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You need :
– an Android phone with OTG support running at least Android 6.0
– an SDR USB dongle with a RTL2832U chipset and R860 (or R820T or R820T2) tuner such as the RTL-SDR blog v3 or Nooelec NESDR SMArt v4 (Many other models exist) and its antenna.
– a USB OTG cable
– the free SDR driver from Martin Marinov

– And the TXAdvance app which you can find on the Play Store

Download the user manual and/or the getting started doc on the Getting Started page.

You can use any kind of antenna which is compatible with your SDR dongle. Most of them come with a female SMA input which is the most commonly used connector (with BNC) for audio oriented RF receiver. You can even connect your dongle to any RF distributor like the ones from BSRF, Sennheiser or PSC…

Make sure not to overload the antenna input of your SDR USB dongle (check your dongle specifications) !

They are intermodulation products. The first part (2T, 3T) represents the number of transmitters and the second (3O, 5O, 7O), the order of the intermodulation. For 2 transmitters transmitting at respectively f1 and f2, the 2T3O products are equal to 2*f1 – f2 and 2*f2 – f1. The 2T5O products are equal to 3*f1 – 2*f2 and 3*f2 – 2*f1…

The smaller the order, the stronger the intermodulation is. You should absolutely avoid 2T3O intermodulations products.

The 3T3O can be strong but the likeliness of having 3 transmitters close enough to create 3T3O intermodulations is depending upon your setup.

In order to use the scan function of TXAdvance, your SDR USB dongle needs the Realtek RTL2832U chipset and the R860 (or R820T2 or R820T) tuner. Any other chipset or tuner will not work (at the moment). I also recommend a model with a TCXO for a better accuracy. You can find the recommended models here.

You only need the SDR USB dongle for scanning. Once the scan is done, you do not need the dongle until the next time you want to scan a location.
If you do not have an SDR USB dongle, you can still use the Intermodulation analysis part of TXAdvance, but not the scan function.

Some phone brands (like Samsung or Huawei) kill background apps. When you perform a scan on TXadvance, the app launches the SDR driver in the background and the driver is responsible for receiving data from the dongle and to send commands from the app to the dongle.
You need to authorize the app and the driver to run in the background without being killed. You can check Dontkillmyapp to learn how to do it.

Unfortunately, iOs does not allow to directly plug an SDR USB dongle.
I am working on a potential solution but it will take some time. So at the moment (2022), TXAdvance will stay Android only.