Lightweight and cheap 2-M transmitter

KD9TVI

Newbie
Joined
Aug 26, 2024
Messages
3
TLDR: I'm looking for a very lightweight ( < 50 g) and cheap ( < $25) 2-meter transmitter that stacks directly on top of an associated microcontroller, similar to the ones that exist for 33 cm and 70 cm. It needs to transmit data collected by the microcontroller to an FTM-300DR transceiver up to 3000 feet away. Do they exist? If not, what is the next best option?

I'm participating in a challenge in which a 2-M radio will be launched on a rocket to an apogee of about 5000 feet and transmit data about the launch and landing (apogee, time of landing, max velocity, etc.) to an FTM-300DR transceiver at the base station once the rocket lands. The distance between the rocket and base station at landing will be at most 3000 feet. I've completed a similar challenge in which I used a 70 cm Adafruit LoRa Featherwing, which was dead simple to plug into an Adafruit Feather board and hook up to a couple of sensors, and it worked perfectly.

This challenge requires the data to be transmitted on the 2-meter band. I've been hunting around on the internet for an evaluation/development board that would be as simple as dropping on top of an associated microcontroller like the Feather series, but I haven't had any luck. Do they exist anywhere?

In the event they do not in fact exist, I have found a couple potential options. There's the Great Scott Gadgets HackRF One SDR, which I think would work with a Raspberry Pi, but costs more than the entire budget last year. Next is the ArduTrx, which seems to be by far the best bet. However, I can't tell how much it costs, how much assembly is required, and if it really will work for this application due to the limited documentation and my relative lack of knowledge. The Arrow from Curious Electron might work, but it is designed for a different use case and is apparently very low-powered. It still might be a good option if he published his PCB files somewhere. Finally, I found a few evaluation boards on Mouser such as the EVAL-ADF7021-NDBZ5, which also might work but again is over three times the price of what I was hoping to find.

Let me know if there's something out there I missed, or if you have a recommendation out of the options I found. Thank you!
 

KD9TVI

Newbie
Joined
Aug 26, 2024
Messages
3
Get a Baofeng UV-5R and remove it from its case. It will be small, lightweight and cheaper than any transmitter you will find.
I looked at those, but they are designed primarily for talking/ real-time audio communication. The radio needs to get data points from a set of sensors and transmit those upon landing, which means it needs to do that without human interaction. I assumed this would be a text-based transmission like the projects I've previously done. I suppose I could have a speaker on the computer that reads off the data points to the radio- that seems overly convoluted though. Am I fundamentally misunderstanding something here, or can those radios send text?
 

prcguy

Member
Premium Subscriber
Joined
Jun 30, 2006
Messages
16,332
Location
So Cal - Richardson, TX - Tewksbury, MA
I looked at those, but they are designed primarily for talking/ real-time audio communication. The radio needs to get data points from a set of sensors and transmit those upon landing, which means it needs to do that without human interaction. I assumed this would be a text-based transmission like the projects I've previously done. I suppose I could have a speaker on the computer that reads off the data points to the radio- that seems overly convoluted though. Am I fundamentally misunderstanding something here, or can those radios send text?
It’s just a radio but you can have sensors send data to a tiny modem that will blurt out any type msg you want. Can’t say I’ve seen a VHF transmitter with built in modem that takes in sensors and transmits text msgs.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
25,125
Location
United States
Have you looked at Byonics? Mainly for APRS, but they make some small transmitters that might be a good starting place. Not as inexpensive as a CCR, though.

 

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
7,390
Does it have to be VHF? These are small. Don't know if it will program below 450 MHz but cheap enough.

 

AK9R

Lead Wiki Manager and almost an Awesome Moderator
Super Moderator
Joined
Jul 18, 2004
Messages
9,911
Location
Central Indiana
Interesting that the Friendcom data radios were mentioned.

Argent Data used to sell a T2-301 which was a Friendcom FC-301 with an Argent Data Tracker2 board built in. I have two of them. While they were intended for APRS, they could be operated as a TNC for sending serial data over the air.

The FC-301 has been replaced with the FC-302. Though, the FC-303 appears to be smaller and lighter.
 

KD9TVI

Newbie
Joined
Aug 26, 2024
Messages
3
Have you looked at Byonics? Mainly for APRS, but they make some small transmitters that might be a good starting place. Not as inexpensive as a CCR, though.

Interesting. It seems possible to program a Raspberry Pi to configure a MicroTrak-1000 to do this, a couple of other pieces of hardware over there look reasonable. I am not overly familiar with APRS, but it seems like it should be reasonable to update our data points in the status portion of the protocol. Thanks for the tip.

Does it have to be VHF? These are small. Don't know if it will program below 450 MHz but cheap enough.

Yes, it needs to be VHF. Specifically, it must be 144-148 MHz. The competition mandates the 2M band and the specific channel will be designated later.

Running one of these without the case will be 59 grams, maybe a way to cut back some more weight if you worked on it.


You can often find these used on e-Bay for cheap.
Looks good. Might work, no VHF ones on ebay right now it seems. Thanks for the tip

Interesting that the Friendcom data radios were mentioned.

Argent Data used to sell a T2-301 which was a Friendcom FC-301 with an Argent Data Tracker2 board built in. I have two of them. While they were intended for APRS, they could be operated as a TNC for sending serial data over the air.

The FC-301 has been replaced with the FC-302. Though, the FC-303 appears to be smaller and lighter.
Ooh, it looks like the 302 can transmit on 144-148 MHz, though. Thanks! They're pretty freakin expensive for our budget but seems like most of the options are

plus 1 for byonics, also take a look at big red bee. they're main focus is balloons and rockets. BigRedBee, LLC
Interesting option. Looks very similar to the byonics options but lighter. Thanks for the tip

What I'm seeing in general is that the most out-of-the-box option in terms of hardware would probably involve plugging a ~$200 transceiver or transmitter into a Raspberry Pi or other SBC and programming the SBC to configure it after landing, most likely slightly misusing the APRS protocol. Looks like there may be one or two options out there that allow a more streamlined process, but this is a pretty good starting point. Thanks for all the options folks! If anyone's got better options please make a post, I'll keep checking in here periodically until we finalize our design and order some hardware, probably around a month from now
 
Top