Amplifier - Ham Radio Projects

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Amplifier

IM MEASURING KIT

For the purpose of baseline measurements I used the two-stage amplifier developed for other purposes. Gain of the amplifier is adjustable from -40 dB to +20 dB using analog or digital (1024 steps) control. It works in HF range 1 - 60 MHz with approx. flat gain, at 100 MHz gain decreases 1,7 dB. PIN attenuator HSMP3816 is used for gain control. The amplifier operates in a linear mode (class A).  Passive attenuators were added to achieve a better reverse isolation.



Next pictures show some of measuring results for two gain levels. Reverse isolation depends on the gain and varies from -70 dB to -90 dB. Maximum gain of 20 dB is not enough, but linearity and reverse isolation basically meet the requirements.

I decided to add one more stage behind the amplifier. This will add another abt. 10dB of gain. Mitsubishi MOSFET RD06HHF1 in class A was used as a final stage in every section. On the right hand side of the board 2 dB attenuators and combiner are visible. Total gain of every amplifier including attenuator is abt. +28 dBm. It means that at the output of the combiner I can calculate with max. +22 dBm of output signal level, depending on the frequency (+21 dBm when LPF will be added). Amplifiers use an analog gain control, stages in every section will be shielded separately.


I have not only achieved the desired output level, but particularly a very good reverse isolation values, as seen in next pictures. Compare to previous 2 stages at the same amplification reverse isolation is more than 30 dB better (-103 dBm at 9 MHz) now.
 
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