Shared Link: https://eax.me/arinst-vna-pr1/
ARINST VNA-PR1 is a portable vector network analyzer for frequencies from 1 to 6200 MHz. The device allows you to build VSWR graphs and measure the input impedance of antennas, measure the frequency response / phase response of filters and amplifiers, find breakdown points in coaxial cables, and solve other practical problems. The retail price is $ 560. Let's look at the pros and cons of the device, carry out several experiments with it, and also find out what is inside.
Note: I would like to thank the again patrons of this blog . Such reviews are possible thanks to your support. I am also grateful to Crocs for the special conditions for providing the device for review.
Main characteristics
ARINST VNA-PR1 looks like this:
This is a box measuring 135 x 80 x 27 mm (excluding connectors) and weighing 367 g. Attentive readers may already have noticed a slight oddity in the photo. The device uses RP-SMA connectors, into which adapters to SMA are inserted. Moreover, factory calibration is performed with adapters. This is done to extend the life of the device. It is not the device connectors that wear out, but the adapters. They are easy to replace.
The device is powered by a built-in 5000 mAh Li-Ion battery. The claimed battery life is 2.5 hours. In reality, it turned out to be more than 4 hours. But perhaps this is because the battery is brand new. Full charge time is 3.5 hours, according to the documentation. The measured time turned out to be slightly longer, by 20 minutes. Charging is carried out via the mini USB connector.
The touchscreen is resistive, with a diagonal of 4 "and a resolution of 800 x 480. Technically, you can use it without a stylus. But pressing work with varying success, and the screen quickly collects handprints. Better to start a stylus. It is not included in the kit.
It is allowed to input a signal with a level of up to +10 dBm and a constant component of up to 25 V. The signal power of the tracking generator does not exceed -5 dBm. The declared dynamic range when measuring S21 is > 60 dB at 1-1.5 MHz, > 80 dB at 1.5-4500 MHz, > 70 dB at 4.5-6.2 GHz. According to the documentation, the error in measuring the magnitude is 0.25 dB, and the phase is 0.7 °. The last statement is true provided that the device is warmed up for 5 minutes and the room temperature changes by no more than ± 3 ° C. Frequency resolution - 100 Hz at 1-100 MHz and 10 kHz at 100-6200 MHz.
Experiments
First of all, it was decided to measure the antenna SWR from the TP-Link N600 router, on which we at one time installed OpenWrt :
Unfortunately, ARINST VNA-PR1 cannot save screenshots in BMP or PNG, and I had to photograph all the graphics. Don't judge strictly the quality of the pictures.
The router has two RF connectors and two antennas, which are completely indistinguishable in appearance. Most likely, an antenna operating simultaneously on the 2.4 GHz and 5.8 GHz bands was used. It was decided to put this antenna together with the router in duplicate, so that the user would definitely not confuse anything. In this case, the SWR at 2.4 GHz is a bit high, but considering the influence of any metal objects on my desk, this is normal. Other antennas have been tested for these frequencies. In all cases, the device showed something believable.
For example, here is the input impedance of a conventional 2.4 GHz dipole:
The dipole was made from an SMA connector and two copper wires. to suppress Ferrites were common-mode currents used . The measurement was carried out through a short piece of LMR-200 cable with low losses at this frequency. The theory says that we should see an input impedance of ~ 73 ohms. We got it.
In the spectrum analyzer mode, the device also works:
Here the frequency response of the "reference" notch filter at 88-108 MHz is measured. Previously, we measured it with NanoVNA , RTL-SDR and noise generator , as well as Rigol DSA815-TG . It is easy to make sure that the graph is identical to those obtained earlier. In the photo you can see that the device is also aware of the phase response of the filter.
Let's complicate the task and measure the CW quartz bandpass filter :
The device copes. But the bandwidth of this filter is only 320 Hz! The filter insertion loss is the same as previously measured, up to the stated device uncertainty.
I won't bore you with a bunch of graphs. I will just say that I did many other measurements with the ARINST VNA-PR1. The device coped with the task in all but one case. I was unable to measure the inductance of the coils at 1 MHz. Instead of inductance, the device always showed "inf uH". If we translate the displayed complex resistance into inductance, then we get some kind of nonsense. I contacted the manufacturer about this. It turned out that this is indeed a bug. It has already been eliminated in the new firmware version.
