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RTL-SDR seems deaf, any ideas?

Posted: Thu Nov 21, 2013 8:51 am
by VK2AVR
I bought an E4000 based dongle via ebay a while ago.. was trying to get it going recently to have a play around and it was quite hard to pick up meaningful signals with it.

As an example, with the included antenna it seemed pretty much useless. I replaced the PAL connector with an SMA so I could put a decent antenna on it and with a handheld whip attached it was less sensitive than my HT receiver (HT receiver could key local VHF repeater and receive almost full signal in return but the SDR couldn't see it at all). Even with a magmount antenna on the filing cabinet the SDR could barely detect the repeater output. Broadcast FM could be received but was weak and scratchy, it definitely shouldn't be in that location!

I tried fiddling with the gain / AGC settings in SDR# options but didn't make much improvement, have I missed anything or is it likely to be a dodgy dongle? (I'm tempted to get an R820T based one anyway?)

Re: RTL-SDR seems deaf, any ideas?

Posted: Thu Nov 21, 2013 11:50 am
by ZL1RS
I don't know about the E4000, but the R820T here is pretty good and hears pretty much what my 2m rig does from the same antenna ... and it really sings on 144 MHz with a 2m GaAsFET preamp in front. (My QTH is 40km away from any significant commercial transmitter sites so minimal overload effects noted). It is streets ahead of an all band portable radio with telescopic whip on the FM broadcast band ... I can hear all sorts of FM broadcast stations with a 1/4 WL of wire poked into the antenna socket that the Sony just doesn't know is there.

My dongle came with a MCX antenna socket and a cable with MCX plug to a stupid little mag-mount antenna. I chopped the stupid little mag-mount antenna off and threw it in the rubbish, then fitted a BNC plug to the chopped cable end (MCX to BNC cable) so I can connect to the various antennas here via inter-series adapters.

Sounds like you've got a dud? ... or ESD-ed the front end? ... or fried it with a nearby transmitter? ... and for the $20-odd purchase price, is it worth even trying to find the problem on the "old" one?

73,

Re: RTL-SDR seems deaf, any ideas?

Posted: Thu Nov 21, 2013 6:29 pm
by VK2AVR
Agreed, I bought an R820T based dongle on ebay earlier along with an MCX to SMA pigtail. Will try again!

Re: RTL-SDR seems deaf, any ideas?

Posted: Fri Nov 22, 2013 12:09 am
by VK5ZD
I have a DVB-T dongle (from eBay) which uses the E4000 chip and it's as deaf as the proverbial post :(

Re: RTL-SDR seems deaf, any ideas?

Posted: Fri Nov 22, 2013 8:35 am
by VK2AVR
^^ Thanks.. good to know someone else had the same experience. It seems as usual that it's luck of the draw when buying cheap stuff from unknown sources! Plenty of people have commented about how sensitive the radio is obviously they were lucky and I was not. I ended up buying the R820T version via a link on this forum praising it so hopefully it's a reputable seller this time.

Re: RTL-SDR seems deaf, any ideas?

Posted: Tue Dec 31, 2013 2:27 pm
by VK2FAK
Hi all...

Just having a read through the forum and started looking at SDR topics..

Geoff...VK2MIA how did the new purchase go, and did that fix the problem you had..? Have you found a continued use for it or just experimenting ?

Has anyone ever sourced these USB tuners inside Australia...or know the brands that sell here and which actually work..?


John

Re: RTL-SDR seems deaf, any ideas?

Posted: Sun Jan 12, 2014 6:15 pm
by VK2AVR
I'm still waiting for the hong kong purchase! Had to open a payment dispute before the opportunity lapsed.. I have a feeling it got lost in the post.

I ended up buying another dongle from rf_outlet_australia on ebay: http://www.ebay.com.au/itm/201001953564

Arrived in a couple of days!

Out of interest I just did an A/B comparison on broadcast FM. Surprisingly, the E4000 seems much more sensitive. I guess I need to work on my antennas more, since the problem isn't the dongle :)

Here are a couple of screencaps of broadcast FM, using the same outdoor antenna for each dongle. In both cases, when the station I am tuned to went silent (classical FM station) the signal peaked at -50dB. Aside from a much lower noise floor, there is also another FM station at 102.3 that is visible on the E4000 and totally masked by the background noise on the R820T. So I'd have to pronounce the E4000 to be a better tuner for broadcast FM, but sensitivities change over the operating range and I know the R820T is favoured at higher frequencies. For my test pictures attached, both tuners had RF and Tuner AGCs enabled.

E4000 tuner:
E4000.jpg
R820T tuner:
R820T.jpg
Measurements!
Some-Measurements-on-E4000-and-R820-Tuners.pdf
(448.33 KiB) Downloaded 192 times

Re: RTL-SDR seems deaf, any ideas?

Posted: Sun Jan 12, 2014 6:49 pm
by VK2AVR
Oh how I love technology, it makes you look like a muppet when you don't know what you're doing!!

The Tuner AGC on both units overloads badly in the presence of strong signals. It also gives aliases that appear as phantom radio stations.

Below is a better screencap tuned lower in the band, with the RTL AGC enabled and the tuner AGC set manually to just below the point of causing aliases (I found that an increase of one tick of AGC suddenly produced a MASSIVE alias with both dongles). The alias appears on the right hand side (where the decode marker is set on the E4000 screenshot). There's nothing to choose between them now, and I know to stay away from the Tuner AGC.

E4000:
E4000-manual-gain.jpg
R820T:
R820T-manual-gain.jpg

Re: RTL-SDR seems deaf, any ideas?

Posted: Sun Jan 12, 2014 7:04 pm
by VK2AVR
Overload with both RTL-AGC and Tuner-AGC enabled.. The E4000 handles it more gracefully I guess, only one major alias. The R820T just blots out everything if you tick all the idiot boxes :) (although it's not a conclusive comparison, Tuner-AGC performs horribly for both radios and I'm sure I could show the E4000 being worse if I tried hard enough).

Stay away from the Tuner AGC! Use the manual slider. Enabling RTL-AGC doesn't seem to cause much of a difference to performance it just moves the whole display up or down without adding any (apparent) distortion.

Also, that weaker station I "found" at 102.3 on the E4000 was an alias of the strong station at 101.3. You can see on the first E4000 screenshot I posted today, how the weak station is an exact mirror image of the strong station on the left in the waterfall. D'oh!

Summary: at least as far as broadcast FM is concerned, there's nothing to pick between them. Will have to find a consistent weaker signal to play with next.

E4000 Tuner-AGC overload:
E4000-Tuner-AGC-overload.jpg
R820T Tuner-AGC overload:
R820T-Tuner-AGC-overload.jpg