SDR, RTL, NWT4000, HackRF... What?

[Bicurico]

Adding this fine link: https://www.rudiswiki.de/wiki9/SpectrumAnalyzer_LTDZ

Regarding SDR, RTL, HackRF, ...

These are different type of devices altogether. They are normally based on the RTL2832 chip and use Fast Fourrier Transformation (FFT) as opposed to swept spectrum analysts (SSA). They allow "realtime spectrum analysis" on the supported frequency bandwith, which varies from around 2MHz to 10MHz (or more) depending on the devices.

This is nice for very fast spectrum refresh rate and, especially nice, because these devices allow DEMODULATION of the received signals!

However, as a spectrum analyzer they offer less precision and no tracking generator (TG) functionality. You *could* implement your own, but I have not seen any sofwtare doing so.

Then there is the problem that few devices/software support sweeping this FFT window over larger spans.

There is the ADALM Pluto, a decent and cheap device, for which there is a software implementation of a spectrum analyser.

Also, there is a nice spectrum analyser software for the HackRF.

Overall, for the RF enthusiast, I would definitely recommend a HackRF One with the Portapack. Both can be bought at fairly cheap prices from China. Such a combination offers a lot of possibilities!

Software-wise, GNU Radio is very interesting to explore, too.

Take a look at this website for further RTL/SDR based devices: https://www.rtl-sdr.com/

Regards,
Vitor

[MikeLud]

Vitor

Can you add support for joseluu D6 firmware to your software?

Thanks
Mike

[Bicurico]

Doesn't it use the same protocol?

Please test and tell me if/what adjustments are necessary.

[DH1AKF_Wolfgang]

LTDZ:
With the newest PC software from DL4JAL dl4jal.de it works like a charm. On Windows 10 .
But you have to read the manual, or, much better: the source code comments.

[MikeLud]

Vitor

The default calibration is way out see attached 0dB and noise floor sweep. Also attached is SNASharp def file, Joseluu D6 firmware works with SNASharp. I am not sure if this helps

Code: [Select]

<RawMode_0dB_Reference>2040</RawMode_0dB_Reference>
<VerticalResolutiondB>0.048</VerticalResolutiondB>
Thanks
Mike

[masterx81]

Adding this fine link: https://www.rudiswiki.de/wiki9/SpectrumAnalyzer_LTDZ

Regarding SDR, RTL, HackRF, ...

These are different type of devices altogether. They are normally based on the RTL2832 chip and use Fast Fourrier Transformation (FFT) as opposed to swept spectrum analysts (SSA). They allow "realtime spectrum analysis" on the supported frequency bandwith, which varies from around 2MHz to 10MHz (or more) depending on the devices.

This is nice for very fast spectrum refresh rate and, especially nice, because these devices allow DEMODULATION of the received signals!

However, as a spectrum analyzer they offer less precision and no tracking generator (TG) functionality. You *could* implement your own, but I have not seen any sofwtare doing so.

Then there is the problem that few devices/software support sweeping this FFT window over larger spans.

There is the ADALM Pluto, a decent and cheap device, for which there is a software implementation of a spectrum analyser.

Also, there is a nice spectrum analyser software for the HackRF.

Overall, for the RF enthusiast, I would definitely recommend a HackRF One with the Portapack. Both can be bought at fairly cheap prices from China. Such a combination offers a lot of possibilities!

Software-wise, GNU Radio is very interesting to explore, too.

Take a look at this website for further RTL/SDR based devices: https://www.rtl-sdr.com/

Regards,
Vitor

Thanks for your great answer!
In the meantime i've already taken a genuine NWT4000 35/4400 (the one without housing, i need to do one by myself), so i try for sure your software (as from what i've read, is the better one to use with this hardware)!
So you suggest the HackRF One also if it has only 8bit resolution?
And, the same things that can be done with the Portapack can be done with a pc software? As for now i'm not too much interested in portability, but maybe i can add it in future if needed.

[Bicurico]

The HackRF One is a great device works really well with common SDR software designed for RTL2832 devices.
It works nice with GNU Radio, too. The advanced functionality is all done on the PC.

The Portapack is basically a bigger case with buttons and a screen (a on new versions a built-in battery) that allows to use the HackRF One as if it was a portable radio device. If you are always using it at home, sitting on your PC, then you might not need it (it still works as a regular HackRF when fitted with Portapack).

But in order to try some attacks or to receive some special transmissions (Air, Ship, etc.) it is nice to be portable.

Regards,
Vitor

[masterx81]

When arrive the nwt4000 i'll start playing with it. If i get a bit more involved in rf i'll try the hackrf+portapack - that seem can be found in the 2.8'' variant (H2 a bit more with 3.2") at 130eur shipped from aliexpress, with 5 antennas and tcxo upgrade. Quite cheap!

[cdev]

How about building your own SDR with the ability to demodulate (not simply a spectrum analyzer) from a signal generator, a mixer, and a low noise amplifier and filters, and maybe some of those skyworks switch chips? The noise figure should be determined from the front end devices, is it possible to take a modular approach to build a receiver?

is that practical?

