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Licensed RF Antenna System - A beginner's troubleshooting guide.

Updated: Feb 26


This blog is for anyone interacting with remote water or wastewater antenna systems. My goal of this guide is to connect the dots and remove the mystery to these systems. Help you to identify common failures which create common communication outages.


 

Written by: Phillip A. Yancey - BCI Technologies Sales and Support Manager.

BCI is a GE MDS Channel Partner for FL, GA, AL, MS, NC, SC, TN


Topics covered:




 

Review of antenna system hardware.

 
Yagi, Coax, Weather stripping, butterfly hanger, Jumper Cable, Connectors, Polyphaser, DC Block and Feedline and feedline grounding.
Common Remote RF Infrastructure Hardware


Yagi Antenna (#1) - A directional antenna made of several short rods mounted across an insulating support used in transmitting or receiving a narrow band of frequencies.

Review of a directional Yagi antenna and how to troubleshoot within an antenna system.
Yagi Antenna

  • Yagi are rated and measured by gain dB or dBm and EIRP.

  • There are multiple styles of directional antennas which can vary depending on frequency.

  • Some low band frequency antennas require tuning prior to installation.

  • Antenna Analyzer is required for best-case tuning.

  • Some Yagi's may be turned vertical or horizontally to change EIRP.





Weather Proofing (#2) - Sealing exposed coax connectors to prevent moisture and dust and adding UV protection.

Using coax weatherproofing to secure connectors from elements that can impact an antenna system.
Coax weatherproofing

  • Cover coax connector with a 15" strip of tightly applied rubber splicing tape.

  • Wrap around connectors starting 1' before and after connectors.

  • Overlap previous wrap by 50% to ensure good seal.

  • Cover splicing tape with PVC electrical tape for UV and additional protective jacking.



Butterfly Hangers (#3) - A common way to mount coax is by using a standard butterfly hanger with grommet kit.

  • There are universal mounts.

  • Branded mounts for specific tower also exist.

  • These support the weight of the coax and can also help with grounding.

  • A grommet is used to cover and protects the coax from the hanger.



Coax Feedlines (#4) - The feedline is also called the transmission line and is the conduit between radio and antenna.

Sizes of different Coax cables commonly found in telmetry systems.
Standard RF Coax sizes

Example of Coax Bend Radius with real-world example.
Coax Bend Radius

  • When buying a remote feedline consider buying a pre-made, pre-terminated cable to simplify replacements.

  • Coax has bend radius restrictions which are pointed out in red circles. The top circle shows two bends one acceptable and the other not.

  • Bends and breaks will show up on analyzers with Time Domain Reflectometer (TDR) tests.

  • These increase losses, reflection quirks and impedance mismatches which translate to higher VSWR.

LMR-600 Attenuation vs. Frequency chart found on Manufacture datasheet for coax sizing.
LMR-600 Attenuation vs. Frequency chart


Feedline Grounding (#5) - Feedline grounding is when we usually clamp to the outer copper conductor on the feedline directly.

Grounding kit includes weatherproofing tape, grounding wire and clamp.
Standard or Universal Grounding Kit

  • These grounds should be run directly into the outside earth ground and not panel ground.

  • More common on longer feedlines or AP feedlines.





Jumper Cable (#6) - Used to connect Radio to DC block/Feedline.

LMR-400 NM Jumper with NM terminations used in telemetry panel.
LMR-400 NM Jumper

  • Consider using Ultra-Flex (UF) coax which provide a greater bend radius. Common sizes are LMR-240/ UF or LMR-400 / UF.

  • Consider Right-angle connectors for tight spots and female adaptors for direct feedline connections or existing jumper extension.

  • Bulkhead connectors are also available for specific applications where you might want to mount into a panel wall.

  • The size of jumper coax is not the same as a feedline since it would be difficult and bulky as shown in the photo above. Here you can see the feedline being brought through the cabinet and terminating inside the enclosure.

  • This has made it very difficult to work in the panel along with putting the point of lighting block inside the cabinet.

  • When testing with a Bird meter or Analyzer always start from the jumper to rule out individual components.





