m/a-com, inc. north america: tel. (800) 366-2266 n asia/pacific: tel. +85 2 2375 0618 n europe: tel. +44 (1344) 869 595 fax (800) 618-8883 fax +85 2 2375 0350 fax +44 (1344) 300 020 1 specifications subject to change without notice. lightning and emp protection devices id 2012 v3.00 introduction m/a-com has developed a unique series of lightning and emp protection devices for use in cellular infrastructure including gsm, dcs 1800, and pcs 1900 systems. these devices are designed to offer the cellular operator protection against emp (electro-magnetic pulses) caused by lightning strikes. direct or even near strikes produce fast rising electric fields within micro- seconds. these fields generate high voltage pulses through unprotected antennas and transmission lines which lead to the primary communication equipment. high voltage pulses can cause extensive damage leading to costly repairs as well as significant loss of service to subscribers. these protective devices come in two different categories: surge protectors and quarter wave stub tuners. the intent of this application note is to comprehensively explain how the devices work, the electrical parameters of each system, and how to choose the device best suited to your application. surge protectors these devices incorporate gas discharge tube (gdt) technology. a gdt is a hermetically sealed tube containing an inert gas. the tube is inserted in the side of the device through an easily accessible weather sealed port. during normal operation the tube is inactive. when an installation is struck by lightning, a high voltage impulse will appear on the coaxial line. as the impulse amplitude rises, a level is reached where the impulse surpasses the dynamic voltage threshold of the tube and the electrodes arc over to discharge the energy to ground. prior to activation of the tube, there will be a short period of time where energy will be present on the line. this residual pulse is equal to the dynamic voltage threshold of the tube. the maximum impulse voltage a tube can handle without discharging is referred to as the impulse sparkover voltage. this capacity of the gdt is quoted as follows: in the case of the above chart, the voltage will rise at one kilovolt per microsecond and the tube will fire after 650 nanoseconds. during activation a small percentage of voltage (called arc voltage) will still pass through. this will be approximately 20 volts. when the pulse subsides, the tube again becomes inactive leaving a small residual voltage on the line. a direct lightning strike results in an impulse current of high amplitude. the capability of a device to protect a system is defined as the impulse discharge current rating. this is defined as the peak current of an impulse which the device can withstand ten times (5 at each polarity at fixed intervals) without affecting the device. maximum impulse discharge current is the peak current of an impulse the device can withstand once. surge protectors are often used in applications requiring a standing dc line voltage. this is typical in applications with mast top electronics. the maximum voltage capacity of a surge protector prior to it surpassing the static voltage threshold and discharging it to ground is defined as its d.c. sparkover voltage. this capacity is quoted as follows: characteristic symbol definition impulse typical value impulse u zdyn dynamic 1kv/ m s 650v sparkover voltage voltage threshold characteristic symbol definition impulse typical value d.c. u zstat static n/a 230v sparkover voltage voltage threshold
m/a-com, inc. nor th amer ica: t el. (800) 366-2266 n asia/p acific: t el. +85 2 2375 0618 n europe: t el. +44 (1344) 869 595 f ax (800) 618-8883 f ax +85 2 2375 0350 f ax +44 (1344) 300 020 2 specifications subject to change without notice . in these applications it is important to select a device that will assur e the tube can r eturn to its inactive state after the passage of a sur ge. this featur e of the sur ge pr otector is known as the holdover vol t age. if the device continues to conduct, the pr otected line will be short cir cuited and the tube will heat up (glow mode). if left in this state, the tube can over heat and destr uct. gdt? have a finite life span which is inversely pr oportional to the ener gy dissipated. at extr emes it is possible to r each a level wher e the tube is unable to dischar ge all the ener gy and is destr oyed. it is ther efor e necessary to schedule r outine maintenance checks and periodically r eplace the tube within