Hi Chris,
Your revised circuit is just built and tested.
Same testing configuration as before (10 pF series input cap with 51 ohm termination at input, to generator; 1 uF output cap; jfet gate bias adjusted for best 2IMD. -10 dBm each tone at the output to the spectrum analyzer.)
+21.5 dBm OIP3, +45 dBm OIP2.
Vcc 12.82 volts, 26 mA.
Drain 4.58 volts, 12 mA approx jfet current
Emitter 5.21 volts, 13.6 mA bipolar current
Source 1.80 volts
Gain/Frequency response
20 kHz -8.5 dB, 50 kHz -4.1 dB, 100 kHz -2.9 dB, 1 MHz -2.5 dB, 10 MHz -3.0 dB, 20 MHz -3.2 dB, 30 MHz -3.7 dB, 40 MHz -4.9 dB
73,
Steve
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----- Original Message -----
From: "Chris Trask" <christrask@...>
To: <loopantennas@...>
Sent: Saturday, June 09, 2007 12:24 PM
Subject: Re: [loopantennas] Re: Active antenna design
Okay, I see what I did here that made a mess of things. I had hurredly
adapted a two bipolar transistor circuit used for low power applications by
substituting a JFET for the NPN device and then changing the bias resistors
without properly thinking about it. With the JFET, it turns out that the
emitter of the PNP needs to be degenerated so as to accomodate the wide
range of Vgsoff of the JFET. Doing so allows me to increase the JFET drain
resistor so as to improve the open loop gain. The gain is now
around -0.5dB. And you can now vary the bias current from 5mA each leg to
12mA by applying a voltage to the JFET gate instead of changing out the
resistors as before:
Chris
