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From my understanding a RF amplifier boosts the transmission power of your antenna, this will in turn give you a higher gain.
However I've read that this only will give you a further "transmission gain" and not "receiving gain" which would mean you could see networks which are far away but not receive signals from them I.E use them?
This doesn't seem right to me, a RF amplifier allows you to transmit signals further as well as receive them further, right?
Amplifiers, as commonly used in amateur radio, are unidirectional. e.g. separate amplifiers, if any, are used for transmitting from a station, and for receive.
So if you have an amplifier in the transmit path (on signals from a transmitter to an antenna). It likely has little affect on the receiver (other than parasitics, relay contact resistance, etc.) when not transmitting.
An amplifier in the receive path (either an LNA at the antenna, or stuff inside the receiver), similarly, has little effect on the transmit signal (except perhaps as part of a sophisticated adaptive pre-distortion scheme, such as "pure signal").
An amplifier in the receive path amplifies both environmental and antenna RF noise and signals of interest, so may or may not help that much (improve S/N), if the receiver is already sensitive enough to pick up the RF noise floor in the band of interest with a few dB of margin.
So, neither, potentially, allows "hearing" weaker signals, which may or may not be further away, due to propagation, antenna gain, terrain, and many other parameters.
Two basic facts:
An amplifier increases the power of a signal. Whatever goes in its input, comes out the output, only "louder".
Successful reception depends on the ratio between signal and noise at the receiver.
When you use an amplifier to transmit, the amplifier's input comes from your radio, and it's (ideally) 100% good signal. The amplifier gives that signal more power. More power is transmitted by the antenna, more power makes it to the receiver, the signal-to-noise ratio at the receiver is higher, and the receiver "hears you better".
When you use an amplifier on a receiver, the amplifier's input comes from the antenna. That input already contains both signal and noise, and the amplifier makes both of them louder. This can be useful, if the receiver's sensitivity isn't good enough, or if there's a long length of cable between the antenna and the receiver that will cause signal loss. This is sort of like a person with hearing loss putting in a hearing aid.
But if the receiver already has enough sensitivity to "hear the noise", then amplifying signal and noise together won't improve the signal-to-noise ratio, and it won't improve reception quality. Imagine you're standing in a room with a thousand people all talking at once, and your friend is whispering to you from ten feet away. Would it help you to use a hearing aid? No, it would make a thousand people all sound louder and hurt your ears, but you wouldn't have any more chance of making out a whisper. But if your friend spoke louder, you could probably hear them. That's the difference between an amplifier at the receiver and an amplifier at the transmitter.
In common ham radio usage, an amplifier (as a separate device, rather than part of a receiver or transmitter) amplifies the transmitted signal, but does nothing to amplify received signals. A low-noise amplifier (LNA) amplifies the received signal, but does nothing to amplify the transmitted signal.
Modern receivers have essentially unlimited gain. (My HF transceiver has an RF Gain knob, but its function is to limit the gain when needed.) The problem is that an amplifier circuit amplifies both the signal and the noise, and also adds noise of its own. On HF and lower-frequency bands (< 30 MHz) there is natural noise from lightning (QRN) and noise from other transmitters (QRM), which typically dwarfs the noise added by the receiver, so the receiver noise is usually not a problem.
On VHF and higher-frequency bands (> 30 MHz) there is typically much less QRM and QRN, but the desired signal can be very faint, so the noise added by the amplifier, quantified in decibels as the "noise figure", is more of a problem. It is often worthwhile to use an external LNA device to boost the received signal, rather than relying on the receiver's noisier internal amplifier to supply the necessary gain.
Amplifiers are typically an integral part of the receive circuit. Adding more amplifiers to the receive circuit typically doesn't help, as there are usually enough to start with if the receiver is well designed and complete.
The reason for this is because when you amplify what comes out of the antenna, you amplify the signal and the noise. Also, the amplifier itself adds more noise. So if your signal was weak in the first place, it was probably close to the noise floor, and amplifying it more at best will just make the noise louder, and at worst will add more noise and make it less distinguishable.
It may be easy to add an amplifier to increase distance, but the most effective way to increase gain is to get a more directional or more selective antenna. The point here is to gather more energy from the direction of the signal and less noise from other directions. Or, reciprocally, aim more of your power in the direction you want to be heard.
Also, unless you are working with signals that reflect off the ionosphere (roughly below 30MHz), its the height of your antenna that gives you distance, and above a certain power threshold, more power doesn't help that much. Radio waves (neglecting reflection and refraction) are line of sight and the horizon is your limit.