We open the case
Let's see what's inside. The user manual [PDF] describes how to properly disassemble and assemble the instrument. You may need to do this when the battery is used up. The block diagram of the device is also provided.
Let's start with the display. This is how it looks from the reverse side:
These displays can be found on eBay for “4 inch lcd module 800 x 480”. It's good. If something happens to the display, it will be easy to replace.
There is a battery under the display:
The battery, as we have already found out, is Li-Ion with a capacity of 5000 mAh. Its size is 90 x 60 x 7 mm. The battery is glued to the board with double-sided tape. As far as I could figure out, there is nothing under the battery. Therefore, I did not tear it off.
In the photo you can see small boards that are attached to the main one with bolts. They provide electrical contact with the housing. The side boards are 1mm thick, just like the main board. Why this is done is not entirely clear. Perhaps at some stage in the development of the project, a certain building was chosen, and with this technique it was possible to accurately fit into its size.
From the reverse side, the board looks like this:
The marking reads "07/31/2020". Here we see all the main components:
- Microcontroller STM32H743;
- 40 MHz crystal oscillator;
- The three chips labeled "9939 AUB" are most likely the MAX9939AUB programmable two-channel amplifiers ( datasheet [PDF] );
- Six white cubes "LTC 455DU" - piezoceramic bandpass filters with IF 455 kHz and bandwidth 20 kHz ( datasheet [PDF] );
- Winbond 25Q32JVSIO - ordinary SPI flash ( datasheet [PDF] );
- BQ24297 - Li-Ion battery charge controller ( datasheet [PDF] );
- QUK TI38K ADXD and QUJ TI73X 1619 are voltage regulators manufactured by Texas Instruments. According to the structural diagram, one should be at 3.3 V, and the second at 5 V;
Some of the components are hidden under the screens. The screens could be ripped off, but I didn't want to. There is a risk that the calibration will go down the drain. Fortunately, you can find out what is under them using the materials on the manufacturer's website :
- The two chips labeled "2871E" are MAX2871, 23.5 MHz to 6 GHz ( synthesizers datasheet [PDF] ). These chips are located under two different screens;
- Under one of the screens, the MAX2871 is located along with the good old Si5351 . According to the structural diagram, it can be assumed that it uses two channels (Gen 2.1, Gen 2.2). Considering the frequency resolution of the device, I wouldn't be surprised if the Si5351 is used at frequencies of 1-100 MHz, and the MAX2871 comes into play higher;
- The ADL5801ACPZ are used in a quantity of three. These are mixers for 10-6000 MHz ( datasheet [PDF] );
On identifying the main components, my interest in the internal structure of the ARINST VNA-PR1 waned, and it was decided to return the device to its previous form.
Conclusion
There is a lot going on at frequencies between 1 GHz and 6 GHz. It houses the 2.4 and 5.8 GHz ISM bands along with Wi-Fi, Bluetooth and ZigBee. Equipment and FPV for quadcopters and many radio modules work here. Here the radio amateur band is 23 cm (1240 MHz), which, in particular, is used by the satellite AO-92 . Also here are ADS-B (1090 MHz), Inmarsat (1546 MHz), Iridium (1620 MHz), GPS (1228 MHz, 1575 MHz), 3G and 4G mobile networks, and much more.
In Russia, an “adult” spectrum analyzer and directional coupler for these frequencies (for example, Rigol DSA875-TG and Mini-Circuits ZHDC-16-63-S +) cost $ 9000 + at the time of this writing. ARINST VNA-PR1 for significantly less money allows you to solve the same problems. Besides the price, ARINST VNA-PR1 has other advantages. These include, for example, the ability to measure phase response, portability, and quiet operation. Of course, the device also has its limitations. Its dynamic range, frequency resolution, and uncertainty are inferior to serious laboratory instruments.
I hope you found this review interesting. If you still have questions about the device, feel free to ask them in the comments, and I will try to answer.
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