Noob question regarding 75mhz vs 40mhz

[JustSomeOldDude]

Greetings.
I am a 100% noob here planing to build my first RC submarine.
(Legal issues aside for the moment)
Is there any truly notable advantage of the UK FM 40mhz over the US FM 75mhz in terms of water depth penetration?
Also does TX wattage influence penetration? I think most TX's run from 1 to 2 watt is that correct?
finally , I've noticed a lot oh 27 Mhz surface TX's on the market. Am i correct in assuming those are AM radios?
Thanks in advance for the help and info.
Regards.

[bigdave]

In a nutshell yes.
The lower the frequency the easier it will penitrate water.
Will you see any difference with how we use our radios, not sure but I don't think so.
Not enough to run an illegal frequency anyway.
But I am no RF engineer. BD.
BTW
They do make 27 MHZ in FM. I have one.

[JustSomeOldDude]

Thanks Dave. I wasn't aware of the 27mhz being FM, Im guessing that is still legal for surface in the US? Going to be googling this

[Guest]

27mhz sets were made back in the day. Futaba M-series and Fleet radio are tow outfits that I recall used FM on 27mhz. But it's likely to be pretty old kit by now.

[JustSomeOldDude]

Ok , im confused.
27mhz Am and Fm RC systems are legal in the US for surface
YET
CB (Citizens band) 26.9650 MHz to 27.4050 MHz 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
It's all totally confusing to me.
Why couldn't i take an old cheep 27mhz AM TX controller (legal) and boost it through a handheld 10w CB (also legal) radio signal amplifier? Surely even at that wattage a AM signal would get very good penetration though water.

[Guest]

I think you are over theorizing. I think the regulations in The USA are tighter than here in the UK with regards to tinkering with standard equipment. Having said that, if you get a sub going with standard equipment, it's rare you find range is a big issue. The simple fact is it's your own vision which is the biggest limitation, beyond a few feet from the side of the pond, pool, etc, you cannot see what the boat is doing when submerged.

So my advice is get yourself a decent FM set, and concentrate on the other aspects of model submarine construction.

[chips]

You seem to be familiar with Subpart D - CB Radio Service portion of the FCC Regulations. Subpart C is the Radio Control (R/C) Service rules.
R/C transmitter power output varies by the frequency.

27.255 MHz max output of 25 Watts
26.995-27.195 MHz max output of 4 Watts
72-76 MHz max output of 0.75 Watts

Use of a transmitter which has power output in excess of that authorized voids your authority to operate the station.

Boosting your R/C transmitter signal through a CB signal amp appears to violate several of the FCC rules; such as: R/C Rule 9; R/C Rule 10; and R/C Rule 22. R/C Rule violations carry fines up to $10,000 for each violation.

It's best to play by the rules as published by the FCC. We should be thankful that the FAA hasn't talked more with the FCC to reign in the foolish drone pilots - and the other R/C modelers who are mush more responsible than some of the drone idiots.

[JustSomeOldDude]

Very helpful info chips.
Seems to be so much different interpretations on the net as to the rules.

[southern or]

I felt weird this weekend with my yellow ribbon and my 3ft antenna standing next to a bunch of 40mHz boats... I guess 40mHz is more of a guideline now? These weren't home builds but off the shelf RTR boats. I could've saved SO much money.

[Guest]

I felt weird this weekend with my yellow ribbon and my 3ft antenna standing next to a bunch of 40mHz boats... I guess 40mHz is more of a guideline now? These weren't home builds but off the shelf RTR boats. I could've saved SO much money.

Do not worry !

Frequency bands are coming and going.

In my youth (1960ies) we operated our RC gliders exclusively at 27,12 MHz.

A few years later 40,68 MHz was allowed.

In the 90ies, the 35 MHz band was introduced.

Today we all fly at 2,4 GHz (frequency-hopping).

Good thing is: All the toys are quite rapidly following these changes (mass market) and the "old frequencies" are nowerdays free of interference.

At least here in Germany.

Cheers

Volker

[bensid54]

So is it safe to say 2.4ghz would be useless in an RC Submarine?

[Ralph --- SSBN 598]

You have that correct.
2.4ghz is useless unless you keep the antenna or use a buoy to keep the antenna above the waters surface.

[bensid54]

How far below the surface can 24 mhz penetrate? I have a Fat Shark system that uses 5.8 ghz is that useless under water? What systems work under water and how far can the signals go? I have never done this so I'm trying to learn how because submarines have always interested me.

[salmon]

The 2.4GHz will not penetrated, or if it does not well and not far at all. The 5.8GHz is also not a good frequency. MHz is what you need. 75MHzis what I use here in the U.S. of A.
The signal can go a long distance, depending on the particulates dissolved in the water. Salt water and chlorinated pool water are not good for working with subs. On the pool it does depend on how much chemicals are in there. The guys up in Canada that run in some very clear water, can testify to the depth they get. For me it seems like most guys (and gals) run their subs no more than a few inches below the surface.

[bensid54]

OK I think I'm understanding a little better. Below a few inches or even a foot or two underwater the radio signal could become quite spotty and if there are contaminants then all bets are off for depth. Because I want to go six feet or more below surface then I will need a remote antenae for the Fat Shark and radio. Basically I like to build, make it work then move on to something else. Here is one of my latest projects.https://youtu.be/Hl-6qccVwQE