Tag Archives: Antenna

Indoor LTE/GSM/UMTS mobile antennas, primarily used for in building coverage.

DIY RAN Adventures – Antennas

EUTRAN, LTE, Mobile Networks, RF, , , ,

Note: This is one part of a series of posts where I cover my adventures attempting to bring on air a commercial Macro cell site for my lab, with scrounged components.

So the Huawei BTS3900 unit I’ve ended up with, is only one part of the overall picture for building a working LTE RAN. Power systems, feeders, connectors, CPRI, antennas, baseband processing and transmission are all hurdles I’ve still got to overcome. So today, let’s talk about antennas!

For the output/TX side (downlink) of the RF Unit, I’ve ordered some 25w 50 ohm dummy loads (I’ll still need to work out how to turn down the RF power to less than 25w on the RF units). Even with the dummy load, a tiny bit of RF power is leaked, which should be enough to provide the downlink signal for my UEs – Time will tell if this works…

This option is fine for the power being pushed out of the RF unit, into the dummy load, where we have a lot of power available (too much power), but what about our very weak uplink signals from UEs?

For this I’d need some decent antennas to pickup the signals from the UEs, so I ended up with some Kathrein (Now owned by Ericsson) indoor multi-band omni antennas I found on an online auction site for $10 each. (I bought 4 so I can play with MIMO.)

Unfortunately, the RFUs I have are Band 28 (roughly 700Mhz-750Mhz uplink and 758Mhz to 798Mhz downlink), and reading the datasheet it seems this doesn’t cover the bands I need;

But beggars can’t be choosers, so I ran a calibration on the NanoVNA and swept the antenna from 700Mhz-750Mhz (Band 28 uplink frequencies) to see how it will perform when I get the rest of the solution together;

At the upper end of Band 28 Uplink (748Mhz) I’m getting a fairly respectable VSWR of 1.6 (Return Loss of -12.4dB), so I should be able to get away with these for what I’m doing,

I’v seen these white domes inside shopping centers and office buildings, so I was keen to crack open the case and see what magic inside, what I found was kind of underwhelming, just an aluminum plate with an aluminum reflector cone…

My ideas of putting the parts into the lathe and trying to lower it’s operating frequency by taking material off, were dashed when I realised taking material off would raise the operating frequency, not lower it…

NanoVNA showing LCD contents

Using a NanoVNA to analyse SDR Base Station Antennas

GSM, Mobile Networks, RF, ,

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!