FMDX – DAB+: my logblog!

April 16 2021 – LNA and DAB

Posted on 2021/04/162021/04/17 by FMDX

The other day I bought a Low Noise Amplifier from Amazon UK.
The device is designed by RTL-SDR.com.
Inspired by Nils Schiffhauer’s review of Qirx 3.1.2 Beta (part 1 and part 2) it was time to check out the RTL-SDR + LNA + Qirx 3.1.2 Beta combo.
Data was always gathered in the same time span and with the same antennas.

Reception conditions were flat during these observations, no lift at all.

With nesdrSMArtee the same results are obtained. However the BIAS TEE cannot be switched off when using nesdrSMArtee!

Click on the pictures below to enlarge them.

Wideband LNA purchased from Amazon.

My set-up: coaxial lead to the Emme Esse stacked antennas is about 20 metres in length.

SNR (db) readings in Qirx are virtually equal when using a LNA or not. There’s certainly no deterioration in signal quality when using this LNA.

With the LNA hooked up to the RTL-SDR Qirx’s AGC does a great job and the Gain (db) drops considerably.
You can switch off the AGC and go for manual Gain settings, but there’s no need to do so: Qirx’s AGC works just fine.

The LNA performs very well when considering Strength in Qirx. Strength is represented on a scale from 0 to 1.
Nearby strong transmitters at my QTH like Veltem, Liège or Wavre are of the same ‘Strength’ with or without the LNA.
However more distant transmitters showing up in the TII are a different matter and spectacular improvements can be seen.

Conclusion

Do you need this LNA next to your RTL-SDR when doing some serious DAB listening?
It all starts with a good rotatable antenna with a clear view and positioned as high as possible and not too long a coax lead. That’s of course almost impossible, so one needs to find a satisfying compromise.
When there’s no lift or ‘conditions’ at my QTH there’s not much of a difference when using a LNA. No muxes are found which could not be heard under normal conditions, although signal strength has definitely and considerably improved.

What will happen when there’s a great opening like e.g. on December 29 2019?
We’ll have to wait and see…

To be continued.

Update April 17 2021.

A quick indoors test: a laptop with a short whip. QIRX and RTL-SDR with or without LNA.
Without the LNA 4 muxes can be received. With the LNA 5 are captured.
The test was done several times and always the same results were obtained.

April 15 2021 – Qt-DAB: R820T vs RSP1A

Posted on 2021/04/152021/04/15 by FMDX

As mentioned in the previous post QT is a great tool to explore the world of DAB.
It works well with RSP1A and AirspyR2.
However R8220T dongles are not that great with QT. As can be seen in the video below this text there is indeed a big difference in performance between R820T and RSP1A. The antennas used were the same in both cases.

April 9 2021 – Comparing Qt-DAB and QIRX

Posted on 2021/04/092021/04/10 by FMDX

DAB DXing has become a quite popular niche in the European DX scene. Distances up to 800 km can exceptionally be covered.
Of coures a good antenna is advised. I’m quite happy with my stacked Emme Esse aerials.
Good DAB radios are not too expensive, but I prefer using SDR hardware like RSP1A, AirspyR2, RTL-SDR and nesdrSMArtee as these fine pieces of kit are affordable and offer some great possibilities when using software like QT-DAB and QIRX. Qt-DAB is being developed by Jan Van Katwijk (NL) and QIRX by Clem Schmidt (D).

What’s the best set-up with this hardware and software? Opinions differ as some set-ups are amazing for certain users and a disappointment for others.

Time for a quick test and review. All ‘eyes and ears’, no fancy equipment which I don’t master anyway.
SNR (db) readings are compared in different configurations.

1. RSP1A with QT and QIRX.
This is clearly a great set-ups and differences between QT and QIRX are mininal.
If you want to do some serious DAB DXing this is a good choice.

RSP1A
	QT 3.71	QIRX 3.1.2
5D	21,5	28
6D	26	24
7A	11	16,2
8D	20	20
9B	7,5	7,5
11A	20	27
11C	15	12,2
12A	26,5	24,5
12C	17	13,5

2. RTL-SDR (R820T) with QT and QIRX.
The RTL-SDR (R820T) dongle is a very compact and cheap alternative for an Airspy or an RSP1A.
RTL-SDR and QIRX perform extremely well.
However QT struggles with R820T and some strong muxes just won’t decode data at all. It also produces lots of audio dropouts, which can be countered by carefully fiddling with the settings.

RTL-SDR and nesdrSMArtee are on par.
After running a while RTL-SDR becomes pretty warm, while nesdrSMArtee becomes hot, even warm when hooked up to a pc that is turned off (drawing current from the USB port).

RTL-SDR (R820T)
	QT 3.71	QIRX 3.1.2
5D	12	28
6D	18	21
7A	–	17
8D	–	21
9B	9	8,5
11A	20	25
11C	–	12,1
12A	17	25
12C	–	13,4

nesdr (R820T)
	QT 3.71	QIRX 3.1.2
5D	12,5	28,5
6D	19,5	21,5
7A	–	16,7
8D	–	21,5
9B	9	8,4
11A	20	25
11C	–	12,7
12A	17	22,5
12C	–	13,5

3. Airspy R2 with QT and QIRX.
The numbers look great and both QT and QIRX seem to do well. QT and AirspyR2 are in my set-up a match made in heaven. Decoding is swift and accurate.
QIRX and AirspyR2 don’t like each other. 5C DR Deutschland from Aachen, next to powerhouse 5D DB+VLAANDEREN2 from Veltem, is impossible to decode.
11C DAB+ from Eys and 11D BXL-BW1 from Wavre are tricky.
Sometimes QIRX will only run after a few tries and after closing it down a background process keeps running.

AirspyR2
	QT 3.71	QIRX 3.1.2
5D	18,5	26
6D	26,5	24
7A	17	21,5
8D	20	22,5
9B	15	12,5
11A	20	24
11C	18	12,5
12A	24,5	24,5
12C	20	16

What’s the final verdict? Which is the best set-up in my view?
6. QIRX+Airspy
5. QT+R820T (5C – audio dropouts!)
4. QIRX+RSP1A
3. QT+RSP1A
1. QT+AirspyR2 and QIRX+R820T.

April 7 2021 – Qt-DAB 3.71 released

Posted on 2021/04/072021/04/07 by FMDX

Today Jan Van Katwijk released Qt-DAB 3.71.
What’s new?
Qt-DAB 3.71 differs only in two details from the 3.7 version
1. for Linux only, it is possible to configure for use with pluto-rxtx rather than pluto, in which case – on selecting pluto
as device – the audio output is transmitted as stereo FM signal, augmented with the text of the dynamic label as rds.
2. the snr view now shows the snr measurements directly, i.e. over 10 measurements a second. The output can be compressed by a setting in the configuration widget.

Download Qt-DAB 3.71 here.

April 4 2021 – QIRX 3.1.2 Beta released

Posted on 2021/04/042021/04/06 by FMDX

Clem Schmidt today released QIRX 3.1.2 Beta.
DAB: an audio spectrum has been added.
The audio dropouts problem with RTL-SDR dongles, due to sporadic sample losses, has been tackled.
WFM: new stereo decoder and a de-emphasis filter.

Tons of small errors cleaned, like the empty small tooltip boxes.

Let the installer delete your qirx3.config, because the new Audio Spectra got new entries in the config file.

Download QIRX 3.1.2 Beta here.