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BITX20A

Nov. 29th, 2008 01:08 pm New BITX17A Transceiver Kit Available from KI6DS


It has been a while since my last posting on this blog.  During that time several interesting things have happened, the most interesting to me being that Nigel G0EBQ worked up a modification of a basic BITX20A Kit PCB for operation on 17 meters.  After Dan performed spectrum tests on Nigel's conversion (it meets FCC spurious emission requirements), I wrote a BITX17A Assembly Manual for the new BITX17A Kit.  That manual, pictures of the BITX17A, and ordering information is now available at <http://www.qrpkits.com>.  Doug has even made a 20M to 17M conversion kit available for those who wany to convert their BITX20A units to be BITX17A transceivers.  I will be working up a short "conversion Instructions Manual" for that in the very near future.  After that...I plan on doing a total re-write of the existing BITX20A Assembly Manual so it will include things that we have learned in the past 8 months.  This new re-write will also include a troubleshooting section with schematic modules and DC voltage charts.  Until this new BITX20A Assembly Manual is available, you can download the BITX17A Assembly Manual if you need troubleshooting information for your BITX20A Kit.  The schematic sections and DC voltage charts are valid for both BITX17A and BITX20A.  To make the conversion of a BITX20A to a BITX17A, only the crystals and a few component values were changed to make it operate on 18.068 to 18.168 MHz..



Also during the past 10 months, Leonard KC0WOX has developed many excellent image files and videos to help with various BITX20A, BITX17A, and BITX Version-3 transceiver builds and related troubleshooting.  These are located at <http://golddredgervideo.com/kc0wox/>.

Over the past 14 months Sunil VU2SWX has continued to develop and improve his marketing and availability of the BITX20 Version-3 kit.  Information on this may be found at <http://www.cqbitx.blogspot.com/>

Information on the UK based 80 meter version of the original BITX transceiver is available at <http://www.radio-kits.co.uk/>

==========

Feb. 4th, 2008 02:04 pm Post-Construction notes and suggestions...

February 4, 2008 Update:

Although most BITX20A kits have been stable, a few have experienced problems with oscillation in the RF PA section.  If you have that problem, then you might be interested in suggestions from  Martien PE1BWI


Re: BITX20A PA Oscillation?

My BITX-20 is not the famous kit but my own build unit. However I
liked the PA design so I build that part of the kit last week. My
unit also oscillated and I cured it by mounting a 220 Ohm resistor
between connection point C6/R13 and the collector of Q3. In this way
any parasitic effects from T3 (that could cause oscillation) are
attenuated by the resistor. Further I also mounted a 1000 Ohm resistor
between the drains of Q18 and Q19 for the same reason. The effect is
that the amplifier is now absolutely stable under all antenna
impedances (open/ short, various phases).

Since the impedances at these points are lower then the mounted
resistors no degradation of power could be measured. In fact mine
easily produces 15 Watt PEP without noticeable distortion.

You can try quickly and see if it helps in your situation.
             Success,
Martien PE1BWI

In some cases instability has been traced to fluctuations in DC power.  If you are going to run your BITX20A from battery power, it is suggested that it should be a battery with relatively high ampere-hour rating, like maybe an automobile battery.  7 AH or so rated gel-cells do not seem to provide the necessary low impedance DC power to work properly.  However, if your power source is possibly part of the problem, you might try placing a 4700 MFD capacitor directly across the 12 volt power input on the PCB or very near that point.  Of course you do need to use power feed wiring of sufficient size to minimize voltage drop (remember that this rig may be drawing up to 3 or 4 amperes on voice peaks).  You have to allow for that current in both power supply used and in wiring between power supply and the BITX20A.

Arv K7HKL
_._
 

Oct. 5th, 2007 10:13 pm Alignment Method

Hendricks QRP Kits
BITX20A
 Alignment Method

  5 October 2007

  Alignment of your BITX20A is not very complicated:.
  • Peak the receiver RF input tuning (C-14 and C-18).

  • Set your VFO so the BITX20A covers the part of 20M that you need for normal operation.  Monitor the VFO output at the top of resistor R-27 to measure the oscillator frequency.

