Date   
Re: BITX20 made in brasil...!!

Arv Evans <arvevans@...>
 

SANDRO - PY2PE

It seems like the BFO mixer is causing you some problems. 
There are two slightly different schematics available for the BITX20 design.  How we troubleshoot your particular circuit is somewhat dependent on which schematic version you used to build your transceiver.  The major difference is that one has a resistive pi-network attenuator at the output of the BFO Mixer, and the other does not have this attenuator.  Maybe Farhan could tell us which one is the correct schematic?  Without knowing which diagram you used, I will assume that you have the one with the resistive attenuator after the BFO Mixer.  If you have the other, you can ignore step 5 below. 

Listed below is a set of things to check:

  1. BFO Injection Level:  The unloaded output of Q8 should be at minimum about 6 volts AC.  If you disconnect the 1K going to the base of Q9 and using a simple half-wave RF detector you should find in excess of 5 V AC on the emitter of Q8.  Reconnect the 1K to the base of Q9 and disconnect the 0.1 between the emitter of Q9 and the mixer transformer.  You should measure in excess of 2.5 V AC as the unloaded output of Q9.  Re-connect the 0.1 between the emitter of Q9 and the mixer transformer.
  2. Audio Levels:  Disconnect the 1 MFD cap from the collector of Q10 (microphone amplifier).  With no load on the output of the microphone amplifier you can expect to see something near 6V DC on it's collector and about 2 V AC with a loud whistle into the microphone.  If you have an oscilloscope, this waveform should be close to a good sine-wave. Reconnect the 1 MFD to the collector of Q10.  Now, if you look at the output of the microphone amp with an oscilloscope, the waveform may be distorted at higher audio levels.  This is due to the loading factor caused by the base-emitter conduction of Q4, and it is normal.
  3. Mixer Transformer:  Proper phase relationships between windings of the mixer transformer is critical.  The two secondary windings must be connected as a push-pull center-tapped winding.  If they are erroneously connected in-phase, you may be able to receive, but you will not be able to transmit.  Farhan's schematic shows exactly how this connection should be accomplished from both a physical and electrical viewpoint.
  4. Mixer Diodes and Mixer Balancing Capacitors:  If the polarity of one of the BFO mixer diodes is not correct, you may be able to receive, but you will not be able to transmit SSB.  With one of the diodes reversed, you will not get a good dip in carrier output when trying to balance out the carrier.  If you disconnect the two mixer balancing capacitors (the 10 pf fixed and 22 pf variable units) you will still get a dip in un-modulated carrier output when adjusting the 100 ohm carrier balancing potentiometer.  However, it may not be as definite as can be obtained with the capacitive balancing components connected.  Remember to re-connect any capacitors or diodes that you disconnected for testing.   NOTE: The carrier balancing potentiometer must be a non-inductive (not wire-wound) type device.
  5. Mixer Attenuator/Diplexer:  Check the attenuator at the SSB side of the BFO mixer to make sure that you did not put the 22 ohm to ground and one of the 220 ohm resistors in-line with the signal path.  This attenuator should have a 220 ohm to ground, then a 22 ohm in series with the signal path, and another 220 ohm to ground.  If you accidentally swapped the 22 ohm with one of the 220 ohm resistors, this could result in the extremely low mixer output that you are experiencing.

Beyond the tests indicated above, you may need to check the voltages on Q11 to insure that it is working properly.  Also, maybe change out Q11 on the chance that this device may have an Ft that is not high enough to provide sufficient amplification at 10 MHz.

I hope this helps.  Please let the forum know what you found, as others may have similar problems.

Good luck,

Arv - K7HKL
---   -   ---

On Mon, 2004-09-20 at 19:29, py1pe@... wrote:
          hello friends, 
 
     my bitx20 is with problems in the production of DSB (1st mixer), I already did of everything and he/she didn't find a way, it exists but it is extremely small, there is not apparent cause for the problem (mysteries of the electronics). 
I should set up an entire new block. 
the receiver works very well. 
forced to all that tried me to help!! 
 
      SANDRO - PY2PE

Re: BITX20 made in brasil...!!

