Nick vs Networking

Category Archives: RF

DIY LTE RAN Adventure – POWER! (systems)

All the gear I’ve got so far for my DIY RAN Project requires -48vDC to power it up.

Back to online auction websites and preso I’ve ended up with an Eltek MPSU3000, from the mid 2000s.

The fellow I bought it from was even nice enough to throw a binder full of printed documentation, which included a full circuit layout diagram, however this was obviously in the days of old school printers, and each of the colours were offset, providing a literal headache when reading and a bit of a reminder of what printed documents were like to deal with…

I get a headache just looking at the colours in this…

So after a bit of tinkering, wiring and reconnecting the temperature probe, I managed to fire the unit up,

While it complained about the absence of batteries (As well as rectifying AC to DC it manages and maintains banks of batteries to provide a backup power supply), it worked, and provided a very stable, clean -54v DC.

I’ve got a very old (1948) Ring Generator / Ring Machine, (same as this one) so I wired it into the rectifier and it came to life, drawing 3 amps in the process.

The Huawei gear uses proprietary power connectors, I’ve managed to start it using crocodile clips and good luck to get it powered up, but I’ve got to work out a more permanent solution before I can rack all the gear and have it setup properly.

The Eltek rectifier has a number of relay contacts in the unit that can be programed to trigger in different conditions, ie mains power lost, battery fault, over temperature, etc.

These relay contacts are then wired into some sort of alarm input, to share alarm state with external monitoring equipment. (Modern rectifiers just have Ethernet and connect over TCP/IP, but this one just has a serial port and an AT command set for connecting it to a dialup modem.)

The BTS3900 has the Universal Power and Environment Unit (UPEU), which allows me to connect external alarm inputs, for things like this, water sensors, smoke detectors and intruder alarms, so hopefully I’ll get that in place when I’m further down the line.

But to program these requires the software, which I couldn’t find anywhere online. As a last ditch attempt I reached out to the manufacturer, Eltek, and asked if they’d be so kind as to send me a copy. I wasn’t expecting much, but the next day, they sent me back all the manuals and the software the next day, for a 15 year old, long surpassed product. Very impressed!

So with the aid of VMware, Windows XP, USB-Serial adapters and jumper wires, I managed to connect to the Rectifier Controller with the software and had a poke around.

While the unit can do some very clever things with battery management, for my lab setup I can’t see myself going to the effort of adding batteries. So for now the Rectifier’s just converting AC mains into -48vDC, but I may string some batteries in the future.

For anyone who’s ended up here looking for info on these units, or the first generation Eltek Flatpacks, I’ve attached some documentation below. The software isn’t readily available online, so I won’t post it here, but you can get it from Eltek directly.

So power system check! Now onto configuring the unit and getting the radios online…

Dumb Lesson in RF Connectors

When the YateBTS project launched 6 or 7 years ago I went out and purchased what was to be my first “real” SDR – The BladeRF x40.

At the time I wanted to play with GSM stuff, and so I grabbed two rubber duck antenna off an Alarm GSM Dialer I had in a junk box, thinking they’d do a better job than the stock “everything-band” antenna that came with the SDR hardware.

The offending antennas

These two became my “probably roughly aligned with the common commercial RAN bands” antennas,

I’ve used these antennas on pretty much all my RAN related projects on the BladeRF, HackRF and the LimeSDR,

I had some issues a recently I attributed to “probably rubbish antennas” so decided to get a pair of paddle antenna tuned for the frequencies I was working with.

While working out what to get I had a look and noted the connectors on all my SDR hardware is SMA-Female connector. Easy, so I need an SMA-Male connector on the antennas, purchase made.

Cut forward to today when the antennas arrive at my door, they’re exactly as described, however I notice some resistance when connecting them, the male pin is stiff to go into the LimeSDR, whereas there’s no resistance at all from my “trusty” rubber duck antennas.

That’s when I realised.

The two antennas I’ve been using for about 7 years at this point, have the wrong connectors (SMA and RP-SMA) and have not made contact on the signal centre pin that entire time…

They’re RP-SMA male and I need SMA male.

Wasn’t just reverse polarity – it was no polarity.

I’m a walking encyclopedia of connectors, acronyms and layer 1 stuff, but apparently this I missed.

I’m an idiot – a lucky one who didn’t burn out his SDR hardware.

An idiot with greatly improved RSSI though…

NBN Skymuster Satellite Technical Overview

I’m a bit of a radio nerd & I’ve worked Satellites before, so the Skymuster / LTSS program had me curious. So here’s some nitty-gritty details on NBNCo’s Skymuster Satellite service.

