|This is a basic preamp I adapted from some magazine article (maybe ARRL or Nuts and Volts).
I've built and applied many of these with good results. The two 2498's seem to be quieter that the MAR 5 MMIC circuits I had been using, although the MMIC's are much easier and faster to build (see Minicircuits Web site). I have since found that Ramsey has a preamp called the SA-7 which has a close configuration to the above one. That is where I found out about the 2570A. I can't tell you one is quieter or more broadbanded than the other since in my usage it really doesn't matter.
In my Preselector circuits, I use these amps at 18 dB (3 S-units), from 100 kHz to 30 MHz. They are fine way up to above 900 MHz.
Maybe I'm getting lazy, but for about $19.00, the SA-7 (with mods as required) seems to be a good deal. I get all the parts and a "real" PC board and no tendency to oscillate as was a bit of a problem when I "dead bugged" the first versions of this on perfboard.
For a gain control to serve unknown receiving antennas, hang a 5k pot off the input. For a 50 ohm invironment I use a 500 ohm pot or 50 ohm step attenuator, and transformer couple the input and output at 1:1 for isolation (minicircuits or coilcraft).