Published:2012/12/13 21:31:00 Author:muriel | Keyword: Feedback amplifiers
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Published:2012/12/13 21:29:00 Author:muriel | Keyword: Audio Amplifier
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Published:2012/12/13 21:27:00 Author:muriel | Keyword: XTal Filter, RF Amplifier
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Published:2012/12/12 21:21:00 Author:muriel | Keyword: cascode , BJT , RF amplifier
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Published:2012/12/12 21:19:00 Author:muriel | Keyword: Variable Q1, Emitter Degeneration
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Published:2012/12/12 21:19:00 Author:muriel | Keyword: Q1, Q2, bias version
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Published:2012/12/12 21:18:00 Author:muriel | Keyword: fixed bias version
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Published:2012/12/12 21:17:00 Author:muriel | Keyword: cascode , 2N3904, IF amplifier
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Published:2012/12/12 21:17:00 Author:muriel | Keyword: cascode amplifier
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Published:2012/12/12 21:14:00 Author:muriel | Keyword: Cascode, BJT, RF Amplifier
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Published:2012/12/12 21:13:00 Author:muriel | Keyword: 5 MHz , WWV Cascode, Bipolar Amplifier
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Published:2012/12/12 21:11:00 Author:muriel | Keyword: Tuning, Whip, Other Frequencies
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Published:2012/12/12 21:10:00 Author:muriel | Keyword: broadband version, W7ZOI
The broadband version W7ZOI suggested to try building. I modified the output transformer in the Figure 6 project and tested it with Tom, VE7TW. We really liked it. By adjusting the network trimmer capacitor, I was also able to tune the 30 meter Amateur radio band as well. For 30 meter band use, I peaked the tank circuit at 10.125 MHz by listening to receiver noise with a home brew direct conversion receiver and was suitably impressed.
This is the active antenna design I wll use for my future projects where strong voltage gain is required. If your receiver has a higher impedance such as 500 ohms, you might try using a couple more links on the output transformer secondary winding.
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Published:2012/12/12 21:09:00 Author:muriel | Keyword: Cascode JFET Amplifier
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Published:2012/12/12 21:09:00 Author:muriel | Keyword: Common Gate Amplifier
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Published:2012/12/12 21:08:00 Author:muriel | Keyword: Tuned Whip
Previous experimentation confirmed that it is easy to tune a short whip antenna by connecting it to the hot end of an L C (inductor and capacitor) tank circuit. The high impedance whip antenna was matched to a JFET RF amplifier by placing a high value (1 megohm or greater) on the JFET gate to ground. Although this method is practical, I desired a network to transform the output impedance of the tuned whip tank tank circuit to a known impedance. I do not possess the knowledge or mathematical skill to design such a network and asked Wes Hayward if he might consider doing this for me. My desired parameters for the network were 10.0 MHz, a 50 ohm output impedance and a 4 foot (122 cm) whip. Please refer to Wes' calculations and schematic in Figure 2 below. This math is difficult, however, a practical design for experimentation is provided. (View)
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Published:2012/12/12 21:07:00 Author:muriel | Keyword: experimental , broadband , cascode, JFET VPA
Many builders emailed me requesting a simple, broadband VPA (voltage probe antenna) design with more power gain than the common gate versions I have presented elsewhere on this web site. Connecting a whip antenna to a cascode JFET stage described by W7ZOI in Experimental Methods in RF Design is 1 method I considered.
I built the version shown in Figure 1 almost 2 years ago. This VPA. although more powerful, overloaded the front end of my test receiver with multiple RF signals. Clearly some tuning on the input was needed.
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Published:2012/12/12 2:32:00 Author:Ecco | Keyword: dual JFET , input op amp, main characteristics
Input offset voltage is 10mV ; temperature drift is 75μV / ℃; bias current is 2pA ; Gain Bandwidth Product GB = 1MHz; conversion rate is 6V/μs ; Current consumption is 4.5mA ; power supply is ± 18V; differential input voltage is ± 30V ; common-mode input voltage is ± 15V; power consumption is 500mW.
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Published:2012/12/12 0:40:00 Author:muriel | Keyword: 50 Watt, Amplifier
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Published:2012/12/12 0:39:00 Author:muriel | Keyword: 8 Watt, Audio Amp
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