5760 Preamplifier

This preamp uses an Agilent ATF36077 FET, followed by an ATF54143 FET device.  The design incorporates feedback to achieve simultaneous gain and noise match.  The noise figure is approximately .9dB, and the input return loss is approximately 20dB.  The preamplifier, which is the unit to the right in the photo, is shown attached to a 4 resonator preselector. 

1296 Preamplifier

This amplifier uses the Agilent ATF54143 FET device mounted on an Agilent demo board.  The amplifier uses inductive feedback to achieve simultaneous gain and noise match.  A noise figure of .35dB and an input return loss of 20dB were achieved using this technique.  These conditions permit the use of a 3 resonator interdigital filter at the input of the amplifier.  We use a pair of these amplifiers in tandem at the base of the tower on our 1296 station.  The enclosure was milled from a small solid block of aluminum.

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6 Meter Preamplifier

We upgraded our 6 meter station with the addition of stacked 7 element Yagi antennas and an Elecraft K3. We sought a high intercept, double tuned input preamplifier based on one of the new CATV transistors to complement the K3.

We decided to build a 6 meter preamp based on the YU1AW amplifier we saw in an article at http://yu1aw.ba-karlsruhe.de/bfg135aeng.htm.  We laid out the amp using software and manufacturing facilities from Express PCB.

This is an interesting preamp with almost 500mw of standing power. It performs largely as suggested on the YU1AW website. Gain is also adequately close to the article.

Input match and noise figure are interesting. Keep in mind that these are actual measurements, not simulations, done on an HP 8553 analyzer with tracking generator and an AIL 75 noise figure meter. The reflectometer has slightly over 25 dB directivity. All return loss photos are 10dB/div vertical and the 0 dB reference is at the top of the screen.

This preamp demonstrates the typical bi-modal input properties where Zmatch differs from Znf-opt. In the photo on the left, the amp is tuned for best input match. The span is .1MHz/ div with the center at 50.125 MHz. Notice that this is super tuned, the displayed return loss of 50dB is far better than the bridge with a good 50 ohm load. The next photo shows the noise figure of about 3dB with the input match.

We tuned the amp for best noise figure which is about 2 dB. The photo shows a much flatter input return loss of about 9 dB. In the next photo, the span was increased to 1 MHz per division to show the gentle shape of the return loss.

It appears that there is some slight inductive feedback effect internal to the 135 due to the emitter ballasting resistors and bond wires, but not much. The delta NF between best NF and best match is about 1 dB NF. Considering the approximately 5,000 Kelvin sky on six meters, I think either setting would work well. The decision could be made on the basis of the existence of interfering services.