    The IF is on 11.0 MHz, so for 14.0 MHz operation your VFO would need to be at 14.0 - 11.0 = 3.0 MHz.  For 14.350 MHz operation your VFO would need to be operating at 14.350 - 11.0 = 3.350 MHz.  From this description you should be able to calculate your required VFO frequency for the particular 20 meter frequency range that you want to use.

    The polyvaricon tuning capacitor that was provided has two sections, with each section having it's own trimmer capacitor.  This gives you the option of using just the A-section tuning, the B-section tuning, or both A and B sections in parallel.

  • Monitor the output of the IF strip on transmit and adjust the Cxr/BFO mixer R & C for a carrier null (disconnect the mike input for this measurement).

  • Adjust the BFO/Cxr oscillator on receive so that any signal below 200 Hz or so drops way down the filter sideband, and check it on-air for audio quality when receiving normal USB signals.  Monitor the transmit IF at it's output and check the BFO/Cxr oscillator frequency to insure that it is actually 40 db or so down the lower side of your crystal filter.

  • While keying the transmitter with no microphone connected, monitor the voltage across R-7 (2.2 ohms) and adjust R-8 slowly for a reading of 0.1 volts.  This equates to around 50 ma of idling current in the driver transistors (Q-18 and Q-19).

  • Using an ammeter, measure total current draw while keying the transmitter.  With no microphone connected, slowly adjust R-91 for an increase of 30 to 50 ma.  This adjusts the idling current of Q1.  Next, adjust R-2 for another increase of 30 to 50 ma.  This adjusts the idling current for Q-2.  These two RF PA transistors need to be idling at approximately the same current for best linearity.

  • With a dummy load connected to the output and a 1000 Hz tone inserted into the microphone AF input, temporarily key the transmitter and slowly bring the drive level (R-83) up until you have around 5 watts of RF output.  Do not hold the key down for more than a few seconds because the final may overheat from running at 100% duty cycle.  If you don't have a suitable 1000 Hz tone source, you can temporarily unbalance the balanced modulator section to cause some carrier insertion and use this to set the transmitter output level.  Just don't forget to go back and re-balance the modulator before attempting on-air use.

    The transmitter is capable of more than 10 watts output, but it's linearity may not be adequate if operated above the 10 watt level.
    If running a high duty cycle mode like PSK or MSK, you should turn the drive level down to a watt or two to avoid overheating the RF PA stage.  Those heat sinks are small and were sized for running SSB.  A cooling fan might allow higher output use for 100% duty cycle modes.
That is about it.  You should hear signals on 20M when the band is open (and sometimes when it is not).  This is a very quiet receiver design so don't be surprised if there is not a lot of background noise in receive mode.

Transmit output should be above 5 watts with 12.0 volts of power and almost 10 watts with 13.8 volts.  It is possible to turn the drive level control way up and get even more power out, but linearity will suffer if you go above 10 watts.  Your power supply should be capable of 5 amps to power this rig.  Do not transmit into a short or open circuit.  Always connect a dummy load or your antenna tuner & antenna.

=============

Oct. 3rd, 2007 10:28 am Latest Schematic (2-October-2007)



7 October 2007 Schematic v-1.3c.gif
Click on the schematic to see larger image.
Click again for an even larger image.

Sep. 28th, 2007 03:51 pm



Hendricks QRP Kits
BITX20A
 Assembly Manual

Step-By-Step Assembly
October 2, 2007


Receiver AF Amplifier

[ ] C-36, 100 mfd Observe Polarity

[ ] C-83, 0.1 mfd

[ ] R-81, 10 ohms  brn-blk-blk

[ ] C-82, 10 mfd Observe Polarity

[ ] IC-1, LM386,

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C86, 100 mfd Observe Polarity

[ ] R-82, 10 ohms  brn-blk-blk

[ ] R-79, 220 ohms  red-red-brn

[ ] R-80, 10K ohms   brn-blk-org                             NOTE: Off-board component. Use 6 inch leads.
                                                                               Gnd lead near C-82, Hot lead near Q-16.

