Re: Blown by nearby transceiver #bitx40help

Jerry Gaffke
 

Possible.

Do we know what the transmitted frequency was?  Was it 40m?
I figure the series loop of L3,C6,C7,C5 to be resonant at 7.45mhz,
    C-total-in-pf = 1/(1/1000 + 1/470 + 1/100) = 76pf
    F-resonance =  1/(2*pi*sqrt(L*C)) = 1/(6.28*sqrt(76e-12 * 6e-6)) = 7.46mhz
Loading from C4,C11,C41 will likely bring that down a bit in frequency.

I'd be looking at the base and emitter DC voltages of Q1 (during receive) and,Q13 (during transmit)
to see if they got blown.  Compare to Randy's chart as previously suggested by Marco: 
    https://groups.io/g/BITX20/files/K7AGE/BITX40%20Voltage%20Measurments.pdf
If  Q1 got blown, then also check Q4.

I am still quite surprised that enough energy got coupled in to blow the trace. 
The traces do form a moderately large loop, a single turn inductor, perhaps that was all it took.
Or perhaps those toroids are not as self shielding as I had figured.

Jerry, KE7ER


On Sun, Feb 11, 2018 at 08:27 pm, Raj vu2zap wrote:
Looks the L and C formed a series resonant circuit at the transmitted frequency.

Join BITX20@groups.io to automatically receive all group messages.