"Joel Koltner" wrote in
:

Yet many designs for HF/shortwave antenna amplifiers don't bother with
a matching network, just feeding the antenna directly into a FET. So
why is this? Is the extra gain just not needed on HF? Or too
unwiedly to build when you're trying to cover everything from
1MHz-30MHz?

Joel, you might hope that a good receiver provides some degree of band
pass filtering prior to the RF amplifier for IMD protection.

For best receiver weak signal performance at SHF, you would usually match
for optimum noise figure rather than best front end gain.

At HF, receiver internal noise is usually lower than ambient noise, so
receiver NF is less an issue, but... intermodulation performance is very
important. "Noise" can be created in the RF amp due to intermodulation
distortion, so designs often focus on optimisation of IMD rather than NF
directly, or front end gain. For example, I note that the TS2000 does not
use a high performance signal FET for the HF RF amp, but uses a couple of
power FETs.

The 144MHz case you mention is somewhere between the two, ambient noise
in the city is usually much higher than a state of the art LNA, and often
higher than a modern transceiver with a NF of 5dB. In my experience, IMD
noise is a bigger issue on 144MHz than NF measurements made in a shielded
room. A high gain amplifier with poor NF or high IMD noise delivers a
high volume low S/N output from the receiver. (Try an IC706IIG on a
discone antenna in the city.)

Owen