GSM Mobile Networks RF

Using a NanoVNA to analyse SDR Base Station Antennas

Using a NanoVNA to analyse antenna performance for SDR driven Base Stations for GSM / LTE.

A few months back I posted my secret shame regarding some rubber-ducky antennas I had been using thinking they were on the GSM bands, that turned out to have the wrong connector and had never made contact in all the years I’d used them.

I recently got my hands on a NanoVNAv2 and thought I’d take a look at the antennas I’d purchased for my GSM SDR experimentation,

These antennas claimed to operate on 900/1800/2100MHz and this time had the correct connector (SMA not RP-SMA)…

I ordered two of these antennas for the princely sum of $3 and hooked them onto the NanoVNA to analyse the antennas – the poor man’s Anritsu SiteMaster!

The buttons on the NanoVNA are a bit tough to use but there’s great software out there for driving the NanoVNA from your computer (NanoVNA-saver), which is what used in the end,

I was operating the GSM network using ARFCN 871 with the SDR which translates to 1782 MHz for Uplink and 1877 MHz for Downlink, so I plugged in the values into the VNA to take a look at how it performs in those ranges,

Performance is actually pretty on point,

On the Uplink frequency we’ve got a VSWR of 1.15 which is about as good as it gets,

And in the downlink we’ve got a VSWR of 1.221, still pretty good.

Performance on the remainder of the 1800MHz band is pretty decent, with clear drops in VSWR where the Uplink and Downlink channels lie.

I measured the full band for Uplink on the 1800Mhz band (1710Mhz – 1785Mhz):

Analysis of Uplink Bands

Which shows not all channels are created equal, if you were looking for real performance on these antennas and not just playing, you’d probably want to put your uplink channel on one of the frequencies shown by the marker,

And the full band for Downlink on the 1800Mhz band (1805Mhz – 1890Mhz):

Again, varied performance, but the peaks and troughs line up on the uplink and downlink, so a lower ARFCN in the 1800Mhz band would put you about on the red marker for both,

Comparing the output of each of the antennas I’ve got

In reality I could be using a bent coat hanger for an antenna, the signals shouldn’t be able to leave the room, but it’s a good excuse to use the toys!

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