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Handheld Users Group

Handheld Users Group

Delivering leading solutions for today's field and maintenance challenges

Interference hunter

With over 20 years leading the way in handheld testing Anritsu has a well earned reputation for superior measurements in not so superior conditions. learn more about the very latest handheld testing technology.

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Tips for Hunting (and Finding) RF Interference

Spectrum Master

As wireless services grow, interference, once uncommon, becomes a fact of life. The first indicators of interference are noisy links in analog systems, and limited range, dropped calls, or low data rate for digital transmissions. A second indicator with digital signals is a high noise floor in the receive channel. Once a high receive noise floor has been identified and located, it’s time to get a spectrum analyzer and look for interference on receive frequencies. If you are working on a cellular issue, and the base station has a high noise floor, look on the uplink channels. If the issue is cell phone reception in a given area, then focus on the downlink frequencies. Two Way Radio and other Push-to-Talk systems often use the same frequency for both the uplink and the downlink so this distinction becomes less important.

A key point is that an interfering signal does not need to be on the receive channel to cause interference. It only needs to be within the receiver bandwidth, which normally means that it only needs to get past the receive pre-filter. Once the interfering signal is spotted, it’s important to characterize the signal before disconnecting from the receiver’s signal. To characterize the signal, adjust the spectrum analyzer to best view the signal by using the pre-amp, reference level, span, and resolution bandwidth controls. Observe the signal’s shape, bandwidth, and behavior. Look for frequency drift, amplitude changes, and frequency hopping.
While looking for signals that don’t belong on the input to your receiver, it’s important to know what signals are typically present in your bands. In some cases, it may be possible to demodulate the signal and listen for the station ID call sign. TV and radio station call signs can be heard when using AM or FM demodulation techniques on the spectrum analyzer. Pagers typically transmit a Morse code station ID at the start of every page that can be heard using FM demod.
Many signals do not yield to the easy identification techniques and you need to find them by hunting. That’s when you need an instrument such as the Anritsu MS2720T Spectrum Master™.
Before hunting interference, ask yourself these questions:

  • Is it On-Channel interference?
  • Is it In-band interference?
  • Is it Impulse Noise?
  • Is it Harmonics?
  • Is it Passive Intermodulation?
  • Is it a Near Far problem?
  • Is it intentional?


Questions and Answers

Question: Why are there three level offset adjustments in the MS2720T and MS271xE tracking generators?

Answer: Each adjustment – RL Offset, Generator External Gain/Loss, and Transmission Offset – serves a specific purpose. RL Offset is used to adjust the power level (not gain) readings on the graph to account for an attenuator or amplifier between the DUT and Spectrum Master. Generator External Gain/Loss is similar to RL Offset, but it corrects the indicated (and set) output amplitude by the gain or loss of an external attenuator or amplifier. Transmission Offset is for use after Normalization, and applies only in a special case.

Question: Why is a filter combiner used in the PIM Master™?

Answer: The MW82119A PIM Master uses a filter combiner to maximize RF efficiency and minimize power consumption. It is one reason the MW82119A is superior to alternatives that use a hybrid combiner, which requires two times the input power to achieve a given output power. That is inefficient for field use.

Question: Can I work with all VNA Master™ S-parameter traces with Line Sweep Tools?

Answer: Line Sweep Tools (LST) PC post-processing software is for people doing large numbers of cable and antenna sweeps. It is designed to work with field mode traces from many Anritsu handheld instruments, including the VNA Master and LMR Master™. LST also supports the S-parameter equivalents to the field mode traces. For instance, it supports both Return Loss and Log Mag S11 vs. Frequency.


Test Tip

When trying to locate intermittent signals, two features on the Spectrum Master are helpful. For bursty signals, use Max-Hold on Trace B, while keeping Trace A in the normal view. This allows you to see the shape of the signal and may help with visual identification. For signals that are intermittent over a longer period, use the “Save-on-Event” to automatically generate a mask to spot unusual changes in the signal.

LMR Master Helps Students Learn About Cubesat Design

Students attending the PolySat Electrical Engineering school at California Polytechnic University at San Luis Obispo (Cal Poly), part of the California State University (CSU) system, are participating in cubesat satellite programs that not only give them real-world experience but also help design the next generation of satellites. A team working on a project dubbed IPEX is relying on the Anritsu S412E LMR Master to improve its design verification process.
cubesat funded by NASA’s Earth Science Technology Office (ESTO), is designed to validate onboard instrument processing and autonomous payload operations for the proposed NASA Hyperspectral Infra-Red Imager (HyspIRI) mission. Recently, the team designing IPEX took the cubesat to the top of a boulder on Bishop Peak, a 471–meter high mountain about 2.53 kilometers from campus. Once there, they communicated with the satellite using a Yagi antenna located on the lab’s roof. The team decreased the signal strength until communication was lost to determine the measured receive sensitivity of the satellite. All the measurements were conducted using the handheld S412E LMR Master, which was a welcome improvement over previous methods.

“In the past, we would have to carry our benchtop spectrum analyzer, which weighs more than 100 pounds, to the roof or simply do free space path loss equations. We were never able to measure the signal strength at the satellite; only the ground station,” said team leader Craig Francis. The mobility and measurement capability of the S412E LMR Master allowed the team to record the actual signal strength incident in the spacecraft and measure the actual receive sensitivity. Because of these measurements, they were able to construct an accurate link budget and estimate the necessary gain and power needed for the ground station. “We have been able to dramatically improve our receive sensitivity by researching EMI reduction techniques and measuring changes in performance using the LMR Master. I have enjoyed using the normal span mode of the spectrum analyzer functionality, as well as the zero span mode, which allowed me to record temporal changes in the noise floor due to different electronic subsystems running and the result on receive sensitivity,” said Francis.


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