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G8MNY  > TECH     14.10.18 10:30l 126 Lines 5686 Bytes #6 (0) @ WW
BID : 41766_GB7CIP
Read: GUEST
Subj: Realistic Pro2005/6 mods
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 181014/0818Z @:GB7CIP.#32.GBR.EURO #:41766 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

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.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
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      
읕컫컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컫컴컫컴
    ~~~                                                       ~~~
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
              330                                           
                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
   ground.
        旼컴컴컴                旼220컴
   Squelch                            
   Control<컴쩡              R컵훀158컨횵C2-12
       Pot  10K                +  4k7
        읕컴컨컴               ===
                                쿎185

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.


Conclusion
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
more".


Why Don't U send an interesting bul?

73 De John, G8MNY @ GB7CIP


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