Chris van den Berg
 

Hi Sandro,
if the mixer works while receiving, it should also work with
transmitting?
You should have added the attenuator resistors otherwise the mixer
do not work.
It can be seen with an osciloscoop: without the attenuator you only
see a lot of LF, with the attenuator (or a RFC coil to ground) you
see HF signal 'trapped' in the LF signal.
Indeed it is a very low level but it works.
Best regards,
Chris.

--- In BITX20@..., py1pe@a... wrote:
hello friends,

my bitx20 is with problems in the production of DSB (1st
mixer), I
already did of everything and he/she didn't find a way, it exists
but it is
extremely small, there is not apparent cause for the problem
(mysteries of the
electronics).
I should set up an entire new block.
the receiver works very well.
forced to all that tried me to help!!

SANDRO - PY2PE

Re: BITX20 made in brasil...!!

py1pe@...
 

          hello friends, 
 
     my bitx20 is with problems in the production of DSB (1st mixer), I already did of everything and he/she didn't find a way, it exists but it is extremely small, there is not apparent cause for the problem (mysteries of the electronics). 
I should set up an entire new block. 
the receiver works very well. 
forced to all that tried me to help!! 
 
      SANDRO - PY2PE

Re: BITX20 made in brasil...!!

Chris van den Berg
 

Hi all,
the information that I posted before, does contain a major mistake!
I was forgotten that the 10 dB attenuator was still connected while
measuring the output of Q14. So the output was not 0,3 mw but 3 mw.
However, now I measured again and the output of Q14 is 1,2 mw and
the output of the 2N2219 (2N2218) is now 80 mw (gain of 18dB).
I wonder where the 3 dB went (may be this is the negative aspect of
adding shielding ;-( )

Increasing of the oscillator level did not result in better
functioning mixer (it can be tested easily by adding a 0,1 uF
capacitor over the 1K resistor between Q8 and Q9).

By the way, adding a RFC on the 100 ohm potmeter (in the mixer) gave
a better reduction of the AF component, however, the AF component
will not pass the filter.

Sorry for posting the wrong information,
Chris.

some additional measurement results (all loaded with 50 ohm):
The output of Q14 is 0.3 mw, output of the 2N2219 about 150 mw
(with much LF in the microphone stage). This means a gain of 27 dB
(but I am sure you should not measure it all with 50 ohm load).
Chris.

Re: PCB Parts Layout

Rahul Srivastava
 

Hi!
 
Some real efforts made there in labeling all components in original BITX layout. It appears the RIT is indeed the fine tune control.
 
Very true the Rx front end device indeed determines the overall sensitivity and performance. I suggest giving a try to devices like 2N3866, 2N5109, 2N5179, BFW16,BFR91-96 and other devices in its class,  for RF amp as well as for post mixer one too. In past I have used 2SC2570A ( very cheap CATV component) in these places with very good results. The resistive nature of the amp would lend themself to easy adaption as well as stability. I have also noticed that 2N3904/6 has a lesser loading capacitance than the BC547s
 
A true homebrew project in all aspect this is.
AGC design is now what we all look forward too.
 
73
 
Rahul VU3WJM
 
 
 
 
 


Arv Evans wrote:
Manuel - EB7HPM

Thank you for the quick reply. 
I had noticed the notation of "RIT" on the top-left of your PC Board image and took that to indicate
that you had a new way of doing that function.  Now I understand that this is actually the main
VFO tuning adjustment.

The web site you referred to is quite impressive.  It is nice to see home made (homebrew) ham
radio equipment that has a very professional look.

On my first BITX (a BITX20 version) I also experienced limited sensitivity, but when I replaced the
2N2222 RF amplifier with a 2N3904 that had been selected for high gain the performance
became very good.

You seem to be working on some very interesting modifications of the BITX design.  I am sure
that others would be very interested in more detail about your work.

Several persons have commented about interest in building a BITX-144 for 2 Meters.  It seems like a worthwhile effort, and your use of heterodyne oscillators to generate the required higher
frequencies would seem like the way to do it.  I am sure that others in this forum would be
interested in seeing your designs.

