SO2R bandpass filters - Part 1 

I know ICOM IC7300 S-meter is not the right tool to measure filters. But it is a fact that at full power, 100W means plus 50dBm and transceiver second harmonic is at minus 50 or 60 dB below carrier, which means 0 dBm.
My tests was done by injecting 0dBm at 14 Mhz into my 7 mhz filter , and the result is S1 signal, which is minus 121 dBm.
Not having a real spectrum analyzer at hand, I would say that S1 as it is on S-meter is not bad at all, I can happily live with it !
The second major problem is IC7300 who itself produce second harmonic at levels over S9 + 20,
harmonic produced by transceiver front end where internal filters switching is made using diodes instead of mechanical relays. To overcome this, another notch filter for F/2 should be added or maybe a high pass filter for each band. Of course, using separate antennas allow us to use coaxial open stubs waveleght/4 for frequency/2 to notch out signals below inband frequencies in order to reduce outband levels below minus 40 dBm.
73's , Gabriel YO8RXP

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