Some early observations


I’ve taken the opportunity to make some measurements and comment on some on-the-air observations to see how the new FCD+ weighs in.

The noise figure on 2m and 70cm is pretty much the same as on the original FCD, at about 3.5dB. In production, I measure for 0.15uV for 12dB SINAD in NBFM because that’s much easier to measure. However I also took the opportunity to set up a noise figure measurement mentioned to see how that measured up. On 6m, the noise figure’s 2.5dB. At 23cm, I measured a 5.5dB noise figure. I used VK1OD’s NFM software in conjunction with an RFD 2305 noise source to make these measurements.

Although the TCXO reference oscillator (26MHz) specification says it’s 0.5ppm I get more like 1.5ppm when I compare it with the rubidium source on the bench. Either way, it beats the original FCD hands-down.

Comparing the receiver blocking experienced by some on the FCD at 2m, this is like night-and-day on the FCD+. Interference previously experienced that was caused by VHF broadcast (and VHF pager transmissions here in the UK) has disappeared. This is due to a number of factors, including a new LNA, 3.15V RF section and the front-end filtering.

Despite having some pretty strong local FM broadcast transmissions, airband reception just above the FM broadcast band appears unaffected, even though the same bandpass filter is used. Again, this is due to the improved LNA performance and the increased headroom in the RF section.

VHF wideband FM is super crisp and clear, no longer distorted, due to the 192kHz sampling rate.

Reception below 32MHz does not use the LNA, and goes through various specially designed passive bandpass filters. Comparing with other MF/HF receivers, the SNR seems on a par. I have not yet experienced any overloading myself on MF/HF.

On LF/long wave, the FCD+ appears a bit on the deaf side, although I’ve had no difficulty picking up RTE Radio 1 on 252kHz or Radio 4 on 198kHz with an HVU-8 antenna sat outside my kitchen window. I was unable to pick up the MSF time signal that another receiver I have here could just about resolve, but that is down at 60kHz, so out of the FCD+ specification anyway.

When receiving with a sampling rate of 192kHz with no antenna connected, there is a noise “blob” at about +/-86kHz, about 10dB above the noise floor. Interestingly the ADC manufacturer also shows this on one of their application notes. It wonders around a couple of kHz over time. It’s not clear what this is, perhaps an on-chip LDO or other votage converter, perhaps for its PLL. Once an antenna is connected, the “blob” is under the noise floor so it’ll usually be of little consequence in practice.

Many thanks, Howard

31 Responses to Some early observations

  1. Philip says:

    Hi Howard.

    If the LNA is not used below 32 MHz, why does turning it on or off in the control software have an affect.
    Very please with new Dongle, well done.

    Thanks Philip.

    • admin says:

      Hello Philip.

      The LNA on/off actually refers to the preamp stage on the tuner chip, not the front end LNA used at over 32MHz which is always on over 32MHz.

      Many thanks, Howard

  2. Chris says:

    Hi Howard,
    first let me thank you for nice christmas parcel, wich arrived a few days ago.

    I can also see the “blobs” in the spectrum on the band edges. But there is another effect, which I recognized, while tuning along 80m. If a signal disappears on the upper end it appears on the lower end only for a few kHz. For example I heard a ham at 3,4MHz in LSB, who in reality sent on 3,6MHz. If I tuned on the edge of the spectrum, I could see the signal on the upper and lower end of the 192kHz spectrum. It’s no mirroring because sideband wasn’t changed. I confirmed this also with a 2m beacon signal and several kind of software.

    I wish you a happy new year 2013!

    Chris, DH3CS

    • admin says:

      Hello Chris

      Many thanks, yes right at the edges, particularly in the filter skirts, you’ll see the antialiasing effects as although the digital filters are sharp, they’re not perfect.

      Thank you, Howard

  3. Bill McCourt - WF1L says:

    I have just purchased my FCD and await it’s delivery. What type of antenna should be used? My station uses long wires for the HF amateur bands. Will these work adequately?

    I’m hoping to use this radio to supplement my receiving during contests and DX-ing.

