Minima QRP BFO and Mixer

I started with the BFO, put in an inductor 3,3 uH with one trimmer CT5 to minimum c, frequencies was 20,003 MHz, I tray to put in 2N7000 to connect the other trimmer CT4 butt F go 2-3 kHz lower without fet switched on. I try BA482 in serie to ground it only lower the frequency a few hundred Hz. Turning on the diod i found a value 2,2k to 4,7k will be fine, frequency is 19,995 MHz.

Dc is  T5:e = 5,6V T6:e = 5,2V it means 11 mA to the BFO. I winding the T3 6.5 turn trifilare on BN43–2402. Then time to do diode matching. see Diode... i think 2,2k to 12V is to mutch current 6mA, it take to long time to stabelesise.

The BFO gives 1,5Vp-p on C27 with no load. 600 mVp-p @ 50 ohm. I can now hare a IF 20MHz 1mV in to C38 also see 20MHz signal on osciloscope when tx and audio to mic amplifier.

Next its time for Bi-direction-amplifier.

Marry Christmas and a Good New Year, 

de SM4HNG Leif.

Minima QRP Transceiver The Audio part.

AF Amp

After reading on the freelists i decide to test the audio amplifier, because there was lot of ides to change the design i have LM380 and LM386 in the box. The original amplifier could give around 600mV rms over 8 ohm before clipping. The LM386 could give 2,8V rms over 8 ohm P = U*U/R = 2,8*2,8/8 ~ 1W, LM380 give less power.

47 uF out. -3dB @ 200 Hz, 0 dB @ 100 kHz

5 mA no input signal.

135 mA @ 1 W out.

input 150 mVrms  @ 2,8Vrms  out.

Pre Amplifier

Max out 940 mV rms before clipping. Around 1 mV in. T16:c = 11V.

T15:c = 8,2V , T15:e = 6,4V, Around 2 mA current.

Mic Amplifier

30 mV in around 40 mV rms out.  -3dB @ 20 Hz  -3 dB @ 10 kHz. there is a little maxi-ma @ 200 Hz around + 5-6 dB. T13.e = 1.5V T13:c = 5.1 V must be 7 mA.

Side Tone

Wen tone on gives around 100mV @ max volym on speaker output, Tx monitoring.

Around 1 mV @ C28 modulator. T17:c = 6,7V T17:e = 0,27V.

Next it is time to do the BFO, stay tuned SM4HNG, I relay like this building the Minima