Can a 40mW Tx transmits up to 20-30km????? Amazing!!!!! Few are saying...

Here-
www.sm0vpo.com/tx/bug9.htm
Harry Lythall is saying about his 40mW Tx- "The range is about double that of the V5, that is to say about 2km under "ideal" conditions. If used for NBFM in the lower ham bands then you should easily be able to get 10 - 20km with line-of-sight and decent gain antennas. If you use a decent comms receiver then this transmitter can be used for much greater distances." Does he mean- Lower ham band has greater performance in range? Or talking about decent antenna and receiver only?

Another; Here-
http://www.talkingelectronics.com/projects/Spy Circuits/SpyCircuits-2.html
Collin is saying- "We produce a 30mW bug called the AMOEBA and it was tested by a hobbyist on top of a mountain and it transmitted 40km (26 miles) to his home." Unbelieable!!!

Any experience do you have?

Noise level is the limiting factor. The higher the frequency, the lower the terrestrial noise.

Reflectivity in the atmosphere has an effect here on earth. Different radio frequencies will be reflected at different times of day,different seasons, and different sun spot cycle.

The Voyager spacecraft is billions of miles away and transmits at less than 15 watts. We receive it's transmissions by using an array of dish antennas and slowing down it's baud rate.
I guess I'm just rambling.

I received a 145MHz 40mw beacon from a high-altitude balloon more than 250km distant. I'm using a 5/8λ omni-directional antenna, and an NBFM receiver with a sensistivity of ~0.25uV (-120dbm), much better than a broadcast FM receiver.

The theoritical distance one could detect such a signal is shown here:

This shows I had a fade margin of 16db, which means that the power of the transmitter could be reduced 16db (from 40mw to 1mw), and I should still be able to detect it...

Amateur radio operators (hams) operate "QRP" (low-power) equipment all the time. As mentioned, noise is a limiting factor and frequency affects a lot of this as well. Don't expect 40mW to get much outside your house at 150KHz. But expect to do some decent communication on the short-wave bands where "skip" is a contributing factor. I've a friend who regularly "worked" around the world with 15 watts on the 10-meter band, often cutting through past hams running a full kilowatt!

How a sensitive receiver works as high sensitive receiver? It amplifies the received signals first? Anybody has basic antenna amplifier circuits for receiver?