RTL-SDR ghost signal at center frequency & hangs in GR spectrum view

Benedikt Heinz zn000h at gmail.com
Sun Apr 15 12:02:00 UTC 2012


Hi everyone,

can someone explain to me, what the origin of the ghost signal close
to center frequency is?
It can be seen at [1] and [2] - both are EzTV668 with no antenna connected.
It seems to me, that the higher the frequency, the more one can see
the "burst-like" nature
of this signal. Is this some mixer artefact from the E4k tuner?
The best workaround is probably tuning a bit off the actual target
frequency and using frequency xlate?

Also, in [3] (german) the blind spot at 0Hz due to the coupling
capacitors between E4k & RTL is mentioned.
Is it possible to replace the capacitors with 0-Ohm resistors to work
around this issue, or will this cause
other unwanted side-effects?
Or does this make no sense at all since one should always tune a bit
off and use xlate due to the ghost signal?

I guess it should also be possible (w/ some hot glue & wires) to
insert some jumpers (like OsmoSDR)
instead, so one can use the ADCs directly for LF/MF with some extra
analog stuff?

Regarding the OsmoSDR source - I also gave the RTL-source from gr-baz
a try and noticed,
that with averaging enabled in the spectrum view in GR, the top-block
GUI usually won't react to user input
any longer when using OsmoSDR, but this doesn't happen with the gr-baz
RTL source, although I used
the same sample rate in both cases. Does anyone understand why it
doesn't hang with the gr-baz source?

Thanks for your answers!

Regards,

hunz

[1] http://hackdaworld.org/~hunz/rtl-sdr/wo_ant_2m_osmo.png
[2] http://hackdaworld.org/~hunz/rtl-sdr/wo_ant_70cm_osmo.png
[3] http://www.mikrocontroller.net/topic/253371#2610540

--
Benedikt Heinz
hunz at jabber.berlin.ccc.de




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