the sur ge pr otector . sur ge pr otectors of fer excellent lightning pr otection for br oadband systems and ar e usable up to 2.5 ghz. standar d interfaces include 7-16, n, and sma. configurations include straight and bulkhead mounted adapters which allows for ease of assimilation into existing systems. quar ter w ave stub t uners these devices ar e thr ee port coaxial connectors. the thir d port extending fr om the main thr ough path is terminated in a short cir cuit at a pr e-determined distance calculated to be exactly one quarter wavelength at the desir ed center fr equency (see graph). unlike sur ge pr otectors, this design eliminates concerns about r esidual pulse, sparkover voltage and r esidual voltage ensuring gr eater pr otection for sensitive electr onic equipment. as opposed to sur ge pr otectors, stub tuners will absorb lightning strikes without need for r eplacing components. these devices yield very low vswr and featur e high attenuation within a r elatively narr ow pass-band (+/- 70 mhz) but ar e application specific. stub tuners also pass ener gy in bands that ar e harmonically r elated to the fundamental center fr equency . the graphs below show a typical test impulse and the r esponse of a stub tuner . l i v i v r l r 0.3 1.0 1.9 0.5 0 v t 1 = 1.67t t 2 t 0 1 t 1 t 326.400 110.308 vka 244.800 94.5588 vka 163.200 78.8088 vka 81.6000 63.0588 vka 0.0 47.3088 uv ka -81.600 31.5588 vka -163.20 15.8088 vka -244.80 58.80 va -326.40 -15.691 vka 01/16/96 14:07:02 -640.0ns, 80.033280 v 10.98us, 49.45920ka 0.0ns 20.00us 40.00us 60.00us 80.00us 0.0ns 20.00us 40.00us 60.00us 80.00us l /4 shor ting stub b asics typical test impulse typical l /4 test response
m/a-com, inc. nor th amer ica: t el. (800) 366-2266 n asia/p acific: t el. +85 2 2375 0618 n europe: t el. +44 (1344) 869 595 f ax (800) 618-8883 f ax +85 2 2375 0350 f ax +44 (1344) 300 020 3 specifications subject to change without notice . stub tuners ar e classified into two br oad categories- simple and br oadband. the simple stub tuner exhibits a v -shaped r esponse on the vswr vs. fr equency plot. the tr ough of the v is designed to occur at the r equir ed fo and the bandwidth is r estricted to appr oximately 8%. the br oadband tuner employs extra rf techniques, similar to multiple cavity filtering, which incr ease the ef fective bandwidth by appr oximately 20%. m/a-com of fers a wide variety of stub tuners for the most popular fr equency bands to facilitate pur chase without need for custom design and manufacturing. designs exist for gsm, pcs 1900, dcs 1800 fr equencies with standar d industry interfaces including sma, 7-16, and type ?? configurations include cable assemblies, cabled connectors, and adapters for ease of assimilation into existing systems. stub tuners ar e maintenance fr ee since they incorporate no active components though it is r ecommended that a check of the stub tuner af fixment be made following heavy dischar ges at an installation. selection of a lightning pr otection device below ar e the basic advantages and limitations for both types of pr otection to use in the pr oper selection for your application: surge protectors advantages br oadband allows dc bias on the transmission line. (critical for applications using mast top electr onics.) no harmonic passband ease of r etr ofitting antenna sights gdt easily accessible for r eplacement limitations routine maintenance r ecommended 2.5 ghz maximum fr equency initial pass-thr ough voltage l /4 stub t uners advantages low vswr in passband minimal maintenance pass - thr ough voltage eliminated no sparkover or r esidual voltage concerns ease of r etr o-fitting antenna sights limitations fr equency specific harmonic passband does not allow dc bias on transmission line glossar y of t er ms arc v oltage - voltage that continues to pass thr ough a sur ge pr otector during activation of gdt (appr ox. 20 volts ) d.c. sparkover v oltage - defined as the maximum voltage acr oss a device befor e it dischar ges the ener gy to gr ound when subjected to a slowly rising voltage ramp. a rate of rise of 100v/s is usually chosen for testing purposes. gas discharge t ube (gdt) - hermetically sealed device containing an inert gas. glow mode - condition in which the gdt continues to conduct after an impulse passed. characterized by a visible glow in the device caused by over -heating. v oltage hold over - r efers to the maximum line voltage at which r ecovery of the gdt to its inactive state will take place within a specified period period of time (normally 150ms) after an induced lightning pulse (normally 10/1000ms) has been applied. impulse discharge current - defined as the peak curr ent of an impulse which a gdt can withstand ten times (5 at each polarity) without af fecting the device. impulse sparkover v oltage - defined as the maximum level of voltage acr oss a device befor e it dischar ges the ener gy to gr ound when subjected to a voltage impulse. the thr ee common waveform pr ofiles used to determine this capacity ar e: t 2 t 2 =1.67t t t l 0 1 t a t 8 0 0.3 0.5 0.9 1.0 v