[ ] C-81, 10 mfd Observe Polarity

[ ] C-80, 100 mfd Observe Polarity

[ ] R-78, 4.7K ohms  yel-vio-red

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-16, 2N3904

[ ] Q-25, 2N3904

[ ] R-88, 4.7K ohms  yel-vio-red

[ ] R-89, 22K ohms (red-red-orange)

[ ] C-47, 0 pf  (This is an artefact from an older PCB design.  Do not install any capacitor here.)

[ ] C-79, 0.022 mfd

[ ] R-77, 3.3K ohms  org-org-red

[ ] C-8, 10 mfd Observe Polarity

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Speaker or Headphone Jack Connection. Use 6 inch leads.
    Ground is pad near C-75.

[ ] D-18, SB320 Diode  Observe Polarity

[ ] C-87, 0.1 mfd

[ ] C-74, 100 mfd Observe Polarity

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Transmittter AF Amplifier

[ ] R-76, 10 ohms  brn-blk-blk

[ ] R-92, 4.7K ohms   yel-vio-red               NOTE: This is power for FET mike. Omit for dynamic or crystal mike.

[ ] C-60, 10 mfd Observe Polarity

[ ] C-76, 0.01 mfd

[ ] R-73, 2.7K ohms  red-vio-red

[ ] R-72, 10K ohms  brn-blk-org

[ ] R-75, 1K ohms  brn-blk-red

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-15, 2N3904

[ ] R-74, 100 ohms  brn-blk-brn

[ ] C-73, 100 mfd Observe Polarity

[ ] R-93, 220 ohms  red-red-brn

[ ] C-77, 10 mfd Observe Polarity

[ ] C-75, 100 mfd Observe Polarity

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

BFO Mixer Assembly

[ ] T-6, 8:8:8 turns #28 tirfilar on FT37-43 (black) core. This is three wires, each 6 inches long.

[ ] C-66, 15 pf

[ ] C-65, 30 pf variable capacitor.        Note: flat side is RF side, round side is ground.

[ ] R-66, 200 ohms PCB type potentiometer

[ ] R-65, 220 ohms (red-red-brn)

[ ] R-63, 22 ohms (red-red-blk)

[ ] R-64, 220 ohms (red-red-brn)

                        NOTE:  Pay particular attention to the location and  values of R-63, R-64, and R-65. 
                                      If you get these in the wrong places your receiver sensitivity and transmitter
                                      power output may be degraded.  Swapping the 22 ohm resistor with one of
                                      the 220 ohm resistors is a common mistake in early BITX20 units and
                                      possibly in BITX20A kits.

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

BFO & Carrier Oscillator

[ ] C-88, 33 pf              NOTE: May not be needed, but provided to insure adequate tuning range.

[ ] C-72, 30 pf variable capacitor, Note: flat side is RF side, round side is ground.

[ ] L-5, 8.2 uh molded inductor 

[ ] X-5, 11.0 MHz Crystal

[ ] C-68, 220 pf

[ ] C-69, 220 pf

[ ] R-70, 150K ohms  brn-grn-yel

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-14, 2N3904

[ ] R-71, 1K ohms  brn-blk-red

[ ] C-70, 100 mfd Observe Polarity

[ ] R-69, 100 ohms  brn-blk-brn

[ ] R-68, 1K ohms  brn-blk-red

[ ] Q-13, 2N3904

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-67, 0.1 mfd

[ ] C-71, 0.1 mfd

[ ] R-67, 1K ohms  brn-blk-red

[ ] D-14, 1N4148 Observe Polarity

[ ] D-15, 1N4148 Observe Polarity

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections


Receive 2nd IF Amp and Transmit 1st IF Amp

[ ] C-64, 0.1 mfd

[ ] R-58, 1K ohms  brn-blk-red

[ ] R-57, 2.2K ohms  red-red-red

[ ] Q-12, 2N3904

[ ] R-60, 4.7 ohms  yel-vio-gld

[ ] C-61, 0.1 mfd

[ ] R-59, 470 ohms  yel-vio-brn

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] D-13, 1N4148 Observe Polarity

