I think it is possible, but not too likely to develop naturally.
Radio transmissions are not a fixed power output. You can have a 700MHz sender with 1MW or 1µW. It mainly changes the range of your transmission, depending on setup.
What you need
...is something that generates the signal and an antenna. Neither I know of examples in nature, but I doubt it would be impossible.
I just do not see any evolutionary benefit over acoustic communication as this is probably a lot simpler to build that 700MHz communication. And the potential range benefit is not something immediately useful for survival - to make use of that you'd already need a complex social species that could use this to take advantage of the range.
So here on earth for basically every species long range communication is almost pointless. (There are very few exceptions - including humans)
However, this is a reason for why I think it did not develop on earth - not that it is impossible to develop naturally.
The signal generation is something it think is more difficult. Sudden electric discharge like eels is not helpful as it is just one-directional discharge and not a rather high-frequency oscillating signal - which is your requirement with 700MHz.
I am not aware of any examples in nature of anything like this, but there might be something.
Acoustic vs Electromagnetic
Any physical body makes sounds when it interacts with another physical body in some way. Even if the sound can not be heard by us or is incredibly quiet. There is always some sound.
It is easy for an organism that already has a physical body to use this to make sound on purpose as well as use sound to detect objects in its vicinity.
An electromagnetic sender-receiver system has a significantly higher base requirements to be useful for a species. With sound you can imagine organisms detecting and reacting to a sound to gain an advantage. Soon organisms create sound on purpose to trigger reactions by others. That way you can develop something like a communication slowly building it bottom-up instead of top-down like engineering works.
Bottom-Up vs Top-Down
Top-Down refers to a design process starting with the question "What do I want to achieve?" and then designing a mechanism that somehow achieves what was desired.
Bottom-Up is what evolution does. It starts with something and then randomly builds upon that. Some things work - others not so much. After a long period of time you have developments of entirely different complex systems all looking like they were designed for a purpose to fit in the ecosystem. The truth is that nothing was ever designed. Beneficial alterations had a better chance of making it to the next generation. This means an efficiently working organism exploiting an ecological niché is simply more likely to survive than a less efficient or less focused organism. (Within limits, but that's just a summary)
Why do I talk about design processes?
Electromagnetic communication as used by humans was designed Top-Down. We built a complex process of signal-generation, encoding, sending, receiving, decoding and interpreting. While it appears similar to acoustic communication, its requirements are a lot more difficult to build in a living organism as well as need a lot more well-adjusted parts.
There is no advantage for an organism having basic versions of electromagnetic communication over significantly easier-to-build acoustic communications - with the downside of significantly lower range.
The main problem
While I doubt it is impossible to solve the problems of signal-generation and building of an antenna using only biochemistry, I think it is extremely unlikely to occur naturally. The antenna is the simple part. All you need is something with even a slight capability of receiving the 700MHz signal. Even a paperclip works easily if the power output and transmission medium are good enough. Smaller and simpler structures are also possible.
Eels (Credit to @ColonelPanic for the link) are an example of complex electromagnetic mechanisms being used in nature. So it is not too far-fetched that it could be built slightly different to create a signal.
It could be genetically-engineered.
Assuming there is a way to have something like these built into an organism, but it would make no sense to develop naturally, you could - with sufficient sci-fi-level knowledge - theoretically code this into an organisms DNA (or whatever alien equivalent they might have).
Either that or you come up with a really good reason why your species developed a rather elaborate means of long range communication using High-Frequency electromagnetic signals.
I am aware that this answer does not specifically address, how the creatures would develop such a signal, but that is simply because I do not know a mechanism that could work naturally.
I do see a possibility having a burst signal based on biochemical reactions with an equivalent bonding-energy of $E = h \times 700MHz$. That way sudden bursts of signals could be transmitted and possibly received. For details you should probably ask RF engineers and biochemists.
However I did feel like OP had some misunderstandings about radio communication and wanted to clear to clear things up a little bit.
On a side note:
If your space colonists use 700MHz and the surrounding frequency-band then they will unavoidably have interference with these radio waves. If they do not use those frequencies, they will not. You can not send multiple signals simultaneously on the same frequency without more elaborate polarity tricks.
@ColonelPanic helped improve my answer regarding the radio transmission. Thanks!