[NLRS] FunCube

[Dr. Gerald N. Johnson]

Or maybe the SDR-IQ for wide range and great dynamic range at the same time.

73, Jerry, K0CQ

On 12/29/2013 10:22 PM, Doug Reed wrote:
>
>
> The Funcube was developed shortly before software developers found out
> the DVB-T dongles could be used as SDR receivers. The Funcube uses the
> E4000 tuner chip but instead of using the RTL2838 chip to generate IQ
> data, it uses a stereo audio A-D chip to generate IQ data.  (That is
> not the right terminology, but if you recognize how wrong the
> description is, then
> you know what I'm trying to say.)
>
> As result of the E4000 tuner, the Funcube and DVB-T dongles cover the
> same 64MHz-1700MHz range, with a hole around 1100MHz. As result of the
> A-D IQ process, the Funcube provides 12-bit(?) data at a 96KHz data
> rate versus the DVB-T stick providing 8-bit data at up to 3.2MHz(?)
> data rate. The IQ data rate means the Funcube can show a 96KHz slice
> of the band with about 90dB dynamic range, while the DVB-T dongle can
> show up to a 3MHz slice of the band with 48dB dynamic range. (I didn't
> verify these numbers but they are close.)
>
> NOTE, the lower dynamic range does not directly translate as lower
> receive sensitivity. It does determine if I can show the difference in
> signal levels within the receiver's bandwidth as determined by the IQ
> data rate. It may help you visualize the issue if you think of a
> receiver S-meter that goes to S8 as the max rather than S9+30dB.
> Within the limitations of the receiver (chip) you can hear the same
> things but can't tell how much stronger one is over the other.
>
> In practical terms, the higher dynamic range is a good thing, just
> like it would be in any other high-performance receiver but the type
> of applications you can run is limited by the bandwidth provided by
> the IQ data rate. For any typical ham radio modulation, the 96KHz
> bandwidth is entirely practical. Even for use as a 2M panadapter. But
> you can't due a quick spectrum analyzer display of a transmitter
> without using software to combine multiple sweeps. However the DVB-T
> dongle can't display enough dynamic range to be useful for FCC
> readings....
>
> Bottom line, "you pays your money and you takes your pick."
>
> If you are looking for your "first" SDR receiver, I still recommend
> the DVB-T dongle using a R820T tuner chip. For under $20 you can get
> your feet wet and learn what SDR can do by finding how the DVB-T
> limitations effect what you want to do with it. In most cases, the same (or at
> least similar) SDR software will work with either dongle and all other
> SDR hardware. Once you have an idea what you want SDR to do, then you
> can decide what SDR to buy for your next venture. You may decide the
> $200 Funcube isn't what you want for a second step or you may be
> entirely happy with it. .
>
> It has been over a year since I did any research on what was new in
> SDR hardware. The DVB-T and Funcube dongles are both "old news." The
> last time I looked, some groups were trying to develop high-speed
> high-dynamic range interface hardware to use for SDR. If there is a
> new generation of USB3.0 interface in a 12-bit or 14-bit RTL2838-type
> chip, we could see a really nice generation of pocket size SDR
> hardware coming.....
>
> The problem is that high-speed A-D chips are difficult to design and
> more difficult to build in real hardware. That is one reason we tend
> to have two "groups" of SDR hardware. I would call it the "audio"
> group of SDR hardware that uses a stereo audio A-D to get 96KHz
> bandwidth, or a "high-speed" group of SDR hardware that uses faster
> A-D chips with less resolution.
>
> Of course the real limitation of the DVB-T and Funcube is that they
> are receive only. Wouldn't it be fun if they could transmit too????
> But to be a practical transmitter I think you will need to use
> something more than an 8-bit D-A since you need to control modulation
> products more than 60dB down....
>
> My suggestion would be to concentrate more on the applications you
> wish to run and less on the hardware. What makes SDR fun is the
> software can turn the hardware into almost anything. If any of your
> applications require more than 96KHz bandwidth, you have eliminated
> 98% of the off-the-shelf SDR hardware. If you need to display more
> than 50dB of dynamic range, you have eliminated the DVB-T and similar
> hardware. If you want to display 90dB dynamic range and more than 1MHz
> bandwidth, then you need deep pockets to buy a late model
> Rhode-Schwartz or Agilent spectrum analyzer.  :-)
>
> 73, Doug Reed, N0NAS.
>