A short guide to search for interfering links in a Radio Link
Introduction and purpose
With the advent of next-generation networks becomes more and more interference must be searched to verify the availability of frequencies and / or channels are free to set up, expand or replace links in Radio Link
With the advent of next-generation networks becomes more and more interference must be searched to verify the availability of frequencies and / or channels are free to set up, expand or replace links in Radio Link
Network.
This article is intended as a guideline introdutiva to run a check for the research of any interfering signals on the link.
We can identify a dual purpose for this type of activity:
This article is intended as a guideline introdutiva to run a check for the research of any interfering signals on the link.
We can identify a dual purpose for this type of activity:
- Search free channels in order to properly allocate the frequencies for the new radio link (or expansion of existing ones).
- Verify potential interferents which may affect the functionality of the radio link connection to existing or to be installed.
Normally the tests are to be carried out in all the stations on the radio link.
Instrumentation and Tour
By way of reference, we can identify the following types of instrumentation:
By way of reference, we can identify the following types of instrumentation:
- Horn Antenna type reference (in many cases, also known as "piccolo trumpet").
- Low-noise amplifier with accessories (cooling fins, and accessories for DC power supply).
- Spectrum analyzer.
- RF cables in the correct frequency ranges.
- Transitions and steps in relation to the various RF outputs present on the antenna, cables and tools.
One can imagine a scheme of the bench as shown in Figure:
Some specifications:
Some specifications:- Antenna: gain of about 20 dB and angle of irradiation at 3 dB, between 20 and 30 degrees.
- Spectrum Analyzer: Model similar to or higher than the Agilent HP 4408B ESA. In any case, with a minimum level of noise less than -100 dBm.
- Amplifier: Gain of about 30/40 dB, noise figure: within 3 dB
+ Additional accessories such as cooling fins, and DC power - RF Cable: Cable, low attenuation.
- Series of RF coaxial transitions: According to the specifications terminations on the cables and instruments, typically N-type (m) / N (m), N (f) / N (f), N (m) / SMA (f), etc ... .
- DC power source to the amplifier.
Typically between 9/15 Volts and 70/300 mA (depends on the specific model). - Also make sure to have compass, binoculars and support with goniometer for the antenna.
It 'important to remember that a lack of quality in the choice of instruments, in particular the spectrum analyzer and the low noise amplifier, can adversely affect the measurement results.
Have at hand the specific ITU-R of reference, in particular frequency bands correct and funnels RF.
Useful to know some specifications of the radio system that will be installed, in particular the thresholds of degradation and specifications of noise, in order to understand if a measured signal can be considered or not, can interferent.
Have at hand the specific ITU-R of reference, in particular frequency bands correct and funnels RF.
Useful to know some specifications of the radio system that will be installed, in particular the thresholds of degradation and specifications of noise, in order to understand if a measured signal can be considered or not, can interferent.
Installing and Configuring Tour
If possible, it is preferable to carry out the measures will be installed at the same height where the parable of the new radio link.
If this is not possible, stand still as close, otherwise there is a risk of obtaining unreliable results, interfering in how some might be "masked."
Install the antenna Horn preferably on a rotating support (possibly provided with a disc goniometric).
The support system (for example on a tripod) must allow easy rotation of the antenna.
Enable the counter and configure the spectrum analyzer as references below:
If possible, it is preferable to carry out the measures will be installed at the same height where the parable of the new radio link.
If this is not possible, stand still as close, otherwise there is a risk of obtaining unreliable results, interfering in how some might be "masked."
Install the antenna Horn preferably on a rotating support (possibly provided with a disc goniometric).
The support system (for example on a tripod) must allow easy rotation of the antenna.
Enable the counter and configure the spectrum analyzer as references below:
- Start Freq.: According to RF channel to be analyzed
- Stop Freq.: According to RF channel to be analyzed
- RBW and VBW: 300 Khz
(It is suggested to keep the same value in order to simplify the calculations and measurements of power) - Sweep: Automatic
- Attenuation: 0 dB
- Reference power: -10 dBm dB
- Scale (dB / Div): 10 or 5 dB / Div
The values above are for reference, but typically you will get a background noise appears around - 60/-70 dBm.
The use of a line of aplificazione least 30/40 dB serves precisely to be able to display on the instrument signals having powers even of the order of - 90 dBm.
I would suggest making sure that the sum of the gains of the antenna and the amplifier is roughly about 50 dB. This in order to have a sufficient dynamic detection on the part of the instrument.
The use of a line of aplificazione least 30/40 dB serves precisely to be able to display on the instrument signals having powers even of the order of - 90 dBm.
I would suggest making sure that the sum of the gains of the antenna and the amplifier is roughly about 50 dB. This in order to have a sufficient dynamic detection on the part of the instrument.
Regarding the handling of the antenna, it will perform the measures on both polarizazioni and preferably on an angle as broad as possible.
The analysis at 360 ° (or less) depends on the specific objective of the measure.
Consider, however, that the antenna has an angle of detection of the order of 15/20 degrees, so you might divide the research in most areas around the main direction.
The figure below shows an example.
The analysis at 360 ° (or less) depends on the specific objective of the measure.
Consider, however, that the antenna has an angle of detection of the order of 15/20 degrees, so you might divide the research in most areas around the main direction.
The figure below shows an example.
Sequence of controls and measuresThe control will follow 4 main phases:
- Control in the same direction of the remote station in polarization V
- Control in the same direction of the remote station in polarization H
- External control the direction of the remote station (coverage with N segments) in polarization V.