[ ] R-61, 220 ohms  red-red-brn

[ ] C-63, 0.1 mfd

[ ] R-62, 100 ohms  brn-blk-brn

[ ] R-56, 100 ohms  brn-blk-brn

[ ] C-57, 0.1 mfd

[ ] D-12, 1N4148 Observe Polarity

[ ] Q-17, 2N3904

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-58, 0.1 mfd

[ ] R-53, 470 ohms

[ ] R-55, 4.7K ohms  yel-vio-red

[ ] R-52, 1K ohms  brn-blk-red

[ ] Q-11, 2N3904

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-54, 4.7K ohms  yel-vio-red

[ ] C-59, 0.1 mfd

[ ] R-51, 220 ohms  red-red-brn

[ ] C-89, 100 pf

[ ] C-62, 100 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Receive and Transmit Changeover Relay

[ ] D-17, 1N4004 diode         Observe Polarity

[ ] K1, 351 Relay

[ ] Connect push-to-talk part of microphone connector, or a temporary momentary switch as PTT.

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Crystal Filter

[ ] C-56, 82 pf

[ ] C-55, 100 pf

[ ] C-54, 82 pf

[ ] X-1, 11.0 MHz   Add ground wire soldered to crystal case

[ ] X-2, 11.0 MHz   Add ground wire soldered to crystal case

[ ] X-3, 11.0 MHz   Add ground wire soldered to crystal case

[ ] X-4, 11.0 MHz   Add ground wire soldered to crystal case

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Receiver 1st IF and Transmitter 2nd IF

[ ] C-53, 100 pf

[ ] R-46, 1K ohms  brn-blk-red

[ ] R-45, 2.2K ohms  red-red-red

[ ] Q-10, 2N3904

[ ] R-48, 10 ohms  brn-blk-blk

[ ] C-44, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-47, 220 ohms  red-red-brn

[ ] D-11, 1N4148 Observe Polarity

R-49, 220 ohms  red-red-brn

[ ] C-45, 0.1 mfd

[ ] C-46, 0.1 mfd

[ ] R-50, 100 ohms  brn-blk-brn

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-52, 100 pf

[ ] D-10, 1N4148 Observe Polarity

[ ] R-43, 220 ohms  red-red-brn

[ ] C-42, 0.1 mfd

[ ] R-44, 100 ohms  brn-blk-brn

[ ] Q-9, 2N3904

[ ] R-39, 2.2K ohms  red-red-red

[ ] C-43, 0.1 mfd

[ ] R-40, 1K ohms  brn-blk-red

[ ] R-41, 220 ohms  red-red-brn

[ ] R-42, 10 ohms  brn-blk-blk

[ ] C-40, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

1st Mixer

[ ] T-4, 8:8:8 turns trifilar, 6 inches per #26 on FT37-43 (black) core. Twist to 8 twists per inch

[ ] T-5, 8:8:8 turns trifilar, 6 inches per #26 of FT37-43 (black) core. Twist to 8 twists per inch

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] D-4, 1N4148 Observe Polarity

[ ] D-5, 1N4148 Observe Polarity

[ ] D-6, 1N4148 Observe Polarity

[ ] D-7, 1N4148 Observe Polarity

[ ] R-26, 100 ohms  brn-blk-brn

[ ] C-30, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

VFO

[ ] R-35, 100 ohms  brn-blk-brn

[ ] D-8, 1N4739A,   9.1 Volt Zener                  Observe Polarity

[ ] R-33, 10K ohms  brn-blk-org

[ ] R-34, 10K ohms  brn-blk-org

[ ] C-33, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-8, 2N3904

[ ] Q-7, 2N3904

[ ] Q-6, 2N3904

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-31, 1K ohms  brn-blk-red

[ ] C-32, 0.1 mfd

[ ] R-28, 1K ohms  brn-blk-red

[ ] R-27, 1K ohms  brn-blk-red

[ ] R-30, 10 ohms  brn-blk-blk

[ ] R-29, 100 ohms  brn-blk-brn

[ ] C-31, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-36, 2.2K ohms  red-red-red