[Bicurico]

My guess is that it will end up more expensive than a HackRF or Pluto. Plus there is a ot of software development involved.
Hardly a reasonable task unless you want to make money out of it.

[radiolistener]

How about building your own SDR with the ability to demodulate (not simply a spectrum analyzer) from a signal generator, a mixer, and a low noise amplifier and filters, and maybe some of those skyworks switch chips? The noise figure should be determined from the front end devices, is it possible to take a modular approach to build a receiver?

is that practical?

you can use HDSDR software, it consists all popular demodulators (CW, AM, FM, SSB) and allows to pass a part of spectrum to another decoders. For example you can use DRM/DIG mode to pass the data to Dream decoder, which allows you to listen DRM stations.

Actually you don't need very expensive equipment in order to listen the radio. You can use just a simple RF generator as LO source and feed it to RF mixer. The output of RF mixer just put to the sound card input. And such configuration allows you to listen radio even without filters. Adding filters allowing you to eliminate mirror channels and improve noise floor and dynamic range.

If you want to experiment with your own signal processing, you can use GNU Radio. It provides signal processing blocks and you can put them together to configure your own signal processing structure. You don't need to know software development in order to deal with GNU Radio.

[radiolistener]

for example, you can use this RF mixer module:
https://www.aliexpress.com/item/32798750251.html

this mixer have 10 dB amplifier and allows to listen for any frequency from 0 Hz to 500 MHz. If you want to listen for higher frequencies, you're needs another mixer for GHz range.

Just connect:
- RFin to the antenna
- IFout to the sound card input
- LOin to the generator

You can use some cheap amateur generator like PSG9080 / FY6600 / UTG962 as LO source. Also you can use some more cheap Chinese RF generator module like si5351 and other. You're needs any RF generator which can produce stable frequency near the frequency which you want to listen.

How it works: you're put some RF frequency to LO input of the mixer and the mixer shifts frequencies down from that frequency. For example if you put 7000 kHz on LO input, then you can listen 7020 kHz station at 20 kHz. It shifts all frequencies from 7000 kHz to zero (DC). So, you will be able to receive it with usual sound card on any PC.

Just use HDSDR software and select sound card as input.

I recommend to use LO with signal level -20..-30 dBm (amplitude 10-30 mV) for AD831. If you use some CMOS generator with 3 Vpp output, just use 30-40 dB attenuator on the LO input. Note: SMA-male is the input and SMA-female is output for such attenuators, don't confuse otherwise the attenuator may burn out due to large amplitude. Such attenuator can handle max 2 W (amplitude 14 V) on the SMA male side, but I don't recommend to exceed 1 W (amplitude 10 V).


In order to improve reception quality, just add low pass filter with cut-off which corresponds to your sound card capabilities. For example, sound card which supports 192 kHz sample rate need LPF with cut-off below half of the sample rate. For 192 kHz it needs LPF with cut-off at about 80-90 kHz.

Also you can use BPF filter for desired frequency band on the RFin to improve dynamic range.

Of course, you can use LNA on the input to improve sensitivity, but ususal 16-24 bit sound card have good enough sensitivity to listen the radio at short wave (1-30 MHz).

[MikeLud]

Note: SMA-male is the input and SMA-female is output for such attenuators, don't confuse otherwise the attenuator may burn out due to large amplitude.

radiolistener

I did not know this, I thought they were bidirectional, attached for clarification

[radiolistener]

I did not know this, I thought they were bidirectional, attached for clarification

I burned several attenuators just out of the box during the test, just because sellers don't write warning about that.

When I burned next 30W attenuator with 5W power just out of the box, the seller wrote that this happened because attenuator is one way direction and I need to put power into SMA male connector. After that I realize why I burned several other Chinese attenuators.

Now I know that Chinese attenuators are designed to apply power on SMA male side. It's incredible, but most of the Chinese sellers who selling these attenuators, even don't know about that.

Also I found they marking SMA male connectors with "SU" mark. I think this is an indication that this side is designed as high power input.


Here is what is inside of these attenuators (this one also was burned out), you can see 0805 capacitors on the background for size comparison:

[radiolistener]

Here is another firmwarwe for LTDZ:

http://wkiefer.de/x28/test/data_LTDZ.bin
http://wkiefer.de/x28/test/data_LTDZ.hex

[DH1AKF_Wolfgang]

What does it mean:
"Here is another firmwarwe for LTDZ:" ?

I made a memory dump from my original LTDZ device and posted the link to "radiolistener".
This is the original firmware of my device.
Best regards, DH1AKF

[radiolistener]

What does it mean:
"Here is another firmwarwe for LTDZ:" ?

The firmware from your LTDZ is different from my one that I shared before.
So, now we have at least two different firmware for LTDZ.
Also firmware from D6 is compatible with LTDZ.

[Bicurico]

Changing the FW will not improve the low sensitivity/high noise level.

[DH1AKF_Wolfgang]

"Changing the FW will not improve the low sensitivity/high noise level."
... But for adjustment of my QO100 helical antenna (2.4 GHz) the original firmware was completely adequate, in combination with the DL4JAL software.