PIM (Passive Intermodulation Distortion)

PIM may become a major problem when Tx and Rx signals share one RF path. Luckily, VSWR measurements are standard procedure after network installation. Such measurements determine how much RF energy the antenna emits, and how much unwanted energy is reflected back into the transmitter. VSWR meters are however not capable to detect non-linearity in system components. Validating PIM network quality requires special PIM test systems. The preferred scenario for best network quality is – preventing PIM in the first place. For achieving this, it is paramount to utilize only high quality, low PIM components, apply proper installation procedures and ensure excellent grounding of the RF system.

Why is it critical to eliminate PIM?

Intermodulation products may be generated whenever base stations transmit RF signals. The resulting intermodulation frequency products are often found within the receiving bands of a network. Since RX signals are by nature very low power, interference with regular voice and data traffic occurs. Unwanted PIM interference may desensitize one or more receiving channels to such degree that not only creates very high BER that reduce network bandwidth, but may even drop calls completely. It the worst case it can even lead to permanently unusable receiver channels. Loss of already sparse network capacity caused by PIM is in no way acceptable for high volume, high speed wireless data networks. 

What causes Passive Intermodulation?

• Ferromagnetic metals, like iron, nickel and steel, show hysteresis effects with applied energy. The resulting signal levels are altered and the signal response is no longer linear.
• Dissimilar metal plating on connectors constitutes potential voltaic elements that act like a diode, causing unwanted random modulation effects.
• Corroded surfaces cause PIM. Corrosion may happen on unprotected component surfaces or by human influence (e.g. touching a connector pin with bare fingers).
• Irregular contact surfaces, even on a microscopic scale, can cause an inconsistent flow of charge carriers and generate inhomogeneous electromagnetic fields. Causes can be of mechanical or electrical nature: Low quality components, shearing by forced connections and disconnections of components, spark craters caused when “hot” connections are disconnected.
• Wind load and dissimilar expansion coefficients of tower and feed lines stress both, connectors and cables and will cause deteriorating connection quality.

Conclusion

Minimizing Passive Intermodulation (PIM) is critical for achieving maximal system capacity and efficiency of wireless high-speed networks. PIM awareness is paramount for PIM prevention. Installers need to be trained properly ensuring familiarity about PIM causes and expertise on how to prevent them. Manufacturers have to deliver products that not only come with low PIM characteristics but guarantee sustaining specifications over a long time under environmentally harsh conditions. System designers have to consider appropriate products, and they need to pay special attention to material and plating of mating component surfaces. Finally, wireless operators have to maintain their network ensuring that PIM behavior is not deteriorating during operation of the system.

More Information

• LTE forces Network Designers to re-think (WTG Blog)
• The Importance of Low PIM components (Recorded Webinar)
• The Importance of Low PIM Components (PowerPoint Presentation)
• Proper Torque prevents PIM (Whitepaper)
• Microlab Products (Catalog)
• PIM 21 (2W PIM Test System)
• PIM 21 (Datasheet)

Highest Detail Representation
Accuracy – Repeatability.

Boonton customers use top-end 4500B RF peak power analyzers for many years to measure and analyze most complex RF pulses and pulse trains. Whether for military or commercial applications, this peak power analyzer is the instrument of choice for engineers who have to calibrate their million dollar electronic equipment.

By spending large amounts of Marcom dollars proclaiming  superior parameters and even comparing screen sizes, Agilent tries hard to gain market share in a domain that is well served by Boonton with our established 4500B Peak Power analyzer and a huge variety of sensors. 

Our response is: Boonton’s customers who work with most complex RF pulses are really experts in what they are doing. They can quite well distinguish if certain specification claims are indeed meaningful for them. We can demonstrate that the 4500B peak power analyzer can not only perform any pulse analysis task, but can do that often superior when compared to much higher priced equipment in the market. 

Hewlett Packard, Agilent’s predecessor, was long time considered the leading T&M technology company in the world. To no surprise, it makes us incredibly proud that Agilent’s launch strategists recognized Boonton’s analyzer as the golden standard for high-end peak power analysis and are trying to compare their new product with the well established 4500B.

