R820T vs. E4000

Sylvain AZARIAN sylvain.azarian at gmail.com
Fri Mar 15 11:33:31 UTC 2013


Well, there can be lots of possible reasons... They are both direct
conversion receivers, with local oscillator going from low vhf to high uhf
band.
We can expect lost of silicium bugs here : power level of the local
oscillators frequency dependant, quadrature mismatch, mixers with
conversion loss not constant etc. etc.
honestly it is not easy to know; I guess this also depends on the part
itself. My experience show that from one E4000 to another, the preamps can
completely behave differently. On some units, when manually set to more
than 17db, it works as an attenuator :-( the power level received
decreases....

For me the most interesting plots were the "no antenna" ones, showing the
LO leakage ;-) If I understood clearly your plots, you have at some places
high power ghosts. Maybe you are close to powerful transmitters, but this
is more probably a LO to RF isolation problem: the receiver receives
himself...

I usually play with the E4000, but I am waiting for some 820T to try.


2013/3/15 Benedikt Heinz <zn000h at gmail.com>

> Hi everyone,
>
> although there are some comparisons between the R820T and the E4000
> already [1, 2], I also did some tests with another use-case in mind.
> I'm working on a thing similar to RTLSDR-Scanner [3]. I want to
> monitor a large part of the spectrum continuously.
> So I compared the R820T with the E4000 using RTLSDR-Scanner w/ and w/o
> an antenna.
> My results are here:
>
> https://docs.google.com/folder/d/0ByDAKwyEiyx_XzZ5ZnpRV1VZWDQ/edit?usp=sharing
> There's much more spurs with the E4000 than w/ the R820T. According to
> [1, 2] one also would expect a better overall sensivity compared to
> the E4000.
> However, the GSM900 signals for example seem to be way better with the
> E4000 according to the RTLSDR-Scanner. Tuning to a certain channel w/
> OsmoSDR Source in GNUradio gives about the same SNR - contrary to the
> RTLSDR-Scanner output. Can anyone explain this?
> Also, the DVB-T channel at 502MHz is quite weak in the R820T
> RTLSDR-Scanner output when compared to the E4000. I had a closer look
> at the lower limit of the channel in gnuradio. This can be seen in the
> 502MHz_*.png pictures. The E4000 produces a nice +20dB step while one
> can hardly see the channel in the R820T spectrum. I don't understand
> this as well. Is this AGC-related? Manually setting a fixed gain
> didn't really help though...
>
> Any explanations?
>
> Thank you!
>
> Best regards,
>
> Hunz
>
> [1] http://steve-m.de/projects/rtl-sdr/tuner_comparison/
> [2]
> http://www.hamradioscience.com/rtl2832u-r820t-vs-rtl2832u-e4000/#more-1852
> [3] https://github.com/EarToEarOak/RTLSDR-Scanner
>
>
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