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G8MNY  > TECH     12.10.18 11:30l 97 Lines 4589 Bytes #4 (0) @ WW
BID : 41431_GB7CIP
Read: GUEST
Subj: RTT Automatic Mod Meter (100)
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 181012/0928Z @:GB7CIP.#32.GBR.EURO #:41431 [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)
     _________________________________________________________________
    /                                                                 \
   ³   _____________________________________________________________   ³
   ³  ³                      ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿%                     ³  ³
   ³  ³     ON               ³  8  8  8 . 8  ³kHz            Vol    ³  ³
   ³  ³    ( )               ³_______________³Rad            ( )    ³  ³
 ÚÄ´  ³                       _______________                       ³  ÃÄ¿
[³ ³  ³ (ú)                  ³ÜÜÜÜÜÜÜ________³                  (ú) ³  ³ ³]
 ³Ú´  ³ MOD  AM  FM  PM   3k  15K WB   +   -   /2   AF TEST REM  RF ³  ÿ³
 ³³³  ³ OUT [  ][  ][  ] [  ][  ][  ] [  ][  ][  ] [  ][  ][  ]  IN ³  ³³³
 ³³³  ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ  ³³³
 ³³³     RTT Series 100 Modulation Meter                               ³³³
 ³³ \_________________________________________________________________/ ³³
 ³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³
  \_____________________________________________________________________/

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 50ê, 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
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³    ( ) Front panel PCB  [±]    ³
³  o                          o  ³
³________________________________³
 Rx Converter & IF modules
 below Digital PCB underneath.
 _____________________________mod out        PRESETS
³           1        Wide  2  .. ³           1 Bar Graph
Å                    Filter     :³_FM Rx     2 PM Cal
³              Filter           :³_AM Rx     3 Cal test tone 1
Å                SW  HiFi        ³           4 10x gain Cal
Å            3       Filter   5  ³           5 FM Cal
³            4  Mode          6  ³           6 AM Cal
Å   9            SW  Comms     7 ³           7 Cal test tone 2 
Å 10                 Filter    8 ³           8 AM/FM/PM Gain Cal
Å____________________            ³           9 DC A-D cal (batt,12v)
   Upper Analog PCB  ³     Det   ³          10 DC A-d offset (+5V,-6V)
                     ³.        11³          11 +Det gain
                   LS³:   LS     ³          12 Set +12V
                     ³    amp    ³
                     ³___________³    Calibration is VERY a long winded
 ________________________________     round robbin if you upset A-D converter
³12       |  |  |  |  |          ³    (gain & offset?) presets 9 or 10!
³ Mains XF|  |  |  |  |  charge  ³
³         | Batteries | regulator³
³PSU under|  |  |  |  |          ³
³_________|__|__|__|__|__________³
   [LS]
 .ú'  'ú.    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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