Boonton 4500B – trusted performance

More information:

• 4500B Datasheet
• Request a 4500B demo
• http://boonton.com/power-measurement-guide
• Power Measurements of Complex Pulse Trains
• 4500B Advanced trigger capabilities
• Time Matters – How Power Meters Measure Fast Signals
• Analysis of Complex Modulated Carriers using Statistical Methods
• 4500B Power analyzer the Built-In Precision calibrator
• Boonton 4500B QAM Power Level Test
• Amplifier test Part 1 – replacing Your Diode detector 

RF power measurements are essential in any RF product phase: design, production, maintenance, alignment and service. Hence, it is very important to have a RF power meter which can provide high speed measurements in a production environment, as well as the simplicity of operation for bench top or field use. Boonton 4240 series average power meters are the successors of 4230 series. This average power meter series is fully backwards compatible and can be paired with all available Boonton CW diode and Thermocouple sensors. The power meters automatically load frequency-response data stored in the memory of the sensors when they are connected. In addition, older sensors can be upgraded with a data adaptor in order to take advantage of this automatic calibration feature in the meters.

Fig 1: Boonton 4240 performs better than any legacy average power meter

4240 allows to measure RF power from -70 dBm to +44 dBm with a maximum dynamic range of 90 dB which is very similar to Boonton’s legacy product 4300 series, but it has higher measurements speed (200 readings/sec for 1 CH) than 4300’s measurement rate (100 readings/sec). The frequency range is 10 kHz to 40 GHz for RF power measurements and 10 Hz to 1.2 GHz for voltage measurements (optional). This meter also includes standard GPIB and RS-232 interfaces for connection to external computers and ATE systems for display and processing of measurement results. Integration of either power meter into an ATE system is routine by means of simple software control via SCPI language or a Lab VIEW driver from National Instruments.

The 4240 Series offers a backlit LCD, which provides simultaneous readings of one or both channels, displayed with individually programmable units and resolution.

Automatic step calibration “AutoCal” function uses built-in 50 MHz sweep calibrator to offer best-in-class power linearity.

The instrument can measure gain and output power, and perform sum, difference, ratio and relative measurements. Selectable dual bar graphs assist with gain and peaking adjustments.

Why 4240 is still the best choice?

There are several reasons why I believe that 4240 series is the best choice as an average power meter. It helps to reduce test and alignment time due to its very fast measurement process capability with the convenient display either in logarithmic or linear units with five digit resolution. 4240 has channel math functionalities for up to two channels which is not that great compared to 4300’s six channel math functions. But It has another great feature of selectable dual bar graphs assistance with gain and peaking adjustments and also has a low power consumption. 4240 also has the capabilities of HP437/438 emulation and also legacy Boonton 4220A/4230A emulation. Moreover, it has a very reliable Boonton quality at a very affordable price.

Additional Resources:

[1] Data Sheet for Boonton 4240 Series RF Power Meter (ttp://boonton.com/~/media/Boonton/Datasheets/4240_Series_Datasheet_WEB.ashx )

[2] Boonton 4240 Product Information (http://boonton.com/products/power-meters/4240-rf-power-meter )

Many instruments consists of several single components. An example would be an RF power meter with two RF power sensors. They all have different serial numbers, but since they are most likely purchased together, it makes sense calibrating them also together. No problem with our new online RMA feature  – up to four components can be entered at one RMA form.

Why factory calibration?

Many independent “calibration” houses offer their services. However many of them have actually no possibility to apply new alignment data tables. They  just measure if instruments meet the data sheet specs and if the result is within the datasheet specifications, they consider the instrument as “calibrated”. This even if the measurement show, that calibration is right at the edge of its limit. Obviously this methood is not sufficient at all; normal termal drift may move the instrument soon after the “calibration” out of its limit – a situation that is clearly undesirable.

Boonton factory calibration is thourough. It is performed to much tighter specs than those that are listed on the datasheet. Furthermore, the instruments are aligned to the center of their limits. This garantees that even with normal thermal drift, all instrument stays calibrated during the full calibration period.

Boonton – Reliable RF Instruments.

Further information:

General Boonton Service Information

Come join us next week September 13-15 at the 2011 IEEE Autotestcon Show at the Baltimore Convention Center in Maryland. Our booth #838, is right across from our company sponsored Internet Café where you can browse the internet and catch up on some e-mail.

While at Autotestcon don’t forget to play, engage and win – Wireless Telecom Group is once again participating in Evaluation Engineering’s tech trek game. Pick up your game card at the EE booth #1047 and then stop by our booth to pick-up the Wireless Telecom Group sticker you are going to need to complete your card. You can then return your game card to the EE booth in time for the incredible prize drawings like an ipad2 or netbook.

