[chbot] OT: SDR

[Richard Jones]

The SDR question is a little bit like asking which is the best capacitor.

The RTL-SDR with its $8US dongle could be dismissed out of hand or may be
ideal for a given application. Its 8 bit A-D conversion with AGC, wide band
front end and frequency coverage around 24MHz - 1.7GHz has hopeless
adjacent channel performance being deafened very easily. Used within its
constraints it can be amazingly useful. I used it with an external mixer to
get both uplink and downlink into the passband for a DMR monitor. Gnu radio
was used to simultaneously record every uplink and downlink data channel
for an entire wired trunked communications site during development. This
approach allowed precise timing relationships to be measured and protocols
to be analysed as all channels originated from the same data stream. It did
require a careful level plan to ensure that uplink and downlink levels were
similar so that the 8 bit a-d could cope. All bets would be off for using
this system with an aerial, as it would depend on whether your wanted
signal was within a few dB or louder than all other signals in the passband.

So for just a few cents more I wonder what kind of performance you could
get with an addon front end filter?

I think Greg Smith contributed to an open source SDR transceiver project a
while ago. You could try asking him.

Richard

On Sun, Nov 13, 2016 at 4:17 PM, Charles Manning <cdhmanning at gmail.com>
wrote:

> I don't have any recommendations per se, but I think a lot ill come down
> to what he wants to actually achieve.
>
> There's a lot going on in SDR and it would probably make sense to start
> out in the shallow end of the pool with something like:
> http://www.rtl-sdr.com/
> USD25 or so, then figure out what he really wants to achieve and then go
> from there.
>
>
>
> On Sun, Nov 13, 2016 at 9:59 AM, Robin Gilks <robin at gilks.org> wrote:
>
>> A mate of mine in the UK asked me about Software Defined Radio, other than
>> just using a DVB-T tuner (do they have useful sensitivity?).
>>
>> As you'd expect he's looking for something that tunes from DC to light for
>> less than $1 but is expecting to pay for what he gets but can get no sense
>> of what the various offerings are capable of.
>>
>> Any recommendations?
>>
>> --
>> Robin Gilks
>>
>>
>>
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