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Discussion in 'Software Defined Radio (SDR)' started by N2DTS, Jun 30, 2021.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

  2. N6YWU

    N6YWU Ham Member QRZ Page

    The Raspberry Pi SDR product, linked to above, appears on eBay in versions either with or without the Raspberry Pi included.

    The RaspberrySDR receiver appears to be a slightly lower cost clone of the KiwiSDR design (http://kiwisdr.com),
    except using a Raspberry Pi 3 as the compute platform underneath the ADC+FPGA, instead of a Beaglebone Green,
    and using a 16-bit ADC instead of a 14-bit ADC.

    Here's a test report from last year on some of the differences between the KiwiSDR and RaspberrySDR :
    https://ka7oei.blogspot.com/2020/09/comparing-kiwisdr-and-raspberrysdr.html

    The software interface is via your web browser to a server on the Pi, no extras programs to install,
    and there appear to be a large number of KiwiSDR sites online for you to try, perhaps some in your region :
    http://kiwisdr.com/public/

    There appear to be several of these small no-front-panel networked SDR projects and products, including the above 2, the Hermes Lite 2 QRP transceiver, the Radioberry Raspberry Pi hat, the Red Pitaya 122-16, and others.
     
  3. N2DTS

    N2DTS Ham Member QRZ Page

    Thanks for the info and link, looks interesting in a very basic way.
    I find the web based sdr's lacking over a Flex or Anan, or a radio like the 7300.
    I guess its more compressed and simplified to work over limited bandwidth.

    There are a lot of sdr rigs around, from cheap to expensive, but not many cheap direct sampling 16 bit ethernet based receivers
    for sale.
    One that ran a version of Powersdr would be nice.
    The airspy HF discovery plus works well but its usb (latency) and the programs are not quite as good for ham use.
    The Hermes lite 2 is not bad but has limited dynamic range and you pay for a transmitter you may not want.
     
  4. N6YWU

    N6YWU Ham Member QRZ Page

    The Red Pitaya 122-16 is an ethernet based SDR with dual 16-bit ADCs and DACs. The Red Pitaya 122-16 is around twice as expensive as an HL2. The 125-14 is less expensive, but only has 14 bits. Neither includes a Tx power amplifier (just an approx. 10 dBm output), so good for Rx only, multi-band skimming, or as a test signal generator. I've run a 122-16 over ethernet from the same software I use to run my HL2. I would add a bandpass filter, and an controllable attenuator/LNA in front of the Rx input.

    Both the 122-16 and 125-14 appear to currently be in-stock and available from DXEngineering.
     
  5. K4PP

    K4PP Ham Member QRZ Page

    I use a Red Pitaya 125-14 for RBN. I know the 122-16 has the 50 ohm input. I have to a run transformer on the input of my 125-14 because of the high input impedance.
     
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    You can do the same using a USB SDR and RPi3. No Fan required.
     
  7. N6YWU

    N6YWU Ham Member QRZ Page

    I run my SDRs (both USB and ethernet types) from Raspberry Pi's as well. But another advantage of a networked SDRs (other than low latency) is that I can also run them remote over the network from a laptop computer or iPad or even from my iPhone, all of which have 10X+ more compute power than a Pi. My M1 MacBook supposedly has a fan, but the Mac runs cooler than my Raspberry Pi 4's, so I've never heard the fan.
     
  8. KX4OM

    KX4OM Ham Member QRZ Page

    Right, and it is an even lower cost USB "dongle" as the other part. In other parts of the world, these dongles are TV VHF receivers that plug in via USB. Some companies have modified and commercialized them for down-converting SDRs for HF frequencies. In their native form, they are $10 devices on eBay and elsewhere. RTL-SDR and Nooelec are two of many companies who sell these SDR sticks. Many hams started out in SDR with these devices. Typically they are 12-bit devices, whereas SDRplay's SDRs are 14-bit. FlexRadio 6400 SDR are 16-bit. The more bits, the better. That determines the sampling capability.

    Also, the Raspberry Pi is not a "chip", it is a single-board computer (SBC) that runs (free) Linux for an OS. The "16GB" that is touted in the eBay add is a 16GB microSDcard, and 16 GB is about the lowest you can buy these days, $7 on Amazon. The Raspberry Pi Model 3B+ is still being sold for $29 (I have one, along with a Model 1 B+ and two Raspberry Pi Zeros, but it is not the latest PI; that would be one of the Model 4 devices, which need a better heat sink, and the have between 2 and 8GB RAM, priced accordingly.

    In my opinion, there is a whole lot of pure profit in that "SDR" on eBay. Especially considering that there is a lot of free SDR software out there.

    Ted, KX4OM
     
  9. N6YWU

    N6YWU Ham Member QRZ Page

    That RaspberrySDR uses a very different radio front-end than a much cheaper 8-bit RTL-SDR. It’s far more similar to the kiwiSDR, with a 66 MHz direct sampling ADC plus a Xilinx FPGA, which results in a far more costly BOM, but provides a lot more bandwidth (enough for multi-band skimming), more ADC bits, as well as lower latency (due to direct GPIO connection to a Raspberry Pi 4), than any RTL2832U based USB dongles.

    No idea how well the ones on eBay work. But Don’t confuse the two very different receiver designs.
     
    KX4OM likes this.

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