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

FA-SDR-TRX FunkamateurIn 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.


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.


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.


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.


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)

Building up the FA-SDR-TRX

Here is a video of DO1HBF which shows the assembly of his FA-SDR-TRX in fast forward.

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.



About Tobias (DH1TW)

Self-confessed Starbucks addict. Loves to travel around the globe. Enjoys the technical preparations of Amateur-Radio contests as much as the contests themselves. Engineer by nature. Entrepreneur. For more, follow him @DH1TW


  1. Thank you for this article – I do hope you do some follow articles. This could well get popular this side of the pond also.

    73 de Ken H. K9FV

  2. Tobias, thank you for the Softrock Group post. I have just begun using a Softrock Lite for an Elecraft K3 bandscope. I am excited that for the first time in many years with SDR technology it is possible to build your own high performance receiver and transmitter. I am adding Funkamateur and your website to my list of internet favorites. I know enough German to make my way through the articles that interest me.
    73, Dick, AD7AF

  3. James Williams says:

    Tnx for info…

  4. Art, KY1K says:

    I’m involved in a similar project called the MOBO.

    I note your reference to a DL7AV preselector, which can potentially replace allot of individual tuned circuits and is very much needed by the softrock community. Where can I get information on the DL7AV preselector?



  5. Hi Art,
    You can find the original paper of the BCC (DL7AV) Preselector on the webpage of the Bavarian Contest Club at http://www.bavarian-contest-club.de/projects/presel/presel.pdf Unfortunately it’s in German. I suggest the following step:
    1. Download the PDF with the schematics
    2. Use Google Translate (http://bit.ly/cLJtM); it’s give you a rough idea about the content

    73 Tobias

  6. I worked YU1LM in CQ WW CW with new G9 xcvr! I was SOAB HP even without CW Skimmer. I prefer preselector with two serial circuits in series and coupling capacitor in the middle directly on 50 Ohm. Not suitable for 10/15 m but two more in/out caps can be added. I had SMD 1 uH and 4,7 uH coils.
    Nice to hear OM Tom, DL7AV mentioned. My article on FT1K IF SDR with 455 kHz ceramic resonator tuned 12 kHz lower in serial resonance is in forthcoming CQ ZRS with due credit to Toby, DH1TW.

    MX & HNY & LP MMM S56A, N1YU

  7. Herbert says:

    Gut zu Wissen. Kommt hier noch ein Folgeartikel? Möchte gern mehr darüber wissen. Könntest du mir per Mail eine Antwort geben?

  8. Kees PA5CW says:

    I have the FA-Syn working.

    It was shortcut in pcb.

    Kees PA5CW

  9. Mark Vice says:

    Great post!

  10. Würde etwas Hilfe benötigen. RX funktioniert einwandfrei – TX macht Probleme. Sender schaltet auf Sendung, es geht auch Leistung raus … aber kaum messbar…. auch dann nicht, wenn die 1-w-PA aktiviert wird. Stromaufnahme steigt auch nicht an. Die Aussendung ist ein Pfeifton … auch wenn nichts am Eingang hängt. Mit R1 und R3 sollte man auch noch die Spiegelfrequenz unterdrücken können …. hier weichen die von mir gemessenen Werte aber von denen der FA ab …. und wenn man die Schleifer verstellt, verändert sich die Spannung auch nicht …..

    Irgendjemand ne Idee??

    Vy 73’s

    PS: Mail-Adresse findet ihr bei QRZ.com

  11. Kees PA5CW says:

    Is the software installation correct:
    1. new DLL from CD rom
    2. First define softroc si570 and tick the usb box
    3. define flexradio as tranceiver.
    4. is transmit enabled

    If you push transmit, you should see dBm in screen and when you talk, cariier in screen should move.

    Do you use 2 soundcards with softrock?
    You need 1 for receive and 1 (EMU) for transmit.
    Kees PA5CW
    mail also in qrz.com

  12. Kopke says:

    Today i received the kit: I was stunned about the good quality of the kit.
    I can really recommend it!

    Be aware that beside the SDR kit, at minimum you need the FY-SY synthesizer kit as well.
    I also ordered the 1W amplifier kit and the casing for the kit.
    The latter is also of very high quality.

