Category: GNU Radio

Articles and blogs about the GNU Radio, written by Alexandru Csete OZ9AEC.

Smaller dish for tracking UNITEC-1

As you probably already know the UNITEC-1 launch got scrubbed today (17th May). Fortunately, there is a launch window every day for the next few weeks.

During the last few days I learned that tracking UNITEC-1 will be very difficult because the available trajectory data can be very uncertain. Therefore, we decided to use a smaller antenna with wider beam width in the first few days after launch. One option was to mount the IKEA dish to piggyback the 7m dish, another option was to use a 90cm dish which is currently equipped with a 2.4 GHz feed. We decided to go for the second option.

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Preparing the 7m antenna for UNITEC-1

AMSAT OZ staff are preparing the 7 meter dish for tracking the UNITEC-1 interplanetary spacecraft.

Related articles:

UNITEC-1 Link Budget

Below you will find the link budget summary calculated for a few distances during the interplanetary cruise of UNITEC-1. The link budget calculator sheet containing all the details is available here.

Parameter Value
Frequency 5840 MHz
TX Power 4.8 W / 6.8 dBW / 36.8 dBm
TX Ant Gain 5 dBi
EIRP 11.8 dBW
Distance (km) 20.000 200.000 2.000.000 15.000.000 20.000.000
Distance (AU) 0.0001337 0.0013369 0.0133692 0.1002687 0.1336916
Free Space Loss 194 dB 214 dB 234 dB 251 dB 254 dB
Atm. losses 2 dB
Signal at RX ant -184 dBW -204 dBW -224 dBW -242 dBW -244 dBW
Pointing loss 0.4 dB
Receiver G/T 23 dB/K
S/N0 67 dBHz 47 dBHz 27 dBHz 10 dBHz 7 dBHz
SNR @ 500 Hz BW 40 dB 20 dB 0 dB -17 dB -20 dB
SNR @ 100 Hz BW 47 dB 27 dB 7 dB -10 dB -13 dB

Assumptions

  1. Attenuation due to rain, ionosphere and atmospheric gasses set to 2 dB[2]
  2. TX power is 4.8 watts/antenna[3].
  3. TX antenna is microstrip patch, linear, assuming 5 dBi gain[3].
  4. Our beam width is 0.5° and I assumed a pointing error no greater than 0.1° (very optimistic) giving a 0.4 dB pointing loss.

TBDs and TBCs

  1. Measure the receiver noise floor, i.e. local interference contribution to sky temperature (important)
  2. Re-assess sky noise taking expected solar noise, etc. into account[2]

Conclusions

  1. An optimistic estimate suggests that we should be able to receive UNITEC-1 up to 10-15 million km distance.
  2. There is plenty of margin in the beginning and we can use a low gain antenna for initial acquisition. The IKEA dish has ~25 dBi gain and it could be used up to 1 million km where after the trajectory is hopefully well known.

Related Articles

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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GRC Examples

On this page you will find a few software defined radio (SDR) examples implemented in the GNU Radio Companion aka GRC. They are very simple yet functional examples I created while I was learning GNU Radio and SDR. I hope other who are learning GNU Radio and SDR might also find them useful.

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SSTV Robot OZ9STV with USRP and WBX

I was fooling around with the USRP / WBX on the 2 meter band tonight when I suddenly stumbled upon some very strong SSTV transmission. It turned out to be the OZ9STV robot located only a few kilometers from me. That explained why I had more than 40 dB SNR even though I was only using a bad whip antenna indoors.

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UNITEC-1 5.8 GHz Receiver Test Using OZ7IGY

USRP with WBX and TVRX

Tuesday, April 13, 2010 we finally got a chance to test the 5.8 GHz receiver for the UNITEC-1 ground station on the air. The weather was nice and the weak wind allowed us to be on the roof and listen for the OZ7IGY beacon 40 km away.

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GNU Radio SSB/CW/AM/FM Receiver v0.6

New update of the simple receiver – version 0.6 – with the following changes:

  • Added frequency entry widget to change USRP frequency
  • Also created AM and narrow FM versions

Continue reading “GNU Radio SSB/CW/AM/FM Receiver v0.6”

Binaural CW Receiver with GNU Radio and USRP

Today I felt like doing an experiment that is not quite on my TODO list – a binaural CW receiver. A binaural CW receiver is a receiver that gives a spatial feeling while you are tuning. As I understand it, you have to use stereo where the signals move from one side to the other as you tune and are in the middle when you are tuned to the frequency.

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Frequency xlating filter vs. complex multiplication

When I upgraded the simple GNU Radio receiver to single side band, I decided to separate the band pass filter and the frequency xlating filter and the frequency xlating filter got equipped with a wide low pass filter instead. The low pass filter is useful but really not important. Therefore, I decided to replace the frequency xlating filter with a simple complex multiplication (aka. local oscillator) and thereby save some CPU cycles – I figured that removing a filter would save something. Continue reading “Frequency xlating filter vs. complex multiplication”