While at our booth you will see exciting new product demos for Boonton and Noisecom which include:

• Utilizing White Gaussian Noise as precision reference for calibration and frequency response analysis. Constant power over a linear frequency range can be utilized for a huge variety of test and measurement applications. Replace your signal generator with calibrated White Gaussian Noise sources. 
• Optimize digital signal transmissions and modulation schemes for high throughput and the best QoS. Automated Signal to Noise measurements and monitoring, analog and digital. Noisecom’s CNG-EbNo allows the user to simulate challenging up & downlink conditions. See how easily measurements can be performed. 
• RF Power Meters with full 14 bits of measurement range
  Experience high dynamic RF power measurements without range switching. Why true peak power measurements are far superior to diode detectors.  Boonton 4500B and 4540 RF Power Analyzers are set up at our booth. 
• Amplifier Test Bench. Critical RF Amplifier Measurements automatically performed and documented. New Software package measures pulsed and linear, small signal and high power RF Amplifiers.

 As always we will have our applications engineers at the booth to assist you with any questions or information you may need. We look forward to seeing you there!

Whether we talk about cellular base stations (BTS, eNodeB) or outdoor Distributed Antenna Systems (DAS), wireless infrastructure is always subject to the environment. Still, it has to work flawlessly and  under quite challenging conditions. Let us just imagine the scorching heat and the dust storms of Phoenix, Arizona, the crackling cold in Alaska, North Dakota or Siberia, or the all-time-wet environment of rain-forest regions and coastal lines, nevertheless – we simply expect the network to perform and deliver high quality service for our mobile devices.

To make this happen, designers must be prudent when selecting components for their networks.  Choosing parts only by their basic electrical characteristics is no longer sufficient; planers have to consider another vital attribute: components used for outdoor installations have to be weatherproof –  over their full life cycle.

Whether planning an outdoor DAS or a regular wireless base station, the same question applies: how can network designers determine if the components they need are weatherproof? The answer to this question is actually quite simple: the best indicator for this characteristic is the Ingress Protection rating or IP-rating. Ingress Protection rating is based on clearly defined product tests that analyze both, particle and liquid ingress. If a product is “IP rated”, data sheets provide this information as “IPxy”. The “x” stands for protection against particles, the “y” for protection against fluids: the higher the digit the better the protection. If a component is rated “IP67”, it is guaranteed that absolutely no dust will enter the housing (“6”) and can be submerged in water for up for 30 minutes (“7”). The table below shows the rating levels and their degree of protection.

Is it not best to use  IP67 components for all applications?

If components are directly exposed to the environment, the answer to this question must be  “yes”. However, the highest IP rated components are more difficult to design and manufacture, which again reflects in the price. Different materials, more precise milling, additional sealing, multi-layers of paint, and many other measures may be required to reach these high IP-ratings. While it would certainly guarantee excellent protection, always using the components with the highest IP-rating may not be necessary to achieve optimal system reliability. The selection of the right components depends on the local circumstances. Microlab solutions cover all needs by offering many components with different IP-rating levels; economic for closed infrastructure areas (e.g. in-building DAS) or fully protected when used outdoors. Check with the specialists. Our global offices will be glad to answer all your questions.

Find more literature on outdoor components here:

-       Outdoor Infrastructure / DAS – Ingress Protection

Mazumder Alam

Noise is an unwanted electrical or electromagnetic energy that degrades the quality of signals and data.  Noise occurs in digital and analog systems, and can   affect communications system of all types. Noise is generated by random vibrations of conducting electrons and holes in the material. Noise is often referred to as thermal noise. Thermal noise is white and has a Gaussian amplitude distribution. In general, noise originating from outside the system is inversely proportional to the frequency, and directly proportional to the wavelength. All materials produce noise at a power level proportional to the physical temperature of the material.

An object emits White Gaussian Noise at a level proportional to its temperature, KTB.