The Payload

NBNco called the LTSS (Long Term Satellite service) but before launch they re-branded as “Skymuster”.

NBNco provided an Interim service called ISS (Interim Satellite Service). before the launch. IPSTAR satellite (Formerly ABG) and Optus services delivered this. Both of these had limited bandwidth and has since been largely replaced by the Skymuster / LTSS.

NBNCo contracted Space Systems / Loral, a US based satellite manufacturer to design and build the payloads. It’s based on the SSL 1300 platform.

When deployed, the payload itself measures 26 metres long, 9 metres tall and 12 metres wide, and weighs in at 6400Kg. Before deployment, in the satellite’s compressed form it fits within a 5-meter launch-vehicle fairing.

Communication to earth is via Ka-band frequencies which allows for greater density of spot beams and frequency reuse. However, capacity improvement through higher frequencies does come with some tradeoffs. Ka-band frequencies, are more susceptible to weather related conditions compared to Ku-band frequencies. Directional accuracy becomes way more important when aligning the customer dishes in Ka band also.

SSL provided image of SL-1300
DirectionMin FreqMax Freq
Earth to Satellite27Ghz31Ghz
Satellite to Earth17.7Ghz22Ghz

These emissions are within the range of the higher end software defined radio receivers. I’m curious to see what’s being transmitted, but that’s a topic for another day.

The downlink uses RH and LH circular polarisation.

The Journey

SSL assembled the satelite in California.

SSL staff packed it into a crate and loaded into the belly of an Antinov An-124 which is flown to the launch site.

There are two Skymuster Satellites, NBN-Co 1A & 1B. 1B provides infill / capacity layer for 1A but both are identical. If the 1A satellite was lost during launch / deployment, 1B could be sent up in it’s place. This is still a real risk when launching anything.

NBN-Co 1A was the first launched, riding on a Ariane-5ECA from Guiana Space Centre in French Guiana, South America. 1A launched on 30.09.2015 and 1B launched 05.10.2016 in the same configuration.

After launch to a transit orbit, the satellites had to navigate up into a geostationary orbit at ~36,000Km. This was done using it’s 4 × SPT-100 plasma thrusters, which are exactly as cool as they sound. The final navigation process took up 40% of the fuel in the satellite. Fuel is the determining factor for the expected ~15 year lifetime of the two satellites.

SPT-100 – Source: NASA

Once in final position SSL performed 2 months worth of tests referred to as “In Orbit Testing”. SSL then handed over operational Telemetry, Tracking and Command (TT&C) to Optus Satellite (Singtel). Optus are tasked with keeping it in it’s current position.

Customer Hardware

Ericsson manage the installation, and subcontract to Hills and Skybridge for the actual work.

Out Door Unit (ODU)

There are currently 3 Satellite Antenna options that are available for
installation, 80cm, 1.2m & 1.8m.

NBNco’s Test Setup

Narrower Ka-Band signals drops off more rapidly than Ku-Band signals. This means that aligning the Ka-Band antenna within the degrees of usable Azimuth within the Line of Sight maximises the antenna gain.

Required accuracy for each of the antennas:

  • 80 cm: 1.4 degrees,
  • 120 cm: 1.0 degrees
  • 180 cm: 0.7 degrees

The below graph shows being off by 1 degree from the required accuracy, leads to -30dB drop. This translates to a power ratio of 1000, or 1/1000 of the power if correctly aligned.

The alignment process is done by the installer pointing the dish in the correct azimuth / elevation. This is based on compass / inclinometer readings, or smart phone apps. Once a rough alignment has been set, a tone-generator on the TIRA is used to align the dish.

This process requires a 16 digit installation key.

The key containing the frequency used in the installation, beam Assignment & TRIA Polarisation (The 6w version has automatic (Polarisation).

That’s entered into the installation setup page at:

http://192.168.100.1/install

TIRA’s has a built in Tone Generator which is used to “Point and Peak” the dish from the roof. The tones are:

  • Heartbeat 3KHz
  • Pointing Tones 2.5 – 3.1KHz
  • Peaking Tones 2.5, 2.95, 3.1 and 3.3KHz

ViaSat have videos on how the alignment process is performed.

IDU (Modem) / NTD

The modem itself is manufactured by ViaSat. I can’t find any specifics it seems to be in the RM511x line of Satellite modems.

There were some issues with a firmware update on these in 2018, that saw firmware getting rolled back.

The modems / IDU / NTDs for the ISS are not compatible with the LTSS.

There’s some nice teardown photos of a similar ViaSat modem here.

