All about Racal RA3701 and RA3712 Receivers

Front panel display of Racal RA3701


  General

        This receiver had been manufactured by Racal Communications Ltd. England from 1987.
        Microprocessor is Intel 68000,  its clock is 8MHz. Firmware is P87915/14.
        Latest Firmware is P87915/20 which enables changing  tune rate widely.
        ROM is comprising 2 pieces of 27C210A.


  About circuit

        RA3701 is different from RA3712
          RA3701:
        1st IF: 41.4MHz
        1st Mixer: BSV81x4
        Frequency range: 15kHz to 29.999999 MHz
        Ref OSC: 9442 Opt.001
        FIL Opt.: LA (5filters)

         RA3712:
        1st IF: 81.4MHz
        1st Mixer: SI8901Y
        Frequency range: 500kHz to 40MHz, but possible down to LF.
        Ref OSC: 9420 Opt.002
        FIL Opt.: LG (3filters)

       
       RA3702 control circuit from the manual. (tnx JK1BNR)
       



Block diagram of the RA3701 with option modules.
From HF-Funkempfaenger by DJ9DV
















        Nicely provided RF amp 10dB(above 480kHz), however complicated needed to make it happen by 5 steps.
        1st IF 41.4MHz 2nd IF 1.4MHz.
        Hard to get new 1.4MHz IF Xtal filters. Smaller than old Racal's 1.4MHz filters.

        Front End module: input LPF is 0 to 30MHz and protection for RF damages.

           
        Input return loss span 50MHz, white dot is 30MHz/12dB         RF amp on

           1st Mixer schematic diagram used 4 FETs (BSV81)

           
        1st LO span 100kHz, there is spurs +-20kHz                  Span 20kHz: level is 13dBm

        This is the copy of Table A-1. (pdf file 2Mb)
        Can alter SSB voice pitch along this table.
        Process: Check the BW through PBT. For details below. AF char. of Xtal filters
                     Also interesting to use other filters such 6kHz BW for SSB receiving.
        Capable Hi-Fi receiving for SW Broadcasting, 'Select sideband method' Escape from QRM.

        SECURITY CODE:
                    All RA37xx series models are 7926.



Ref. Racal's 1.4MHz Xtal filters from the HP of LA8AK.
Those filters are used for RA1772, bigger than RA37xx.
Racal RA1771, 1772, 1794-1796, 6772, 6778, 8772 receivers uses
1.4MHz Xtal filters.











        
        Rear view of chassis, pulled off all modules    Red dip SW are use single/dual receiver

       
        Receiver exploded view

 





RA3701 with option modules.
From HF-Funkempfaenger by DJ9DV














       
        Rear side connection cables. Used coaxial cables, using SMB connectors for RF

       
        Upside view, Front end module.

            Bottom view

           Roofing filter is CF: 41.4MHz and BW: 12kHz

           Roofing Filter characteristics. 15kHz/-6dB, 45k/-50dB at wideband IF out

           Over load protect, LC IF Filters and 2nd Mixer DBM

           1st Mixer compartment using BSV81 FETx 4

           First LO Synthesizer Module

            IF/AF Module 5 crystal filters mounted Opt.LA

           Power Module

          REF/BFO Module


Processor Module: CPU is 68000, Firmware is P87915/14
Using 0.047F super capacitor for Memory back up.













          Bottom view of Processor Module



           Power Transformer and capacitors.



       

        Rear view of  Front Panel.  Lamps are backlight of LCDs.



          Dial mechanism



          Lamp for LCD back light. Generating soft orange color.



             Available 5V/60mA lamp for replacement



RA3712 Front End and Reference OSC  Photo courtesy of JA2AEV
            LC IF Filters and 2nd Mixer DBM
         Put the mouse you can see RA3701's one


         
        1st IF frequency is 81.4MHz, and mixer (SI8901Y( left)) is built in the rear side.

