# Lowest noise MMIC for HF? (160-20M)

I recently learned that these fancy modern ultra-low noise MMIC, while having <1dB noise figure around 1Ghz could be quite bad at low frequencies due to 1/f noise.

What is lowest noise MMIC then for 160-20M bands? I am only aware of MAR-6 and INA-02184/INA-02186 having noise figure of ~2-3dB.

Does it even make sense to try to reduce noise figure of preamp below 3dB in these bands or environment noise is stronger anyway?

• As you suspect, a truly low noise amplifier is only required for very short antennas, perhaps under 1 metre. From this length and longer, other concerns dominate, mainly the amplifier's strong-signal performance. Also as the antenna impedance is so high, you may get lower overall noise with an op-amp, rather than a 50 Ohm MMIC. Feb 22 at 3:15
• According to Rec. ITU-R P.372-8 the antenna temperature (of a full size dipole not a short whip) can be as low as 290 K for a few percent of the time, at the top of HF, but is usually more like 10000 K and much more. So the amplifier noise figure doesn't matter unless you have a very small antenna, or a very quiet location (the empty quarter?). Feb 22 at 3:23
• @tomnexus Sounds like two parts of a helpful answer! Feb 22 at 11:26

The ambient noise on HF is so high that such a low noise figure will not appreciably improve performance. On 20 meters, the minimum ambient noise temperature you will encounter is about $$3 \times 10^6 \:\mathrm K$$, which corresponds to a noise figure of about 40 dB. Noise goes up with wavelength, reaching $$3 \times 10^{10} \:\mathrm K$$ or 80 dB around 1 MHz.