73's

Arv - K7HKL
On Mon, 2004-09-20 at 01:21, eb7hpm wrote:
I'm sorry, but muy rig doesn't have RIT, although I hope soon to
have it. However you can try some configurations. I remember one
with suming AO. You can take it from here:
http://www001.upp.so-
net.ne.jp/jg1ead/allbander/e_ab.html

Sorry also for my bad english :-(

I have mounted a BITX15 in order to use it in 15m because I
am "licensed C" in Spain and it work very well. I use FI of 10MHz
and one external oscillator VXO to 31MHz. I have not mounted yet the
power amplifier.

However, the reception is a little weak and I added an cascode
amplifier with two transistors and a coil in the FI. How it change!!
Now I have the problem of excessive gain in some cases and I am
working in an AGC.

For the oscillator I am triying a VCO of 10 to 40MHz controlled by
PLL 145170 and when it work I will control everything with a
PIC16F84 with LCD and codec. Here some info:

http://lpistor.chez.tiscali.fr/syntheblucw.htm

I have put the diagram only for others have it like reference.
I want to prepare a PCB more ambitious, with multiband change, CW,
AGC, PLL and AM/ FM.

As I have each part working I will put the schematic.
I am not much spare time. :-(

The BITX can work to 144MHz?? I hope so.

Greetings
Manuel EB7HPM/EC7ALV.


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    Re: PCB Parts Layout

    Arv Evans <arvevans@...>
     

    Manuel - EB7HPM

    Thank you for the quick reply. 
    I had noticed the notation of "RIT" on the top-left of your PC Board image and took that to indicate
    that you had a new way of doing that function.  Now I understand that this is actually the main
    VFO tuning adjustment.

    The web site you referred to is quite impressive.  It is nice to see home made (homebrew) ham
    radio equipment that has a very professional look.

    On my first BITX (a BITX20 version) I also experienced limited sensitivity, but when I replaced the
    2N2222 RF amplifier with a 2N3904 that had been selected for high gain the performance
    became very good.

    You seem to be working on some very interesting modifications of the BITX design.  I am sure
    that others would be very interested in more detail about your work.

    Several persons have commented about interest in building a BITX-144 for 2 Meters.  It seems like a worthwhile effort, and your use of heterodyne oscillators to generate the required higher
    frequencies would seem like the way to do it.  I am sure that others in this forum would be
    interested in seeing your designs.

    73's

    Arv - K7HKL
    On Mon, 2004-09-20 at 01:21, eb7hpm wrote:
    I'm sorry, but muy rig doesn't have RIT, although I hope soon to
    have it. However you can try some configurations. I remember one
    with suming AO. You can take it from here:
    http://www001.upp.so-
    net.ne.jp/jg1ead/allbander/e_ab.html

    Sorry also for my bad english :-(

    I have mounted a BITX15 in order to use it in 15m because I
    am "licensed C" in Spain and it work very well. I use FI of 10MHz
    and one external oscillator VXO to 31MHz. I have not mounted yet the
    power amplifier.

    However, the reception is a little weak and I added an cascode
    amplifier with two transistors and a coil in the FI. How it change!!
    Now I have the problem of excessive gain in some cases and I am
    working in an AGC.

    For the oscillator I am triying a VCO of 10 to 40MHz controlled by
    PLL 145170 and when it work I will control everything with a
    PIC16F84 with LCD and codec. Here some info:

    http://lpistor.chez.tiscali.fr/syntheblucw.htm

    I have put the diagram only for others have it like reference.
    I want to prepare a PCB more ambitious, with multiband change, CW,
    AGC, PLL and AM/ FM.

    As I have each part working I will put the schematic.
    I am not much spare time. :-(

    The BITX can work to 144MHz?? I hope so.

    Greetings
    Manuel EB7HPM/EC7ALV.


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  • Re: PCB Parts Layout

    eb7hpm
     

    I'm sorry, but muy rig doesn't have RIT, although I hope soon to
    have it. However you can try some configurations. I remember one
    with suming AO. You can take it from here: http://www001.upp.so-
    net.ne.jp/jg1ead/allbander/e_ab.html

    Sorry also for my bad english :-(

    I have mounted a BITX15 in order to use it in 15m because I
    am "licensed C" in Spain and it work very well. I use FI of 10MHz
    and one external oscillator VXO to 31MHz. I have not mounted yet the
    power amplifier.

