Effects of Radio Interference on Proximity Readers

INTRODUCTION

Integrated Systems & Services, Inc. was requested to perform an evaluation of the effects of radio interference on access systems for several clients over the past year.

The study was performed due to various complaints from customers located throughout the nation regarding slow card reads and miss reads.

This evaluation consisted of dialogue with all concerned parties, reviewing the system programming in the front ends, evaluating archive reports for card use, the environment of the facilities, a physical inspection of the equipment installed and technical testing at various sites.

A radio frequency audit was performed for each site and we discovered each site had several cellular radio transmitters located within close proximity to the facilities. These towers utilize radio frequencies which occupy the same radio frequency bandwidth as the WSE access cards.

The above findings, explored in detail within this document, are indicative of the problems experienced by the end user. As such, the system evaluation focused on the aspects of the installation and potential radio interference at each site. This path was proven upon the conclusion of our site inspection and evaluation. This document is the compilation of our findings.

The inception of or study consisted of a physical walk through of each controlled entry at each affected site. These inspections were conducted throughout the nation at potential radio interference sites. This inspection consisted of evaluating the appropriateness of the equipment installed and a visual observation of the card reader LED for any strong environmental noise. Numerous readers were found with high levels of noise. This was determined by monitoring the flash rate of the reader LED. The reader LED is located in the center of the WSE reader. Normally, the reader LED will flash with a rate of 0.25 sec. When a card or noise is present, the reader flash rate will slow to approximately 1.5 sec.

Upon the conclusion of the above observations, we initiated technical testing of the installed systems. These tests included electronically measuring the system cables and associated power supplies. These tests were performed to eliminate any potential internal causes for the system deficiencies.

Each site was checked for the proper cable, cable path and terminations. Additionally, each system component was tested to confirm operation within factory specifications.

A through evaluation of external sources of noise was conducted as part of our evaluation. Radio frequency interference is a leading cause of poor system performance. The complaints we had received from our end users are indicative of environmental noise.

The WSE access system utilizes radio frequency technology to interact with an access card. The access control reader consists of a tuned radio antenna that monitors the air space surrounding the reader for the presence of a card. The access control card is a radio frequency transmitter tuned to a specific, unique frequency for each card. When the card is placed within the radio frequency field of the reader, the card transmits its unique frequency to the reader. This action occurs several times in rapid succession before the door unlocks. When external radio frequency noise occurs in the readers RF field, the noise affects the frequency transmitted by the card. This affect causes the reader to “receive” the wrong card frequency and pass the wrong card number on to the ACU. As a result of this, a valid access is subsequently denied.

WSE provides a test utility to monitor RF interference which is internal to the Access Control Unit or ACU. This test utility allows the installer to view the level of radio interference present on each reader. This test scans the readers environment for noise within the products operating range. The frequency range evaluated is 2MHz to 27 MHz. This noise test provides a report which indicates the frequency of noise present for each card sweep. Each card sweep lasts approximately 0.023 sec and a minimum of four good sweeps of a card is required to properly interpret the card frequency and subsequent card number.

WSE card types and numbers provide an end user with insight into the cards frequency. WSE offers several card technologies which operate at different frequencies. The 1030 type cards occupy the low end of the bandwidth while the 1060 type occupies the high end of the bandwidth. The 1040 and 1050 type cards fall between the 1030 and 1060 type. In addition, the card number also has a correlation to the card frequency. A low number equates to a lower frequency than a similar card type with a higher number. The problems encountered at the facility are more prevalent with those cards of a 1030 type and any number and 1050 type cards with lower numbers. The noise induced into the system is at the low end of the bandwidth. As such, 1030 type cards and low number 1050 cards will experience the most trouble. However, it is important to note that the frequency of the interference is only one component of concern. Each source of radio energy is “pushed” by radio energy. The closer the source of noise, the higher the induced energy. By example, a noise source outside of the frequency range of the system but of sufficient power, can and will cause noise problems.

BANDWIDTH RELATIONSHIP

| 2 8 12 16 20 24 27 mhz|

1030 1040 1050 1060 type card

The systems evaluated were wrought with external noise. In particular, readers oriented towards the radio source were found to have the most significant interaction with the noise source. Readers oriented away from the radio source were found with less levels of noise and hence better interaction with the client population.

Cellular transmitters utilize a carrier frequency within the frequency range of WSE 1030 keys. Some end users indicated the problems appear to be with those clients utilizing the older technology cards.

