Dynamic Attenuation Dynamic attenuation tracks the input signal level, automatically adjusting the reference level to protect the MSB in situations of high RF signal levels, or enhancing the instrument sensitivity in situations of low-level RF signal input. With the built-in preamplifier, dynamic attenuation automatically activates or de-activates the preamplifier according to signal environment. Additionally, the MSB can conduct a series of spurious measurements when analyzing a wireless base station transmitter, and can use field strength mode to measure propagation and coverage or to pinpoint electromagnetic leakage in broadcast systems. The tracking generator function can be used to measure gain, frequency response, flatness and even return loss of wireless communication systems. Multilingual User Interface The new multilingual user interface features on-screen menus and messages in 6 different languages English, Chinese, Japanese, German, French and Spanish. An internal speaker or headset easily interprets signals of interest.
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The photos shown a turned on analyzer, and some signals noise appeared in the LCD. The LCD had some dead lines at the bottom, but nothing serious. A small size spectrum analyzer is very tempting. I have another two full-size spectrum analyzers but they are so big and my space so limited I rarely use them. After a few minutes, I decided to buy it. Waiting for the package The package took almost two weeks to arrive. There are no Anritsu service manuals, neither schematics available.
The only thing I found was a maintenance manual, which is only a testing procedure list. I started to think that buying it maybe was not a good idea. I even started to think how to sell it by parts, just to minimize money loss.
The package arrived Once the package arrived the first thing I did was to turn it on and test the unit. It worked. I was able to see some signals generated by myself but as soon as I saw them on the screen something was clear: it was deaf. Deaf as a doorknob. It measured 50 to 60 dB less than the real amplitude. In the maintenance manual there is the only clue about how the MSA works inside: a block diagram.
Maybe the attenuator was faulty? Maybe the protection circuit was burned out? Maybe, just maybe, it was possible to repair it. The attenuator When opened, I saw the analyzer is built in sandwich form. The lower board, full of metallic shields, is the actual RF board. So it was clear the attenuator was inside that shield.
I soon started worrying. Someone has already removed that shield, and placed it back using a small amount of solder: someone tried to repair it, and that is usually bad. Because the shield was soldered with a few solder points it was easy to remove. MSA input attenuator The first thing I saw is some grounding was missing. Surely it was teared when they removed the shield the first time. Anyway the layout was quite clear. The SMA left-lower bottom goes to a DC blocking capacitor, then to an attenuator section constructed around a miniature Teledyne relay, a microstrip low pass?
First thing I did was to figure out the schematics in this section: First guessed attenuator schematics click to enlarge All resistors markings were still visible, so it was "easy".
Two components are marked with an interrogation. They are ceramic, maybe compensating capacitors? Once the schematic was drawn some things caught my attention. First, the protection diodes seems to work as a rectifier device. At first I thought it could be reverse biased to keep stray capacitance to a minimum but it is not. After the coils there are 5. Maybe an overload sensing circuit?
Second, the three attenuator blocks seem quite classical, except the first one. The second one is a 10 dB T attenuator. The third one is a 20dB pi attenuator. It is obvious the first one, the one with the relay is another 20 dB one, but resistor values do not matched.
The first two resistor are ohms in parallel, making a But the series resistor differs: vs ohms. And the last resistor also differs, Suddenly I remembered these resistor had hand made soldering, so I figured out immediately the one who first removed the shield found those resistors burned and for sure he tried to replace them with the closer ones he had.
Then I decided to remove all parts and check all of them. This was the point where things started to become scary: Faulty components Many resistors were damaged, and all pin diodes where killed. But what about the pin diodes? They all have AF3 marking on top. A RF switch with a varicap diode?
Also SMV is common cathode, and these diodes should be common anode. A clue come from the switching signals, A, B, C and D in my schematics. When the analyzer wants to baypass an attenuator for example, the second one it puts 0 volts on A, and -5 volts on B.
When it wants the attenuator to be active, it puts -5 volts on A, and 0 volts on B. These voltages does do not make sense with pin diodes. One for each attenuator block. The control lines were intended to provide 0 and -5 volts. How those pin diode switches could work with 0 and -5 volts?
Suddenly everything had sense. They were not pin diodes, they were N-FET transistors. I was happy. I really have no idea. Even Google had no idea. Except for the small number of resistors easy to find , I had six unknown FET transistors, and an unknown DC blocking capacitor. At this point, concerns increased even more. With no components in attenuator PCB, I injected signals at the output, this is, at the input of the next stage. This is the same as set the attenuator value to 0 dB.
The analyzer was still deaf. There must be more components broken in the next stage, under a really big metallic shield. Under the mixers shield According to the block diagram, the MSA uses two different mixers, each one for a different frequency range.
They are switched by some kind of device, and taking into account the entire attenuator block were damaged it was easy to expect that switching device to be also damaged. The problem is the mixers shield is really big.
I was afraid to damage the PCB removing it but using hot air it was easy to remove. The mixer block click to enlarge I immediately saw the switch. Pins 1, 3 and 4 are ground. Pins 4 and 8 are RF outputs, and pins 6 and 7 are control signals with the same levels as the signals used in the attenuator block: 0 and -5 volts.
With all these clues it was not difficult to find what IC is. The SSW appeared as a candidate: it is marked as W2, it has the same layout, it has the same packaging The SSW has a heat sink plate at the bottom and has ceramic encapsulate. This one has no heat sink plate and is made of plastic. I removed the switch and applied signals directly to pins 5 and 8, and I saw the signals on the screen This seems to be the last component damaged in what there is no doubt it was an excess of power applied to the input.
At this point I had all the damaged components delimited, but The logic board and its missing RF components The logic board caught my attention from the first time I saw it. One side has a lot of RF traces, but only passive components mounted.
There were six large delimited areas intended to be covered with RF shields, and many components soldered, but not all. It was clear all this stuff is just the tracking generator, which is an option in this spectrum analyzer. It is not an installable module, just the PCB has or has not the required components soldered. The upper side of the logic board The block diagram of this tracking generator were quite clear. It seems to be very similar to the receiver side.
In fact, you can see the places for the two mixers, the microstripline filters, almost identical to the ones at the RX side. I could identify the "tracking generator power amplifier", a chain of 3 MMIC, and after it, something that at this point was quite familiar to me: Tracking generator output attenuator Yes! There are nine! The only part missing was the limiter or protection device, the one marked PM-something at the RX side. I desoldered the DC blocking capacitor and measured it.
It was a 47nF one. Because the maximum DC voltage that can be applied both at the input and tracking generator output is 50V, this capacitor must be at least a 50 volt one, and a very good one to work up to 3 GHz. I soldered it again in the input attenuator.
I also desoldered all resistors needed and resolder them in the correct places at the input attenuator.
Then, I desoldered one of those AF3 transistors and tested it using my chinese transistor "texter": Just as expected, they are FETs transistors!.
Anritsu Spectrum Master MS2711B Spectrum Analyzer
The Spectrum Master series by Anritsu is full of the quality features that you would expect from Anritsu, the inventors of the handheld spectrum analyzer. Items in the Spectrum Master series are designed for field use, as they are small and compact by nature. The MSB Spectrum Master is a Handheld Spectrum Analyzer created by Anritsu and is ideal for field use maintaining, troubleshooting, and installing modern wireless communication systems. This model has a frequency range of kHz to 3.
Spectrum Master - Handheld Spectrum Analyzer