I'm building my second QMX, now for 20 m - 10 m.
Today I was winding the toroids for the LP filters. I was curious about the real inductance. Using two vectorial analyzers I checked the values of the coils. For each I've found values with a huge difference to the values provided by the assembly manual. Here are two examples:
L511 640 nH, 0.80 ?H, 855 nH @ 14 MHz and L513 270 ?H, 0.43 nH, 445 ?H @ 28 MHz (first value from assembly manual and calculated for the toroid, second with one analyzer and third with the second analyzer).
With these the shape of attenuation should go to lower frequencies, also the notch made by L513 and C522.
I've simulated the LP for both versions with LTspice and got the desired and the shifted graph.
I've build the LPF with the toroids on a tiny rf board and got these expected graphs.
Reducing the windings the graph was more like the assumed for the values from the manual.
What were the main results by the LP with the higher conductivitys?
1. Additional attenuation of 1,6 dB for 28 MHz (69 % of Power out)
2. less attenuation for the harmonics, but maybe enough (?)
Do you have some information about these topic?
73, Ludwig
