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Since writing the original article on the L & S band LNA, many new devices have become available for our use...the proliferation of cell phones likely contributed to this, making quite a few of these devices affordable and plentiful for amateur use.
Whether it is an MMIC, E-PHEMET or GaasFET, they are all similar in form, usually in a small surface-mount package. Their uses vary, from a simple gain block used to amplify low-level signals to more useful levels (pre-drivers), to Low Noise Amplifiers (LNA) used in receiving systems for satellite TV, EME, or weak-signal terrestrial work.
small PC board shown to the left (next to a quarter) was designed to be
adaptable to many of the common device form factors available to us. The next
few photos show some examples....
Here's my favorite package (SOT-89), shown with a Minicircuits PGA103+ device, a $2 part. I Like this package the best because it has a large grounding tab at the top, which helps to draw heat from the device (these operate at 3 to 5v @ up to 100ma).
The PGA103 is quite easy to use...50 ohms in and 50 ohms out, just give it the required supply voltage and a few parts, and it works; not all of the part locations on the board are in use, as this type of device only needs the 8 parts shown (including the PGA103). The following measurement results are at 3v and 60ma when used with a 5v supply, and performed courtesy of W6QIW (Steve), who owns equipment able to make accurate NF measurements, and who was kind enough to oblige:
Steve also reports the NF did not change at higher currents, though gain was
a bit higher. All in all, this one seems to be a very economical solution for
the VHF and UHF ranges. The intercept point is high, so one can get away without
an input filter in most cases, though a simple bandpass filter would be a wise
addition between the LNA and the receiver.
The device used on this next one is just a broadband gain block, set up for use in the 100-3500 MHz
range. Though the device used here has more than 20 db gain through 1500 MHz,
the noise figure is also reasonable, just 2 db or so. The most common
application for a device
like this one is to amplify the output from a transmit mixer up to a useable
level for a driver stage, in the range of 50 to 100 mw.
This one is an LNA designed for use on the 23cm band, and uses a E-PHEMET device requiring the few extra parts for bias and stabilization. NF on this one is in the range of 0.5 db at 1300 MHz.
an MMIC (SGA-6386) in a SOT-86 package shown positioned where it should be mounted.
When I finished building this one, it had 21.3 db gain and a NF of 1.7db at 1296MHz, a few tenths better NF
than the manufacturer claimed. The schematic and values for the
parts for whatever MMIC you will be using should be taken from the manufacturers
Here's how to position one of the E-PHEMET or other devices in the SOT-343 package; note the wide lead is at the top, and the device is rotated about 45 degrees to make the proper connections.
The schematic for the SAV-541+ is below this photo.
Now it's time to be controversial, an opportunity for me to express my personal feelings about LNAs (or pre-amps as they are more commonly called) for terrestrial receiving...this isn't about EME or satellite antennas pointed at quiet sky, that's a different situation. So here it is:
Most of us do not need a pre-amp ahead of our receivers. Here are some of the reasons:
If you do determine a legitimate need for an LNA for terrestrial work...perhaps you prefer not to fuss with the adjustments in an in-warranty radio, your receiver is older and has a poor front end, or your feedline losses are abnormally high, etc; you'll be happy to hear these things are quite easy to make, though you should be aware they require protection from your transmitter (see the LNA sequencing and protection) article.