[ ] C-90, 33 pf

[ ] C-35, 470 pf Polystyrene

[ ] C-34, 470 pf Polystyrene

[ ] C-15, 180 pf

[ ] C-37, 220 pf Polystyrene

[ ] C-39, 33 pf

[ ] R-32, 4700 ohms  yel-vio-red

[ ] C-91, 56 pf

[ ] D-9, 1N4752A,        33 Volt Zener (used as fine tuning varicap)   Observe Polarity

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-38, 150K ohms  brn-grn-yel

[ ] L-7, 50 turns #36 on T-37-6 (yellow) core

[ ] C-38, 160 pf Variable Capacitor. Polyvaricon used as main tuning. See diagram for which leads to use.

[ ] R-37, 10K Potentiometer. This is the fine tuning adjustment.

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Receive and Transmit RF Amplifiers

[ ] C-27, 0.1 mfd

[ ] C-29, 0.1 mfd

[ ] R-20, 2.2K ohms  red-red-red

[ ] R-21, 1K ohms  brn-blk-red

[ ] R-23, 10 ohms  brn-blk-blk

[ ] R-22, 220 ohms  red-red-brn

[ ] C-26, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-5, 2N3904

[ ] D-3, 1N4148 Observe Polarity

[ ] R-24, 220 ohms  red-red-brn

[ ] R-25, 100 ohms  brn-blk-brn

[ ] C-28, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] D-2, 1N4148 Observe Polarity

[ ] R-18, 220 ohms  red-red-brn

[ ] C-23, 0.1 mfd

[ ] R-19, 100 ohms  brn-blk-brn

[ ] R-16, 220 ohms  red-red-brn

[ ] R-17, 10 ohms  brn-blk-blk

[ ] C-21, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-14, 2.2K ohms  red-red-brn

[ ] Q-4, 2N3904

[ ] R-15, 1K ohms  brn-blk-red

[ ] L-10, 1.2 uh molded inductor

[ ] C-25, 100 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Receive and Transmit Front End Filter

[ ] C-24, 8.2 pf

[ ] L-6, 18 turns (20 inches) #26 on T-37-6 (yellow) core

[ ] C-18, 30 pf               NOTE: The rounded side connects to ground and the flat side to RF

[ ] C-20, 82 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-19, 10 pf

[ ] C-17, 56 pf

[ ] C-16, 10 pf

[ ] L-4, 18 turns (20 inches) #26 on T-37-6 (yellow) core

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-14, 30 pf                 NOTE: The rounded side connects to ground and the flat side to RF

[ ] C-13, 82 pf

[ ] C-11, 10 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

T:R Switches

[ ] Q-23, 2N7000

[ ] R-86, 4.7K ohms  yel-vio-red

[ ] R-87, 4.7K ohms  yel-vio-red

[ ] Q-24, 2N7000

[ ] Q-26, 2N7000

[ ] R-94, 4.7K ohms  yel-vio-red

[ ] C-41, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-85, 4.7K ohms  yel-vio-red

[ ] Q-22, 2N7000

[ ] R-84, 4.7K ohms  yel-vio-red

[ ] Q-21, FQN1N50C  FET

[ ] C-50, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

Antenna Filter

[ ] C-47A, 100 pf

[ ] C-47B, 100 pf

[ ] L-2, 14 turns #26 (10 inches) on T-37-6 (yellow) core

[ ] C-48A, 180 pf

[ ] C-48B, 180 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] L-1, 12 turns (8 inches) #26 on T37-6 (yellow) core  NOTE: L1 is 14 turns for kits 1 thru 100, and 12 turns for kits above number 100.

[ ] C-92, 68 pf          NOTE:  C-92 is not provided on kits 1 thru 100, and is provided in kits above number 100.  

                                  The provision of C-92 and reducing L1 from 14 to 12 turns is a late change that provided
                                  additional harmonic reduction.