DC Block Lighting Arrestor (#7) - Found between the Feedline and Jumper. This is common for remote coax grounding and blocks energy from passing into the Radio device.

Common telemetry bulkhead DC Block / polyphaser IS-B50LN-C2
DC Block - Polyphaser IS-B50LN-C2

  • Intended for direct earth ground.

  • Commonly installed inside or though panel.

  • Most RF systems operate on a 50-ohm load. When an improper "Polyphaser" or DC Block is used, such as a 75 ohm, we have an impedance mismatch.

  • Equipment and Antenna is labeled and since protection is directional this is important.

  • Top connector is bulkhead style and can be mounted though panel so that feedline connects outside panel not inside.

  • Most common connector type is N Female (N/FM) for polyphasers but is not limited to only this.

  • There is no easy way to test a DC Block the simplest method is using an antenna analyzer with the DC block in inline or, the swap with good method.




Common Connector Types (#8) - This is a simple list of common connectors you're going to find in the field. Don't worry if you've mis-matched an adaptor there are converters available but remember every connection adds loss.

RF Telemetry system connectors for help on troubleshooting Remote telemetry sites.
Common Connectors Found on Remote telemetry stations.

  • N Male connectors will be most common on feedlines and to the polyphaser side of a jumper. Alternatively, the Polyphaser side will be N Female.

  • TNC Male connector is most common for radio side of jumper. Alternatively, the equipment side will be TNC Female.

  • SMA Connectors will be most common on Cellular and Wi-Fi devices.

  • A plug style connector refers to a Male connector and a Jack style connector refers to a Female connector.




 

Determining antenna system performance.

 


What is VSWR?

Voltage standing wave ratio (VSWR) refers to the voltage standing wave ratio. VSWR is the ratio between the maximum voltage and the minimum voltage on a line (antenna) and is an expression of Return loss.


What is the ideal value of VSWR?

1:1 is the ideal VSWR value and indicates a reflected power is 0. This signifies that there is no power wastage or %99 perfect power through power. VSWR is commonly known as SWR with the primary difference being a ratio of voltage.

  • 1 = 1 0% reflected power.

  • 3 = 25% reflected power.

  • 6 = 51% reflected power.


Why is SWR/VSWR important?

A high SWR indicates poor transmission-line efficiency and reflected energy. This can in turn damage the Radio transmitter and decrease its efficiency.

  • An Antenna Analyzer is the faster and easier way to test VSWR.

  • A bird 43 can also be used to test VSWR when using the conversion chart provided in manual.

  • Useful in antenna testing and tuning.


When testing VSWR we use a general pass or fail rule:

  • less than < 2.5 is a General Pass. This means that 18.4% power or -7.36 dB is being reflected back.

  • more than > 2.5 is a General Fail. This means that 25% power or -6 dB is being reflected back, or worse.

  • The lower number the better.



What is Return Loss (RL)?

Return loss is the difference in dB between the forward and reflected power. (Forward power - reflected power = Return loss). Return loss is related to SWR and increasing RL corresponds to a lower SWR.


What is the ideal value of Return loss (RL)?

It may seem a little backwards, but the higher the loss the more energy into the antenna system. So, the higher the RL value the better! A low RL indicates less energy going into our antenna which of course is bad.


  • 0 dB = 100% energy reflected by antenna system

  • 3 dB = 50% energy reflected by antenna system

  • 10 dB = 10% energy reflected by antenna system

  • 14 dB = 5% energy reflected by antenna system

  • 20 dB = 1% energy reflected by antenna system

  • 30 dB = 0.1% energy reflected by antenna system


Why is Return loss (RL) important?

A good return loss indicates how well our devices and lines are match. When this isn't true it tells us that discontinuities or impedance mismatches exist in the antenna system. A discontinuity may be caused by a bent or kinked cable or improper terminations or corroded jacks and plugs within coaxal lines. Impedance mismatch are usually component-to-component related including incorrect connectors, DC block specifications, and coaxal types.

