I am testing a QDX-M for the 10m Band. I would like to find out if there is any difference in power output at this frequency using the supplied BN43-202 core for the T1 transformer by comparing it with the BN61-202 core. ?I have fitted header sockets for the T1 transformer to save re-soldering the board. The transformer leads make good connection with the PCB. T1 is wound the same for 9 volts for both cores. I measured the primary inductance of the 43 core (23.5 uH) with the secondary open circuit and found 0.08 uH with the secondary short-circuited. The secondary circuit measured the same. The primary and secondary inductance of the 61 core was lower as expected: 4.3 uH (opposite winding shorted: 0.08 uH). These measurements were not done at signal frequency. ?
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The power output (43 core) was measured as about 3.9 W (repeated); the power input was 9.0 volts x (0.85A-0.15A) = 6.3 W (The RX = 0.15A), ? ? ? ? ? ? ?Efficiency about 62%
The power output (61 core) was measured as about 3.8 W (repeated); but the power input was lower: 9.0 volts x (0.77A-0.15A) = 5.6 W ? ? ? ? ? ? ? ? ? ? ? ? ?Efficiency about 68% ?
My SWR/Power meter is an old Daiwa CN 620B and using the 20W fsd range. I have once calibrated it with a 50 ohm load and using an oscilloscope. Needs to be checked again with a better oscilloscope. ? ?
The power outputs are very close but the power input difference is about 0.7 W?
Typical output on 10m is quoted as 3 - 4 W. My outputs seem OK, but I cannot explain the power input difference. ?The T1 impedances for 43 and 61 cores are quite different. I'm no expert but I have read that the transformer has to be matched with the combined output impedances of the BS170s and the input impedance of the LP Filter? Their impedance difference does not seem to bother the BS170s??
Perhaps more data is needed for a conclusion.
Comments?
73, Robin?
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