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  • Antenna SWR meters and Impedance Analyzers Testing Setup Proceedures and Best Practices

The availability of numerous low cost non-commercial Antenna SWR meters / Impedance Analyzers has made it easy to add a great tool to almost everyone's test bench. Now you can quickly check your antenna and cable for a variety of conditions, including SWR bandwidth and resonance.

Below are listed some suggestions for testing setup procedures and best practices for obtaining meaningful results and good performance. Also listed are some observations and reasonable expectations to consider when testing Commercial Antennas as opposed to Amateur Radio Antennas and Scanner Antennas.


BASE ANTENNA TESTING SETUP:
(These recommendations are valid for mounted and non-mounted, new antennas)

  1. Make sure the antenna is outside and not mounted near any metallic objects, other antennas, close or parallel to a tower, guy wiring, aluminum gutters, aluminum siding or support structures and especially other antennas. The antenna has to be vertical and at least 5-10 feet off the ground. Mounting the antenna on a temporary test stand using a tripod and a 10-foot section of pipe away from surrounding objects gives best results.

  2. Do not test the antenna inside a building, horizontally or lying flat on a table or the ground.

  3. Make sure you use high quality connectors and that they are properly installed. It's best to have a commercial cable manufacturer make the cable and put on the connectors unless you have extensive experience installing connectors. Cable and connector problems are the most common failure point in any antenna system.

  4. Don't use any adapters, jumpers, splices, switch boxes, multiplexers or other devices in line with your coax. Any device in line between your analyzer and the antenna can cause an "impedance bump" which will degrade the accuracy of your measurements. It should be a clean run from your test equipment to the antenna.

  5. Make sure your mounting brackets are on the bottom metallic support section of the antenna and not on the fiberglass (sounds silly but this happens all the time).

  6. If your readings seem high or inconsistent try changing your cable length a foot or so if possible and take the readings again. Make sure you're using high quality 50 ohm coax (LMR400 or better) or hardline with the proper connectors and no splices, coax switches, duplexer or multiplexer in the cable path.

  7. If you're using an in-line SWR meter be sure your transmitter output is clean, any spurious output (spikes from power amps especially) will raise your SWR. Test at the lowest power possible, 5 watts is fine.

  8. There can be considerable differences in calibration accuracy between different models of Antenna Analyzers, if possible try at least two different models to make sure your readings are generally accurate.

  9. When using an Analyzer to evaluate Multiband Scanner Antennas keep in mind that the manufacturer is using complicated design techniques to get multiple band coverage in a single antenna housing or structure (except for the Discone). Your analyzer readings will vary widely from band to band and frequency to frequency. Scanner Antenna design is usually for "receive only" so low SWR is not a primary objective and will usually be the lowest near the receiving band centers.

  10. Your scanner is not very concerned with SWR and has little difficulty receiving signals from a higher SWR antenna source, e.g., the metal rod antenna it usually comes with in the box. One of the most important factors in an efficient Multiband Scanning Antenna system is using a high quality low loss coax cable and quality connectors between the antenna and your scanner. Keep your cable as short as possible and purchase the best cable you can afford, preferably commercially made with connectors installed. A much higher than 2.0:1 SWR is acceptable and most Multiband Scanner Antennas will receive very well outside their stated band ranges.

  11. Avoid "Antenna A" vs. "Antenna B" comparisons. Manufacturers use different design techniques to lower SWR, some of which can degrade performance. No two antennas, unless they are of identical manufacturer, design, frequency range, test position and model are going to be useful in comparison tests.

  12. ANTENNA SWR WARNING:

    Specific frequency tuning for lowest SWR is usually not done by antenna manufacturers unless explicitly specified. Requesting a specific tuning frequency / lowest SWR frequency is no guarantee a manufacturer will be able to produce it. Most antennas are made from a preset pattern to cover the specified range of the antenna and custom tuning is simply not possible. Most antennas are designed to cover a very defined bandwidth with a guaranteed SWR of usually <2.0:1 (see spec sheet for your antenna) over that range. This means you may see considerable variation of SWR over the specified frequency range but it will generally remain within the guaranteed spec sheet number (usually <2.0:1 or <1.5:1). This must be considered when purchasing or making measurements on any Antenna.

    A low SWR/high return loss on your antenna analyzer over the entire frequency bandwidth of your antenna or at your requested "tuning point" usually won't be possible. An SWR of approximately 2.0:1 or less is typical but can vary greatly over the bandwidth range of the antenna.

    BASE ANTENNA EXPECTATIONS:

    1. Make sure you understand the differences in the specifications and product design goals of different types of manufacturers, especially Commercial vs. Amateur. Commercial Two-Way Antenna manufacturers design their products for police, fire and industrial users and are required to meet their published specification sheet parameters for a particular model. Amateur Radio antenna manufacturers have a much more defined market and design for it specifically. Their design techniques are usually for Amateur Radio service only and are not suited to Commercial Two-Way service. Commercial Two-Way Antennas will work well in Amateur Radio service if the user can tolerate generally higher SWR in parts of its specified band range.

