VMA Simple Spectrum Analyser: Geekcreit® Spectrum Analyzer USB LTDZ 35-4400M is now supported!

Hello,

Today I received the Geekcreit® Spectrum Analyzer USB LTDZ 35-4400M, available here:

Geekcreit® Spectrum Analyzer USB LTDZ 35-4400M

This is the "new" version, that comes with a metallic case:

Front view: RF connectors and two status LED's showing current operation mode

Back view: Micro-USB connector, button to turn TG on/off and two status LED's:

Power on/off and TG on/off 

And indeed it did not work with my software, as many of you told me.

After some analysis, I figured out the issue: this particular device uses the "a" command instead of the "x" command. The difference, as explained in the LinNWT manual is:

As of firmware version 1.14 there are new commands:"a": This command is similar to the "x" command, but in this case a time value in microseconds is specified for a pause between each measurement.

The original SMA/NWT devices work fine with the "x" command, but this LTDZ device does not recognize the "x" command and only works with the newer "a" command. But that is not all: I found out that the pause needs to be at least 10 microseconds, otherwise the device will hang.

So I added the required settings to the latest version of my software, which you can download here.

When you configure this device in the setup tab as shown in this picture:

the minimum pause of 10 microseconds will be considered, even if the Wait ComboBox in the Spectrum tab shows "0 us":

The spectrum shows my CATV spectrum composed of 60 analogue channels and 9 DVB-T transponders.

Selecting a higher Wait period did not produce any noticable differences.

Because values higher than 90 microseconds traditionally ended up hanging both my software and the device, I replaced the preconfigured pause times to more reasonable values.

So what do I think of the LTDZ?

Unboxing:

1. It is cheap: I bought it for little over 50 Euro plus shipping. It arrived in around two weeks.
2. It is considerably smaller than the original SMA/NWT devices!
3. The case looks actually quite good, it has a nice finishing and some labels. Also, there are a total of 4 LED's to signal IN/OUT ports operating, TG ON/OFF and general power ON.
4. It uses a Micro USB connector instead of the much bigger USB-B connector.
5. No accessories were included, except for the USB cable.

Performance:

Well, performance is even worse than the unmodified D6 JTGP-1033!

The background noise at -70dBm is similar to the D6 JTGP-1033, but the sensitivity is really bad. 

This device cannot be used for radio DX or satellite DX, as the signals are normally at -60dBm and as such almost invisible to the LTDZ.

Here are three pictures showing my local DVB-T transponder:

SMA/NWT:Noise floor is -80dBm and sensitivy is good.
The DVB-T transponder can be seen clearly and measurements are can easily be done.

Unmodified D6 JTGP-1033:

Noise floor is -70dBm and sensitivy is worse.
The DVB-T transponder can still be seen, but measurements can only be carried out using the Average trace, as there is too much noise on the Live trace.

LTDZ:Noise floor is -80dBm and sensitivy is really bad.
The DVB-T transponder practically cannot be destinguished anymore, except for some additional noise where the transponder should be shown. Impossible to measurements on this transponder.

Conclusion:

My software does now support this device, but please bear in mind that the quality of the LTDZ is directly proportional to the money it costs!

Unless you want to measure signals above -60dBm, do yourself a favour and buy a SMA or NWT device from BG7TBL. The refresh rate is a bit slower, but at least you will be able to do proper measurments.

Regards,

Vitor