    Bill – WF1L
    Reston, VA

    • admin says:

      Hello Bill

      If they’ll match reasonably well to 50 ohms there should be no problem, you may already have an ATU there anyway.

      Many thanks, Howard

  4. Scott says:

    Hi Howard

    I received my Pro + over the Christmas Holiday. What a great device. Even more fun to mess around with than my Icom R9500. I’ve been using it for everything from SWLing (including PSK31) to decoding pager services and DRM. Very pleased! Well Done!

    Thanks, Scott

    • admin says:

      Hello Scott

      Glad you’re enjoying it! IT was a lot of fun playing with it when I first developed it back in August, pretty much reinvigorated my own SWLing.

      Many thanks, Howard

  5. jose says:

    cooperation could tell me please, reception sensitivity and HF has the Funcube Dongle Pro +.
    Thank you very much.

    • admin says:

      Hello Jose.

      The sensitivity on HF is lower than on VHF and above. This is deliberate as the ambient noise floor on HF is much higher than at higher frequencies, so providing single-digit dB noise figures would be of no practical use on HF.

      I do however test the sensitivity across HF as part of my testing procedure by testing SINAD with a narrowband FM signal and typically an FCD+ will achieve 14dB SINAD for a -108dBm signal. Compare this with 12dB SINAD on 2m for a -123.4dBm signal.

      The HF sensitivity is on a par with other HF receivers, and indeed during development I used other commercial HF receivers as a yardstick for comparison.

      Many thanks, Howard

  6. Mike says:

    Received my FCD Pro + very quickly after ordering. Thanks Howard for a fun device.
    I have noticed 2 oddities I hope you can comment on:

    Testing the FCDPP with SDR# v1.0.0.1000 on Windows XP
    If I increase the centre frequency with the up arrow on the ‘Center’ text field, the graticle markings on the FFT move to the left as expected (we are moving up the frequency scale), but the signal peaks in the FFT move to the *right*, the opposite direction. This also means that if a peak is off centre, and you place the Frequency line over the peak, it shows the incorrect frequency of the peak, even though it receives the audio fine. Something is switched around left-to-right here, I think its the direction of increasing frequency of the FFT. I dont know if this is a problem with SDR# or FCDPP?

    Second issue when using FCDPP with gnu radio 3.6.4 on Linux and gnuradio-companion. If you have a sketch with a Funcube Dongle source, when the sketch is executed, I get an error message oin the gnuradio-companion error window:
    audio_alsa_source[hw:1]: unable to support sampling rate 96000
    card requested 192000 instead.
    My tests seem to indicate that in spite of the message, the gnuradio funcube source does indeed open and read the dongle at 192ksps, and the dongle does indeed provide 192ksps. But the warning is odd. If I edit the source code of gr-fcd/lib/ and set the sampling frequency to 192000, recompile gnuradio, and test again, there is no warning message, but I dont detect any change in operation.
    Is that expected? Is the USB device always going to operate at 192ksps no matter what?

    • admin says:

      Hello Mike.

      Originally I designed the FCD+ with multiple native sampling rates.

      However, in Windows, the way that the OS chooses the “best” (cough) rate overrides the 192kHz rate and left us with a maximum of 96kHz. The only way I could figure out how to make Windows use 192kHz sampling was to only give it that option. A shame, I must’ve burned a week’s worth of work on supporting multiple sampling rates natively. In Windows all those lovely sampling rates were recognised, but it wouldn’t let you select the 192kHz option.

      So the only USB sampling rate supported natively currently is 192kHz with 16 bit depth. You can’t have 192kHz with 24 bit or higher depth as it is not supported in full speed USB due to the maximum 1023 byte isochronous buffer size per 1ms frame. I did have it working perfectly with 48kHz/16bit, 48kHz/32bit, 96kHz/16bit, 96kHz/32bit and 192kHz/16bit supported in the firmware, and I’ve left it in the source code, although anything other than 192kHz/16bit is #defined out during the compile stage.