pr inted in u .s . impulse discharge current - is defined as the peak curr ent of an impulse which the device can withstand ten times (5 of each polarity at fixed time intervals) without substantially af fecting device performance. the test normally used to determine this capacity uses the 8/20ms waveform as depicted below wher e t1=8ms and t2=20ms. maximum discharge current - defined as the peak curr ent of an impulse which the device can withstand once without substantially af fecting device performance. residual impulse - defined as the voltage that will pass thr ough the device prior to activation of the gdt . residual v oltage - defined as the small amount of voltage left on the line after an impulse passes fr equently asked questions 1) if lightning r ods ar e installed in an antenna site is additional pr otection r equir ed? y es. lightning is highly unpr edictable and can strike locations other than the lightning r od. when lightning does strike a r od, ther e ar e still secondary pulses which installations should be pr otected against in key ar eas. 2) wher e should lightning pr otection be positioned within the cellular infrastr uctur e? normally pr otection is installed at the junctions wher e the transmission line joins the antenna and wher e the cable joins the base station electr onics. lightning pr otection needs to be tailor ed to the particular infrastructur e. the type of devices used and locations depend on the sensitivity of the electr onics and their location within the infrastructur e (i.e. mast-top electr onics vs. standard base station location). 3) what is the shelf life of a r eplacement gdt? the typical shelf life of a r eplacement gdt is 5 years. this enables the maintenance pr ovider to inventory gdt s for r outine maintenance and insur es a speedy r eturn to service in case of sever e lightning strikes. 0 1 t 2 t 1 = 1.25t t t t 1 a b 0 i 1 -0 0-1 0-5 0-9 4) when should a gdt be r eplaced within the sur ge pr otector? gdt s ar e capable of withstanding multiple strikes of varying intensity dependent on the specification of the device. however , ther e ar e no outward signs of how many strikes a gdt has absorbed. routine r eplacement should be scheduled based on the fr equency and magnitude of storms in the ar ea of the site. 5) w ill lightning pr otectors contribute to inter - modulation ? ther e is always potential for intermodulation when a device is placed in an rf transmission line between the antenna and the filter . m/a-com has taken pr ecautions to manufactur e these devices using non-ferr ous materials and to pr ovide a superior plating finish to ensur e this condition is minimized. 6) can existing antenna sites be r etr ofitted with lightning pr otection? these pr oducts can be easily r etr ofitted into existing systems. m/a-com supplies pr otection devices to be cabled as complete cable assemblies or as adapters. all of these ar e available with standard rf interfaces including n, 7-16, and sma. the above information gives the basic guidelines for determining which pr otection system is corr ect for your application. please contact m/a-com s global application engineering team for additional specifications of this exciting new pr oduct line. m/a-com is continuing to work on new and innovative pr oducts for the wir eless market to complement our complete line of quality coaxial rf connectors and cable assemblies. m/a-com is iso-9001 certified so you can be assur ed that these new pr otection devices will meet the same high standards for performance and workmanship as you have come to expect fr om the leader in rf/micr owave inter connect pr oducts. north america t elephone: 1-800-366-2266 fax: 1-800-618-8883 central america t elephone: 602-949-1642 fax: 602-941-1703 south america t elephone: 770-956-0351 fax: 770-953-9056 europe/middle east/africa t elephone: +44 (1344) 869 595 fax: +44 (1344) 300 020 asia/pacific t elephone: +85 2 2375 0618 fax: +85 2 2375 0350
|