The WSE test utility displays each sweep of the reader and reports the number of frequency “hits” received on each sweep. An asterisk indicates hits greater than 10. The following is a sample report of a single read display;

In the above example, noise is detected on the first 5 of 15 sweeps. This level of noise will be transparent to a system user. The below example is illustrative of the readers located in line with the radio source;

In the above example, each sweep reports noise and a card presented to a reader with this level of noise will perform poorly, if at all. The effects of this noise will be seasonal. The foliage on trees will mitigate some noise when the trees are in line with the radio source and affected reader(s). during the winter months, the absence of foliage will increase the affects on the affected readers. As the leaves develop, the noise will diminish somewhat due to the effects of the foliage on the transmitters frequency. A radio transmitters propagation patterns are affected by the cellulose in the tree leaves. As such, the effects of the noise will be more apparent in the winter than summer months.

After discovering the excessive noise, we focused our evaluation on specific doors within the evaluated facilities. A door with high levels of noise was studied in greater detail. Progressive tests were performed on this door. The tests consisted of the following configurations;

Coax only without MSM and reader reported low noise.

Coax and MSM without reader, reported low noises.

Coax and MSM with reader reported excessive noise.

As indicated by number 3 above, the addition of the reader to the cable caused the noise level to reach unacceptable levels.

Radio frequency interference is typically positional to the reader. The tested reader was mounted on a

northerly plane. As such, we did perform tests with the reader to determine the positional affects of the noise.

Reader in existing northerly plane reports unacceptable noise.

Reader moved 90 degrees on easterly plane reports unacceptable noise.

3. Reader moved to a northeasterly plane reports acceptable noise levels.

The above tests provide conclusive evidence of environmental noise impacting the performance of the system. When this reader is positioned “edge on” to the compass direction of the cellular transmitter, the noise is sufficiently mitigated to acceptable levels. The reorientation of the reader(s) will mitigate the noise.

Although this document was developed to determine the effects of cellular transmissions on WSE systems, other sources of RF energy exist. These sources include CB radio, microwave communications and general commercial radio. These sources of energy will only affect a system when in close proximity. The effects of these sources is detected and treated in the same manner as the cellular communications. Details’ regarding each type of energy is provided below.

CB RADIO

In the late 1970’s, CB radio reached its peak in usage. The original design provided for a personal transmitter transmitting at a 4 watt limit. Over time, these radio users modified the transmitters through the use of a pre amplifier to provide up to 1,000 watts of energy. These devices, when fixed, will cause interference to a system whenever the transmitter is in use. Frequently, the effects of these transmitters are discovered in the evening and weekend hours. This is due to the devices being used in residential structures after working hours. These units can also be installed in vehicles. Frequent application of these high power transmitters is found in commercial trucks. The effects of the mobile units are typically experienced when the system is located within close proximity to highways.

Commercial radio applications utilize the UHF and VHF frequencies. These units will cause system problems when the units are located within close proximity of the system. These transmitters are typically located on towers or building rooftops. In addition, the UHF frequency provides for a user to utilize a directional antenna. These directional antennas will cause system problems when the antenna is directed at the reader.

The advent of cellular communications is having a direct impact on proximity access control systems. As the need for clearer communications grows, and the number of cellular carriers continues to increase, clients will suffer the effects of the radio interference.

Customers who have had trouble free installations over the years and begin to experience slow reads and miss reads, should have their system evaluated for noise. This evaluation can be completed by the end user utilizing the information contained within this document. The proximity reader provides a diagnostic tool; the reader LED, which can be utilized to provide a visual indication of radio interference affecting the reader. In those instances where radio interference is identified, the installing company can relocate or reorient the reader to minimize the affects of the noise. Unfortunately, the proximity reader is designed to interrogate the environment for radio frequencies such as those emitted by a valid access card. Therefore, the radio interference from external sources cannot be completely mitigated. Eliminating the noise eliminates the ability to read a valid card.

Based on these findings, customers must be cognizant of the impact of cellular communications on access systems. We find that customers seeking alternate sources of revenue are considering or have implemented the installation of a cellular carrier within their facility. The consequences may be the wholesale replacement of an access system. Customers have successfully installed cellular carriers within their facility with negligible impact to their system. Proper placement of the tower and orientation of the readers does allow the systems to coexist within a facility.

The findings within this document are the first stage in addressing the problem. With the knowledge gained in this study, we have implemented certain installation practices to mitigate problems for new installs and add ons to existing systems.

Clients with installed systems and radio interference will need to evolve towards new reader locations and possibly new technology to mitigate the problems caused by radio interference.

Please contact our office should you have any questions or concerns regarding the information presented within this report.