Flying PigRig (5) -- Oscillator ok, keyer problems

 Link to PigRig schematic

Link to PigRig assembly instructions

At this point I am at Step 12 in the assembly instruction.  This step covers the winding and installation of remaining toroids.  The remaining steps involve installing the antenna lowpass filter toroids and L2, the inductance in the 12V power feeding the centertap of the finals. 

Before proceeding, I decided that this would be a good time to stop and test the low power circuits before proceeding to mess with the transmitter finals. 

Oscillator check

The oscillator works well, and voltages are in line with the table of oscillator voltages given in the instructions.  The trimmer capacitor C26 was bad, it jammed and wouldn't turn.  I replaced it with a capacitor from a trimmer assortment I bought a few months ago. 

The trace above is at the base of oscillator transistor Q4.  7.4 volt peak to peak. 

Keyer Ckt:

The keyer circuit consists of  a small ATtiny13A microcontroller programmed as a simple keyer chip. On powerup it defaults to a 15 wpm iambic keyer.   The circuit appears to be working except that the keying is modulated by pulses with 760 us period and about 10% duty cycle as shown below.   This is the "KEY" output of the keyer. 

I was thinking this is some kind of PWM signal but there's no integrator circuit that would convert the signal to an analog voltage.  I've put an inquiry on the 4 State mailing list about whether this pulsing is normal or not.  If I can find the source code to the keyer, I can check it to see if the pulsing is programmed in.  For now,  I guess I'll work around the problem

Checking U4 (keyer) pin 2, for the sidetone,  I get a square wave that's 641 Hz, which is within 3% of the nominal 625 Hz given in the instructions. 

The dot and dash intervals on the keyer KEY output are shown below, left and right respectively.  Notice the pulse modulation:

The dit interval is 74 ms, dah is 232 ms.  Using Farnsworth: 

$WPM = \frac{60}{50\cdot\tau_{dit}}=16.2 WPM$

which is close to the nominal 15 WPM in the instructions.  

For now I'm going to remove the keyer chip and wire a straight key from the drain of Q10 to ground.   I won't have a sidetone signal, but that's not a big deal.  

I'll test transmit stage 1 amp at it's input to T1, then move on to test the receiver.