      However, I found that other operating systems simply resample for you in the OS anyway so I didn’t consider it a problem.

      Many thanks, Howard

      • Mike says:

        Could sample rate be managed through the API? If you have the code already maybe non-windows applications could make use of it. It could default to only offering 192 to fool windows.

  7. Mike says:

    Hi Howard,

    Thanks for your reply about sampling rates.
    But what about the issue with SDR#. Do you see the same behaviour with SDR# as I described above?


    • admin says:

      Hello Mike

      Not sure I understand exactly what you’re saying, but at a guess did you remember to swap I/Q as per the FCD+ manual?

      Many thanks, Howard

  8. Mike says:

    Ah, that fixed it.

    • admin says:

      My pleasure!

      Historically, the “standard” I used for I/Q matching L/R stereo channels is the same as that used for Spectravue. The reality is that although I tried to use a standard, there isn’t one in reality.

      Many thanks, Howard

  9. Ken Brown G3XQE says:

    Hi Howard;
    I have a new FCD Pro Plus purchased from Martin Lynch.
    Everything installed as per instructions and working but I have a problem with a large amount of digital noise even without an antenna connected.
    When I connect my antenna 2m or Hf the displayed signals are of the same level as the spiky noise signals. On your U tube demo video I do not see this noise.
    I was wondering if you use a powered hub or powered extension lead with a linear power supply to help with the noise ???
    Any suggestions gratefully received as at the moment I am a disapointed customer.

    Regards Ken G3XQE

    • admin says:

      Hello Ken

      Thank you for your email.

      You definitely shouldn’t have digital noise everywhere. Can you email me some screen prints please? g6lvb at amsat dot org.

      Many thanks, Howard

  10. Ken Brown says:

    Hi Howard;
    Thanks for your prompt reply, below is an update.
    When I received the Dongle, I intended to run it with SDR Consol V2 (Preview) but was not able to get it to talk to the dongle so I followed your recommendation and and installed SDR#. I was so unhappy with the switching noise and poor signal to noise ratio that I put the dongle to one side and have not used it until receiving your request for screen prints.

    When I fired up the dongle and then SDR# to produce screen prints, I immediately noticed that the signal to noise ratio was much improved and after producing the screen prints, I decided to try SDR Consol V2 again. After some head scratching and and exploring I finally figured out how to get it to talk to the dongle and to my great suprise, there was no switching noise present at all and and the signal were nice and clean. I spent most of yesterday afternoon and evening playing with the setup on 20m and 40m cw with no sign of switching noise ???

    My PC is an old P4 2.5Ghz IBM ThinkCentre machine running XP Pro.
    The dongle is connected via a 2m long USB extension cable.
    This machine is a little slow for the 198kHz sampling rate and stutters when Windows goes off and does one of it’s mysterious background operations and the cpu useage as indicated by task manager goes up to 100%, as a result I am running at 98khz sampling rate which covers the CW ends of the bands nicely.

    I have just started the system again while typing this to ascertain that things are still working ok with SDR Consol V2 and they are so I am happy but I don’t know why but it is obviously software related rather than Dongle hardware.
    My screenshots using SDR# will be on the way to you shortly via email.

    Regards Ken G3XQE

    • admin says:

      Hello Ken.

      Sounds a bit weird that it’s suddenly resolved itself, but I guess that’s a good thing, although it sounds like you’re like me, it’s nice to know what went wrong initially so that it can be fixed properly.

      Many thanks, Howard

      • Ken Brown G3XQE says:

        Hi again Howard;

        Well ran SDR # again today and found the same problem, the switching noise is the same amplitude as the wanted signals on 40m CW.

        Looking at a previous post about sampling rate, think this may hold the key with SDR Sharp the screen says the Dongle is connected at 198kHz sampling rate but the operating system is re sampling at 98kHz and I have the problem. Running SDR Console V2 Preview I am given the option of selecting 98khz sampling rate which when selected tels me the Dongle is connected at this speed and I have no noise problems.

        I am guessing that the difference is that the lower sample rated is selected and used with SDR Consol but is called on the fly with SDR# and this is causing the problem.

