Hi!
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For those going in for ver3 board , I once again repeat the mods.
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1) Q1 I have used 2SC2570A a high ft cable TV transistor for higher gain and lower NF. So the pin out is B-E-C which is different from other transistors. C-B-E? L-R for other devices. For 2SC2570?you cab also substitute BFR90.91,96?or MPS571 etc type. Lately one more interestind transistor I have come across 2SC1393/94 this is used is portable BW TV tuners and is easily available.??
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2) Mixer is now doubly balanced so one more trifilar binocular? core to wind.
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3)Q13 has one pad missing on 100?E collector supply resistor but that can be tagged to the adjacent 220E resistor lead on top of board.
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4)Q3 has been replaced by 2 transistor shunt feedback amplifier. However if you wish ,there are sufficient spare holes to retain the original circuitry.
As a result of added ckt you can reduce 2K2 feedbak C-B resistor on Q11 for slightly improved match.
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5) Frontend bandpass uses 10mm adjustable coils. I have used 2.7uh 10.7mhz readymade FM radio IF coils with caps changed. You? can roll your own,? value can be in range of 2-2.7uH. The coupling has been also changed to 2 turn link type.
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6) BFO has now a abt 6uH inductor in series for proper and smooth setting of freq.
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7) VFO has provision for both tuning by variable capacitor or varicap as well as to configure as series tuned colpitts.
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8)LM386 has a .001uF bypass on pin 3 for better stability and a 220uF cap on output for improved LF response.
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With bit care the rigs comes on in one go.
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73
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Rahul VU3WJM
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PS: Do the filter cap changes it results in much improved TX audio.?
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bambazonke01 wrote:
The Far circuits boards are away too big for my application so I'm
strongly considering a run of the CCA design by VU3WJM (Rahul).
This board design is 6.5 X 4.25 inches and will fit nicely inside
the Chinese 884 VHF packset which you can buy off E-bay (Call
up "Military Radio")
I've recently relocated homes and will have to restock on G10 pcb
and resist etc.
Jim VE3DDY
--- In BITX20@..., "ajparent1" wrote:
> Hello,
>
> This may not be of help to everyone but for North Americans
> it would be handy to know.
>
> FAR circuits? www.farcircuits.net
>
> They have the the BIT-X board as drawn by the creator.?
> The one I have measures 221mm by 82mm [8 11/16" by 3 1/4"
> for the non metric].? At 19.00$US it's expensive but may
> save
construction time.
>
> Allison,
> KB1GMX
>
>
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