       
       Front end module view, the roofing filter is different type. (tnx JA1FOJ)

          
        Inside of the 81.4MHz roofing filter (tnx JA1FOJ)
        Uses 6pole! crystals


Reference OSC of RA3712 ,
5MHz OCXO Reference OSC Opt.002 9420 accurate+-5x10-10/day














Reference OSC of RA3701
5MHz OCXO Reference OSC Opt.001
ST86497, 9442/12 accurate +-3x10-9/day
















  Crystal filters for RA3712 Courtesy of JK1BNR


81.4MHz Roofing Filter 16.4kHz/-3dB SF2.3,
better than RA3701 though it is 41.4MHz IF.












            2.7kHz LSB Filter 2.87kHz/-3dB SF1.33


            1.8kHz Filter 2.30kHz/-3dB SF1.75


            300Hz Filter 343Hz/-3dB SF2.0



Group delay performance of 2.7kHz Xtal filter.
Approximately 1600uS delay time at both edge sides(tnx JA2TY)













 RA3701 Front Panel description




Right-hand keypads and their displays.
Keypads: M1 to M4 for menu settings,
            meter, menu, run/hold, l/s loud speaker on/off,AUX,
            mode: fsk, isb, lsb, usb, am, fm
            squelch, man, AGC- +, BW- +
Displays: mode, AGC, squelch, bandwidth, BFO, ANT select








CW, AGC LONG manual , BW 1kHz, BFO +0.8kHz, ANT 5
 MODE,  AGC ,  SQ
 BW ,    BFO ,  ANT




Left-hand keypads and their displays.
 Keypads: Remote receiver address, numeric keypad, main knob function,
              Memory input/output, scan, sweep, tune rate, BFO +/-
 Displays: address, channel, frequency kHz, different mark, scanning, remote,
             master, fault










            RF meter displays 0 to 120dBuV


            AF meter displays -10dBm to +2dBm


            Center meter view from a instruction manual.


 Specifications                                                                                           ( ): RA3712 specifications

Frequency Range

 15kHz to 29.999999 MHz                                                                       (500kHz to 40MHz)

Resolution

 1 Hz -- tuning steps 1/200/1000 Hz Ver.20 can selectable 1/ 2/ 5/ 10/ 20/ 50/ 100/ 200/ 500/ 1kHz

Readout

 8 digit LCD readout -3 digit BFO +- 9.99 kHz to 10 Hz, RF/AF Level  Mode LCD

Conversion Type

 Dual Conversion -- 41.4 MHz 1st IF -- 1.4 MHz 2nd IF                                     (81.4MHz 1st IF)

Stability

 +- 1.5 parts in 10 to 6th (TCXO), +- 3 parts in 10 to 9th/day (OCXO)--OPT001            (OPT002)

Mode

 ISB(option) -- USB -- LSB -- AM -- CW -- MCW -- FM

AGC

 Short/Medium/Long 2sec

Sensitivity

-113 dBm for 16 dB s+n/n 2.7k SSB, -103 dBm for 16 dB s+n/n in 6 kHz AM (RF amp on) NF<15dB

Selectivity

 Xtal Filters--SSB Upper/Lower-- 2.7 kHz--AM/FM/CW--12 kHz--6.0 kHz--1.0 kHz--0.3 kHz (OPT.LG)

Intermodulation

 3rd order intercept point -- greater than +32 dBm/ +22 dBm RF amp off/on

Remote Control

 Serial ASCII -- 25 pin dSub rear plug -- Built in Self Test

Power

 100/120/220/240 volts changeable a rotary SW, 45 to 65 Hz-- 60 watts                          (80W)

History

 Original Price $? -- 1987 -(?)

Dimensions

 19"(48.3cm) wide -- 5.25"(13.33cm) high -- 17.7"(45cm) deep -- 31 lbs.(14kg)

Resolution: 100Hz/ turn in 1Hz

       Newest RA379x DSP receivers has a Noise Blanker. But analog receivers has no NB.