        I hope this may help others who run into this problem and think it is a harware problem with the Dongle. Perhaps it might have been a good idea to leave the sample rate selectable in Dongle as originally programmed ???

        Bye for now and good luck with the supply of Dongles.

        Ken Brown G3XQE

        • admin says:

          Hello Ken

          Thanks for your update.

          What’s interesting is that part of my test procedure that I use on every unit uses Spectravue at 96kHz sampling rate.

          Now it is possible that the host software that has a problem attempts its own resampling rather than using the OS’s integrated resampling.

          The standard sampling rates by the way should be 96kHz and 192kHz: if it’s using 98kHz and/or 198kHz that is quite hard to resample.

          Many thanks, Howard

  11. I just got my fcdpro+ yesterday and amd running it with HDSDR thanks to Mike’s dll.

    After copying HO68, FO29, CO65, and CO66 this morning, I’d say that the pro+ is more sensitive than the flex5000, more stable the the rtl el cheapo dongle and controls well from an old GrafTrak derivitive tracking doppler with the frequency rolling so fast I cannot read it with straight line waterfalls (at audio). Antenna is a m2 eggbeater fed with 50 ft of 1/2 inch Heliax. No mast-head preamp (yet).

    Nice job guys. HF reception is an added bonus.

    Richard W5SXD

  12. Tony Peiffer says:


    Received the FCD+ late last week.

    Had a chance to work with it this weekend, and I am impressed.

    This SDR has performance equal to or better than any WB receiver or scanner I have ever used. I have had no issues with front end overload, even here in NYC!

    Thanks for a great piece of gear, at such a reasonable price!

    Tony P., W3AAP
    Brooklyn, NY, USA

  13. Paul PD0PSB says:


    I’m running 2 FCD pro+ devices remotely via SDR-Radio V2.
    Both of these have an antenna switch adressed by the bias-T voltage, connected to a V/UHF dualbander and a HF/6/4m dipole.

    In this way I can switch antennas and receive location from the SDR-Radio V2 program.

    The FCD P+ performs surprisingly well on all of its coverage. I use them for HF,sporadic E bands, broadcast, sattelites, utility, airband,etc,etc..

    In fact the combination with antenna switching and remote control over SDR-Radio V2 is so much fun, I hardly use my “expensive” SDRs anymore (Perseus, FDM-S1,SDR-IQ)

    When SDR-Radio V2 gets a public network it will be so much fun using all those dongles on the globe.

    Thanks for such an amazing little device!

    (I can highly recommend building a 5v antenna switch to use from the bias-T supply, it opens many possibilities and is very easy to build)


  14. Paolo says:

    I appreciate the mods You added to FCDpro.
    But now I am in strong doubt and have a question for You.
    Can the signals outing from the new FCDpro- plus be
    elaborated as the signals outing from the FCDpro???
    In internet I found plenty of literature and applications
    related to, like WIRESHARK and OMOCOM, but all refere
    to FCDpro version. Has the new FCDpro-plus the same
    funcions like the previous FCDpro ???
    Tnx in advance
    Paolo Cavallo

    • admin says:

      Hello Paolo

      The FCDPro and FCDPro+ have fundamentally the same USB interfaces: standard USB HID and standard USB Audio. However, the USB product ID (PID) for the FCDPro+ is different because the USB Audio descriptor is different to support the increased bandwidth. If the USB PID was the same, Windows would get confused between the Pro and Pro+ as Windows caches the USB descriptors.

      There are also some changes to the control interface that runs over USB HID between the two devices, where it was not appropriate given the different hardware used. However basic things like setting the frequency are identical.

      If you have software that already supports the FCD if it has not already been modified to deal with the FCD+, it is easy to change it as the underlying interfaces are identical.

      The USB PID for the FCD is 0xFB56 and for the Pro+ it is 0xFB31.

      Many thanks, Howard

  15. Vince says:


    How can I tune FCD+ LNA Gain and mixer gain? It is not possible in the control interface. Many thanks,

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