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

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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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Improved AGC for the simple SSB receiver

Few days ago I wrote about how I upgraded the simple double side band receiver implemented in the GNU Radio Companion to a simple single side band receiver. This initial implementation used some default values for the AGC attack and decay rates. These values were acceptable; however, I wanted to spend some time trying to find better values that would correspond to Fast, Medium and Slow AGC – just as we are used to in commercial radios.

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Simple SSB Receiver in GNU Radio Companion

The simple SSB software defined radio receiver is now functional!

Few days ago I wrote about how to upgrade the simple double side band receiver to single side band. The modification was supposed to be very simple and involved changing the band pass filter from using real taps to use complex taps. The upgrade wasn’t quite as easy, though.

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From double side band to single side band reception

Simple CW receiver 0.3When I presented the Simple CW Receiver few weeks ago I also mentioned and demonstrated that it is actually a double side band receiver (it’s around 2:35 in the video). This is good for AM and FM, but can be very inconvenient for receiving CW and SSB (single side band). If the station we are trying to receive is surrounded by other stations on the neighbouring channels, these will interfere via the opposite side band. Therefore, it was time to look into single side band reception.

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WBX receiver sensitivity in CW

After finishing the initial “smoke tests” on the 5.6-5.9 GHz receiver setup – in particular the KU LNC 5659 C PRO down converter, we decided to measure the sensitivity of the WBX receiver over the whole range. We define sensitivity in this respect as the weakest CW signal that:

  1. Gives an SNR of at least 5dB on the spectrum scope in GNU Radio (before filtering)
  2. Produces a clearly audible signal in the speaker

This corresponds roughly to the weakest Morse code signal we could decode using the receiver and while it is definitely not a universal measure for the performance of the receiver, it is a good figure to compare with other ham radio equipment. Noise figure and IP measurements are available from Ettus Research.

I already had some very good results on the air with the WBX receiver and transmitter but I was excited to put some numbers on this “goodness”.

The USRP/WBX receiver was connected directly to a well calibrated signal generator using 50 cm of AIRCELL 5 coax cable. The computer was running the Simple CW Receiver V0.3 🙂

We found that a -130 dBm signal is clearly detectable over the whole range, which is quite good. The screenshots below were all taken using a -130 dBm signal, except the 70 MHz measurement, which was taken using -133 dBm. As you will see, we increased the RF gain at the higher frequencies to get a better SNR. Click on the images to get a full resolution screenshot.

WBX receiver on 70 MHz WBX receiver on 145 MHz
70 MHz using a -133 dBm CW signal. 145 MHz using a -130 dBm CW signal.
WBX receiver on 435 MHz WBX receiver on 1296 MHz
435 MHz using a -130 dBm CW signal. 1296 MHz using a -130 dBm CW signal.
WBX receiver on 1.6 GHz WBX receiver on 2.1 GHz
1.6 GHz using a -130 dBm CW signal. 2.1 GHz using a -130 dBm CW signal.
WBX receiver on 2.2 GHz
2.2 GHz using a -130 dBm CW signal.

Simple CW Receiver V0.3

Just a quick note before I’m leaving to OZ7SAT for the smoke tests of the KU LNC 5659 C PRO low noise down converter – attached to the USRP+WBX.

I had some time to improve on the simple CW receiver by adding the frequency translating filter to allow easy tuning within the sampled spectrum. This feature was missing from the previous versions because I did not know how to specify the filter taps parameter of the gr_freq_xlating_fir_filter_xxx block in GRC. Of course, all I had to do was RTFM to find out. GRC is smart enough to allow entering complete python statements (including function calls) for parameter values, so all I had to do was to create a variable filter_taps and use firdes.band_pass(1, samp_rate, low, high, trans, firdes.WIN_HAMMING, 6.76) as value, then use filter_taps as parameter for the xlating filter.

OZ7IGY beacon with GNU Radio, USRP and WBX

I was playing with GNU Radio, the USRP and the WBX daughterboard tonight preparing for the tests of the 5.7/5.8 GHz receiver setup tomorrow. For some reason that I can not remember, I have decided to tune in to 432.471 MHz – the UHF frequency of the OZ7IGY beacon, which is located approximately 50 km (24 mi) from me.

I knew I could receive it even when I am inside using my FT-817 but I didn’t really expect to receive it with the USRP+WBX. Well, I was wrong. Already with the lousy multi-band whip I could hear it. It wasn’t strong but I could hear it. I decided to try with the Arrow antenna and voila, suddenly I could receive it with 40+ dB SNR!

Watch in high definition on YouTube or get the 80 MByte .mov file.

The software was a slightly modified version of the simple CW receiver I posted yesterday, implemented in GNU Radio Companion. The modification consisted of adding a waterfall display after the band pass filter. I have included the GNU Radio flow graph at the end of the video, the one below is without the waterfall display:

So, what do you think, how does the CW sound in a so simple software defined radio?

Simple CW Receiver with GNU Radio

I have been playing with GNU Radio and GRC (GNU Radio Companion) over the weekend and I ended up implementing a very simple CW receiver. This will be very handy on Tuesday when we will be testing the 5.8 GHz UNITEC-1 setup for the first time using the OZ7IGY beacon on 5.76093 GHz. Here is a quick video demo of the receiver where I use my Yaesu FT-817ND to transmit a test signal.

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