       The author conducted sensitivity testing of my receivers. December 2008
          Mode CW/BW=0.3kHz/AGC off/F=29.9MHz/BFO +650Hz/s+n/n 10dB used HP 8948A SSG and Shibasoku 796E.
          Result:
                    RA3701 -122.7dBm/-131.4dBm (RF amp off/on)
                    RA6790/GM -116.4dBm, RA6793A -118.3dBm
                    RF-590A -122.2dBm



 Overall AF characteristic by filters

        of: offset frequency

mode/filter

1.0kHz

2.7kHz

6kHz

12kHz

AM 80%

3200@max

6600@max

USB

320-1590

140-3180

6130@max

11k

of; -100

110-3030

of; +100

220-3310

LSB

310-1590

100-3200

6140@max

11k

of; -100

177-3300

of; +100

70-3050

    RF input: 28MHz. AF line output: -3dB point/ 1kHz reference(Hz)

 Overall SSB 2.7kHz and AM 12kHz filters characteristic (tnx JK1BNR)
           

               Audio response curve.



 RA3701 (JA2DJH) and RA3712 (JA2TY)

        Difference of the RA3701 to the RA3712.
        Different IF module opt.LA(RA3701), opt.LG(RA3712)



           

        RA3701's IF/AF module(option LA)                                    RA3712's IF/AF module(option LG)



       

   RA3701(left) vs RA3712(right) different number of modules.


 About optional modules    Photo: courtesy of JA1CEB

           IF filter module: can accommodate 7 filters and even bigger in size.



           Sub-octave filter module



           FSK module



           ISB module



           100kHz IF module




             Home made! The IF filter module. Built by JA1FOJ,  in Tokyo region.



           

        Wow!  He makes 3 of IF filter modules.                           Bottom view of IF filter modules


       Home made IF Filter modules by JA1FOJ

           Home made extension cables made by JA1FOJ



 Break through to built in big filters     (JA2TY attempted)


Use the EDDYSTONE receiver's 1.4MHz filters.(Bigger in size)
Mounted filters (see picture) on the rear side of IF/AF module











        (JK1BNR attempted)

            Used USB and LSB filters in parallel making 6kHz BW (tnx JK1BNR)

       We found 1.4MHz filters in DL Ham Fair 2008.
       Like this (Photo courtesy JK1BNR)
         Useable for AM receiving and wide SSB!
    1.4MHz -6kHz to -300Hz (Bigger in size)            Filter characteristics

 How to default (Reset) the RA37xx receiver
    Beware that all configurations are to be automatically abolished

    1. Turn the power off.
    2. Set S5-SW on the Processor Module S5-SW to the "left" (the non-standard position).
    3. Turn the power on. All memories and settings are set to their default values.
    4. Turn the power off again.
    5. Set S5-SW on the Processor Module to the "right" (its normal position)
    6. Turn the power on.
      Ron W6XY rewrited my memo in Premium-RX.



  Dimpled Knob (Modified)

  (tnx JK1BNR)


       

    JK1BNR made dimpled knob used his lathe.



       

    photo courtesy of JK1BNR


  Review of Major Communication Radio so far used
    Updated in August 2010 written by JA2AEV

    Of three radios are dealt here with:
       a) Racal RA3712
       b) Harris RF 590A
       c) IC-7800 as a reference.
    I should like to describe my personal view as well as evaluation based on actual use for over decade.

   1) Harris Radio
       First military radio was AR-88 ex-RCA some 50 years ago, which was later converted
      for use SSB/CW by employing a mechanical filter for SSB and a product detector
      which performed well enough for entire period., in 1996 a Harris R-2368 ex-US Navy came in and joined to my radio shack,
      from which I have acquainted with various innovative technologies poured in and designing concept
      how those military radios were built for that specific purposes unlike Ham use.
      Later, I acquired a non-used RF 590A (general use version) and traded out the said radio.
      Contrary to ham gears, Harris RF 590 or R-2368 was basically designed with features of non RF-amp,
      and a robust first mixer circuit for handling wide range overload occasions, additionally a brick like filter (sharpness)
      for ISB use together with better in group delay behaviors and LO stability locked by external standards.
      In the meantime, those of modern Ham radios are likely employing RF amps with IF stage with PBT function
      capability or two VFO for dual tuning and many enticing modern features.
      Military or commercial use radios are in principal, designed aiming at higher durability
      and reliability and that there are right parts / components specifically selected as well as building structures.