Noise power P=KTB

K= Boltzman’s constant (1.3807*10^-23 in J/K),

T=Temperature (in ⁰K), and

B=Bandwidth (in Hz)

Noise power is now in Watt. All Noisecom products are Additive White Gaussian type. Noise power can also be referenced to the Earth’s noise floor, or – 174 dBm/Hz. This value is referred to as ENR, or excess noise ratio. It is calculated by using the following formula:

Power Spectral Density, PSD (dBm/Hz) = – 174 dBm/Hz + ENR

Additional Information:

The following links provide the additional information on noise and Noisecom products:

Noise by the Numbers

Noisecom Instruments

Noisecom White Papers

 Smart phones  and tablet PCs claim huge data band-widths and wireless network operators must ensure subscribers’ data demand is sufficiently satisfied. Research conducted by CISCO® in 2011 found that compared to a regular mobile phone, smart phones require 24 times the data bandwidth. Tablets have an even higher demand; they require 122 times the data bandwidth of standard mobile phones. Wireless network operators are upgrading their networks to LTE in order to satisfy the massive data hunger.  Succees requires special network design and installation executed with extra care.

“Designing low PIM into modern wireless high speed data networks is paramount for bandwidth optimization and maximum Quality of Service (QoS)”.

Passive Intermodulation (PIM) has existed since two or more frequencies were combined in one RF path. With the exception of satellite links, early technologies were less susceptible to PIM and adequate bandwidth was available. Network operators were mainly concerned about increasing their subscriber base, but now huge investments are required to expand network capacity.

What is PIM?

PIM is an unwanted effect caused by passive components. Since they are passive one would expect a perfectly linear behavior. Reality is, every single passive component comes with a certain degree of non-linearity. Indeed, any component generates PIM. This is of little concern if only one frequency at a time is transmitted; as soon as two or more frequencies share the same RF path, PIM avoidance becomes very critical. What distinguishes “The Good”  components from “The Bad” is the degree to which it causes PIM.

Frequency spectrum with PIM interference. In this example the IM products are caused by simple CW tones. Broadband carriers generate also broad intermodulation products, which can have a significant influence on the operational quality of cell sites.

Components that have insufficient PIM characteristics cause RF power diversion into other frequency ranges. These intermodulation products interfere with other RF signals.  Obviously this is not desired because for one, transmission in other than the assigned bands is  in most countries plainly illegal.  Furthermore, the most powerful PIM signal is usually the third order intermodulation product, IM3. This signal corresponds very often with the receiving bands of  telecommunication transmitters. Whenever they transmit a multi frequency signal, PIM is generated, disturbing receiver frequencies. This can lead to reduced cell site bandwidth, and reduced QoS. Sometimes PIM signals are so disturbing that they can take our complete Rx channels. This is the last thing operators can afford in a system with already strained capacity.

Prevention

PIM can be prevented with proper planning, high quality components and well trained field personnel. Some materials cause significant PIM when mated with each other. Quality components are specifically designed and manufactured to ensure the lowest PIM values, even after years of operation under challenging environmental conditions.  

Further reading

The following links provide  further information on PIM and how to prevent it:

Importance of Low PIM components (recorded webinar)

Passive Intermodulation

Proper Torque prevents PIM

PIM 21 Manual

Conclusion:

LTE systems are particularly receptive to interference caused by unwanted passive intermodulation effects. Diligent network design, highly trained field personal and high quality components with guaranteed low PIM specifications are paramount to prevent bandwidth-reducing PIM issues. While specific PIM testers can determine if sites present high PIM values, the best and least costly way to deal with PIM is avoiding it in the first place.

Wireless Telecom Group (WTG) is an experienced, well-established company developing and manufacturing test and measurement equipment for a vast variety of RF applications.  We provide precision sources for calibration and analysis, as well as components for wireless network infrastructure.  In short, WTG has developed a great foundation of knowledge, supporting customers whenever there is a need to solve complex RF problems.

To share our expertise, we continually grow our free literature offerings–including whitepapers, application notes and articles. Furthermore, we frequently provide new videos,  webinars, and Twitter tweets containing valuable information  to keep you current on RF technology.

This blog is another way of sharing our expertise with you.  We will discuss wireless applications, and talk about how our products can solve difficult measurement problems. We believe it will be a valuable tool in providing you with a wealth of information. Quality trumps quantity; expect a blog every couple of weeks.

You already know how blogs work.  Sharing information is an important purpose; but a blog really becomes alive with comments and discussions. For this reason we encourage you not only to subscribe to it, but to become an active user, commenting on posts, sharing your opinions and also asking questions. We would like to engage you in an open and lively discussion. The WTG team is quite excited about this new program and we are looking forward to this experience. We hope you will enjoy it as much as we do.

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The WTG Team