TRIA (Transmit/Receive Integrated Assembly )

The TRIA is the equivalent of a feed horn, an all in one Tx/Rx assembly. They are available in 3w and 6w variants, based on the estimated signal levels of the installation location. That’s determined by factors like high rain areas or if the subscriber is on the edge of a beam.

3W Version

The 6W version has an extra F-Connector for the required DC power injection. The 6w version also has a two F-Connector gang-plate / wallplate when installed for the second RG6 run to power it.

Interestingly there’s a minimum length of cable run (8m) specified for these installations. Anything less than 8m leads to lower resistance and possible overheating.

There is a minimum length of 8m for the cable run this is very
important as it provides the right amount of cable resistance so
the modem does not get hot and over heat. Max cable run is 50m.

Configuration

Transparent Performance Enhancing Proxy (TPEP)

TPEP aka Web Acceleration, is a service offered by NBNco to spoof TCP replies, to make the handshake more efficient. It can, unsurprisingly, lead to headaches accessing services, particularly those that employ TLS.

Web Interface

http://192.168.5.100:8080/xWebGateway.cgi
user name = ADMIN and the password = operator (lower case)

Beam Selection

The installer key sets the beam, and his can be remotely changed by NBNco MAC / NOC team.

BIRRAUS have a good article explaining the spot beams available.

Educational Port

Like the other NBNco NTDs, there are multiple UNI-D ports available on the Skymuster modem allowing segregation of services.

One option that seems to be gaining traction is a dedicated port on the modem for educational use, on one of the UNI-D ports on the modem.

Educational Ports are configured to allow access for remote / distance education students.

The local state government sets pricing, speeds and data usages.

Ground Stations

There are 9 active and one standby ground stations, geographically spread across Australia, with a standby in Wolumna, NSW. The standby is capable of assuming control for any of the other ground stations.

ViaSat built the equipment and services different spot beams.

Again, BIRRAUS have this covered in their article, but here’s an extract they’ve made listing the ground stations and beams serviced.

Wolumla ground station

Future

Solar Transit

Solar transits happen twice yearly when the satellite is aligned directly between the sun and Australia.

The immense solar radiation from the sun overloads the transceivers on the ground, as they’re positioned at the satelite, with the sun behind it overloading the signals.

This lasts for about 6 minutes twice yearly, and affects different ground stations and each of the satellites at different times.

Copper Cutoff

Currently the copper decommissioning does not apply to Skymuster services. This means customers with a copper POTS line, can keep it indefinitely.

This has lead to headaches with incumbent providers who had intended to decommission / sell off remote exchanges, but will be required under Universal Service Obligation to keep them active.

3rd Satellite

Due to unexpectedly large uptake of Skymuster services, NBNco had floated the possibility of launching a 3rd Satelite in 2020:

Scenario 3: Third satellite – This scenario assumes that NBN Co constructs and launches a third satellite at the end of CY20. This mitigates the need to build some fixed wireless base stations and FTTN distribution areas. The capacity of this satellite will only be partially required to meet NBN Co’s needs

Scenario 4: Third satellite in partnership – This scenario mirrors Scenario 3, but assumes that NBN Co enters into a partnership with an external party to access only the required capacity on a third satellite rather than building and owning it outright.

Source – NBNco Fixed Wireless & Satellite Review

Portable Services

Apart from spot-beam migration, there are no technical limitations preventing portable Skymuster services from becoming a service offered.

Qantas are using this to power the in-flight WiFi on their domestic fleet of 80 Boeing 737 and Airbus A330s. Though it seems that may no longer be the case.

The NBNco launched a fleet of “Road Muster” 4WDs for promotion of the services. They drive from town to town, spruiking the benefits of Skymuster.

On the roof of the 4WD is a Satellite ODU, which seems to be self / remote positioning.

Online sleuthing reveals it’s a EXPLORER 8120 manufactured by Cobham. It featuring auto-acquire, drive-away antenna system using Dynamic Pointing Correction technology. At $32k USD, it’s rather pricey, and outside the range of most grey-nomads and campers.

If a user wanted to manually position the dish, they could using a service like DishPointer.com or Wolfram Alpha.  This would give a rough alignment and then the tone generator “Point and Peak” for the fine adjustment.

Layer 3 Services

Skymuster services are setup as L2 services.

NBNCo has highlighted from day 1, the option of using Layer 3 for deliver to enable deep packet inspection.

This would allow them to prioritise traffic more easily / efficiently.

Corrections

Please let me know in the comments if I’ve got anything here wrong.

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