FA-SDR-TRX, an allband & low budget SDR TRX

In its october edition, the German Ham Radio magazine Funkamateur started about an multi-article series of an all-band 1-Watt SDR transceiver called FA-SDR-TRX. Read here a first assessment.

Update #1: Here are some pictures of the FA SDR TRX prototype:

First pictures of FA-SDR-TRX

Update #2: Meanwhile I have written a much more detailed review. Its split up into three articles:

FA-SDR-TRX – part #1 – a Systems View

FA-SDR-TRX – part #2 – the Receiver

FA-SDR-TRX part #3 – The Transmitter

This is the first review I published:

During the last few years the publisher Funkamateur expanded his portfolio wisely. He started to offer kits for the most popular devices described in their magazine. Probably the most famous ones are the scalar network analyzer (FA-NWT), an antenna analyzer (Design: DL1SNG) and a series of singleband lowcost SDR receivers. The latter one is a kind of Softrock clone which I personally use in at least 3 different applications. Probably the most important one is a bandscope in an FT1000MP

In the recent edition Harald Arnold, DL2EWN started a multi series article about the FA-SDR-TRX, a 1Watt 160m – 10m SDR transceiver. Before we go into detail the following information beforehand: There will be kit available, most likely in November 2009 January 2010 March 2010 at the end of April 2010. The price for the basic version will be round about 100€ 124€ (~170USD).

As typical for a Software Defined Radio, the FA-SDR-TRX makes maximum usage of the PC. Both, transmission and reception signal are fully processed in the soundcard of the attached computer. To keep the PCB in an handleable format, SMD components were used. I suppose that the kit will come as usually with all SMD parts premounted so that no SMD soldering will be necessary.

Receiver

The starting point for the receiver was the design of Funkamateur’s singleband SDR receiver IQ-SDR4080. It’s a simplified softrock clone which was designed by Klaus Raban, DM2CQL. However several improvements have been implemented over time. Now in the final version, there isn’t too much left from the original design.  The FA-SDR-TRX receiver uses a Tayloe sampling mixer and an SI570 crystal based oscillator to make it tuneable on all frequencies. To avoid unwanted mixing signals, the antenna signal is filtered through a modified DL7AV preselector. Apart from the passive part of the preselector, a lownoise, high dynamic range buffer amplifier was added to ensure a high S12 attenuation so that the local oscillator (LO) signal of the receiver’s sampling mixer doesn’t radiate through the antenna. Prior to the preselector, a 6dB or 12dB attenuator can be switched in, to avoid overloading of the receiver.

Transmitter

The transmitting part consists basically of an sampling excitor, using the same SI570 as LO. To keep the transmission signal as clean as possible, harmonics have to be removed. Therefore the FA-SDR-TRX makes usage of the receivers preselector. In case of a transmission, the mentioned amplifier is used for two purposes: First, to assure 50 Ohm matching to the sampling exciter. Second, to drive the follwing 1W amplifier.

Amplifier

The amplifier is designed as a modular “plugin” device. This shall ensure, that at a later stage it might be replaced with more powerful 5-10W amplifier.

The transceiver can be tuned via USB from the known SDR software like PowerSDR or Rocky. Here the designer of the FA-SDR-TRX incorporated a kit, containing the SI570 and an USB controller. This kit was designed by DG8SAQ and DL1SNG. It’s already available as a kit (FA-SY1) in the shop of the publisher Funkamateur.

Measurements

These are the performance characteristics, measured with the prototype:

MDS = -123dB (80m)

MDS = -127dB (10m)

IP3 > +15dBm (2kHz spacing) (includes +13dB gain of the buffer amplifier)

IP3 > +27dBm (2kHz spacing) (mitigating the 13dB gain of the buffer amplifier with the 12dB attenuator)

IMDR3 > 90dB

Sideband Surpressing >35dB (without Software)

Sideband Surpressing >70dB (with Software)

Pout =<10mW (without 1W amp)

Pout =< 1W (with 1W amp)

Image frequency surpression -60dBc (using 1W amp)

Carrier surpression -65dBc (using 1W amp)

Harmonics -50dBc (using 1W amp)

Personal opinion

Unfortunately the kit still isn’t available The kit will be available in March 2010 most likely available at the end of April 2010. However the measured figures and the design itself look promising. I believe that especially the low price will make it again a very successful kit within the European SDR community. It’s a pitty that none of the Funkamateur articles are available in English language. My wishlist for this device would be a slightly higher level of automation. This could include an automatic switching bandpass filter instead of the manual-tuning preselector and a software-switchable attenuator.

The complete article is published in Funkamateur 10/09 – page 1085 – 1089.