When testing Return loss (RL) we use a general pass or fail rule:

  • More than > 14 dB is a General Pass. This means that 3.98% energy is reflected by antenna system.

  • Less than < 13 is a General Fail. This means that 5% energy is being reflected by antenna system.

  • The higher number the better.



 

Testers and pass or fail testing.

 


Below we will cover two devices used by BCI and covering a basic pass-fail scale in device and antenna system testing. These devices average $600-900 and have trade off in simplicity and complexity.



Brid 43 - Directional Wattmeter

Measures forward power and reverse power on a 50 ohm system. Uses element whose frequency range encompass the range you're transmitting on and power level that is equal to or greater then output of device. This device does not usually do peak reading which means it's not fast enough for active device reading, so you must manually key the radio when using the tester.

How to use a directional Bird 43 Watt meter in remote troubleshooting of a licnesed RF antenna system.
Bird 43 Watt Meter

The Bird 43 Watt meter is very versatile and cost effective. The bird meter can be used for a number of test but does 2 very simply. The two basic test of a bird meter are Forward power measurement and reflected power measurement. Keep in mind the Bird device does not generate power, so you must use the radio device to manually key the RF to perform a measurement test.

  • Must be manually keyed in radio device to generate power.

  • Does not measure SWR or active peak power.

  • Antenna system is defined as Load.

  • Radio device is defined as Transmitter.

  • Uses swappable slugs or elements shown in the center of the image with a directional arrow.

  • Elements/Slug for frequency range encompassing your frequency.

  • Element/Slug power should be equal or greater than device power.

  • Meter scaling is determined by element/slug's max power.

  • Element/Slug storage on left side, and another right side of meter.

  • Quick-change RF connectors show as N Type Female / Jack

  • The direction of the element determines what test is being performed.

  • When transporting or not using meter put arrow facing up or use blank element/slug.


The element direction in a Bird 43 determines the power test being performed.
Bird 43 Element Forward Direction

Forward Power Measurement:

PASS:

  • Radio or transmitter is outputting expected power.

FAIL:

  • Radio or transmitter is outputting less than expected power.

  • Move between different components to identify source of failure.

  • Verify equipment is configured to output expected power.



The element direction in a Bird 43 determines the power test being performed.
Bird 43 Element Reverse Direction

Reflected Power Measurement:

PASS:

  • Radio or transmitter reflected power should be 0 or less then < 4%

  • Unlike with Return loss the lower the Reflected power the better.

FAIL:

  • More than > 4% reflected power.



RigExpert AA-1000 - Antenna Analyzer

The RigExpert is designed for testing, checking, turning or repairing antennas and antenna feedlines.


  • Generates own power for testing.

  • Does not measure forward power and should not be connected to a radio.

  • Setup uses frequency center and range to be configured.

  • Measures SWR

  • Simple reflection test.

  • Always a positive number.

  • Measures Return loss (RL)

  • Result of impedance mismatch

  • Measures Time Domain Reflectometer (TDR)

  • Used for locating faults in transmission lines.

  • Requires coax type be configured in setup.

  • Software included for computer analysis of saved test.

  • Calibration hardware not included and required after frequency setup.



SWR Measurement showing pass and fail when troubleshooting an antenna system.
SWR Measurement showing pass and fail.

SWR Measurement: (Lower the better)

  • General Pass: < 2.5 (Green line)

  • General Fail: > 2.5 (Orange line)




Using Return Loss (RL) showing pass and fail in troubleshooting antenna system.
Return Loss (RL) showing pass and fail.

Return Loss (RL): (Higher the better)

  • General Pass: > 14 dB (Green line)

  • General Fail: < 13 dB (Orange line)






Using TDR to identify open load in transmission line when troubleshooting RF antenna system.
TDR Test results showing open load (Break)

Time Domain Reflectometer (TDR) (0 is normal)

  • 0 = Matched Impedance load

  • No resistance will be 0 until the end.

  • +1 = For open load

  • End or break in cable

  • -1 = For short load

  • Short, crushed, or damaged cable or DC Block (if inline)



 

Review of radio system and related device equipment.

