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  • RTT Automatic Mod Meter (100)

    From G8MNY@21:5/101 to TECH on Sat Jul 13 06:00:21 2019
    R:190713/0853Z 1422@XE1FH.#GDL.JAL.MEX.NOAM BPQ6.0.18
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    R:190713/0852Z @:LU4ECL.LP.BA.ARG.SOAM #:5120 [La Plata] FBB7.0.8-beta2 R:190713/0852z @:F4DUR.FRHA.FRA.EU $:12259_GB7CIP
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    R:190713/0852Z @:GB7CIP.#32.GBR.EURO #:12259 [Caterham Surrey GBR]

    From: G8MNY@GB7CIP.#32.GBR.EURO
    To : TECH@WW

    By G8MNY (Updated Jan 15)
    (8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

    I bought this meter at a recent SK sale. It came with an Operating Guide, but no service information. (nothing on internet)
    _________________________________________________________________
    / \
    │ _____________________________________________________________ │
    │ │ ┌───────────────┐% │ │
    │ │ ON │ 8 8 8 . 8 │kHz Vol │ │
    │ │ ( ) │_______________│Rad ( ) │ │
    ┌─┤ │ _______________ │ ├─┐
    [│ │ │ (·) │▄▄▄▄▄▄▄________│ (·) │ │ │]
    │┌┤ │ MOD AM FM PM 3k 15K WB + - /2 AF TEST REM RF │ ├┐│
    │││ │ OUT [ ][ ][ ] [ ][ ][ ] [ ][ ][ ] [ ][ ][ ] IN │ │││
    │││ └─────────────────────────────────────────────────────────────┘ │││
    │││ RTT Series 100 Modulation Meter │││
    ││ \_________________________________________________________________/ ││
    │└─────────────────────────────────────────────────────────────────────┘│
    \_____________________________________________________________________/

    SO WHAT IS IT?
    It is HF/VHF/UHF AM/FM/PM Digital Modulation Meter (Automatic scanning Rx).

    SPECIFICATION
    Power AC IEC Mains input 230V/115 @ 15VA or internal batt, rear SW RF Input BNC socket 50Ω, Max 7V (1W).
    Frequency range Scanning type 1.5MHz-2GHz. (5-40mV input typical)
    Modulation meter Auto Rx. +/- peak & combined Average. With 20 bit bargraph. Ranges Automatic AM 0-100%, FM 0-9kHz & 10-100kHz, PM 0-5 Radians.(2% typical) AF Filters Comms 300Hz-3kHz, HiFi 50Hz-15kHz & Wideband 50Hz-30kHz.
    IEEE 488 bus Remote control for measurements & reporting test result.
    Mod Out BNC & Volume control for internal rear LS.
    IF Out 410kHz at rear BNC.

    It was made in Feltham UK in 1980s. It has a comprehensive power on self check that tests all the systems & basic calibration.

    ERROR CODES
    90 LEDs & Ram, 80 ROM Checksum, 18 Battery <10 or >14V, 5 +5V, 12 +12V, -6 -6V, 51 +ve detector, 52 +ve det 10x, 43 -ve Det 10x, 55 3kHz filter, 56 15k filter 57 Wideband filter.

    INSIDE
    ┌────────────────────────────────┐
    │ ( ) Front panel PCB [▒] │
    │ o o │
    │________________________________│
    Rx Converter & IF modules
    below Digital PCB underneath.
    _____________________________mod out PRESETS
    │ 1 Wide 2 .. │ 1 Bar Graph
    ┼ Filter :│_FM Rx 2 PM Cal
    │ Filter :│_AM Rx 3 Cal test tone 1
    ┼ SW HiFi │ 4 10x gain Cal
    ┼ 3 Filter 5 │ 5 FM Cal
    │ 4 Mode 6 │ 6 AM Cal
    ┼ 9 SW Comms 7 │ 7 Cal test tone 2
    ┼ 10 Filter 8 │ 8 AM/FM/PM Gain Cal ┼____________________ │ 9 DC A-D cal (batt,12v)
    Upper Analog PCB │ Det │ 10 DC A-d offset (+5V,-6V)
    │. 11│ 11 +Det gain
    LS│: LS │ 12 Set +12V
    │ amp │
    │___________│ Calibration is VERY a long winded
    ________________________________ round robbin if you upset A-D converter │12 | | | | | │ (gain & offset?) presets 9 or 10!
    │ Mains XF| | | | | charge │
    │ | Batteries | regulator│
    │PSU under| | | | | │
    │_________|__|__|__|__|__________│
    [LS]
    .·' '·. Rear Panel IEC
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    FAULTS
    It internal 12V (10x AA 0.5AH) Nicad battery was missing, so I added 4 recovered 4AH Li cells to make a 12-16V pack. A voltage doubler & constant current is used for battery charging with cpu controlled boost if low.

    One of the 2 diodes in the 12V PSU was high resistance & caused the toroid to overheat. The Logic card has it's own 5V reg & there is a -6V PSU somewhere.

    AF Wideband 4 opamp filter, components changed to give 10Hz-60kHz

    If anyone has more info one the unit I would appreciate it.


    See my tech buls on "RTT Comms Test Set", "DYMAR Mod Meter Type 1785",
    "FM Deviation Calibration", & "FM Stereo Radio Principles".

    Why don't U send an interesting bul?

    73 de John, G8MNY @ GB7CIP


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    * Origin: HAMRADIO telnet lu9dce.dynu.com (21:5/101)