Re: BITX20 made in brasil...!!

Rahul Srivastava

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.
Rahul VU3WJM

Arv Evans wrote:

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.


On Fri, 2004-09-10 at 18:48, py1pe@... 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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