- External control the direction of the remote station (coverage with N segments) in polarization H.
For each field and polarization, the operator must:
- Place the antenna in a reference position.
- Configure the "range" of the frequency spectrum analyzer. Measurement bands may be divided into sub-bands so as to accelerate the speed of the measure (are suggested guideline values around 200/300 Mhz according to the width of the pipe).
- Save the "screens" of the instrument for each measurement by placing a reference (marker) on the maximum value of power detected (*).
- Repeat the measurement for both polarizazioni (H and V)
- . In case of detection of specific interfering signal (or any signal "significant"), collect data of the same in terms of bandwidth / power and if possible identify the main direction.
(*) The detection of received power carried out by a mere reading of "Marker", may be subject to considerable error due to the configuration of the same instrument. The video signal is subject to variations dependent on the Resolution Video, The Band, Sweep, attenuation etc ...
Therefore, the power should be measured with specific functions available on the analyzer or re-calculated with appropriate equations.
I will take short to make any picture on this issue.
When in doubt, take note however (along with recordings of the signals this graphic) of average power values of the measured signals. The necessary corrections may be made at a later time.
Remember, however, that once identified the optimal configuration of the instrument, DO NOT change it for all phases of research, could make an exception specific analysis of an interfering signal significatico.
Therefore, the power should be measured with specific functions available on the analyzer or re-calculated with appropriate equations.
I will take short to make any picture on this issue.
When in doubt, take note however (along with recordings of the signals this graphic) of average power values of the measured signals. The necessary corrections may be made at a later time.
Remember, however, that once identified the optimal configuration of the instrument, DO NOT change it for all phases of research, could make an exception specific analysis of an interfering signal significatico.
Analysis signals
Place the antenna on the same azimuth reference provided for the remote station.
Remember that if you use a compass, it can undergo magnetic deviations due to metal structures.
Moreover, in case if we are identifying the directions of remote sites and have only the geographical coordinates, let us remember that in some areas the deviation geografice Magnetic North - True North may be relevant (in Italy is not high).
It is therefore, useful to take the absolute references that can be used subsequently to detect the correct angles and possibly correct the deviations of the compass.
Divide the channeling RF to be analyzed into N sub-bands from a few hundred Mhz to analyze them and start up the exhaustion of the entire RF channeling request.
Place the antenna on the same azimuth reference provided for the remote station.
Remember that if you use a compass, it can undergo magnetic deviations due to metal structures.
Moreover, in case if we are identifying the directions of remote sites and have only the geographical coordinates, let us remember that in some areas the deviation geografice Magnetic North - True North may be relevant (in Italy is not high).
It is therefore, useful to take the absolute references that can be used subsequently to detect the correct angles and possibly correct the deviations of the compass.
Divide the channeling RF to be analyzed into N sub-bands from a few hundred Mhz to analyze them and start up the exhaustion of the entire RF channeling request.
- Scan in both vertical and horizontal polarization, taking care to also search in elevation.
- For each scan store the track and detect / measure the signal indicated by the instrument. If the spectrum analyzer is provided with a specific measurement option, activate and detect the results. Fill in the relevant documentation required measurement.
- In case of detection of interfering signal (or any signal "significant), detect the data of the same in terms of bandwidth / power and if possible to identify the main direction.
- Once the measure in the first sector, using as a reference the angle of radiation of the antenna and turn it to the right (or left) of N multiple segments of the angle.
- Repeat the sequences described above for each angular segment.
Signal significant
An interfering signal can be considered such if it degrades the threshold BER systems of at least 1 dB. The value of the signal interfering signal will thus have a different weight in relation to several factors dependent on the specific product used to make the radio link (bandwidth, modulation, frequency, threshold, received power etc. ..).
It will thus be difficult to define a priori a proper assessment interference without knowing the characteristics of the Radio Link.
In principle, you could define a rule of thumb that considers all potential interfering signals signals that may have detected a real power greater than - 90 dBm.
So each modulated signal (or CW signal) having the above characteristics could be considered potential interferent and reported to the authorities responsible for the study and planning of radio systems.
If during a scan to locate a particular signal defined as "significant", you must:
An interfering signal can be considered such if it degrades the threshold BER systems of at least 1 dB. The value of the signal interfering signal will thus have a different weight in relation to several factors dependent on the specific product used to make the radio link (bandwidth, modulation, frequency, threshold, received power etc. ..).
It will thus be difficult to define a priori a proper assessment interference without knowing the characteristics of the Radio Link.
In principle, you could define a rule of thumb that considers all potential interfering signals signals that may have detected a real power greater than - 90 dBm.
So each modulated signal (or CW signal) having the above characteristics could be considered potential interferent and reported to the authorities responsible for the study and planning of radio systems.
If during a scan to locate a particular signal defined as "significant", you must:
- Detect the data of the interfering signal in the normal conditions of measurement (same parameters of banda and canalization used for the verification interferential).
The detection of the signal must be highlighted for both polarizations. - At the end of the interferential scanning, center frequency in the detected signal and highlight highlighting (providing data on the relevant documents) the parameters of bandwidth and power.
- If possible, try to identify the source (website, Azimuth, etc. ..)
When these scans organize all saves the images stored by the instrument, organizing them for direction, polarization and band, possibly accompanied by photographs of the reports findings.
The following are some examples of paths without interfering with potentially interfering signal and the same feature.
I will provide to make a further Article with a practical example of calculation of the signals.
I will provide to make a further Article with a practical example of calculation of the signals.
Thank you to my friend and Big Telecom Technician Gaetano Elifani for documents.
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