Transmit Data Over Walkie Talkies?

#1
How do you transmit serial data over walkie talkies. I've done a fair amount of searching/ surfing... and have seen it mentioned several times but have not found out how you actually do it. I've heard mention of using DTMF to do it but is there any other way? I would like to have to 08m's talk to each other without a hard line connecting them. Any info on this would be greatly appreciated. Thanks in advance :D
 
#2
depends on data speed. also depends if you want simplex or dupelex.

of course there are a number of wireless modem mudules that can do it nowadays. search the net for acoustic modems and you should find the tech for slow transmission ideas
 
#3
Well, after looking up simplex and duplex, yes I'm that new, I would think that half duplex would be possible. The reason is that walkie talkies are not one way devices, they are designed to both transmit and receive. Probably the most that I would be sending would be sensory readouts. It would be nice, if possible to do simply, to be able to control a servo with it but that may be much harder.
 
#4
@ookid.

A couple of points;

1. What's the potential maximum range of your transmissions?

If it's < 500m, then have a look at post #4 here:
http://www.picaxeforum.co.uk/showthread.php?t=9376&highlight=UHF+data

2. This section of the forum is for finished projects.
You may get more replies if you re-post your question
in the Main / Active Forum area.

There is a huge knowledge base available here on
cheap and accessible 433 Tx/Rx units.

e
 
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#5
My w/t are push-to-talk so Duplex no way.

Have a look into sending tones and tone decoding.

Wait til Stan wakes up. He can give you more info and the technical terms that I can't remember.
Don't confuse DTMF with the 2 tone high/low thing which I've forgotten what it's called.

Are there any restricitions on sending Data via walky talky?

Come on Stan.... wakey, wakey :)
 

hippy

Technical Support
Staff member
#6
[ Moved to Active Forum ]

There may be legislative issue about using walkie talkies, CB or PMR for carrying data transmissions which make what you are attempring to do illegal. Check your local legislation.

With voice radios you have a transmitter and a 'voice front-end'. To use them you need to convert your digital signal to audio ( DTMF, ASK, FSK ) and at the other end convert that audio back again. You may be better off using cheap TX and RX modules specifically designed for the job of digital data transmission, such as 433MHz modules.
 

manuka

Senior Member
#7
Dippy: Waddaya mean "Wakey wakey"- it's bedtime down under!

The query re data over walkie talkie raises numerous involved technical, legal & practical issues. It's akin maybe to trying to explain culture of Facebook to ones grandparents! IMHO the easiest way to wet your feet RF wise is with the globally licence free 433 MHz data devices. Many hold that PICAXEs & these 433 MHz tx/rx devices are made for each other. See diverse comments, circuitry & code => www.picaxe.orcon.net.nz Stan.
 

RexLan

Senior Member
#8
[ Moved to Active Forum ]

There may be legislative issue about using walkie talkies, CB or PMR for carrying data transmissions which make what you are attempring to do illegal. Check your local legislation.

With voice radios you have a transmitter and a 'voice front-end'. To use them you need to convert your digital signal to audio ( DTMF, ASK, FSK ) and at the other end convert that audio back again. You may be better off using cheap TX and RX modules specifically designed for the job of digital data transmission, such as 433MHz modules.

Correct and it is also illegal .... for good reason
 

manuka

Senior Member
#9
Hey- it's not illegal everywhere! Here in NZ & Australia we have 2 free UHF CB channels (~470 MHz) reserved for telemetry/telecommand- although of just a few seconds per hour. This is a source of some local griping, especially since it's considered the "per hour" was a type & should have been "per minute"!

IF it's locally legal, all manner of info can be sent, with even the likes of SSTV (Slow Scan TV), Hellschreiber etc a doodle. Decoding can be via PC sound card software. Radio hams have been especially active in recent decades with new data modes. If you're really keen about these things then consider getting your ham licence too! The traditional Morse requirement has now been largely scrapped, & anyone with an electrotechnical mind would find the licence test straight forward.

For simple audio data use even weak transmissions at the free low end of the 88-108 FM band may be handy. However 433 MHz ISM is certainly THE slot to initially consider, & ranges using simple Yagi antenna can be 100s of metres. Superior 433 MHz gear ( HopeRf, Yishi etc) will go for miles line of sight. This band is often very noisy in urban areas due to numerous other users - hams, wireless doorbells, weather stations, energy meters, security, toys, garage door openers etc.

Way down at 27 MHz MHz & the like -the CB spectrum slot once VERY ugly but now almost deserted- all manner of weak free transmissions are tolerated globally. Kids "~US$5 a pair" 27.145 MHz walkie talkies & cheap R/C models in fact may suit parts hacking for more decent tone/data & control use.

Stan.
 
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LizzieB

Senior Member
#10
The OP is in California and in the US CB on 27 MHz only allows voice or tones for squelch, FRS (current generation CB on 462/7 MHz) does allow some very limited data (and I've seen it suggested for balloon telemetry) but the rules are complex:

(2) The FRS unit may transmit digital data containing location information, or requesting location information from one or more other FRS units, or containing a brief text message to another specific FRS unit. Digital data transmissions must be initiated by a manual action or command of a user, except that an FRS unit receiving an interrogation request may automatically respond with its location. Digital data transmissions shall not exceed one second, and shall be limited to no more than one digital transmission within a thirty-second period, except that an FRS unit may automatically respond to more than one interrogation request received within a thirty-second period.

The radio control service does not allow data.

The 433, or better 900, MHz modules are the way to go.
 
#12
Well then, Thanks all for posting. I have been thoroughly convinced into using a 433 or 900 MHz system. The illegal part is what really decided it though...:D. The thought behind using walkie talkies was that I already had them but had no use for them but it doesn't look like an easy thing to do. Again many thanks to all who replied.
 

LizzieB

Senior Member
#13
Another option would be to get a ham license and use the frequencies that are available to them (us) for telemetry. Your local club and others in the area run "ham crams" which will get you through the tech exam in one day (if you have a half way good memory).
 
#14
yeah i wondered about that. My church is getting volunteers to get their ham license in emergency preparation so I might do that. Would it make it legal to transmit on the frequency of a walkie talkie?
 
#15
yeah i wondered about that. My church is getting volunteers to get their ham license in emergency preparation so I might do that. Would it make it legal to transmit on the frequency of a walkie talkie?
nope, but it'll get you a radio and access to a lot of frequencies to do what you want.

get the liscence, it's well worth it

73
kc9esf
 

manuka

Senior Member
#16
My church is getting volunteers to get their ham license in emergency preparation so I might do that.
I too recommend getting a ham licence for those keen on wireless data comms, especially when well off the beaten track on perhaps missionary work! Cheap mobile voice calls/txt/email/Skype etc have rather weakened the classic appeal of ham radio, but it's a pathway to better gear & bandwidth. Some superb weak signal datacomms ideas has evolved recently to utilise these goodies too! Japanese firms Yaesu, Kenwood & Icom (together the so called "IcKensu" or "YaKenCom") dominate the equipment field, but Chinese made VHF-UHF gear is now often better value- refer such monthly ham mags as "QST" for the coloured glossy details. Don't feel pressured to buy new however, as endless older ham gear is always for sale via local clubs etc.

Almost any one with an electro-technical background could handle the ham test these days- in my era over 40 years back it took months of study on the likes of neutralising the grounded grid triode, Hartley Oscillators etc etc. Not a single semiconductor figured ! The then compulsory 15 wpm of near error free Morse took ages to master as well. Things now are a breeze in comparison, & (here in NZ anyway) there's no longer even an annual re-licencing fee.

73's -Stan (ZL2APS - licenced 1966 )
 
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