts from it since it has most of what I would need for an 8051/52 BASIC computer (minus the 8051/52 which I already have)

author: Stonent
author_rank: Super Contributor
timestamp: January 06, 2015, 06:02:54 am
content: Here's what it came out of apparently. I'm not all that sure what a synthesized repeater does. I sort of have an idea of what a repeater does, just not what a synthesized one does.