Prior to breadboarding this, I went back and forth with the PSpice
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models to determine where the discrepancies. I went so far as to remove the 2N2907 emitter bypass capacitor, but that resulted in a loss of -6dB. So, I rearranged the input to place the 50-ohm termination ahead of the blocking capacitor, changed the blocking capacitor to 10pF, then added a 100K resistor from the JFET gate to ground, and then I saw the -3dB of midband loss. So now I see why my model gain and your measured gain are so far apart this last time around. I was measuring the gain grom the JFET gate to the output, and you're measuring it from the 50-ohm load AHEAD of the 10pF capacitor to the output. That being the case, I now have to wonder what effect this 10pF coupling capacitor has on the IMD performance. So, could you take both of these circuits, replace the 10pF capacitor with 0.1uF, and then measure again? My suspicion here is that the JFET drain voltage in my circuit is feeding back to the gate and combined with your 10pF coupling capacitor is causing the IMD performance to degrade. Chris ,----------------------. High Performance Mixers and / What's all this \ Amplifiers for RF Communications / extinct stuff, anyhow? / \ _______,--------------' Chris Trask / N7ZWY _ |/ Principal Engineer oo\ Sonoran Radio Research (__)\ _ P.O. Box 25240 \ \ .' `. Tempe, Arizona 85285-5240 \ \ / \ \ '" \ IEEE Senior Member #40274515 . ( ) \ '-| )__| :. \ Email: christrask@... | | | | \ '. c__; c__; '-..'>.__ Graphics by Loek Frederiks ----- Original Message -----
From: "Steve Ratzlaff" <steveratz@...> To: <loopantennas@...> Sent: Sunday, June 10, 2007 9:17 AM Subject: [loopantennas] Re: Trask Active antenna design #2 tested Hi Chris,adjusted for best 2IMD. -10 dBm each tone at the output to the spectrum analyzer.)MHz -3.0 dB, 20 MHz -3.2 dB, 30 MHz -3.7 dB, 40 MHz -4.9 dBhurredly theadapted a two bipolar transistor circuit used for low power applications toemitter of the PNP needs to be degenerated so as to accomodate the wide 12mA by applying a voltage to the JFET gate instead of changing out the ---------------------------------------------------------------------------- ---- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.472 / Virus Database: 269.8.13/843 - Release Date: 6/10/07 1:39 PM |