    However, the reception is a little weak and I added an cascode
    amplifier with two transistors and a coil in the FI. How it change!!
    Now I have the problem of excessive gain in some cases and I am
    working in an AGC.

    For the oscillator I am triying a VCO of 10 to 40MHz controlled by
    PLL 145170 and when it work I will control everything with a
    PIC16F84 with LCD and codec. Here some info:
    http://lpistor.chez.tiscali.fr/syntheblucw.htm

    I have put the diagram only for others have it like reference.
    I want to prepare a PCB more ambitious, with multiband change, CW,
    AGC, PLL and AM/ FM.

    As I have each part working I will put the schematic.
    I am not much spare time. :-(

    The BITX can work to 144MHz?? I hope so.

    Greetings
    Manuel EB7HPM/EC7ALV.

    PCB Parts Layout

    Arvid Evans <arvevans@...>
     

    EB7HPM

    The new PCB layout looks interesting.
    How did you design the RIT circuit? Could you upload a schematic of
    the RIT part of your unit?

    Thanks,

    Arv-K7HKL

    New file uploaded to BITX20

    BITX20@...
     

    Hello,

    This email message is a notification to let you know that
    a file has been uploaded to the Files area of the BITX20
    group.

    File : /BITX PCBs (Printed Circuit Boards)/bitx_component_placing.jpg
    Uploaded by : eb7hpm <msraya@...>
    Description : BITX PCB Component Placing

    You can access this file at the URL:
    http://groups.yahoo.com/group/BITX20/files/BITX%20PCBs%20%28Printed%20Circuit%20Boards%29/bitx_component_placing.jpg

    To learn more about file sharing for your group, please visit:
    http://help.yahoo.com/help/us/groups/files

    Regards,

    eb7hpm <msraya@...>

    New file uploaded to BITX20

    BITX20@...
     

    Hello,

    This email message is a notification to let you know that
    a file has been uploaded to the Files area of the BITX20
    group.

    File : /MODIFICATIONS/BITX DC Switching.png
    Uploaded by : k7hkl_arv <arvevans@...>
    Description : PTT for BITX. You may have to alter the resistor values, depending on the gain of your switching transistors.

    You can access this file at the URL:
    http://groups.yahoo.com/group/BITX20/files/MODIFICATIONS/BITX%20DC%20Switching.png

    To learn more about file sharing for your group, please visit:
    http://help.yahoo.com/help/us/groups/files

    Regards,

    k7hkl_arv <arvevans@...>

    Re: BITX20 made in brasil...!!

    Arv Evans <arvevans@...>
     

    Chris


    I will be glad to share what I have done, but my spare time is a bit limited right now (I am in the midst of being hired for a new position...un-retired for the third time!).  Sharing will require that I draw up schematics and take a few pictures.  That will be done just as soon as all the design & construction is done, and as time allows.

    My original BITX was the standard 20 Meter model, but as soon as it was completed it was "borrowed" by my son (also a ham).  But, as Chris alluded to, my second BITX is quite different from the original design.

    Here is an overview of what I did with or to Farhan's original design in building my BITX40:

    1. The VFO has been changed to a PTO (like WA6OTP's product), with a J-FET (MPF102) oscillator, a 2n3904 emitter follower, and a 2n3904 buffer amp.  Most of the effort here involved mechanical design work to keep the knob equidistant from the front panel whilst allowing the threaded brass PTO shaft to move forward & back as it rotates.  The semi-final design involves use of two loops of thin metal that make up a flexible shaft coupling and allow both shafts to rotate while the threaded brass one moves forward & back to adjust the frequency.  Eventually, I expect metal fatigue to be a factor with this design, so I am still tinkering with it.
    2. The Rx AF Amp is made up of discrete devices, as shown in my earlier postings on this forum.  I provided board space and connectivity options for a narrow bandpass AF filter, but that unit is not yet completed.
    3. The PTT switch or relay has been replaced with a 3-transistor power switch circuit that takes care of switching voltages from Rx to TX circuitry.  Simply, the PTT lead (or the VOX circuit) pulls the base of a 4A 40V NPN to ground to lower the Rx voltage.  Lowering of the Rx voltage takes the forward bias off a 2n2222 NPN which allows its collector voltage to rise, forward biasing another 4A 40v NPN which provides the Tx voltage.  This changeover circuitry induced a loss of  about 1 volt on Rx and 1.2 volts on Tx, so I adjusted my power supply for 14 volts instead of 12.6 volts output.   I added three 1K resistors and associated LEDs to indicate (a) Green = presence of DC voltage, (b) White = Rx-mode, & (c) Red = Tx-mode.  NOTE:  I leave the last stages of the RX AF amp powered up during TX.  This allows sidetone injection for CW, and eliminated a nasty "CLICK" on TX-to-Rx transitions.  On suggestion from Chris, I added additional shielding between the RX front end and the TX PA to eliminate a "chirp" on the TX-to-RX transition.  I also lowered the 12 volt supply bypass capacitor in the microphone amplifier from 47 mfd to 15 mfd while trying to eliminate the above chirp, and have not restored this to 47 mfd yet.
    4. The RX-TX antenna changeover circuit is presently a 20 pf capacitor and a pair of back-to-back 1N4148 diodes, with additional Rx circuit protection provided by a forward biased 1N4148 to ground.  There appears to be a slight signal loss caused by this arrangement, so I will continue to work toward something better (but it has to be simple).
    5. Q14 is now a 2N7000 MOSFET.  There is no particular reason other than I had some in my junk box and wanted to see if they would work in this application.  It works great, but did require application of some miniature ferrite beads to tame a parasitic oscillation.
    6. The Rx front-end bandpass circuit was made up using two 10.7 MHz IF transformers.  This has been posted and pictures shown earlier on this forum.
    7. My linear amplifier presently is a pair of Push-Pull 2N7000's, driving push-pull IRF-510's.  I am not completely satisfied with this linear (too many very high impedance devices and some instability at certain settings of my antenna tuner).  I will probably re-design it before I publish anything more regarding linear amps for the BITX units.
    8. CW mode is currently done with an external AF oscillator that plugs into the microphone jack.  The keyed AF tone operates my VOX circuit to provide semi-break-in operation.  Currently the VOX has to be re-adjusted when going from SSB to CW or CW to SSB.  This seems to be because the hold-over timing for CW needs to be greater than the hold-over timing for SSB, and by the difference in switching voltage that is generated by speech versus CW tones.  Eventually, th CW tone oscillator will be mounted inside the BITX itself and switched in-circuit by unplugging the microphone connector.
    9. As mentioned above, the VOX is working, but not yet perfect.  Anti-VOX uses phase-reversal and injection of Rx audio into the VOX amplifier, but this is very problematic.  This may be due to my room acoustics, or to some gain versus bandwidth difference between anti-VOX AF and the AF returned from the speaker to the microphone.  I am still working on this.
    10. I added Rx RIT (Receiver Incremental Tuning) using a fairly complex arrangement of voltages that switch between Rx and Tx mode.  I may publish this later, but in the interim I am looking for a simpler way.

    Work yet to be completed on this BITX40 may include:

    1. Building a better Tx linear amplifier.
    2. Completing and installing the narrow AF bandpass filter for CW-mode operation.
    3. Building the CW-mode tone oscillator inside the BITX chassis, and making it switch in-circuit automatically when I unplug the microphone.
    4. The antenna changeover circuitry still could use improvement, as mentioned above.
    5. The VOX still needs quite a bit of design analysis and corrective work.
    6. The RIT circuit could use some simplification, but it works for now.

    In addition to all this, I am exchanging emails with Hans (G0UPL) about adding a simple frequency display.

    The VFO is quite stable, but it might be nice to add a Huff & Puff type stabilizer...at some later date.

    I have an old PC-XT computer power supply opened up on my workbench with the intention of significantly altering it such that it will provide 12-14 volts for the BITX and 24-32 volts for the linear amplifier.  Yes, I am considering going for QRO with this unit if everything else goes as anticipated.  Think about push-pull pairs of push-pull IFR510 amplifiers and you will see what I am considering.  This idea is not new, as it has been demonstrated in several ham publications over the past 10 or so years.