         Pros of Harris RF 590A:
               - Sensitivity, selectivity and audio output are of excellent level
               - Dial tuning together with keypad input capability
               - Auto-Pre-selector (high speed) installed for better inter-modulation
               - Fluorescent tube display for easy reading and soft touch
               - 100 channel memory
         Cons of what I dislike:
              - Tune rate switching (toggle)
              - Mode selection (toggle)
              - AGC system in particular SLOW position for SSB reception (pumping )

        Things changed and modified
              - Internal SP was cut off and connected to external large SP box
              - Mute function added
              - Modified SLOW mode of AGC to average decay characteristic for pumping free (smooth) from the hang type AGC
             - Squelch function for SSB - AGC threshold setting capability by front panel in SSB mode>

        System in use
          Current system: Harris RA 590A in combination with Harris R-1310A (100 mW exciter) for Ham use as well as listening to
          overseas broadcasting use thanks to 100 memories for quick access in different bands.
          Crystal filters (6 units)) installed ex-Alpha filters Inc. are of super performer for CW, SSB (2.7 KHz) and AM (3.1, 6..8 and 16 KHz)
          for better audio response depending upon conditions.

   2) Racal radio
      In November 2006, we came across Racal 3712 bought from UK and we were fortunate
     that we could acquire six units in excellent condition together with local friends.
     They are like new looking and almost no scratch on those front panels.
     In the meantime, there was another group member JA1CEB and JA1FOJ in Tokyo region, and that they extended us
     a lot of know-how and valuable support during start up period.
     It took a month to really let radios working well.

      For problem solution, various discussions were made on SKYPE platform among local owners for solution (try and error basis).
     At initial stage, what we faced were how to reset processor under jammed situation and to resume it
     to normal operation as all functions are to be configured via command input.
     So far we are fully content with RA 3701 or RA3712, but we did modification on the filter configurations
     (carrier offset and BW) for our desired AF output spectrum.
    I am personally using RA3712 as receiver and MA3751 as exciter for Ham radio use and drive to the amp bringing it up to 500W output level.

  Overall rating:
     Racal radio in general is performing nicely in all respects, in particular of its nice audio quality via additional external speaker.
    I like functions of filter user option, and keypad setting for changing BW, Mode, AGC and Meter and many things to be done via MENU.
    Easy handling:: easier memory access (Read and Write jobs, while Harris radio multi steps required).
    Front panel LCD display unit with normal back light is of an enticing filament lamp one.
    So far they are in good shape in all functions, so I shall keep Racal radios for life time and enjoy it,
    and attempt a joy of a "touch up" enhancement together with local friends from time to time..
    We have completed a project to build a Remote control box(refer to the attachment) to be put on the operation desk for chair set basis
    and easy to operate Racal radios instead of accessing them before the rack..

    3) IC 7800 ex-ICOM
      Almost six years elapsed since IC-7800 came in to my shack.
     Receiving performance in general is excellent in all respects for ordinal Ham use at sensitivity, selectivity and stability, remarkable at its lower noise floors level.
     A memo-pad is so useful during contest or other DX hunting.
    Dual receiver capability is another charming point for chasing DX in the different band monitoring.
     So far I encountered one fatal trouble of internal 10 MHz standard OSC (reference) failed and
     it was hard to detect a source of the trouble as all function of receiving was downed inclusive LCD.
     DSP based filtering process is seemingly fine and various controls achievable, but audio feeling after the demodulation is
     somewhat un-friendly tone to me at its clarity and a lack of transparency like water (as if we were standing in the mist feeling).
     IC-7800 is on a stand-by position mostly only for DX chasing for quick and easy to operate.
     Under recent poor propagation, it is not so often to get on air with IC-7800.
 
