Thanks Rahul
Jim VE3DDY
--- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:
Hi!
For those going in for ver3 board , I once again repeat the mods.
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.
2) Mixer is now doubly balanced so one more trifilar binocular
core to wind.
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.
4)Q3 has been replaced by 2 transistor shunt feedback amplifier.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.
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.
6) BFO has now a abt 6uH inductor in series for proper and smooth
setting of freq.
7) VFO has provision for both tuning by variable capacitor or
varicap as well as to configure as series tuned colpitts.
8)LM386 has a .001uF bypass on pin 3 for better stability and a
220uF cap on output for improved LF response.
With bit care the rigs comes on in one go.
73
Rahul VU3WJM
PS: Do the filter cap changes it results in much improved TX
audio.
bambazonke01 <jimandruth@s...> 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" <kb1gmx@a...> 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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