This weekend I have been playing with a full duplex transceiver version of the simple DVB setup that allows to use only one computer and one USRP as a transmitter and receiver. By using separate daughterboards I can use one side to transmit and the other side to receive. Using two sets and two frequencies the transceiver can be used for two-way video conferencing over the air 🙂
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:
- Gives an SNR of at least 5dB on the spectrum scope in GNU Radio (before filtering)
- 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.
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.
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!
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?
One of the reasons I have been very excited to get the WBX transceiver daughterboard for the USRP is that with one single RF board I can have a full duplex transceiver covering both the 2 m and 70 cm amateur radio bands. This is where most of the amateur radio satellite traffic takes place, including FM, SSB, CW and packet, though modulation is really not an issue when we have a software defined radio transceiver implemented in the GNU Radio framework.
In order to use the WBX transceiver for this purpose, I need to add low noise preamplifiers (LNA) in front of the receiver and power amplifiers (PA) to boost the output of the transmitter. I need them for both bands, since some satellites are in V/U mode, others in U/V mode. Using the usual single-band devices is not optimal, because it would require 4 external devices and a bunch of wiring and switching. That could become too expensive. Therefore, I was looking for devices that cover both bands.
I have often seen wide band LNAs and PAs that would cover both bands and much more; however, I was slightly surprised to find one box that contains both LNA and PA for 2 m and 70 cm – and can even work in full duplex! This is the Microset VUR-30 which is available from Wimo.
- Dual band (144-148 and 430-440 MHz)
- Full duplex
- NF 1 dB on vhf, 1.2 dB on UHF
- 30W RF out
- Built-in duplexer?
- 256 euros
- Requires 1W input. The WBX can give up to 100mW. Hope it will work at reduced output without needing a buffer amplifier between the WBX and the VUR-30.
For some reason I can not find much details about the VUR-30, not even a photo of the rear end to see how it connects to the radio and antennas (one or two connectors, etc.). But from the brief specs and the front photo it looks promising and the price is low enough so that I can just go ahead and buy one.
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.
I have been quite busy during the last weeks doing overtime at work, nonetheless, I have managed to carry out some small on the air tests of my newly acquired WBX transceiver boards for the USRP and GNU Radio. Tonight, I tuned in to Copenhagen VOLMET that transmits AM on 127.000 MHz.
It was a good day today. At long last, I have received my WBX transceiver boards for the USRP!
I have been waiting for this transceiver board for quite some time now because I didn’t really have and transmit capabilities in the VHF and UHF bands. This board was expected to cover 50 MHz to 1 GHz, so it was perfect as VHF/UHF transceiver. On January 13, Matt Ettus has finally announced that the WBX transceiver is now available.
There were more good news in the same announcement. First, the specs have changed and the WBX transceiver actually covers 50 MHz to 2.2 GHz (instead of up to 1 GHz). The improved specifications come at an improved price, namely $450 instead of the expected $400; however, the introductory price for first batch was kept at $400. Needles to say, I ordered mine within a few days.
What do I want to do with a 50 MHz – 2.2 GHz full-duplex transceiver, you might ask… Satellites of course! With most linear and FM satellites working in the VHF and UHF band, this transceiver seems optimal. With the new specs it can even cover the 1.3 GHz L-band, which I think is used for AO-51 uplink. Even in non-amateur space communications this transceiver board provides interesting opportunities: Weather satellites on 137 MHz and 1.7 GHz, GPS on 1.2 and 1.5 GHz, space research S-band communication uplink on 2.1 GHz, and probably many more that I do not remember.
Some specs I gathered from the mailing list and Ettus website:
- The minimum noise figure over the whole band is 5-6 dB
- Typical IIP3 is 5-10 dBm
- Typical IIP2 is 40-55 dBm
- TX power 50-100mW up to 1 GHz, 30-50 mW above 1 GHz
You may say the noise figure is not too impressive and indeed, you may find something with a few dB’s better for such wideband coverage. But does it matter? You will most likely have a long coax cable going form antenna to the receiver, therefore, you will need a low noise pre-amplifier at the antenna anyway and that will improve the system noise figure significantly. Since initially I will be focusing on VHF/UHF applications, the only useful comparison for my case would be to the TVRX daughterboard, which covers 50 MHz to 850 MHz and has a noise figure of 8-10 dB. The WBX is significantly better than that.
What’s the plan?
First, I have to start upgrading my GNU Radio installation(s) to the latest development code to get the drivers for this board. Currently, most of my computers run GNU Radio 3.2.2 on Ubuntu 9.04 simply because of the convenience of having the DEBs. I did, however, make some test builds last week and had no trouble installing the current development code. So this should be no problem.
Once I have the software installed at least my laptop, I’ll take it to the lab to check the specs. Although receiver performance measurements covering the whole spectrum are available, it is always good to make the measurements yourself, just for the sake of exercise 😉
Finally, I’ll work on the software. The building blocks are all there and there are even examples implementing most of the functionality I’m looking for. Unfortunately, the proof-of-concept like examples leave a lot to be desired on the ergonomic areas of the UI. I don’t know if I’ll be able to do much better in wxPython; I have a few ideas for minor improvements that would have significant impact. In the long run, I’d like to have a C++/Qt implementation anyway.
I’ll post updates and videos as I make progress.
Edit 2010-01-27: Schematics of the WBX transceiver are now available in the Ettus document repository.
Tonight I have been testing some ham radio transceiver code written in Python/GNU Radio. It is some student project published on SourceForge. You can find the code on the project page at Sourceforge: http://sourceforge.net/projects/sdr.
As you may already know, the IC-765 has IF-shift but no passband tuning. There is, however, a simple mod originally designed by Gerd Henjes, W2ISB, which allows the IF-shift button to tune the passband while the IF-shit button is in OFF position. This mod is described in the VE3HUR IC-765 notes and reproduced here with some illustrative pictures, as well as a video demonstrating the difference between PBT and IF-shift
The IC-765 has been ICOM’s flagship HF-radio for many years. Even today (2006) it represents excellent value for money as it has one of the best receivers ever made. The IC-765 has 4 IF stages (69MHz, 9MHz, 455kHz, 9MHz), built-in power supply (PS-35) and automatic antenna tuner (AT-150), and it comes with 500Hz CW filters (mounted from the factory. Optional 250Hz CW filters (FL101 and FL53A) are available, too, as is the optional FL102 6kHz AM filter.