  13. Arnaud Vivé says:

    Dear Tobias,

    despite many trials, i didn’t succeed to suscribe to your newsletter.

    Can you help me ?

    Thanks and vy 73’s


  14. Hello,

    I am very deep SDR fan! Unfortunately, I am not able to find the above mentioned article, published in FA 10/2009. Is it possible to have a copy?

    2nd question, where is possible to order complete set?

    With friendly regards

    Vit, OK5MM

  15. Mike says:

    Hi Tobias, I’m a ham from Italy. I have built the sdr-trx and I hope that’s a very good product. I have only difficulties with the adjustments in the software (power sdr 1.9.0-sr40 version) and the hardware (in particular calibration of the frequency of the synth, position of the trimmers on the fa-sdr board).Can you help me? Exist a manual in english for the adjust? Many thanks and bye from Mike – Italy –

    • Hey Mike,

      sure, I’ll be glad to help, however I’m not sure if I understood your problem correctly. Could you please try to explain the software and the hardware problem to a little bit bigger externd? As far as I know, there is no English manual available until today. However it’s always a good idea to check directly with the kit producer at http://bit.ly/9riHtn

  16. Arnaud Vivé says:

    hey Tobias,

    Thanks about your website and your newsletter

    1 – I ordered a full Fa-sdr kit and i’m waiting for its delivery with impatience!

    Do you know where we can find some feedback and comparison between Fa-sdr and the others SDRs ?
    Are the users satisfied ?

    2 – Do you know if an RF amplifier for increasing power to 15/20 w is in progress ,

    73s ++ Arnaud F6BZG

    • Hey Arnaud!

      I’m not aware of any webpage / article which is comparing the FA-SDR specifically to other SDRs, but be assured that the measured results are very competitive.

      Regarding the Amp: Harald, DL2EWN also published recently an article about a very linear 5Watt QRP PA. The kit is also available from Funkamateur at: http://bit.ly/9uaKJt

  17. Hi everybody,

    I ordered the FA-SDR kit and got it very quickly, within a week. Good service! Another highlight was that all smd’s were pre-soldered on the PCB. All I had to do was to solder axial components in place and other electromechanical components like relays, rotary switches and connectors. It took me one evening to complete the job. With software “Rocky” I was able to receive all amateur bands and the sensitivity seems to be adequate, too.

    I also made an one-way contact with my ham radio fellow living about 6 km’s away. He relayed back my 10 mW signal on 2 metres…but it was really a QRPP contact.

    Yesterday I received the 1W PA kit. It was also a nice kit, everything was straightforward and now I have the PA plugged in place. I also adjusted the idle current of the PA fets according to the instructions. It seems that I can get one watt or so out of the transceiver.

    Which is really pissing me is the lack of instructions how to adjust the trimmers on TX chain. Nothing seems to happen when adjusting those damn things. There is a table which suggests to adjust them to certain voltages on a couple of bands but I think it is not enough. I also find the PA output very dirty. How do I adjust the phase and amplitude to get the mirror carrier at minimum, that’s the problem.

    Can anyone help me please.
    Kai OH3WE

    • Hey Kai,

      have you already tried to get in contact with the customer service of Funkamateur?
      The output signal of the FA-SDR is quite good. So there seems to be a problem with your kit!

      73 Tobias

  18. miro says:

    Hallo Tobias,

    Write here, or (om7atx@sanynet.sk) please source web “kapazitive antenne 80m” from Your video FA-SDR. Thank You.

    73, Miro.

  19. Giorgio says:

    Hi all,
    being really interested on FA-SDR kit, wonder if RIT function is provided.
    Thanks a lot.

    • Hi Giorgio,
      RIT is provided with the software package of your choice (e.g. Rocky or PowerSDR). It is not a feature of the Hardware plattform. Which is by the way, one of the big strength of SDR.
      73 Tobias

  20. greg says:

    Hi all

    Is there a possibility to add rotary encoder in simple way to FA-SDR-TRX ?
    Maybe someone done that before ?

  21. Jack says:

    hello where you can order a kit FA SDR TRX please link to the shop You are cordially greet the 73 sp9xu


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