 


A 10-Year-old remote telemetry panel and equipment . This image shows a Power supply, PLC, SD Series radio with power input, LEDs, ethernet, serial, RF port and a bulkhead DC block using a bulkhead connector. This image shows a Power Supply (1), PLC (2), SD Series radio with power input (4), LEDs (3), Ethernet (5), serial (6), RF port (7), and bulkhead DC block using a bulkhead connector 8).
10-year-old Remote Telemetry Panel


This image shows a Power Supply (1), PLC (2), SD Series radio with power input (4), LEDs (3), Ethernet (5), serial (6), RF port (7), and bulkhead DC block using a bulkhead connector 8).


While this photo includes the GE MDS SD Series equipment and other branded the below information is general and not device specific.



Power Supplies (#1) - Power supplies are properly sized and are outputting proper voltage.

  • Improper voltage output which can cause RF power loss along with overall irregularities on the radio and its interface.

  • Undersized, too many devices and power supply are unable to provide adequate voltage or wattage will develop the same sort of problems.

  • Ensure the output of your power supply matches its rating.

  • Powered by a UPS then check both.


PLC (#2) - Programmable logic controller (PLC) or Remote telemetry unit (RTU) are the station bread and butter.

  • LEDs or communication indicators to ensure on and working.

  • Connections and cables configured seating properly and tight.

  • Serial and Ethernet parameters are specific and must match.


RADIO LEDs (#3) - Most telemetry radios will have LEDs for basic troubleshooting.

  • Association LED will confirm if the device is associated or not.

  • Link light or Tx/Rx LED will confirm passing data or traffic.

  • Blinking Red or Alarm LED indicate alarms or events.


RADIO Power input (#4) - Power connector inputs.

  • Inputs can become loss or corroded creating poor contact.

  • A simple way to power off radio when testing.

  • Polarity specific and if incorrectly wired device may not power up.


RADIO Ethernet (#5) - Ethernet ports are used for data and device programming. Port link indicator LED can verify link and speed.

  • Should have link lights if connected and working.

  • No LEDs suggest port is not connected or active.

  • Patch cable should have a clip to keep inside port.

  • Cables can go bad.


RADIO Serial (#6) - Serial ports are still preferred on telemetry networks.

  • Cables go bad.

  • Connections should be tight.

  • Pin-out are important for legacy serial networks.

  • LEDs are usually labeled as com.

  • Serial speed and over air speed should match.

  • Radio and equipment port settings must match.


RADIO RF Port (#7) - The RF port is where a Jumper connects to a DC block for exit out the transmission line to our antenna.

  • Cables go bad.

  • Connectors should be tight and clean of corrosion or dirt.

  • Radio should be powered off when not connected to a cable or antenna.


Grounding & Weatherproofing (#8) - Bulkhead style DC Block with Antenna cable connected at panel base.

  1. Grounding is best kept outside the panel when possible.

  2. Grounding is commonly tied to backplane/panel ground but ideally should be a direct earth ground.

  3. External connectors should always be weatherproofed.



 

Determining radio system performance.

 

A diagram explaining signal to noise within a licensed RF system.
Signal to Nosie

We see received signal shown as a green wave and below is Noise floor shown as a red wave. The difference in the power between these two signals makes up our Signal to Noise ratio.




Received Signal Strength Indicator (RSSI)

  • RSSI is a measure of RF power from a source transmitter.

  • RSSI value is represented in a negative form (e.g. −85)

  • The closer the value is to 0, the stronger the received signal.

  • Does not indicate the quality of signal received.

  • Must be measured from both sides of link.

  • FSK (SD Series) or legacy radios use RSSI to determine data rate.

  • RSSI of -50 or higher (-40 etc) is "too hot" and attenuator should be added.

Link Quality Indicator (LQI)

  • Measured from 0 to 5 and lower the better.

  • Is a measure of quality using multiple factors including RSSI and bit error rate (BER).

  • QAM (Orbit Series) or modern radios use LQI to determine data rate.

  • Requires active data communication for an accurate reading.