    2. Scanner Antennas are a special case since most are designed for receive only with a few exceptions. Scanner Antennas can sometimes overlap Commercial and Amateur service if specifically designed with higher quality, more robust components and are "transmit capable". Some notable designs are the Austin Ferret base and the Austin Spectra mobile antennas. Since these type of antennas are wide frequency coverage, multi band designs the user may have to tolerate somewhat higher SWR in some parts of its specified band ranges if transmitting.

    3. The antenna gain and SWR bandwidth published specifications can differ widely between Commercial Two-Way and Amateur Radio antennas designed for the same band. The terms used and measurement techniques employed are usually not standardized and many performance claims must be taken with a grain of salt. Commercial and Amateur manufacturers have vastly different parameters they must meet to satisfy their customer base. Commercial and Amateur manufacturers can also differ widely in their price, quality of manufacture and quality control.

    4. Specific frequency tuning for lowest SWR is usually not done by commercial manufacturers unless specified. Low profile Commercial antennas are the exception and require specific frequency tuning because of their very narrow bandwidth. Quarter wave antennas are also usually tuned or pre-cut to a specific band range. Most Commercial antennas are designed to cover a very defined bandwidth with a guaranteed SWR of usually < 2.0:1 over that range.

    5. Understanding the differences between Commercial Two-Way, Amateur Radio and Scanner antennas will save a lot of frustration and disappointment when making Analyzer or SWR measurements. Carefully consider your expectations before purchasing an antenna designed for one type of service and applying it to another.

    6. Call for Assistance

    MOBILE ANTENNA TESTING SETUP:
    (These recommendations are valid for mounted antennas only)

    1. Make sure the antenna is mounted on a conductive metal surface and not near any other antennas. The antenna should be vertical and not near any vehicle body metal or rear window defroster wire mesh if possible.

    2. If using a NMO type mount check that the center contact on the antenna base is making proper contact with the mount. Over tightening will crush and damage the contact pin or tab on certain antennas. DO NOT OVER TIGHTEN. If the contact is damaged the antenna may still operate but with high SWR and poor receive performance. The same is true if the mount is under tightened and the antenna base contact pin or tab doesn't make proper contact resulting in high SWR and poor receive performance.

    3. Do not test the antenna unmounted, without a ground plane, inside a building, horizontally or lying flat on a table or the ground.

    4. Note that the shock spring (if one is used) is part of the overall electrical length of the antenna. When making Analyzer measurements or tuning adjustments include the shock spring length as part of the overall whip length if that section of the antenna is adjustable.

    5. Make sure you use a high quality cable and a connector that is properly installed. It's best to have a commercial mount and cable manufacturer put on the connector unless you have extensive experience installing connectors. Cable and connector problems are the most common failure point in any antenna system.

    6. Don't use any adapters, jumpers, splices, switch boxes, multiplexers or other devices in line with your coax. Any device in line between your analyzer and the antenna can cause an "impedance bump" which will degrade the accuracy of your measurements. It should be a clean run from your test equipment to the antenna.

    7. Make sure your mount is installed on a large, flat conductive metal surface. This surface is the ground plane and necessary for the antenna to operate properly. The ground plane should be directly beneath and at right angles to the antenna. The perfect spot is dead center on the cab roof though this is not always practical. No Ground Plane type antennas are available if you don't have any flat metal surfaces to mount your antenna.

    8. If you're mounting your antenna using a mirror mount make sure the mirror support solidly connects to a conductive metal door. The mirror may have insulating washers or spacers which can insulate the mirror ground-wise from the door. Fiberglass doors popular on some vehicles are a problem, especially on lower frequencies since the door is part of the ground plane in this situation. No Ground Plane type antennas are available if you are unable to mirror mount your antenna to a solidly grounded mirror and door.

    9. If you're mounting your antenna on a trunk make sure your trunk is made if sheet metal, not fiberglass. Fiberglass trunks are popular on some vehicles and create a no ground plane situation. No Ground Plane antennas are available but a better solution is to create an artificial ground plane using metal plates, jumpers or conductive tape on the inside surface of the trunk. (see below).

    10. If you're unable to mount on a solid metal ground plane you can purchase special metal plates which will fit under the antenna mount to create an artificial ground plane. Another way to correct for a missing ground plane is to use braided wire mesh as a short jumper to the nearest metal surface near the mount. Strips of conductive metal tape can be used to create an artificial ground plane if there is not a nearby metal surface to ground the mount. The metal tape is available at most building supply stores.

    11. Magnet mounts should be tested in the middle of the cab roof, the next best spot is the middle of the trunk. Both roof and trunk should be made of conductive metal, preferably steel so the magnet will stick. Keep in mind that a magnet mount base serves two important functions: 1. It holds the antenna system to the vehicle. 2. It connects the grounded side of the antenna to the metal surface under the magnet to provide a ground plane for the system. Don't put anything between the magnet mount and the surface you're mounting it on or the RF coupling through the bottom of the magnet to the ground plane underneath will be broken giving poor measurements and performance.