  4) Collis 75S-3C converted
      This 75S-3C is the last version of S-line among its RX series and almost reached to a matured stage in 1970
     by several enhancement executed compared to its original 75S-1.
     The basic concept of this radio is still shining and valid in most of circuit designing, in particular RF stage superb concept
     and circuitry..
    Modifications were attempted spending for several years:
      a) Replacement of FA-21 to Rockwell 2.7 KHz BW MIL approved 12 pole MF ( independent LSB, USB )
      b) LM-1496 DBM de-modulation employed
      c) AGC circuit modified for smooth slow recovery at SLOW AGC.
      d) Audio, de-modulator and 455 KHz OSC were converted to semi-conductor based circuit for less heat generation
         AOR DDS-2A was introduced to secure frequency stability instead of conventional PTO, and digital LCD readout
         from analogue dial tuning.
         With those enhancements done, the 75S-3C converted is now standing nicely for daily operation with full of satisfaction.

   Personal review (consolidated) of four radios evaluated at overall audio quality:
    Filter nature difference:
      a) Racal RA3701/3712 (Crystal filter at 1.4 MHz, BW: 2.7 KHz)
      b) Harris RF 590A (Crystal filter at 455KHz, BW: 2.7 KHz)
      c) Collins 75S3-C modified (Rockwell-Collins 12 discs MIL spec MF filter at 455KHz for group delay and phase compensated, BW:2.7 KHz)
      d) IC-7800 (DSP at 36 KHz, Variable BW setting)
    It is indeed interesting to compare with and see those of four radios under different IF filters,
    with which there are tangible differences in filter nature for creating specific coloring onto SSB de-modulation (to voice taste)
    as those are the only component influential along the signal route to vibrate physically like a music instrument and add a specific tone onto the signal.
    As a consequence, I personally feel that Crystal filter with high Q element is good for selectivity,
     but not so enticing in group delay behavior, so it is advised to employ a slight wider filter BW for minimizing the said drawback.
    Actually, those crystal filters used in the commercial radios are purposedly provided at least 300Hz wider than the name plate indicated.
    Mechanical filters ex-Rockwell Collins for MIL spec approved one is vanguard at selectivity as well as group delay characteristics,
    with which operator has less fatigue in long term receiving.
    DSP is a breakthrough device in replacing conventional filters like Crystal or Mechanical ones at its performance
    and long term reliability are regarded as a best solution, but assumed to be problematic at time delay (process time delay)
    and audio coloring or a slight turbidity included.
    It is for sure that any man-made products like DSP can not be a perfect one, and it is often said there is a significant sound differences
    between traditional organ vs. electronic organ in the church.
     Therefore, I am enjoying analogue radio with MF or Crystal filter installed with large size speaker with lower THD audio amp
    rather than radios of modern SDR or DSP based TRX.


 Photo of 37xx series exciter and linear amplifier

    I'm not owned exciter and linear amplifier.



       

   MA3751 exciter and TA3762 250W linear amplifier





Arrived the Racal trio. (Photo courtesy JK1BNR)
TA3762
linear amplifier, MA3751 exciter and
RA3712 receiver. down to up









         If you need information of the MA3751 exciter and remote control,  please ask JA2AEV.
         He has planned transceiv operation via remotecontrol (PIC control) between RA37xx receiver,
         MA3751 exciter and the TA3762 linear amplifier.


 The RC3700 Remote control


This is a test board of the remote control using PIC.
LCD displays
1: AGC, 2: mode, 3: BW, 4: frequency, 5: tuning rate. (tnx JK1BNR)
Put your mouse on, you can see notations of the board.
remote1: use for receiver
remote2: use for exciter and linear amplifier















     
    The remote control box assembled by JK1BNR, it's software written by JA2LZV.

       Power on display

     Locally designed and built the Remote Controller RC-3700 for Racal 3700 series radios.