[ ] C-49B, 100 pf

[ ] C-49A, 100 pf

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

RF PA Drivers

[ ] R-90, 100 ohms  brn-blk-brn

[ ] C-9, 0.1 mfd

[ ] Q-20, 2N5486

[ ] R-83, 200 ohm variable            NOTE: Turn fully CCW (Counter Clock-Wise)

[ ] C-10, 0.1 mfd

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-9, 2.2K ohms  red-red-red

[ ] R-10, 1K ohms  brn-blk-red

[ ] Q-3, 2N3904

[ ] R-12, 10 ohms  brn-blk-blk

[ ] C-12, 0.1 mfd

[ ] R-11, 100 ohms  brn-blk-brn

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] R-13, 22 ohms  red-red-blk

[ ] C-6, 0.1 mfd

[ ] T-3, 8:8 turns (6 inches) bifilar on #26 on FT37-43, (black) core. Twist to 8 turns per inch

[ ] R-5, 2.2K ohms  red-red-red

[ ] R-6, 2.2K ohms  red-red-red

[ ] C-4, 0.1 mfd

[ ] T-8, 10K potentiometer             NOTE: Turn fully CCW

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] Q-18, BS170 MOSFET

[ ] Q-19, BS170 MOSFET

[ ] R-7, 2.2 ohms  red-red-gld

[ ] C-7, 0.1 mfd

[ ] T-2, 8:8:8 turns (6 inches) trifilar #26 on FT37-43 (black) core. Twist to 8 turns per inch

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

RF PA Stage

[ ] C-51, 0.1 mfd

[ ] R-91, 10K potentiometer                 NOTE: Turn fully CCW

[ ] R-2, 10K potentiometer                   NOTE: Turn fully CCW

[ ] C-5, 0.1 mfd

[ ] C-22, 0.1 mfd

[ ] R-4, 2.2K ohms  red-red-red

[ ] R-1, 2.2K ohms  red-red-red

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] C-1, 0.1 mfd

[ ] C-2, 0.1 mfd

[ ] C-3, 0.1 mfd

[ ] D-1, 1N4734A 5.6 Volt Zener Observe Polarity

[ ] R-3, 1K ohms  brn-blk-red

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

[ ] L-3, 8 turns (6 inches) #26 on FT37-43 (black) core

[ ] L-9, 8 turns (6 inches) #26 on FT37-43 (black) core

[ ] T-1, Primary = 6 turns, Secondary = 8 turns #26 on FT37-43 (black) core


[ ] Q-1, IRF510 MOSFET  Bolt to heatsink, then install

[ ] Q-2, IRF510 MOSFET  Bolt to heatsink, then install

[ ] Solder
[ ] Clip Excess Lead Length
[ ] Inspect Solder Connections

====================================

Sep. 22nd, 2007 09:03 am

You have three options for frequency coverage with the BITX20A kit.  Since the polyvaricon tuning capacitor is a two-section unit, you can use the A-section, the B-section, or both A and B sections in parallel.  There are trimmer capacitors built into the tuning capacitor.  These trimmer capacitor plates are visible through the plastic cover on the back of your main tuning cap.

Since the IF frequency is 11.0 mHz, your VFO will need to tune between 3.0 and 3.35 to cover the full SSB and CW sections of 20 meters.  However, it will probably not have that wide a tuning range with the components provided.  The fine tuning pot should only have 6 to 8 kHz (+/- 3 to 4 kHz) of tuning range.  Set it mid-scale when adjusting the main tuning calibration.  Close the main tuning capacitor by turning it fully counter-clockwise.  With a frequency counter or calibrated receiver connected to the top of R-27 (see image above) you can set the lower edge of your tuning range by adjusting the trimmer caps.  Now open the main tuning capacitor to find the top of your tuning range.

Sep. 10th, 2007 12:13 am Parts Placement Drawing by Steve-KD1JV


Click on this drawing to see larger size.

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Sep. 6th, 2007 02:57 pm


You have three options for frequency coverage with the BITX20A kit.  Since the polyvaricon tuning capacitor is a two-section unit, you can use the A-section, the B-section, or both A and B sections in parallel.  There are trimmer capacitors built into the tuning capacitor.  These trimmer capacitors are visible through the plastic cover on the back of your main tuning cap.

