Thursday, November 10, 2016

QRM from a Chinese satellite on 145.725 MHz

After my four year absence from the radio, the main task now is just to get some of the gear working again. Over the last two weeks, I managed to locate the microphone for the 2m/70cm dual band rig and I have put up a vertical half-wave in the attic of the house. Not perfect but at least it gets me on the air again.

Even though the aerial is indoors, I can hear some signals from repeaters and simplex stations from about 100kms away. One of those is the Limerick repeater on R5 (145.725 MHz) which is just over 100kms to the North.


The signal is about S3-5 which means it's clear and easy to listen to but I'd probably need the full 50w to work through it.

I have also managed to get the rig set up to scan both 145 MHz and 433 MHz bands which lets me see who is about. The level of activity is pretty low so it spends a lot of time scanning.

I have noticed though that it sometimes stops on 145.725 MHz with the unmistakable sound of CW coming through. It's not CW on FM but I can hear the white noise on FM getting pulsed by a CW signal. Sure enough, when the repeater opens I can hear the CW beating with the signal and the sound of the CW frequency changing slowly....a sure sign of a satellite.

I came across this a few weeks back when I went looking for info on the Cornwall beacon on 50.042 MHz. I ended up watching a video for the AGM of their Beacon/Repeater group...as you do :o)

During the presentation, someone mentioned that there was interference to their local repeater GB3NC on 145.725 MHz from a new Chinese satellite.

Sure enough when I heard the signal today, I looked up the N2YO satellite tracking website and it was out over the Atlantic and within range. If you want to see where it is at any time or to see when it might be visible, go to http://www.n2yo.com/?s=40911

It seems that a bunch of Chinese satellites were launched in September 2015 and their up links and down links are shown below....


As you can see, the XW-2B has a beacon on 145.725 MHz which is the one I was hearing. The image below shows what it looks like with some specs...


 XW-2B
– Micro-satellite architecture
– Dimensions: 250Lx250Wx250H mm
– Mass: 9kg
– Stabilization: three-axis stabilization system with its +Y surface facing the earth
– Antenna: Deployable antenna, one 1/4λ monopole VHF antenna with max.0dBi gain is located at +Z side and one 1/4λ monopole UHF antenna with max.0dBi gain is located at –Z side, close to the each edge of satellite 
CW Telemetry Beacon: 50 mW, 22 wpm

Essentially it's a 25cm cube with 50mW into a quarter wave whip on 145 MHz. It's pretty amazing to hear it with just a half-wave vertical in the attic.

I presume a lot of others must have noticed this?

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