How 'far' you can go on any frequency depends on a few factors, let me give you a little backgrounder in layman's terms:

**1. Free space loss: **
This is the first thing to consider, as it affects ANY and ALL radio frequency (RF) communications. It is the inherent loss (=attenuation) of a radio frequency wave traveling through the air, the higher the frequency the more loss/attenuation there is per km/mile the radio wave travels. I.e. at similar output power, say 500mW, a 1.2GHz transmitter will give you less attenuation at X km/mile than a 500mW 5.8GHz transmitter, hence the net loss at X km/mile is LOWER when the frequency is LOWER.

http://en.wikipedia.org/wiki/Free-space_path_loss
**2. Transmitter output power: **
It doesn't take a genius to figure out that the more output power your transmitter has the further its signal will travel. However the attenuation seen by the free space loss described in 1. is the same, i.e. if a 500mW 1.2GHz transmitter looses 10dB over X meter/feet then a 1000mW will as well. If you look at transmitter output power more closely it becomes clear that to double your range you need to quadruple your transmitter output power. Hence if you're using a 500mW transmitter and would like to fly further, a 800mW or 1000mW isn't really going to make a difference, that's just adding a mere few (hundred) meters/feet at best. No, if you really want to see a significant increase in range you'll need 4x that, to double your range, which equates to at least a 2W transmitter.

In reality anything over 500mW is overkill because there's more gains to be had, literally, at the receiving end, but we'll get to that later. The more power your transmitter puts out the more power it drains, the hotter it gets due to inherent losses inside the transmitter that are dissipated as heat and the more strain it puts on the sensitive electronics on your plane which are bombarded with an overdose of RF waves. This overdose of RF makes your servos twitch, desensitizes RC receivers and can create all kinds of other problems.

**3. Antennas and link budget:**
Antennas are for RF waves what a reflector is for a flashlight's light bulb. Just like a flashlight's reflector they can focus the beam of RF waves into a coherent beam or pattern, which then can be used to your advantage. As discussed you can increase your range by upping your transmitter power, but that quickly becomes tricky as the output power required to see significant gains in range quickly rises. If you want to double your 500mW range then you need at least a 2W transmitter, if you want to double that again no less than 8W is required and so on. This quickly becomes unpractical and somewhat of a stupid approach, as there's easier, far more efficient, ways of increasing your range.

So, what defines range to begin with you might wonder? Well, maximum range is where your receiver can no longer distinguish the signal your transmitter is putting out from the background noise. The point at which the signal gets lost amidst the noise is your maximum available link budget. That link budget however is a simple equation determined by 1., 2. and 3. (the antennas you're using.) Basically the link budget is described by:

*Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)*
Simply put, if the received power equals the maximum sensitivity of your receiver you loose the signal, so if you have a typical receiver with -85dBm sensitivity then that's a known variable, so lets enter that:

*-85 = Transmitted Power (dBm) + Gains (dB) − Losses (dB)*
For argument's sake lets say we're using a 500mW transmitter, that equates to a transmitted power of 27dBm, so once more, lets enter that:

*-85 = 27 + Gains (dB) - Losses (dB)*
The gains in the above equation are the gains offered by the transmitter and receiver antenna, lets assume we're using the supplied whip antennas your transmitter and receiver shipped with, which have a typical gain of about 2dBi, hence the total gain is 4dB. Entering those into the equation gives us the following:

*-85 = 27 + 4 - Losses (dB)*
Now the losses are the sum of all losses between the transmitter output and the receiver input, hence this includes connector and cable losses and such. However in this case, as we're trying to keep it simple, lets just assume we're dealing with free space loss only. Now it is trivial to compute the free space loss and thus calculate the maximum range given the variables we entered previously:

*-85 = 27 + 4 - X*
*X = -85 - (27+4)*
*X = -116*
*Losses (dB) = -116*
*Hence the losses are -116dB, from this value the maximum range can be calculated given the frequency used and the equations mentioned in 1.*
Now what would be the easiest way of upping our link budget? Looking at the equation all variables are weighed the same, so where can we get the most gain with the least amount of work?

The answer is antennas. So why is that? Well, I've already compared an antenna to the reflector on a flashlight. What does the reflector do to the light hitting it? Exactly, it focuses it into a coherent beam. Just imagine what happens if you are standing in a dark room and let a flashlight's beam hit the wall across the room, there'll be a bright spot on the wall with the rest of the room still being dark. In that spot however the brightness of the light is magnitudes greater than if you were to unscrew the reflector from the flashlight and just hold the flashlight above your head with the light bulb lighting up the entire room instead.

However the total amount of light the light bulb puts out remains the same, the reflector just bundles the photons into a tight beam. The exact same happens with antennas, just with RF waves and in our case the reflector isn't on the transmitter, but on the receiver.

A reflector that bundles RF waves is typically referred to as a directional antenna. A typical directional antenna has a gain of 8 - 20dBi, which means your link budget grows by the same amount. If you mount a simple 14dBi flat patch antenna to your receiver rather than the stock whip for example, you've more than quadrupled (!) your range. This however does make the antenna more directional, just like the reflector on a flashlight, hence you have to make sure you stay within its 'beam' so as not to loose the signal. But when you do, you'll be able to fly much further than with the stock whip.

So, in summary, how 'far' you can go on a frequency, i.e. the maximum range, depends on 1, 2 and 3. With 3, antennas, being the easiest way of increasing your range, with the downside that you have to stay within the beam of the directional antenna where it offers the most gain.

I hope that clarifies a few things for you pilot's in training, if not, or when further questions come to mind, be sure to leave a reply.