    OK, Chris...is that enough for now?  There will be more as I find the time to work on it.

    73's
    Arv -K7HKL
    _._

    On Tue, 2004-09-14 at 11:28, vdberghak wrote:
    Hi Arv,
    why not sharing the circuits that you use and explain why they are
    better? Or did you already had them from other projects? ;-)
    Chris.

    > I cannot provide meaningful measurements beyond the BFO mixer
    because my
    > circuit from the filter to the antenna is quite different from
    Farhan's
    > original design. 
    >
    > Arv
    > _._



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  • Re: BITX20 made in brasil...!!

    Chris van den Berg
     

    Hi Arv,
    why not sharing the circuits that you use and explain why they are
    better? Or did you already had them from other projects? ;-)
    Chris.

    I cannot provide meaningful measurements beyond the BFO mixer
    because my
    circuit from the filter to the antenna is quite different from
    Farhan's
    original design.

    Arv
    _._

    Re: Coil data for TOKO 10K type former

    Rahul Srivastava
     

    Hi!
     
    Yes yes yes very helpful indeed. The data put up by our good old Rev indeed had my brain kicking. I straight away planned a K2 discreet version. If one goes over the design carefuly one would notice it just uses two varaints of coil for tuned element , 4.7uH and other 1uH making life lot easier. ( Just 2 type of coils for a multibander high class)
     
    I was planning a premixed L/C VFO similar to K1 design but in comes my good friend Niras VU3CNS  and I now have a complete design as well as a programmed chip for a DDS based TRX, have a look here:
     
     
    My  homebrew route to my own K 2.
     
    No doubt BITX 20 group has made us all aware of many invaluable minute details to consider while designing a TRX.
     
    TNX & 73
     
    Rahul VU3WJM
     
     
     


    Arv Evans wrote:
    Friends

    On the GQRP web site <www.gqrp.com> you will find a number of useful
    tables, including one on using TOKO coils for bandpass filters.


    Maybe this will be of interest to others.

    Arv
    _._

    On Sun, 2004-09-12 at 02:38, vu3wjm wrote:

    Dear Friends,

    While going thru my old files I found this small text giving turns
    vs inductance for TOKO coils ( Uploaded under files). This is not my
    work but of an unknown person to whom I am greatful.

    Table shows that abt 12 turns for the required 2uH for frontend
    coils.

    Hope many wanting to replace tap washers may find data useful.

    73

    Rahul VU3WJM


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    Re: Coil data for TOKO 10K type former

    Arv Evans <arvevans@...>
     

    Friends

    On the GQRP web site <www.gqrp.com> you will find a number of useful
    tables, including one on using TOKO coils for bandpass filters.


    Maybe this will be of interest to others.

    Arv
    _._

    On Sun, 2004-09-12 at 02:38, vu3wjm wrote:

    Dear Friends,

    While going thru my old files I found this small text giving turns
    vs inductance for TOKO coils ( Uploaded under files). This is not my
    work but of an unknown person to whom I am greatful.

    Table shows that abt 12 turns for the required 2uH for frontend
    coils.

    Hope many wanting to replace tap washers may find data useful.

    73

    Rahul VU3WJM


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  • Re: BITX20 made in brasil...!!

    Arv Evans <arvevans@...>
     

    Chris

    Re higher readings at output of the mixer:
    I used a diode detector (0.001 series capacitor to a Germanium diode to ground, with a .01 bypass) feeding into the 11 Megohm input of an old Heathkit VTVM.  If there were any spikes arising from the conversion process, these would then be the "peak voltage" detected and measured. 

    If you used a scope to view the signal levels, then your readings would probably be more representative of actual power levels delivered by each stage.

    I cannot provide meaningful measurements beyond the BFO mixer because my circuit from the filter to the antenna is quite different from Farhan's original design. 

