We have tested a number of coils with the current TDO circuit and below are the resonant frequencies for coils of various sizes, number of turns, and with various size capacitors added to the TDO board. The actual frequency is the result of the coil inductance, the added capacitance, the parasitic inductance and capacitance of the coil and twisted pair transmission line connecting the coil and circuit and the parasitics on the board itself. There is also a contribution from the diode capacitance despite the addition of Rp which should decouple the diode capacitance from the coil. In these tests the twisted pair transmission line between the coil and the circuit is kept to 3 mm or less. It is very difficult to make all the coils and twisted pairs accurately at this small scale, and lots of the variation in the results are due to random amounts of parasitic contribution.
As more measurements are made, the tables will be filled out and expanded.
To get an idea of the general trends a figure that summerises some of the results is included at the bottom of the page.
Frequency in MHz.
# 45 wire
# 50 wire
# 56 wire
Turns
Cap
0.5 mm
1.0 mm
0.5mm
1.0 mm
0.5 mm
--
2
0
1530
1185
1454
1078
1310
--
2
1.0
1237
942
1137
860
1086
--
2
3.3
981
709
838
625
--
--
2
5.1
843
609
752
533
664
--
2
10.0
599
444
--
400
--
--
3
0
--
932
1141
853
1150
--
3
1.2
1098
443
921
681
--
--
3
3.3
830
541
659
483
--
--
3
5.1
721
482
555
415
578
--
3
10.0
534
380
413
317
430
--
4
0
1214
687
1042
637
968
--
4
1.2
--
557
827
511
--
--
4
3.3
--
409
590
375
--
--
4
5.1
--
356
503
319
--
--
4
10.0
--
268
381
257
363
--
5
0
--
626
918
573
--
--
5
1.2
--
485
722
463
--
--
5
3.3
--
362
525
340
--
--
5
5.1
--
335
461
292
--
--
5
10.0
--
245
345
226
--
--
The frequency of the TDO with small coils connected to the TDO board. The frequency is in MHz.