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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. ┌───────────────────────────────────┬───────────────────────────────┐ │┌────────────────────────────────┐ │ ▒▒▒▒▒▒▒▒▒▒▒▒▒ ▒▒▒▒▒▒▒▒▒▒▒▒▒ │
││ ┌────────────────────────────┐ │ │ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ │
││ │ 1 2 3 4 5 6 7 8 9 10 │ │ │ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │
││ │ 001ch 1 4 5 .5 0 0 MHz│ │ │ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ │
││ └────────────────────────────┘ │ │ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │ │└────────────────────────────────┘ │ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ │ ├───────────────────────────────────┤ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │
│ __ __ 400 Channel│ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ │
│ / \ / \ . Pro2005│ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │
│ ( ) ( ) ┌──┐ ┌──┐ │ ┌──┐ ┌──┐ ┌──┐ ┌──┐ ┌──┐ │
│ (o) \__/ \__/ └──┘ └──┘ │ └──┘ └──┘ └──┘ └──┘ └──┘ │ └──┬───┬────────────────────────────┴────────────────────────┬───┬──┘
~~~ ~~~
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 +8V──┬────────────────────────────────────────────┐Wire
330 │
│ 0.68u Squelch 1K
├──┤├─┬──2K7──┬───┬────┬─────┐ Diode │
BC212 │ │ │ │10n │ │ D46─┐ ├───o)SQ
│/e │ 10n=== === │ \│ │ │/ │Phono
IC6-1 ────┤ 10K └─┬─┘ │ BC337├─10K─┴─10K─┤BC337 │
│\ │ 820 AFo) e/│ │\e │
│ │ EQ R│ Phono│ │Mute Squelch│ │
IC6-7 0V────┴─────┘ └───────┴────┴───────────────┴────┘

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 output 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.
┌─────── ┌─220──┐
Squelch │ │
Control<──┬── R─┼─R158─┴─IC2-12
Pot 10K +│ 4k7
└────┴── ===
│C185

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 +5V───────┬─┤<├─┐
wire │ │ ┌─────7 Matrix
└100K─┤ │/e │
├─39K─┤BC217 /Manual
+│ │\ │
10u === └─────5 Matrix
│
└─────────────1 Matrix (nearest to 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.

────┐ ┌──FB──┬──┬─┤>├──┬─R─┬────┬─LM7805──+5V
)││( │ │ │ │ 4m7│+ │
)││( │ └─┤<├┐ │ │ === │
MAINS )││( .1u === │ │ +│ └───┤
)││( │ ┌─┤>├)─┘ === │
)││( │ │ │ │2m2 │
────┘ └──FB──┴──┴─┤<├┴─────┴────────┴─────

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. Sensitivity is about 1.5uV for usable signal in wide band mode.

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 with auto switching, 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 splitter box, with a series tuned circuit per Rx, & a Band 2 suck-out trap, all fed from a distant Band 1 broadband aerial. Tx audio switching & a backup AF source, is controlled from the 2 Rx 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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