Single to Noise Radio (SNR)

  • SNR is measured in decibels (dB) and higher is better.

  • Is a ratio of desired signal power to the undesired noise power.

Noise Floor

  • A measured sum created by unwanted signals and noise sources.

  • Noise is defined by any unwanted signal.

  • Types of noises include thermal, cosmic, and atmospheric and man-made noise.

Decibel-milliwatts (dBm)

  • A unit of measure to indicate power expressed in decibels (dB) with reference to one milliwatt (mW)

  • Typically referenced in relation to a 50-ohm impedance.

  • Power level of 0 dBm corresponds to 1 milliwatt.

  • 3 dB increase in level is the equivalent to doubling the power. (e.g 33 dBm = 2 Watt & 36 dBm = 4 Watt)

Effective Isotropic Radiated Power (EIRP)

  • A calculation used to estimate the radiated output power.

  • Takes into account transmitter output power, cable loss, and antenna gain.

  • Used and referenced on FCC licenses.




 

Radio key testing.

 

The radio must be keyed, or transmitter powered on when testing. Keying a radio to test an antenna system is required for a bird 43 meter but not an antenna analyzer. When performing a signal audit, we require someone on opposing ends of the AP and Remote.


The new Orbit series access points provide both up-stream and downstream signals, but not in real-time. The SD series requires key testing for a similar signal audit.


In the case of using test equipment like a bird 43 meter, the key test allows us to manually power up the radio transceiver to use in meter readings. Remember these devices do not read active peak power, so simply having inline of an active radio is not enough.


This video includes a review of LN and SD Radio Key Tests.



 

Questions and answers for the troubleshooting process.

 


Did it stop working suddenly, or was it a slow progression?

If a station is working and suddenly stops communicating, that's an indication of critical failure. Example of critical failure might include a failed power supply or loss of power, failed device like the radio or plc / rtu itself.


A slow progression to failure occurs when we have increased comm losses until completely offline. The time until failure may be an indicator as well.


For example, a path problem resulting from tree growth would increase over many years since the remote installation. As the trees and building increase, our signals path become obstructed. The technical term for this effect is called fade margin.


Alternatively, if the station was working great and within the last week declined until completely offline, you may have a failed power supply or improper voltage output. Bad DC block, grounding, or antenna damage.


Was there any major outages or events recently?

Events around the time of the outage may provide some indication of the cause to failure.

In Florida lighting strikes are very common and nearby or direct can cause all sort of problems. Alternatively, ice covered antennas will also have degraded signals or complete loss.


How old is the station?

Most RF infrastructure last around 10-15 years if grounded and weatherproofed properly. If you haven't done maintenance in a decade, be sure you bring a tester with you.




Thank you for reading!


Please help me improve my post by sharing, offering constructive feedback, corrections and questions you may have.


 

Source links:


New Times Microwave - Cable Calculator:

https://www.timesmicrowave.com/Calculator


Rig Expert AA-1000 Antenna Analyzer:

https://rigexpert.com/products/antenna-analyzers/aa-1000/


Bird Portable Watt Meter:

https://birdrf.com/en/Products/Test%20and%20Measurement/RF-Power-Meters/Wattmeters-Line-Sections/RF-Wattmeters.aspx


Others

https://www.omnicalculator.com/physics/vswr-voltage-standing-wave-ratio#what-is-vswr

https://www.richardsonrfpd.com/docs/rfpd/tower_strikes_and_solutions.pdf

https://www.picwire.com/resources/technical-articles/cable-bend-radius/

https://www.markimicrowave.com/blog/wp-content/uploads/2016/11/return-loss-to-vswr.pdf

https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5432.html

https://www.quabbin.com/tech-briefs/what-return-loss-why-it-important

https://www.youtube.com/watch?v=149AuSmk4M8

https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Signal-to-Noise_Ratio_(SNR)_and_Wireless_Signal_Strength

https://resources.pcb.cadence.com/blog/2020-what-is-signal-to-noise-ratio-and-how-to-calculate-it

https://www.advantage-com.com/


Review of antenna system hardware.





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