Shared antenna for gateway and SDR

Hi everyone,
I am going to setup an IC880A + rasperry pi gateway following this guide:

I’m doing research on the influence of environmental parameters on the radio signal. Therefore I would like to analyze the attenuation of the received signal beyond RSSI and SNR which is how I found out about the SDR-devices.
My knowledge about radios is limited to what I have learned from reading the forum and watching videos on youtube.
So here my very basic question:

  • Is it possible to connect both gateway concentrator board and SDR-USB-dongle to the antenna?

  • If yes, how?

My concern is that the gateway uses the antenna to send waves while the SDR “listens” on the antenna. I read about splitters and taps (here), which can be used to split the signal into two receiver cables. Can signals sent by the concentrator still reach the antenna through a splitter/tap?

Thanks in advance for your answers

raspberry pi 3
u.FL to female SMA cable
male SMA to BNC adapter
2.5 m coaxial cable (50 Ω)
Aurel GP 868 Antenna

SDR-USB-dongle with female SMA

What environmental parameters are you expecting to affect the signal ?

It would be possible to ‘split’ the signal, but far from easy to get it right and prevent the SDR being fried. Plus by implication you have reduced the signal going into the gateway and affected the signal strength.

focus is on precipitation, additionally temperature, pressure and relative humidity

By splitting it, would the signal reduction be constant? What would be the required hardware?

Alternatively (and more probable because easier) I would use a seperate antenna for the SDR

Using a seperate antenna for the SDR would be a lot easier, although with it close to the gateway antenna your going to need some protection to prevent the SDR being fried.

I appreciate we all ‘know’ that water in the atmosphere affects radio communications and it is true. However, the effect only becomes significant above 5ghz.

At the frequencies used in TTN, the affect is minute, its very unlikley you can measure it with simple gear. Think of the order of 0.001dB per km in rain.

A splitter is probably not a good idea at these frequencies. In a perfect world, you will lose 3 dB
(1/2) of your transmit power to the antenna and the same loss on receive. At these frequencies the
layout and components used in building said splitter become critical to insure each port sees the
desired impedance. As mentioned, the output power from the gateway may very well damage the
front-end of the RX dongle, or overdrive it to the point of being useless.

A directional coupler specifies a loss at the reflected port, usually 20 or 30 dB (a lot). Calibrating such a system will require real test equipment to produce any meaningful results. Personally, I would use dedicated RX and TX antennas for what you’re trying to accomplish. The TV splitter and
‘taps’ referenced will almost definitely work at ~900 MHz.

CORRECTION…TV splitter wil almost definitely NOT work at ~900 MHz, sorry, my typo.

ok then, if i shouldn’t even place them to close to each other (like running the SDR and the concentrator on the same rp) i will deploy them independently.
thanks for your help

What you’re saying about the effect of preceipitation sounds quite interesting. Can you give me more information on how you get to that value or point me to a publication or any other source?

Yeah, that sounds discouraging and i guess the gateway would be useless if it looses 20 to 30 dB. I will consider a different way of deploying them. Thanks for your input

Google something like ‘Rain Fade’ or ‘atmospherinc attenuation of radio waves’


I am doing exactly what you are attempting to do. I have my SDR (NeSDR SMART) antenna and my Laird gateway in close proximity to each other.

Connecting splitters reduces the incoming signals by at least 3 db.

I’ve discovered a lot using the SDR, especially a lot of frequency use (905-928MHZ) here in Toronto.
When you compare “noise” to other cities, Toronto has a high noise level.

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