Since the IF frequency is 11.0 mHz, your VFO will need to tune between 3.0 and 3.35 mHz to cover the full SSB and CW sections of 20 meters.  However, it will probably not have that wide a tuning range with the components provided.  The fine tuning pot should only have 6 to 8 kHz (+/- 3 to 4 kHz) of tuning range.  Set it mid-scale when adjusting the main tuning calibration.  Close the main tuning capacitor by turning it fully counter-clockwise.  With a frequency counter or calibrated receiver connected to the top of R-27 (see image above) you can set the lower edge of your tuning range by adjusting the trimmer caps.  Now open the main tuning capacitor to find the top of your tuning range.

With the components provided in the kit, my tuning ranges look like this:

Polyvaricon                                 Trimmer Open                              Trimmer Closed
Section-A                                            60 kHz                                              58 kHz
Section-B                                          124 kHz                                            120 kHz
Sections A+B                                   155 kHz                                            147 kHz


If you wish to change the tuning range(s) you will need to play with the values of C-37, L-7, and C-15.  Alternatively, you could use a switch and capacitor to make an additional tuning range by paralleling additional capacitance across the main tuning cap
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Aug. 13th, 2007 10:20 pm Latest Schematic and Bill-of-Materials


Schematic Version 1.3c.gif

Partlist exported from C:/aRHTitan/Eagle CAD/install/projec ts/BITX v1.2/BITX20H.sch at 4/22/2007 08:59:22p        
                         
Quantity Value Device                    
                         
1 160 pf External tuning cap                  
5 10 uf POLARIZED CAP                  
7 100 uf POLARIZED CAP                  
1 220 pf POLYSTYRENE                  
2 470 pf POLYSTYRENE                  
4 30 pf Trimm capacitor                  
                         
1 0.01 uf                      
40 0.1 uf                     0
3 10 pf                      
10 100 pf                      
1 15 pf                      
3 180 pf                      
2 220 pf                      
3 33 pf                      
1 0.022 uf                      
2 56 pf                      
1 8.2 pf                      
4 82 pf                      
                         
1 33v ZENER_DO35_V                  
1 5.6v ZENER_DO35_V                  
1 9.1v ZENER_DO35_V                  
1 1N4004                      
12 1N4148                      
1 SB320                      
                         
2 HEATSINK                    
                         
1 LM386-4                      
1 RELAY                      
1 1.2 uH molded choke                  
1 8.2 uH molded choke                  
8 FT37-43                      
5 T37-6                      
                      0  
16 2N3904                      
1 2N5486                      
4 2N7000                      
2 BS170                      
1 FQN1N50C                    
2 IRF510                      
                         
2 200 3318_TRIMMER                  
3 10K 3318_TRIMMER                  
1 10k Fine tune external pot                
1 10k Volume control external pot                
1 2.2                      
1 4.7                      
9 10                      
2 22                      
13 100                      
14 220                      
2 470                      
3 10K                      
2 150 K                      
15 1K                      
11 2.2K                      
1 2.7K                      
1 22K                      
1 3.3K                      
11 4.7K                      
                         
5 11 MHz XTAL/S QS CRYSTAL                

Jul. 31st, 2007 09:43 am Completed BITX20A Photos

Here are a front and rear view of a completed prototype BITX20A.


No labels for the knobs yet (I know where they are and what they do, thus no urgent need for labels).  The lower-left knob is for Fine Tuning,  The lower-right knob is Receiver Volume.  Large center knob is main tuning.  Those three LEDs in the upper-left may require some explanation.  The left-most is on when receiving.  The middle LED is on when transmitting, and the right LED shows Forward minus-reflected RF power on transmit.  These LEDs are my own addition and are not part of the BITX20A Kit.



Rear panel connections are Microphone, Speaker or Headphones, Antenna, and power.  A fan was added because my chassis is fully enclosed and it seemed like a good idea to remove some of the heat generated by those two RF-510s in the transmitter final amplifier.  This particular fan was once the CPU cooling fan in an old computer.  The fan is my own addition and not part of the BITX20A kit.

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