Dumb New user trying to understand things needing help.

[OldNoob]

Greetings all
Please forgive my lack of knowledge but i need some help understanding things.
Currently i am building a R/C submarine. The local waters here are quite murky and i will need some powerful signal to penetrate them.
The legal surface frequencies available to me here in the US are 27mhz TX AM or FM and 75mhz TX AM or FM.
Now i am a bit confused
Citizens Band is supposedly 26.9650 MHz to 27.4050 MHz and is legal as long as it's AM, which explains why some CB sets can be as much as 40w of power.
HOWEVER FM/CB is very ILLEGAL in the US and can carry a fine up to $25,000 correct?
yet a fm 27mhz rc controller is legal?

Also would there be anything illegal in taking an old 27mhz AM RC TX which is outputting at maybe .5 watts and reworking it use the signal amplifier in a handheld 10w CB radio. the frequency would remain the same , just boosted to 10w

Bare with me, i don't know anything but i am trying to learn.
Thanks in advance.

 

[KC4RAF]

The CB band has gaps in it.

If you'll go to this site or RR, you'll see those gaps.
https://www.radioreference.com/apps/db/?aid=7731
Those gaps are normally used for RC and other communications.
Also, 75 Mhz is better for under water receptions isn't it?
(there's 5 gaps I think; 26.995, 27.045, .095, .145, and .195)

 

[K5MPH]

If you are a ham you can use 6 meters 53.1,53.2,53.3,53.4,53.5,53.6,53.7,53.8 and also 72 Mhz.....

 

[OldNoob]

Thanks for the link and help.
i have a 72mhz radio but sadly 72mhz is only legal for ground to air RC .

I'm thinking 75mhz , which is legal for surface RC will work. But 27mhz is a lower frequency , having a longer wave it would get better depth in brackish water.
2.4ghz wont penetrate water at all.
Wish i had more understanding of radio and electronics.
---
Having done some more research,, turns out it's a matter of power. a 27mhz FM transmitter is legal if stays below 600 milliwatts or 0.6 watts . So my FM 10w 27mhz transmitter idea is a no go from a legal perspective.
oh well.

 

[OldNoob]

If you'll go to this site or RR, you'll see those gaps.
https://www.radioreference.com/apps/db/?aid=7731
Those gaps are normally used for RC and other communications.
Also, 75 Mhz is better for under water receptions isn't it?
(there's 5 gaps I think; 26.995, 27.045, .095, .145, and .195)

Didn't even notice that, Thanks that's helpful and explains why i have only seen certain RC frequencies within the 27mhz range.

 

[n0nhp]

Penetrating water more than a few inches will be very difficult with any VHF signal (above 30MHz) and 27MHz is not going to be much better at all especially if you stay within legal FCC power limits. A shortened antenna (less than 108") will further degrade the distance the signal can be heard. This is the reason most underwater ROVs are tethered. Not as much fun, but considering the time and dollars put into the project, usually worth it. Besides with a tether you can get real-time video back up the wires.

Depending on distance between the transmitter and receiver if you are set on going wireless, I might try sound. Audio, especially infra sound (below human hearing range) travels great distances in water and a waterproof speaker and mic setup can be accomplished with a fairly low cost. No license needed for audio.

Bruce