07-06-2013, 05:43 PM
New coil 30 turns (with Ct) with the same form as before. The tuning cap is in parallel, the results are as follows,
With 47nFd cap wima O/P frequency 85KHz, Rx coil 34 turns 47nFd cap Rx power very low. Tx Cap cold.
With 0.66uFd cap O/P frequency 21KHz Rx coil 34 turns 0.88uFd cap Rx power much better but not as good as with the original Tx coil.
WRT the earlier results the calculated Rx coil inductance comes out at 59.5 uH when this is used with 0.88uFd the calculated resonant freq is 21.9 KHz so this is close to the observed results unlike the previous findings. with the 12 turn Tx coil.
With 21 KHz the transmission is very limited the 8th harmonic 168KHz was not receivable on my Sony at more than 1.5m and the 10th was around the 50cm mark.
looking at the O/P on a scope, the effect of changing the coupling causes a minimal change in frequency.
The whole setup is running much cooler than before without a load, it remains to be seen what will happen when there is a heavy load.
I realize that there are a lot of variables and that the Rx power assessment is very much dependent on coupling, number of turns and load impedance etc. Tomorrow I will try increasing the Rx coil inductance using the 21KHz option, especially as this would cause the least interference with the radio.
Mike
With 47nFd cap wima O/P frequency 85KHz, Rx coil 34 turns 47nFd cap Rx power very low. Tx Cap cold.
With 0.66uFd cap O/P frequency 21KHz Rx coil 34 turns 0.88uFd cap Rx power much better but not as good as with the original Tx coil.
WRT the earlier results the calculated Rx coil inductance comes out at 59.5 uH when this is used with 0.88uFd the calculated resonant freq is 21.9 KHz so this is close to the observed results unlike the previous findings. with the 12 turn Tx coil.
With 21 KHz the transmission is very limited the 8th harmonic 168KHz was not receivable on my Sony at more than 1.5m and the 10th was around the 50cm mark.
looking at the O/P on a scope, the effect of changing the coupling causes a minimal change in frequency.
The whole setup is running much cooler than before without a load, it remains to be seen what will happen when there is a heavy load.
I realize that there are a lot of variables and that the Rx power assessment is very much dependent on coupling, number of turns and load impedance etc. Tomorrow I will try increasing the Rx coil inductance using the 21KHz option, especially as this would cause the least interference with the radio.
Mike
