EMRFD Message Archive 1689

Message Date From Subject
1689 2008-06-01 07:31:04 Steve Ratzlaff Re: EMRFD FEEDBACK AMPLIFIERS (my own tests)
Thanks to Bob for presenting information from his own tests. I was motivated to try some of my own tests today. My spectrum analyzer only goes to 40 MHz (HP3585A), so my tests are limited to that. I used the Fig. 2.57 circuit, and used the same nominal 10.3 dB gain resistor values (Rf 430, Re 18 ohms). All other passive components were identical to Fig. 2.57; the bifilar transformer used the same FT37-43 with 10 turns. I used 12.00 Vcc. I tried to use the same transistors Bob used, though I didn't have any PN5179 (or 2N5179)--I used a 2N5770 which is more or less equivalent, with the same 900 MHz Ft. I added a 2N4401 to the tests.
The SA has its own 50 ohm built-in tracking generator, which makes sweeping up to 40 MHz easy. I didn't use any pads on input or output of the amplifier.
I measured both gain and IMD response; my favorite two-tone frequencies are 3 and 4 MHz, set for 0 dBm for each tone at the output to the SA. Of course this also makes reading Output Intercepts easy too. Total current was noted for each device--in all cases it was quite a bit more than the nominal 20 mA given for the Fig. 2.57/Table 2.2 circuit. Static beta for each device was also measured, using the M3 semiconductor tester.
The results are listed in order of max gain at 40 MHz--a purely arbitrary choice for presenting the data. (Gains at 1 MHz ranged from +11.0 to +11.6 dB; -1 dB rolloff at the low end ranged from 155 kHz to 175 kHz with the 0.1 uF coupling caps and the FT37-43 with 10 bifilar turns.)

2N3866 217 beta, 28.2 mA 40 MHz gain +10.8 dB. +32.5 dBm OIP3, +47 dBm OIP2

2N5109 55 beta, 26.4 mA 40 MHz gain +10.7 dB. +32 dBm OIP3, +47 dBm OIP2

2N4401 204 beta, 28.5 mA 40 MHz gain +10.7 dB. +34 dBm OIP3, +48 dBm OIP2

2N3904 217 beta, 28.2 mA 40 MHz gain +10.6 dB. +33.5 dBm OIP3, +48 dBm OIP2

2N5770 143 beta, 26.3 mA 40 MHz gain +10.3 dB. +32 dBm OIP3, +48 dBm OIP2

PN2222 298 beta, 29.2 mA 40 MHz gain +8.8 dB. +30.5 dBm OIP3, +43 dBm OIP2

How does this data relate to K3NHI's results? It doesn't really relate at all, except for comparing the gains at 40 MHz. Bob stated his interest was more in the VHF range; my interests are in the 10 kHz-30 MHz range. Bob didn't do IMD testing; I'm able to do that, so routinely include IMD tests for amps I build as well as gain over LF-HF. Bob didn't mention how close his device currents were to the nominal 20 mA the Fig. 2.57 circuit was designed for. I chose random 5% resistors without measuring their values; perhaps my values happened to give higher currents than what W7ZOI's original Fig. 2.57 circuit used.
Thanks again to Bob K3NHI for presenting his test data, I was motivated to try some tests of my own.

Steve AA7U
NE Oregon

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