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G8MNY  > TECH     14.10.18 10:30l 126 Lines 5686 Bytes #6 (0) @ WW
BID : 41766_GB7CIP
Subj: Realistic Pro2005/6 mods
Sent: 181014/0818Z @:GB7CIP.#32.GBR.EURO #:41766 [Caterham Surrey GBR]

By G8MNY                              Correction Oct 18)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Here is a collection of mods I have done to these identical scanners, so they
can be used as unmanned single channel broadcast link Rx, but still leave full
functionality as a scanner if needed.
넬컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴  굇굇굇굇굇굇   굇굇굇굇굇굇 
납 旼컴컴컴컴컴컴컴컴컴컴컴컴컴커   旼커 旼커 旼커 旼커 旼커 旼커 
납      1 2 3 4 5 6 7 8 9 10      읕켸 읕켸 읕켸 읕켸 읕켸 읕켸 
납      001ch  1 4 5 .5 0 0 MHz   旼커 旼커 旼커 旼커 旼커 旼커 
납 읕컴컴컴컴컴컴컴컴컴컴컴컴컴켸   읕켸 읕켸 읕켸 읕켸 읕켸 읕켸 
냅컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴  旼커 旼커 旼커 旼커 旼커 旼커 
쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴 읕켸 읕켸 읕켸 읕켸 읕켸 읕켸 
        __      __      400 Channel 旼커 旼커 旼커 旼커 旼커 旼커 
       /  \    /  \      .  Pro2005 읕켸 읕켸 읕켸 읕켸 읕켸 읕켸 
      (    )  (    )   旼커   旼커  旼커 旼커 旼커 旼커 旼커      
 (o)   \__/    \__/    읕켸   읕켸  읕켸 읕켸 읕켸 읕켸 읕켸      
    ~~~                                                       ~~~
A/ Mod to give Squelch line & WBFM HiFi audio outputs. (Tape out is not HiFi!)

1. Drill 2 holes for 2 additional bolt Phono in sockets, located above the DC
   in connector.
2. Place PNP emitter follower, 330R, 0.68u, & 10K above IC6 with a +8V wire.

   IC6-14 +8V컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커Wire
                0.68u                        Squelch      1K
               쳐캑쳐쩡2K7컴쩡컴쩡컴컫컴컴커   Diode       
         BC212                10n         D46커       쳐컴o)SQ
             /e        10n=== ===         \          /     쿛hono
   IC6-1 컴컴      10K      읕쩡      BC337쳐10K컨10K캑BC337 
             \              820   AFo)    e/           \e    
                         EQ R  Phono    쿘ute    Squelch    
   IC6-7 0V컴컴좔컴컴         읕컴컴컴좔컴컨컴컴컴컴컴컴컴컨컴컴

3. Add 50uS de-emphasis components 2x 10n, EQ R, series 2K7, & Mute NPN on to
   the AF phono socket. These components give flat response into a 20K load.
4. Add squelch NPN to SQ phono socket with the 1K. Add both base 10Ks to top of
   the nearby diode D46.
5. Test functionality, SQ O/P is +8V on good WBFM, with good AF, & it is muted
   with the internal comms squelch on a weak signal. No Op on other modes.

B/ Mod to improve Squelch control action. (all at one end, & huge hystersis!)

1. Improve zero end action. Put a 10K from the Squelch control slider to pot
        旼컴컴컴                旼220컴
   Control<컴쩡              R컵훀158컨횵C2-12
       Pot  10K                +  4k7
        읕컴컨컴               ===

2. Reduce hysterisis by reducing R158 value. Put a 220R from IC2 pin 12 to +ve
   end of C185 (fine wire required!)
3. Test function. Weak signal squelch threshold more easily set, & snap on &
   off action much closer in level.

C/ Mod to set "manual mode" not "scan mode" on power up. (Default is scan!)
1. Connect wire from +5V on LM7805 regulator to a 100K & a 1N4148 diode near
   the front panel upper PCB connector keyboard matrix plug.

   LM7805 +5V컴컴컴컫캑<쳐
              wire              旼컴컴7 Matrix
                    100K캑     /e        
                          쳐39K캑BC217      /Manual
                         +     \         
                     10u ===      읕컴컴5 Matrix
                          읕컴컴컴컴컴컴1 Matrix (nearest LCD)

2. Push -ve end of 10uF into plug pin 1 & hot glue in place.
3. Wire up 39K to PNP's base & push emitter & collector into 5 & 7, hot glue.
4. Wire up the components to the +ve cap lead.
5. Test functionality. On power up the PNP conducts for ~200mS & check the
   scanner always goes into manual mode.

D/ Mod to improve PSU, & RFI. (reduce bad mains crashing & RFI?)
1. Add 2 small ferrite rings (FB) on 14V AC PCB input leads from transformer.

     컴컴  旼횲B컴쩡컫캑>쳐컫훀컫컴컴쩡LM7805컴+5V
         )납(                  4m7+  
         )납(        읕<첼       ===  
   MAINS )납( .1u ===         +    읕컴
         )납(        旼>)켸  ===       
         )납(                 2m2     
     컴컴  읕횲B컴좔컨캑<쳅컴컴컨컴컴컴컴좔컴컴

2. Add more smoothing with 4700uF 25V on the LM7805 input & earth pins.

In use at an RF cluttered Band 2 hilltop Tx site, 2 of these on Band 1 provide
my community station's uplinks, without the cost of 2 bespoke dedicated Rx.

My choice of 2x 50kHz identical mono links channels, for the station's stereo
uplink, is not only cheaper to rent than a single 200kHz wide stereo link
channel, but are 2x more reliable (survive on 1, but 2x the kit needed!), &
mono can give about 20dB better signal to noise than a stereo link can!

Other precautions taken was an aerial box, with a series tuned circuit/Rx, & a
Band 2 suck-out trap, all fed from a distant shared Band 1 broadband aerial. Tx
audio switching & a backup AF source, is controlled from the 2 Squelch lines.

They have given fairly trouble free hifi broadcast up links, but quite a fiddle
to get right!

See my Tech bul on "FM Stereo Radio Principles" & "SUSY RADIO @ 5 years +5

Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP

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