C-band Receiver Hardware for UNITEC-1

With only a few days left until the launch of UNITEC-1 (May 17) to Venus, we are getting ready to track it and I am trying to catch up on the documentation part – this time a brief description of the receiver hardware.

Recall the system architecture where the 5.84 GHz RF signal is converted to 640 MHz using the KU LNC 5659 C PRO low noise down converter, and…

C-band receiver architecture

This article gives a high level walkthrough of the receiver used to convert the 640 MHz IF to digital baseband, i.e. the blue box called USRP in the above diagram.

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Bias-T for the UNITEC-1 Receiver

Today I have been looking at the options for bias tees that we can use for the UNITEC-1 receiver. A bias tee (aka. Bias -T) is a simple device that can inject DC voltage into a coax cable. It is often used to provide supply voltage to devices that are mounted on the antenna without the need for dedicated DC cables. In our case, the low noise converter (LNC) will be mounted on the antenna and the “cable length” between antenna and control room is 40 meters, so it matters a lot that we can use the already existing RF coax cable to also supply the DC voltage. Actually, the KU LNC 5659 C PRO that we will use can only be supplied via the coax.

We have two Bias-T on stock: The KU BT 271 N from Kuhne that was originally acquired for the S-band ground station and something called MSTTR001 from Snec – don’t have much info about this one besides that it should be good up some-GHz and 100 mA current.

As you can see, the KU BT 271 N has two N-connectors while the Snec has two SMA connectors but is mounted on this adapter thing so that the antenna end has an N-connector. The USRP + WBX or TVRX receiver has SMA connectors and the coax cable has N-connector, thus it seems that the Snec would be best suited. Unfortunately, the LNC requires 180 mA so we’ll stick to the KU BT 271 N, which can be used up to 1 A.

UNITEC-1: The KU LNC 5659 C PRO has arrived

Yesterday I have received the C-band down-converter that I have ordered last week for the UNITEC-1 receiver station.

Watch video on YouTube.

I have also uploaded a few high resolution photos to my Picasa Albums:

Close-up the KU LNC 5659 C PRO low noise downconverter (LNC) from Kuhne Electronic.

Close-up the KU LNC 5659 C PRO low noise downconverter (LNC) from Kuhne Electronic.

The KU LNC 5659 C PRO low noise downconverter (LNC) from Kuhne Electronic. It converts 5.6...5.9 GHz to 400...700 MHz. Noise figure 1 dB, Gain 40 dB.

If you can’t read the specs, you can see them on my work-in-progress wiki page about the C-band Receiver Station.

Next step will be to connect it to the USRP equipped with the WBX and TVRX daughterboards (need 400…700 MHz receiver) and use some basic GNU Radio receiver software to test it using the OZ7IGY beacon, which transmits on 5.7 GHz (5760.930 MHz to be precise) and is definitely within our range. We can probably also find a signal generator for 5.6/5.7/5.8/5.9 GHz somewhere for better tests.

UNITEC-1: A New Deep Space Adventure

If everything goes according to current plans, JAXA will launch their PLANET-C spacecraft towards Venus on May 18, 2010. To fill out the empty space and available payload mass on the H-IIA rocket, they will also bring four university built cubesats into orbit. One of these cubesats, UNITEC-1, is very special in that it will follow PLANET-C all the way to Venus, although without any propulsive capabilities to make trajectory corrections it might end up somewhere else – we’ll see about that. Another special thing about UNITEC-1 is that it will be using the 6 cm amateur radio band. Cubesats have a tendency to be stuck on VHF and UHF frequencies for understandable reasons, so a 5.8 GHz signal from deep space will be an interesting challenge!

Our Mission

The mission for us radio amateurs is much more than just trying to listen for UNITEC-1. As I see it, radio amateurs can:

  1. Receive telemetry from an interplanetary spacecraft. UNITEC-1 will transmit telemetry on 5.84 GHz using very simple ON/OFF keying at 1 bit per second. This is quite exciting – I believe it will be the first time that we can receive unencrypted telemetry from an interplanetary spacecraft.
  2. Support the UNITEC-1 operators by tracking their craft. By providing them with accurate measurements of antenna pointing and Doppler shift, the operators can estimate the actual trajectory of the craft (remember, UNITEC-1 does not have any coherent tracking transponder on-board). More tracking data from around the world will improve their statistics significantly.

There is a formal call for support on the UNITEC-1 website requesting the global amateur radio community to help with tracking. You can also read about the actual mission UNITEC-1 will carry out during its journey to Venus. Be sure to check out the PDF file that gives many details relevant to tracking.

System Overview

We plan on assembling a system consisting of:

  • The 7 meter parabolic dish at OZ7SAT
  • A wide band feed that should be good up to 10 GHz
  • A Low noise down-converter (LNC)
  • Universal Software Radio Peripheral (USRP) with an appropriate RF daughterboard (probably WBX trasceiver or TVRX receiver)
  • GNU Radio-based software defined radio receiver

Functional diagram of the C-band receiver

We are going to need a C-band downconverter. From Kuhne we have several choices. One kind uses 1.4…1.7 GHz as IF, the other kind uses 400…700 MHz as IF. Since we already have about 40 meters of H1000-class cable between the antenna and the control room, we chose the UHF version to reduce the cable losses.

The LNC has been ordered and it should arrive next week. We have everything else on stock but will need to write some software. There is plenty of time though until 17 May. In any case, stay tuned for updates during the coming weeks.



Related articles:

WBX Transceiver Tests using GNU Radio and USRP

This video shows my first on-the-air tests with the WBX transceiver using the USRP (Universal Software Radio Peripheral) and GNU Radio.

The receiver was tested using wide band FM broadcast, APT signal from NOAA 17 satellite and Copenhagen VOLMET. I have also performed some tests using DVB-T signal and wireless sensor signals but I wanted to keep the video short so these were not included. I can post them in separate videos if there is interest.

Continue reading “WBX Transceiver Tests using GNU Radio and USRP”

Portable S-band Ground Station Update

I made good progress with the portable S-band ground station this week.

I took the receiver to the OZ7SAT lab to measure its performance. Using the USRP+DBSRX and no LNA we could easily detect a -132 dBm CW signal with modest FFT integration (fraction of a second) in a GNU Radio spectrum scope. Using the LNA we could go down to about -138 dBm, i.e. an improvement in SNR of 6 dB. These figures were measured at an SNR ~5 dB. This is excellent, but please note that this is not real “sensitivity” in the traditional sense because we were not demodulating or decoding the signal. We were simply integrating the spectrum for a fraction of a second to detect the presence of the signal. The measurements were done by sampling a 250 kHz wide spectrum.

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New vLog: Introducing the S-band Ground Station Project for LRO/LCROSS Reception

In this new video blog I am introducing a new project that has kept me occupied for a few weeks now: A low cost S-band ground station for receiving signals from NASA’s lunar spacecrafts LRO and LCROSS. More info at Receiving LRO and LCROSS. Based on the Universal Software Radio Peripheral (USRP) with DBSRX daughterboard, a super low noise preamplifier from Kuhne and GNU Radio software.