I purchased a low cost spectrum analyzer from China.
This is the LTDZ spectrum analyzer that covers a frequency range of 35 to 4400MHz, with some limitations.
The first limitation is that the frequency coverage in a single sweep is limited to 350MHz. This does make the analyzer more cumbersome to use, but id does make it possible to "see" signals up to 4.4GHz, and that I could not do before.
The second limitation lies in the type of detection. The LTDZ uses a direct conversion approach to the frequency making the signal visible twice (no image rejection) in narrow sweeps.
The analyzer does have different "IF" bandwidth settings ranging from 5kHz to 500kHz, so it makes for a fair, but far from excellent, resolution of signals in the low microwave range. I suspect the dynamic range will be the limiting factor for this device, but a good indication of spurious signals is better than none.
The model I purchased has no tracking generator, but it it in a shielded case and it does have a built-in screen and battery, making it a good portable device. Just make sure there are no strong transmitter signals nearby, if you use it with an antenna - another repair job to do. I speak from experience, I destroyed the input mixer of an LTDZ, just by having a hand-held transceiver transmitting nearby.
On the casing it says that you should have no more than "10dB" at the input. I have to assume this means 10dBm. In any case, the linearity of the mixer is probably not sufficient to make good measurements at this level, I suspect that the maximum input level for decent linearity is probably around -20dBm, but this will have to be tested.
When the device arrived the ON/OFF switch had been destroyed. I decided that, rather than having the hassle of sending the device back to China and wait for a repair, I would change the switch myself. OK, I do not have such a small switch at hand, so a preliminary, "emergency" repair has been done.
The existing switch has been removed, and a larger switch has been connected with two wires to the solder pads of the original switch. The external switch is attached to the outside of the casing, duct tape is such a good invention (if it was good enough for the astronaut on Apollo 13, it must be good enough for me ;) ).
I now have a working LTDZ.
One thing, however may need to be attended to. When it is running, the battery indicator seems to jump from a good battery level, sometimes to a zero battery level. It does not seem to interfere with the functionality, but it is annoying to see the battery indicator show an empty battery periodically.
The missing tracking generator is not a huge loss for two reasons:
I do have a NanoVNA v.2, working from 50kHz to 3GHz, so I can make filter and antenna measurements up to 3GHz. Also, when I get the software installed, I do have a PCB based LTDZ board with a tracking generator and a directional coupler covering 3.5 - 8.8 GHz (Would likely work nicely on 3.4GHz, too), so filter measurements are not a problem on the 3.4GHz band. With an external signal generator and a wideband power meter measurements of filters and antennas should work nicely on 5.7GHz.
I do have a signal generator covering up to 13GHz, and with another directional coupler (that I have) and a wideband power meter, measuring on the 10GHz band is possible.
So, in the not too far future a power meter capable of measuring up to the 10GHz band is in the planning. While I do have a bolometer HP-432A, this is not portable, so measuring antennas will be a bit tricky, therefore I intend to get a digital-readout (logarithmic) power meter up and running, and get it calibrated as well as possible.
Oh, yes, I have collected a few pieces of test equipment in my time, but a bit more is needed, now that I have entered a phase of my life with more time for experimentation.
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