FA-SDR-TRX part #1 – Systems View

FA-SDR-TRX-Software-Defined-Radio-PCBThe FA-SDR-TRX is an allband low cost software defined radio. The FA-SDR-TRX was created by Harald DL2EWN an described in an article series in the German Ham Radio Magazine Funkamateur. After the big success of the single band kits like Softrock, SDR4080 or Genesis, the FA-SDR-TRX is the next step in the evolution of SDR kits. Thanks to the support of Harald I’m able to provide a detailed description of the concept behind FA-SDR-TRX.

Related  Posts:

FA-SDR-TRX part #2 – The Receiver

FA-SDR-TRX part #3 – The Transmitter

First pictures of FA-SDR-TRX

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



Harald, DL2EWN’s motivation was to create a software defined radio platform which can receive and transmit on all amateur HF bands (160m…10m). The receiver shall have very good characteristics and the transmitter shall be capable to deliver a clean 1 Watt signal for a serious usage on the bands. The whole transceiver shall be located on a single PCB, but maintaining the flexibility to use the receiving part without having assembled the transmitting path. Having in mind that the FA-SDR-TRX will be assembled by a lot of Hams with different skills, reproducibility of it’s performance was an important requirement. Even if the kit contains SMD components, all of them will be pre-mount on the PCB to simplify assembly. A modular design and the use of inexpensive and widely available components shall ensure an affordable price.


The fundamental components of the FA-SDR-TRX are illustrated in the drawing below:


The transceiver consists out of the 7 major components:

  1. ATT – Attenuator
  2. BPF – Band Pass Filter / Preselector
  3. BUFFER AMP – Buffer Amplifier (actually its part of the preselector)
  4. GEN – Signal Generator
  5. MIXER Rx – Quadrature Sampling Detector (QSD)
  6. Mixer Tx – Quadrature Sampling Exciter (QSE)
  7. AMP – an optional 1Watt amplifier

The FA-SDR-TRX provides the following interfaces:

  1. RF Input – Antenna Signal
  2. Audio RX – Receiving stereo IQ signal – to be connected to LineIn on the Soundcard
  3. Audio TX – Transmission stereo IQ signal – to connected to LineOut on the Soundcard
  4. USB – Tuning the Frequency, CW Signal and PTT
  5. CW – External CW Key

Shared components

The FA-SDR-TRX is sharing some of it’s components between the receiving and the transmitting path. The following drawing shows the grouped components.


Attenuator and RX Mixer are exclusively used by the RX path. Amp and TX Mixer are used exclusively by the TX path. Bandpassfilter, Buffer-Amp and the Signal Generator however are shared components. They are used by both, the RX and TX path.

Block Diagram

This block diagram shows the interaction between the components:

FA-SDR-TRX-with-RX-and-TX-pathPlease note that this is a simplified view

FA-SDR-TRX Receiver

So, lets get into more detail. We’ll start with the receiving part of the FA-SDR-TRX. Meanwhile, the Transmission path is greyed out.

FA-SDR-TRX-with-RX-pathThe RF Signal is fed into an attenuator. Even if the overall performance of the receiver is very good (IP3  >15dBm [actually IP3 would be +28dBm without the buffer amp] and IMDR3 >90dB) an attenuator was implemented to avoid overloading the receiver with too strong signals (e.g. 49m band). Passing the attenuator, the Signal is filtered in an adjustable bandpassfilter / preselector. The following buffer amp (SGA5289) ensures a 50Ohm match to the following stage and suppresses unwanted radiation of the QSD’s switching frequency. The amplifier is an MMIC with 13dB gain.  The following Mixer is a Quadrature Sampling Detector providing the IQ baseband signal for the soundcard. Several classical switching-ICs (FST3253, MAX4614, 74HC4066) were tested. The, still quite unknown 74LVC4066 showed the best results. Making maximum use of existing components, the proven FA-SY1 generator (Si570) was implemented. The FA-SY1 provides a USB interface to tune the frequency.

FA-SDR-TRX Transmitter

The next illustrations shows the transmission path of the FA-SDR-TRX.


With the help of a PC and it’s soundcard, an IQ (stereo) Signal is fed into the TX-Mixer. The frequency of the Quadrature Sampling Exciter is tuned with the Si570 generator (the same which is used by the RX). At this stage, the output power of the QSE is about 1mW. Unwanted Harmonics and intermodulation products are suppressed by the passive preselector. The buffer amp boosts the “cleaned” signal to 10mW. Intermodulation products are with -56dBc well below the carrier. Image frequency surpression is with -60dBc also ok. Before sending the signal on the air, the FA-SDR-TRX allows the use of a 1-Watt amplifier (RD00HHS1 MOSFETs). This amplifier is optional and realized with an additional PCB which can be plugged in the FA-SDR-TRX PCB. However this Amplifier is not part of the FA-SDR-TRX kit. It has to be purchased separately.

Stay tuned

I hope that this article gave you an overview about the concept behind this allband software defined radio. kit. In further article I’ll explain the mentioned components in greater depth. Maybe I’ll also be able to provide the schematics, but this has to authorized by the publisher Funkamateur.

Kits will be available in January 2010. Orders are already taken. If you are interested, you might consider to place an order. Usually the first batch of Funkamateur kits are sold out early after the release. The kit is called BX200 and costs 124€ (approx. 180 USD). Please note that the Si570 Signal Generator (FA-SY1) and the 1-Watt Amplifier (not available so far) have to be purchased apart.

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. donde puedo ver los circuitos ?