    Arv
    _._

    On Sun, 2004-09-12 at 08:18, vdberghak wrote:
    Hi all,
    some additional measurement results (all loaded with 50 ohm):
    - The output power of the oscillator is about 3 mw.
    While measuring the output after the first mixer and increasing the
    LF level until the HF output is not incresed gave the following
    results (between brackets the reference numbers of Arv):
    - LF output (to mixer): 1 volt pp. (1).
    - Output of mixer: 0.6 volt pp. (2).
    - output of Q11: 1 mw. (3)

    Strange that Arv has much more power then I have on these points.
    AC Signal Measurements:
    1) LF: This signal becomes non-linear when the output goes above
       1.4 to 1.6 volts P-P (Peak-to-Peak).
    2) At the BFO Balanced Mixer with measurements taken from
       the wiper of the 100 ohm potentiometer:
       Varying the audio input (signal generator connected to
       microphone input)  causes 0 to 5.4 V P-P DSB output.
       Unbalancing the mixer potentiometer causes a reading of
       3.5 to 4.0 V PP with no audio input.
    3) At the collector of Q11 (Tx DSB amplifier) the DSB signal
       can be varied from 0 to 2 V P-P.

    What I said about the 'calculated level' makes sense: if the output
    power of the oscillator is about 3 mw, an expected conversion loss
    of about 7 dB (likely more), the attenuator of -4dB, indeed the
    measured 0.2 mw at that point looks realistic.

    It also gives me a clue that I should try to make more output from
    the oscillator (if I increase the 3 mw to 30 mw makes 10 dB
    difference to the total output signal?).

    The output of Q14 is 0.3 mw, output of the 2N2219 about 150 mw (with
    much LF in the microphone stage). This means a gain of 27 dB (but I
    am sure you should not measure it all with 50 ohm load).
    What output do others have out of the local oscillator and the stage
    with the 2N2219 (or 2N2218)?

    Best regards,
    Chris.


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  • Re: BITX20 made in brasil...!!

    Chris van den Berg
     

    Hi all,
    some additional measurement results (all loaded with 50 ohm):
    - The output power of the oscillator is about 3 mw.
    While measuring the output after the first mixer and increasing the
    LF level until the HF output is not incresed gave the following
    results (between brackets the reference numbers of Arv):
    - LF output (to mixer): 1 volt pp. (1).
    - Output of mixer: 0.6 volt pp. (2).
    - output of Q11: 1 mw. (3)

    Strange that Arv has much more power then I have on these points.
    AC Signal Measurements:
    1) LF: This signal becomes non-linear when the output goes above
    1.4 to 1.6 volts P-P (Peak-to-Peak).
    2) At the BFO Balanced Mixer with measurements taken from
    the wiper of the 100 ohm potentiometer:
    Varying the audio input (signal generator connected to
    microphone input) causes 0 to 5.4 V P-P DSB output.
    Unbalancing the mixer potentiometer causes a reading of
    3.5 to 4.0 V PP with no audio input.
    3) At the collector of Q11 (Tx DSB amplifier) the DSB signal
    can be varied from 0 to 2 V P-P.

    What I said about the 'calculated level' makes sense: if the output
    power of the oscillator is about 3 mw, an expected conversion loss
    of about 7 dB (likely more), the attenuator of -4dB, indeed the
    measured 0.2 mw at that point looks realistic.

    It also gives me a clue that I should try to make more output from
    the oscillator (if I increase the 3 mw to 30 mw makes 10 dB
    difference to the total output signal?).

    The output of Q14 is 0.3 mw, output of the 2N2219 about 150 mw (with
    much LF in the microphone stage). This means a gain of 27 dB (but I
    am sure you should not measure it all with 50 ohm load).
    What output do others have out of the local oscillator and the stage
    with the 2N2219 (or 2N2218)?

    Best regards,
    Chris.

    Re: BITX20 made in brasil...!!

    Chris van den Berg
     

    chris, in the exit of the 2n2218 (driver, correct?) is it that you
    have 150mw?

    Yes, I have. By the way, the transistor I use is a 2N2219 but this
    makes no difference.

    and in his entrance?
    I will check this again. I remember that it was very little, I
    remember I was suprised about the gain of the 2N2219 stage. May be I
    posted it in an older message.

