APRS over FRS

Short video of an APRS beacon I built working over a pair of Cobra microTALK FRS/GMRS radios.

The APRS beacon was coded in C for an Atmel ATtiny44A, which produces audio tones via an R-2R DAC, which is attenuated and filtered to be sent to the radio's mic input. When the radio receives any transmission, it outputs about 1VDC on the speaker output, which is detected by the microcontroller, which waits 1s before keying the radio and transmitting the packet. The packet is received by the user's radio, which can be connected to a computer to use as a software TNC (I simply used the microphone input of my netbook to receive the packet audio, and MULTIPSK to decode it). The beacon shown in this video does not support GPS/location yet, since the microcontroller does not have any UARTs.

The FCC Part 95 document states: (95.193b) (2) The FRS unit may transmit digital data containing location information, or requesting location information from one or more other FRS units ... 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.

This accommodation for data was given for units like the Garmin Rino, which support transmitting and receiving location data from other units. This project, I believe, is within those bounds. The total on-time of the transmitter when sending a packet exceeds 1s (due to keying/tx on time delays), but the actual data is less than 1s in length.

The reason using FRS for packet location is of interest to me is the widespread availability of cheap FRS radios, no licensing requirements, and (unlike MURS) no antenna height limitations, allowing potential use in high altitude ballooning.

Details about the APRS beacon, including source code, can be found soon on my website: http://rev0proto.com/wiki/index.php/Rev0Trac

Category:

Science & Technology

Tags:

• aprs
• frs
• ham
• radio
• hab
• high
• altitude
• balloon
• multipsk
• cobra
• pr-1050-wx
• avr
• atmel

[ladams00]

MULTIPSK for the win! :)

[nqzdepofltr]

@jkenny1 I just realized that it also said it on the screen :\

[jkenny1]

@nqzdepofltr No kidding.

[nqzdepofltr]

@nqzdepofltr That's what it says

[nqzdepofltr]

!0000.00N/00000.00W>Test5

[mgregggphone]

pretty cool.

Do you have schematics and code?

I do not see either on the referenced website.

fun project. keep it up.