  2. Hola Alfredo!

    los circuitos estan publicados en tres articulos de la revista “Funkamateur”. Estan en los numeros Oct/2009, Nov/2009 y Dec/2009. La revista esta en aleman. Desgraciadamente no se puede descargar los
    articulos. Le propongo de comprar el CD anual de 2009. La CD cuesta 12,90€ y contiene todos los articulos de la revista de 2009. Mandan el CD en todo el mundo. Aqui puede encontrar el CD en el online-shop: http://bit.ly/57Y7Sa .

    73 Toby

  3. Hank Wolfla says:

    Please advise when this kit might be available for purchase and if you have an instruction and construction manual available.

    Thank you,

    Hank Wolfla
    Greenfield, IN

  4. Hey Hank,

    the FA SDR TRX kit should be available at the end of March 2010. As soon as the kit or additional information is released I’ll post an update on this website!

    You might also check directly the publisher’s webshop, where the kit is listed as “BX-200”

    73 & enjoy SDR,

  5. I wait for the kit ! available at end of May only
    Do you think it may work also on 6m with the right filters ?

  6. Kees PA5CW says:

    Just build the FA-SDR, most time took the software installation, read carefully.
    1. replace DLL from CD
    2.in Power sdr define Softroc at setup with correct xtal freq from si 570,
    then select flex1000 as tranceiver!

    Also tick the USB box, or else PTT will not work.

    (seems strange but else you dont get flat frequency on display).

    Kees PA5CW

  7. Carmelo says:

    I’m IW4BYK and I have a question to ask in the FA-SDR kit proposed FA-SY1 and the new FA-SY2 be used both? Which is better to use?
    And another, I can use FA-SY-SP to directly control the frequency of FA-SY# using FA-SDR?

    Many thanks for your very comprehensive article.

    Regards, Carmelo Toscano.

    • Hi Carmelo,
      it is very likely that FA-SY2 is NOT working properly with the FA-SDR-TRX. The reason is, that FA-SY2 provides (a much lower) LVDS level. On the other hand, FA-SY1 provides CMOS level.
      It is not possible to control the FA-SY1 in a FA-SDR-TRX with the FA-SY-SP out of the Box. However changing the controller in the FA-SY1 might be a feasable workaround. But take into consideration that PTT and CW won’t be available anymore with the changed controller.

  8. Tore Sandström SM7CBS says:

    I tried to find the e-mail to DL2EWN with no sucess! But I hope you Tobias can comment some questions.
    I am not so good in german so I hope information will be in english one day. So my wunderings….:
    1. Is it possible to put in the 5 watt PA instead of the 1 watt?
    2. As far I can se there is no QSK so one has the manually change from tx to rx.
    I prefer CW and have full qsk in my TS940. Any idea when this kit will have automatic qsk?
    3. I have built some softrocks kit and know that the sidetone will have a delay that make it difficult to use the sidetone for doing CW manually. But you have probably solved this? If not…when and how do you plan to do it?
    I am very interested so I need to know above before decision.
    BTW. There is a SDR-IF from USA called LP-PAN and it can bu used as an IF-rx to my TS940 that has an IF of 8,83 mHz. Would it be possible to by such a FA-SDR for just that frequency from you?
    Tore Sandström SM7CBS

    • Hey Tore,

      Coming back to your questions:
      1. The FA-SDR-TRX is designed to host max. 1 Watt PA. Due to physical and thermal limitations it is not possible the interchange the 1 Watt PA with the 5 Watt PA. However the 5 Watt PA can be used as a separate component with the FA-SDR-TRX. in this case there is no need for the 1Watt PA, the few milliwatts output power are sufficient to drive the 5 Watt PA.

      2. No, the FA-SDR-TRX does not provide any QSK. as far as I know there is not a single SDR based TRX available which provides QSK like your TS-940. Maybe the Flex5000 is the transceiver which can provide you a kind of QSK. This is a difficult topic since it involves latencies, buffering within your sound card and the way they are integrated in the operating system of your Computer.

      3. What kind of computer are you using with your Softrock Kits? Similar to the Full-BK issue, latencies and computer speed can have major impacts on realtime events like using your CW key.

      4. absolutely, you can use the FA-SDR-TRX on 8.83 MHz as an Bandscope attached to your transceiver. Just be sure that you don’t transmit into the IF stage of your receiver!

  9. Hi Tobias,
    few days ago I have received FA-SDR, which contains FA SY1. All is well, except CW does not work. To use CWX keyboard is not solution for me, as I am using logging program with external keyer K1EL. I am asking for advice, how can I connect keyer on to FA SDR?

    Niko Safaric S53A

    • Hey Niko,
      Could you provide us with some additional information? Can you produce a CW Signal with a straight key connected to the FA-SDR?
      Did you perform the modifiaction of FA-SY1 in order to use it correctly with FA-SDR?

      73 Tobias

  10. Hi Tobias,
    thank you for your quick answer.
    Straight keying does not work despite the change of level of CW input signal at pin 18 of SY1, which is modified according to instructions. As well it does not work PTT via the serial port using RTS. Iam using X61 tablet computer and its soundblaster as I/Q primary card .
    Niko, S53a

  11. Dear Tobias,
    I found a mistake. In the original FA distribution is an incorrect name for driver extension “Sdr 1kUsb.dll-09jan”. The mistake is small, so I need two days to rename it :):) . Hand keying is enabled now.

    Niko S53A, 9J3A

  12. Hi Tobias, I just ended to build my FA-SDR – It works pretty well and seems really confortable to use. I just received a call from another french builder who needed help. So the user community grows up. Do you think a google or yahoo group could help – may be one exists that I don’t know ?

  13. hi tobias,

    my rf input signal 5mw with frequency 24M and 27Mhz and i am designed rf amplifier stage as per as that datasheet but write now i am not succeeded to amplifier rf signal so can you help me.
    i need output 1w


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