LTDZ 35M-4400M Analyzer

(cliquez ici pour une version traduite automatiquement en français )

A year ago I bought an LTDZ analyzer, without finding the needed time to test it. It’s done now.
It is an analyzer that can be found for less than 40 € (with a casing) or around 30 € without a casing. The schematic is identical to the original D6, so with the same design errors, and the only differences concern the firmware and the size of the device. The LTDZ analyzer is the smallest one.

D6 and LTDZ analyzers

Like the D6 this analyzer suffers from a significant overload when used it in SNA mode, the TG output delivers a signal too strong for the mixer located on the input port

Original LTDZ. made with SNASharp in Raw mode, for different attenuators values.

For this reason, if you hope to made relevant measures in tracking mode, you will add (at least) 12dB of attenuators (6dB on each port), as example with these small SMA attenuators.

LTDZ with two 6dB additionals attenuators

As the D6 the input impedance is not matched, the analyzer presents about 30 Ohms instead of the expected 50 Ohms, the author having added an unnecessary 50 Ohms resistor on the input while the mixer is already matched to 50 Ohms.

Return loss of poor matched LTDZ entry

But, as expected, the matching is improved when we add 6dB attenuator.

Return of LTDZ entry with an additional 6dB attenuator

You can also improve the input matching by removing the 50 Ohm resistor..

If you have removed the 50R resistor, the entry become more sensitive and you must add 3dB more attenuation (15dB total) in tracking mode, otherwise the analyzer could saturate.

LTDZ with 50R removed. made with SNASharp in Raw mode, for different attenuators values.

At this point, the issues encountered were anticiped (because they were also present on the D6) , but the reality is worse.
I realized that the analyzer was returning wrongs values, it was exaggerating the level variations by 60% (16dB of variation for 10dB efective).
I think it’s an error in the firmware, maybe the author wanted to compensate for the lack of dynamic range of the device, by returning « amplified » results, sadly this made the measurements wrong .
To compensate this issue, i need to change vertical sensibility in SNASharp device description.
(This new setup will be available of the next SNASharp release, but LTDZ owner can edit this value on current version).
With the right sensibility, the dynamic range of this analyzer down to less as 50dB.

SNASharp device editor VerticalResolutiondB update
D6 Vs LTDZ on dynamic range evaluation, note the poor TG isolation on LTDZ

For this reason it is better to buy a D6 than an LTDZ, especially since the manufacturer of the D6 has taken into account certain comments from this blog to improve it.

Some improvements can be made on this analyzer, the same as the D6 (untested on LTDZ)

– Add attenuator on ports :

– FI filter upgrade :

– Update the firmware :

– Improve the filtering of tension booster as Peter (DL4RDR) :

David, F4HTQ.