    12. If your readings seem high or inconsistent try changing your cable length a foot or so if possible and take the readings again. Make sure you're using high quality 50 ohm coax (low loss RG58 type) with the proper connector and no splices, coax switches, duplexer or multiplexer in the cable path.

    13. If you're using an in-line SWR meter be sure your transmitter output is clean, any spurious output (spikes from power amps especially) will raise your SWR. Test at the lowest power possible, 5 watts is fine.

    14. There can be considerable differences in calibration accuracy between different models of Antenna Analyzers, if possible try at least two different models to make sure your readings are generally accurate.

    15. When using an Analyzer to evaluate Multiband Scanner Antennas keep in mind that the manufacturer is using complicated design techniques to get multiple band coverage in a single antenna housing or structure. Your analyzer readings will vary widely from band to band and frequency to frequency. The design is usually for "receive only" so low SWR is not a primary objective and will usually be the lowest near the receiving band centers. As with all mobile antennas a solid ground plane is necessary for accurate analyzer readings and best results.

    16. Your scanner is not very concerned with SWR and has little difficulty receiving signals from a higher SWR antenna source, e.g., the metal rod antenna it usually comes with in the box. One of the most important factors in an efficient Multiband Scanning Antenna system is using a high quality low loss coax cable and a quality connector between the antenna and your scanner. Keep your cable as short as possible and purchase the best cable you can afford, preferably commercially made mount with connector installed. A much higher than 2.0:1 SWR is acceptable and most Multiband Scanner Antennas will receive very well outside their stated band ranges.

    17. Avoid "Antenna A" vs. "Antenna B" comparisons. Manufacturers use different design techniques to lower SWR, some of which can degrade performance. No two antennas, unless they are of identical manufacturer, design, frequency range, test position and model are going to be useful in comparison tests.

    18. Specific frequency tuning for lowest SWR is usually not done by Commercial Two-Way Antenna manufacturers unless explicitly specified as is the case with low profile and some quarter wave mobile antennas. Requesting a specific tuning frequency / lowest SWR frequency is no guarantee a Commercial manufacturer will honor it. Many mobile antennas are made to be field tuned by the end user and are supplied with cutting charts. Fixed frequency band Commercial Mobile Antennas are designed to cover a very defined bandwidth with a guaranteed SWR of usually < 2.0:1 over that range and are not field tunable. This means you may see considerable variation of SWR over the specified frequency range but it will generally remain within the guaranteed < 2.0:1 specification. This must be considered when making measurements on any fixed range Commercial Mobile Antenna.

    19. Call for Assistance

    MOBILE ANTENNA EXPECTATIONS:

    1. Make sure you understand the differences in the specifications and product design goals of different types of manufacturers, especially Commercial vs. Amateur. Commercial Two-Way Antenna manufacturers design their products for police, fire and industrial users and are required to meet their published specification sheet parameters for a particular model. Amateur Radio antenna manufacturers have a much more defined market and design for it specifically. Their design techniques are usually for Amateur Radio service only and are not suited to Commercial Two-Way service. Commercial Two-Way Antennas will work well in Amateur Radio service if the user can tolerate generally higher SWR in parts of its specified band range.

    2. Scanner Antennas are a special case since most are designed for receive only with a few exceptions. Scanner Antennas can sometimes overlap Commercial and Amateur service if specifically designed with higher quality, more robust components and are "transmit capable". Some notable designs are the Austin Ferret base and the Austin Spectra mobile antennas. Since these type of antennas are wide frequency coverage, multi band designs the user may have to tolerate somewhat higher SWR in some parts of its specified band ranges if transmitting.

    3. The antenna gain and SWR bandwidth published specifications can differ widely between Commercial Two-Way and Amateur Radio antennas designed for the same band. The terms used and measurement techniques employed are usually not standardized and many performance claims must be taken with a grain of salt. Commercial and Amateur manufacturers have vastly different parameters they must meet to satisfy their customer base. Commercial and Amateur manufacturers can also differ widely in their price, quality of manufacture and quality control.

    4. Specific frequency tuning for lowest SWR is usually not done by commercial manufacturers unless specified. Low profile Commercial antennas are the exception and require specific frequency tuning because of their very narrow bandwidth. Quarter wave antennas are also usually tuned or pre-cut to a specific band range. Most Commercial antennas are designed to cover a very defined bandwidth with a guaranteed SWR of usually < 2.0:1 over that range.

    5. Understanding the differences between Commercial Two-Way, Amateur Radio and Scanner antennas will save a lot of frustration and disappointment when making Analyzer or SWR measurements. Carefully consider your expectations before purchasing an antenna designed for one type of service and applying it to another.

    6. Call for Assistance




    NOTE: Features, prices and specifications subject to change without notice.  Not responsible for typographical or technical errors, information presented is for general evaluation only.

    Antenna SWR meters and Impedance Analyzers Testing Setup Proceedures and Best Practices

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    Tags: antenna, testing, swr, analyzer, commercial, amateur, scanner, service, vswr, return loss