       Major features:
       1. RA 3712 Receiver Remote Control capabilities (RA 3701)
          a) Frequency coverage: 0 ~ 39.999999 MHz (~ 29.999MHz)
          b) Mode selectable: LSB, USB, AM, CW
          c) AGC: Short, Medium, Long, Manual
          d) IF Band width selectable: 0.3 kHz ~ 12 kHz
          e) IF gain: 0 ~ 100 dB
          f) S meter indication: S1 ~ S9+60dB
          g) Channel memory: up to 100 channels
          h) Memory pad: 5 channels read and write
          i) Frequency resolution: 1Hz ~ 100 kHz with 6 steps
          j) RIT: +/- 10 Hz ~ 9.99 kHz
          k) PBT
          l) Ten key for frequency setting
      2. Tranceive-operation capabilities with RA3712 / MA3751 / TA3762 with RC3700
          a) Frequency
          b) Mode
          c) Reset
          d) Amp on
          e) PTT
          f) RF Output level reading
      3. Additional features
          a) RA3712 RF Amp to function automatically above 10 MHz
          b) Vacuum Fluorescent Displaying Device for operatorsf friendly
          c) Controllable VFD light intensity
      4. Data
          a) Microcomputer: PIC 18F8720
          b) MPLAB C-18 Compiler
          c) Dimension: W260 x H85 x D170mm
          d) Power consumption: 10W / 5V
          Weight: 2 Kg



         Special thanks to G3XVR Danny for information of remote control.
            G3XVR Danny has built another remote control for RA3702/MA3752/TA3762.

     

     Breaking news
     JA2LZV succeeded!! via PC control for Racal RA3712/3701/MA3752/TA3762, Dec., 2011
      (Win7 and WinXP), with which ADAT, ICOM and Kenwood can be controlled simultaneously.
      (ADT-200A, IC-756 Pro3, IC-7800, TS-590S etc.)


       
Menu display(4 different tranceivers can be controlled)    Front display in Racal

     
         Front display in ICOM

  Major features:
       1. RA 3712 Receiver Remote Control capabilities
          a) Frequency coverage: 0 ~ 39.999999 MHz (RA 3701;~ 29.999MHz) (ICOM & Kenwood; +50~54MHz)
          b) Mode selectable: LSB, USB, AM, CW, FM
          c) AGC: Short, Medium, Long, Manual
          d) IF Band width selectable: 0.3 kHz ~ 12 kHz
          e) IF gain: 0 ~ 100 dB
          f) S meter indication: S1 ~ S9+60dB
          g) Channel memory: up to 50 channels (10CH x 5)
          h) Memory pad: 5 channels read and write
          i) Frequency resolution: 1Hz ~ 100 kHz with 6 steps
          j) Ten key for frequency input
          k) Ham band respective buttons
      2. Tranceive-operation capabilities with RA3712 / MA3751 / TA3762
          a) Frequency
          b) Mode
          c) Reset
          d) Linear Amp on
          e) PTT
      3. Additional unique features
          a) RA3712 RF Amp on/off by one touch
      4. PC connection
          a) Run with WindowsXP and Windows7
          b) Required 25pin to 9pin dSub cable(Racal), 9pin to 9pin dSub(ICOM), USB to USB(Kenwood) and
            9pin dSub to USB (SRC06-USB) for Win7.

Racal TRA 3755
       The TRA3755 DSP tranceiver.
         TRA3755 RACE 125W HF ALE Transceiver
        Photo: courtesy of JH2CLV


  Special Features Built-in to RACE and Javelin

    (tnx JA1CEB)


      SAT-3311/B Survey System
         SAT-3311/B
       u to d   Control Unit, RA3701 Receiver, Digital Signal Processor (tnx JA2LZV)

  Racal communication equipment catalogue
   courtesy of JA1CEB and JA2LZV
    RA37xx receiver
    RACAL Communication


 Links

    eHam RA3702 review  
    Manual of Racal equipment (tnx to F0FJ Feyssac for information ) 
    Home made IF Filter modules by JA1FOJ



    return to ham page