First project, how to transmit and receive radio with arduino and SDR

[Jacob Smith]

Hello!
I live in Stevenage and I am starting my first HAB project. I have done a lot of research and am trying to keep costs down. I have decided to first create the tracker and receiver, but have little electronics experience. I think the following will work.
For the payload: Arduino Uno, NTX2, uBLOX MAX-M8Q SAW/LNA Breakout With Sarantel Antenna, resistors, DS18B20 temperature sensor, pressure sensor, SD card and logger to store temp+pressure data, buzzer.
I have seen the related UKHAS guides but cannot find anything that uses all these in one circuit.
I would like to use SDR to receive the signal, but am unsure about which components are best/are needed.
1) I can buy a RTL2832U & R820T dongle which comes with an antenna from ebay, will the antenna be suitable? https://www.ebay.co.uk/itm/RTL2832U-R820T-DVB-T-E4000-USB-DVB-T-RTL-SDR-Realtek-Tuner-Antenna-Receiver-UP-/182908606793
2) The Newsky RTL2832U R820T from CosyCave comes with no antenna, so I’d need to get one separately. https://www.cosycave.co.uk/product.php?id_product=314
3) Would a preamp eg. https://store.uputronics.com/index.php?route=product/product&product_id=53&search=habamp be needed? If so please can someone explain all the connections that need to be made between antenna, preamp, dongle, computer, Arduino and anything else. I’ve also seen an SMA header in the circuits but no explanation as to why and what it connects to.
Are there any more components I would need for the transmitter/receiver? I’ve read about the Yagi antenna and antennas needed on the payload?
I want to ensure that I will be able to recover my payload and I would really appreciate any advice/help anyone can give. With little experience in creating circuits, for my first flight I would like to follow a proven circuit diagram and set-up.
Thank you for reading all this!
Jacob

[loratra...@gmail.com]

The RTL2832U SDR dongles definetly benefit from using an LNA, I have used the G4DDK VLNA, it makes a big differance. Uptronics do a filtered LNA, a lot of people seem to use it and its cheaper than the G4DDK.

The antenna needs to be outside and as high as possible, above roof level really. An omni directional antenna is fine, a yagi would have more gain but only when pointed in the right direction. I mostly use a Diamond X50N omni, worth the money, but you can easily DIY build something like a Slim Jim in a bit of plastic pipe, lots of DIY plans to be found on the Internet. For short antenna runs you can get away with thin co-ox such as RG58 to connect the antenna, but really you need the much thicker stuff (I use Ecoflex 10 plus) to reduce cable losses.

A UNO will struggle to run a HAB tracker transmitter and SD card at the same time due to lack of memory. Either use an ATmega2560, clones are in-expensive, or use an 'openlog' which is a dedicated micro SD card logger that you can put on the ATmega console serial port to log whatever you choose to print. Openlogs can be got for around £4 on eBay.

There are plenty of low cost Ublox 7 and 8 modules to be found on eBay, the ones with the built in 25mm ceramic patch antenna produce very strong signals. They are in a plastic case and designed for quadcopters and the like. They do accept the navigation model 6 config required for high altitude use, but I have not sent one above 18,000M to see if they keep working.

Bear in mind that a lot of the stuff you are using needs a 3.3V supply and logic levels so a UNO is not the best choice, its 5V based. A low cost Arduino Pro Mini (£1.50) delivered is available in a 3.3V version.

Stuart Robinson
www.LoRaTracker.uk

[MikeB]

Hi

Regarding your advice to use thick co-ax for long cable runs, would it be acceptable to mount the SDR next to the antenna and have a long USB lead back to the PC?

Mike B

[Stuart Robinson]

Not tried it with an SDR, but I have done this in the past with USB WiFi adapters and 3G dongles, on a 10M cable.

Worth a try I guess, its either going to work or not, there would be no weak signal issues.

10M active USB cables are not expensive and are extremly useful when your testing tracker hardware. You can put the tracker and GPS outside and monitor whats happening.

[Steve Aerospace]

Likewise - I've only ever used USB extenders for low data rate
applications.

Ive found the cheaper types only support USB 1.1  data rates
(12Mbits/sec) - and in fact some advertised as USB 2.0 only give you
12Mbits/sec too.   The data rate from SDR dongles can be much higher -
so you might need to look for a high spec USB extender (which might
negate the cost savings over co-ax) or alternatively turn  the SDR
dongle sampling rate right down.

Another point to look at is RF radiation from the long cables used
(typically Ethernet CAT cable).

    Steve G8KHW

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[David Akerman]

Another option, though probably not an ideal project for a first-timer, would be to use a Pi or other small computer up near the aerial, then run an ethernet cable down from that (ideal with PoE).  Then you can have the RTL --> audio side on the Pi, and send audio over the network.  See https://www.rtl-sdr.com/new-raspberry-pi-remote-rtl-sdr-gui-software-mnm4sdr/ for example.

Dave

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