Better Q == Better Response

Yesterday I replaced the inductors in my original 40-meter LPS with larger cores that wound up having about twice the Q.  This morning I replaced the ceramic caps with silver mica caps.  The old caps had a Q around 80.  The new caps have a Q > 1000.  As one might expect this had an impact on the insertion loss of the filter, lowering it by almost a full db from -1.97 down to -1.03 dB.   The tighter cap tolerances also resulted in a cutoff frequency of 7.26 MHz, probably a bit too close to the operating frequency.  Rejection at the 2nd harmonic was -39.2, and at the 3rd harmonic was -35.0 dB.

Actual transmit performance using my original S8050 transistor (which had 2nd harmonic suppression of -10 dB) had a 2nd harmonic suppression of -51.9 dB.

Ceramic Caps Silver Mica Caps
Meter Power 270 mW 240 mW
7.040 MHz -16.7 dBm -19.4 dBm
14.08 MHz -61.6 dBm -71.3 dBm
21.12 MHz <-80.0 dBm < -80 dBm

Note that the measured meter output power was 240 mW, which is down about 30 mW from the ceramic cap solution.  The SA indicated the fundamental was at +20.6 dBm or 115 mW).  Given the lower insertion loss, I suspect this is because the filter with the SM caps and T50-2 toroids is providing a sub-optimal impedance match to the output transistor.

Putting the 2N2219 transistor in the circuit boosted the output power up to almost 280 mW by the meter, with a 120 mW fundamental by the SA., and a second harmonic suppression of -50.6 dB.

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