    Are 150mw enough for exciting the irf510, to 6watts????
    The IRF510 is driven by voltage. I did not make the final amp yet so
    I do not know.

    The voltage output of the first mixer will be measure again by me
    also, I remember that almost no power output was reached at that
    point. The output power (over 50 ohms) of the oscillator is about 3
    mw, with a expected conversion loss of about 7 dB (likely more), the
    output on the potmeter will be about 0.6 mw.

    Best regards,
    Chris.

    Coil data for TOKO 10K type former

    Rahul Srivastava
     

    Dear Friends,

    While going thru my old files I found this small text giving turns
    vs inductance for TOKO coils ( Uploaded under files). This is not my
    work but of an unknown person to whom I am greatful.

    Table shows that abt 12 turns for the required 2uH for frontend
    coils.

    Hope many wanting to replace tap washers may find data useful.

    73

    Rahul VU3WJM

    New file uploaded to BITX20

    BITX20@...
     

    Hello,

    This email message is a notification to let you know that
    a file has been uploaded to the Files area of the BITX20
    group.

    File : /tokoturns.txt
    Uploaded by : vu3wjm <vu3wjm@...>
    Description : Turns vs Inductance for TOKO coils

    You can access this file at the URL:
    http://groups.yahoo.com/group/BITX20/files/tokoturns.txt

    To learn more about file sharing for your group, please visit:
    http://help.yahoo.com/help/us/groups/files

    Regards,

    vu3wjm <vu3wjm@...>

    Re: BITX20 made in brasil...!!

    Arvid Evans <arvevans@...>
     

    Rahul

    I just used the scope to set up levels for the best looking DSB
    signal. But you are right...we probably need to specify the proper
    ratio for AF versus carrier level. That would help those without
    an oscilloscope to set the proper operating point by using just
    a detector and a DC voltmeter.

    Farhan showed us how to build the BITX, now someone needs to put
    together an alignment and operating manual.

    Arv - K7HKL
    _._

    --- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:
    Hi!

    From what I remember from my yester years of setting the diode bal
    Mod ( In my SB 102) idealy the AF signal level should be 1/10 of
    carrier level. ( A thumbrule I guess).

    I may be wrong but possibly we need to have a defined optimum OSC
    level as well as BFO levels as these very much effect the conversion
    gain/ loss.

    73

    Rahul VU3WJM




    Arv Evans <arvevans@e...> wrote:
    SANDRO

    As promised, here are some measurements from my BITX40 circuit board:

    AC Signal Measurements:

    1) Microphone Amplifier output (Q10 collector) is 8V PP with
    the input totally over-driven by my AF signal generator at
    700 Hz.
    This signal becomes non-linear when the output goes above
    1.4 to 1.6 volts P-P (Peak-to-Peak).

    2) At the BFO Balanced Mixer with measurements taken from
    the wiper of the 100 ohm potentiometer:
    Varying the audio input (signal generator connected to
    microphone input) causes 0 to 5.4 V P-P DSB output.
    Unbalancing the mixer potentiometer causes a reading of
    3.5 to 4.0 V PP with no audio input.

    3) At the collector of Q11 (Tx DSB amplifier) the DSB signal
    can be varied from 0 to 2 V P-P.

    DC Voltage Measurements:

    Q10 (Microphone Amplifier):
    C = 7.0 V DC
    B = 2.3 V DC
    E = 3.0 V DC

    Q11 (Tx DSB Amplifier)
    C = 7.1 V DC
    B = 2.4 V DC
    E = 1.7 V DC

    Transistors for Q10 and Q11 are 2N2222 (FT=150 MHz),
    with measured DC gain of about 150.

    OK, I hope this helps.

    Arv
    _._


    On Fri, 2004-09-10 at 18:48, py1pe@a... wrote: hello Arv,

    thank you for the clues
    I don't have 100mw in the exit... 8 - (
    I will verify all the points that you wrote, later I say the
    result.
    the transistors are BCs549 (freq 300mhz)
    I distrust the 1st mixer seriously, because the production DSB is
    already low, I imagine that the audio low seje too much, but I didn't
    still move for not knowing which the appropriate levels.
    thank you and good weekend!
    73 of PY1PE SANDRO
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