LF LOW FREQUENCY UNDER WATER

[john robinson]

I would like to start by saying hello to every body at the sub committee forum, as i have just joined i built a model submarine 20 years ago it is a 12ft gato weight is 500lbs its a beast it has spent the last 17 years in a trailor and my son said why dont you do some thing with it, what came to mind scrap it but no submarine was full of electronics level control, back hydoplanes very sencertive because of lenght of sub depth control unit, could keep sub at preset depth and would hunt within 15mm to keep it there worked on infa red light sub had four way radio link, video, full telemetry giving data back to bank side padgeing system rc radio control 90 channels was all done 20 years ago. One of the new units to go in sub is low frequency radio link for controlling sub would be interested if anybody else has worked on the same thing because lf is a lot better at getting through water than HF bands plus alot of this is all down to how much RF you can put into antenners other unit i have been working on is on screen display which will overlay on video picture coming back from sub compass headings speed battery voltage and all sorts of other data. To give some idear of size of the sub it takes four 12volt 38 amp hour gel type batterys drive motors for props are washing matchine motors dc 240volts
ALL THE BEST JOHN ROBINSON IN UK

[crazy ivan]

Re: LF LOW FREQUENCY UNDER WATER

Now that would make some write-up for our SubCommittee Report (with photos, of course)!

[Guest]

Re: LF LOW FREQUENCY UNDER WATER

Hi John,

Welcome to the forum. I haven't seen or heard of anyone using low frequency radio, so you're in a field of your own there I think. One idea I had considered was using DTMF as a sonar radio for operation in brackish or salty water.

One chap who comes along to the Dive-in pool runs I organise in London and Hertfordshire makes his own radio, which also has telemetry. He uses 27mhz though.

Andy

[scott t]

Re: LF LOW FREQUENCY UNDER WATER

Maybe a sound generator that makes chirps and whistles like dolphins or other sea life, could send commands to a boat in tainted water.
Drop a buoy in the water that recieves signals from regular RC equipment and changes them to sounds under the surface of the water.
Your boat could recieve both RF and sound wave signals. You may have heard sounds like motor boat propellers while swimming under water.
Sorry I can't give any practical help, only my thoughts.

Scott T

[john robinson]

Re: LF LOW FREQUENCY UNDER WATER

HI Andy
fine on trying to use DTMF tones don't no weather you where going to use it as on off functions one big problem with LF you cannot send data very fast, but not sure what frequency you where going to use fine on the guy useing 27 mhz for his sub i also used 27 mhz AM for controlling sub, my receiver in the sub is a much reworked CB radio, radio can hunt me down if i change channels plus filtering is a lot better than useing RX receiver new LF radio going into sub TX can knock out 20 watts of RF at that sort of power level you can feel antenner start to burn you if you touch it. You also said that i must be on my own with this but it does get interesting makes a change instead of useing 10 ghz for video links thanks for the interest all the best John

[JWLaRue]

Re: LF LOW FREQUENCY UNDER WATER

John,

...welcome to the hobby! I think a number of folks would really like to see if there may be a practical alternative to our current radios given the industry-wide push to move entirely to the 2.4GHz radios.......which are useless for our purposes.

Any time you'd like to submit an article for the SubCommittee Report, please let me know!

-Jeff

[Guest]

Re: LF LOW FREQUENCY UNDER WATER

fine on trying to use DTMF tones don't no weather you where going to use it as on off functions one big problem with LF you cannot send data very fast.
John

The idea I had was to use this with servo powered robotic fish (so not a fast 'model'). Send the data as a single packet using infra red protocols but using the sound instead of light. Resolution need only be about 4 bit nibbles for control purposes. A fish would be better controlled with a button pad than set of sticks IMO.

[roedj]

Re: LF LOW FREQUENCY UNDER WATER

While using DTMF tones may work on an individual basis (I really don't know) wouldn't it result in total chaos in a situation like the Sub Regatta with several boats in the water at the same time? In other words, how would a boat "know" which tone was meant for it?

On using LF for model subs, the resonant wavelength for antennas at those frequencies is measured in miles not inches. The efficiency, and thus energy transfer, of any antenna that could be used in a model sub would be abysmal, on the order of probably less than 0.0001%
Dan

[Guest]

Re: LF LOW FREQUENCY UNDER WATER

Well I don't think anyone else would be operating such a system. But if you had several working, you could send a coded byte specific to your system with each transmission. That would allow 256 models.

[john robinson]

Re: LF LOW FREQUENCY UNDER WATER

HI Dan
you said that an antenna lenght at LF would be in miles in length if you look at the antenna in a long wave radio down on a few khz it is not miles in length but you can listen to radio station 100s of miles away, just to give you some idear and also if you look at people that do DF directcion finding looking for people that do pot holeing and can be a few houndred feet down they use very small antennas on a few khz and they are not miles in length, some times you have to look out the box to find the answer. Plus we are not looking for miles of range with a model sub one of the things i worked on over the winter was to make a resonant antenna to work under water on 27mhz a full wave antenna on 27mhz would be around 33ft but if you make it to work under water it is many times smaller again you have to look outside the box
all the best John Robinson call sign G7SCL

[roedj]

Re: LF LOW FREQUENCY UNDER WATER

John,

My mistake. I was thinking of ELF or even VLF.

If we can agree on LF being from 30kHz to 300 kHz then the shortest resonant length would be on the order of

300/.3 = 1000 meters. If we assume a velocity factor of .3 for water we'd get a resonant length of 1000 * .3 = 300 meters.

That's still one honking big antenna. OK, but if we use an active antenna (commonly used on LF for direction finding and general listening) we'd be able to shorten it considerably.

I am always amused when I read about warnings that the receiving antennas supplied by manufacturers should never be shortened. Airplanes, other surface use - maybe - but underwater the velocity factor throws all the careful calculations out the window.

Some 30 years ago I was working on buried antennas, ones that could survive an atomic attack. I got quite familiar with velocity factor and was always amazed just how short one could make an effective resonant antenna.

73's

Dan K8XW

[john robinson]

Re: LF LOW FREQUENCY UNDER WATER

HI Dan
Fine on LF being 30 KHZ to 300 KHZ, and it is a honking big antenna. Some of the antennas designs that i have seen down on a few KHZ are very compact and do work very well, one of the things i have done in the sub is to transvert up from LF to 27MHZ reason being if LF does'nt work in the sub i can soon pull it out and go back to 27MHZ with out much problem but i have also made it that if i switch from 27MHZ to LF the sub will switch to which ever band to find me. You said that you worked on buried antennas must have been very interesting but don't like the idea of atomic attack very much. Somebody said about doing DTMF tones to work for control of i think it was a model fish, what you could do for controlling it is to use a remote control for a t.v set and use the decoding chip out of a tv with a bit of moding and that would work well for on off functions and could be linked to what ever transmitter and receiver you won't to use
73's
john G7SCL

[john robinson]

Re: LF LOW FREQUENCY UNDER WATER

this is a link to a small video of my 12 foot sub my son did

http://www.youtube.com/watch?v=n7ActoYN3SE