the apparatus preferably is installed and the signal coupler mounted on the distribution cable at the point where a branch line begins . this has the effect of maximizing the signal in the branch line as the low impedance of the trunk line provides a return path for the current . it also has the effect of partially isolating the branch line from the trunk line , as the coupler has a series impedance at the signal frequency ( approximately 15 – 95 khz ) which is higher than the impedance on the trunk line . to automatically vary the impedance of the coupler , the method in the block diagram of fig1 preferably is used . the coupler has 16 turns of wire that is used to form a parallel tank circuit with selectable external capacitors . the medium tension insulated power distribution line passes through the center of the coupler . two transmit signal wires pass through the coupler ; one carries a carrier signal at the selected frequency , while the other carries the modulated data signal at the same frequency . transmitter # 2 is turned on at the desired frequency , passing the carrier frequency signal through a 250 - ohm resistor and the coupler . the receiver is connected to the same circuit and is used to sense the amplitude of the signal at the coupler . the microprocessor sends modbus protocol commands to the di - 509 controller to control the relays , which switch capacitors in and out of the circuit until the maximum signal is received at the coupler . this causes the coupler to be tuned to the maximum impedance for the selected frequency . maximum impedance is desirable because it provides for maximum signal coupling efficiency , as shown in the table in fig2 . when the auto - tune sequence is completed and maximum signal coupling ( highest signal - to - noise ratio ) is achieved , transmitter # 1 is then used for data transmission . in one preferred embodiment , the coupler is mounted to a section of cable ( e . g ., two meters long or so ) and then surrounded by weather - resistant material ( e . g ., plastic molding ). this improves durability and enhances installation . the invention has numerous advantages over the prior art that will be apparent to those skilled in the art . for example , as discussed above , because of the relative impedance of the trunk line being low and that of a branch being somewhat higher , the coupler tends to isolate the signals that are on the branch from the coupler , preventing them from being sucked into the branch . so it gives it a higher impedance for sending the signals out and receiving them back . they have to pass through the coupler before they go into the trunk line , so that the coupler tends to capture the signal ( as a receiver ). for transmission , having a lower impedance behind the coupler is good for sending signals down the branch . another advantage is ease of installation , which often entails merely replacing a pre - existing section of cable ( a “ loop ”) used to couple a trunk line to a branch with the cable - mounted coupler of the invention . an advantage of auto - tuning is that it enables not only re - tuning as needed to compensate for temperature changes , but it also enables re - tuning due to signal frequency changes . preferably several different frequencies are used ( e . g ., 16 ), to reduce interference problems or to enable different frequencies to be used on adjacent branch lines . in an alternate embodiment , the coupler is fitted or in communication with a temperature sensor , to enable re - tuning as a consequence of temperature values ( or temperature change values ). in another embodiment , the coupler is fitted or in communication with a frequency detector , to enable re - tuning as a consequence of a frequency change . in further embodiments , when temperature or frequency changes are detected , total re - tuning does not necessarily occur . instead , the coupler is tuned to the state that was used previously when that frequency or temperature was detected . this reduces the number of re - tunings required . frequent re - tunings can be problematic when , for example , frequencies are changed often . coupling to the point where a branch ( or lateral ) feeder splits off from the trunk ( or express ) feeder is best employed ( for economic reasons ) where there are more than 50 – 75 customers on the lateral feeder to which the coupler is connected . a coupler typically is installed together with a transponder ( a bidirectional communications device for powerline communications sold by quadlogic controls corp of new york , n . y ., usa (“ qlc ”)). the total cost of the coupler plus the transponder merits careful planning of the deployment of the coupler / transponder sites . 1 ) on the main feeder by adding high voltage blocking capacitors ( for example metallized polyester 0 . 25 microfarad 12 kilovolt ac capacitors or commercially available oil filled power factor correction type capacitors ). to use this method , install a dual bushing capacitor on a utility pole . connect one bushing to a 12 kv phase line , connect the other bushing to an adjacent phase line or neutral via the coupler described previously . this places the coupler in series with the capacitor . this can be accomplished using a commercially available 10 kvar capacitor with dual bushing from a manufacturer such as abb ( asea brown bovari ). 2 ) wherever there are banks of power factor correction capacitors already installed before the coupler is installed , a coupler should be installed on the existing capacitor bank . existing capacitor banks are installed on the trunk or other feeders for the purpose of correction of power factor . these capacitor banks most likely use capacitors such as the one described in the previous point . the end result of this is the same as the point 1 above . the coupler ends up in series with a capacitor , connected either phase to phase or phase to neutral . the only difference is whether the capacitor bank was existing before the coupler was installed or whether it was installed as part of the coupler installation . transponder / coupler placement : the main factors influencing the location of a transponder / coupler are the number of laterals ( branches ) and the number of clients per lateral . if there are enough meters on a lateral to warrant the installation of a transponder / coupler , the transponder / coupler should be located on that lateral . a . one transformer b . three branches ( e . g . express to lateral to sublateral or lateral to sublateral to sub - sublateral ) c . upwards of 15 km ( field proven at 15 km ) of express line a . 3 ph . 3 w .— 1 coupler b . 3 ph . 4 w . 3 couplers c . single phase loads — 1 coupler per phase 1 . inline lateral coupler : this unit replaces the drop wire from the feeder to the lateral . this coupler should be used on laterals which have large numbers of customers ( greater than 75 .) 2 . express feeder coupler : this unit is installed directly on the express feeder with the addition of a 10 kvar 12 kilovolt dual bushing capacitor ( abb manufactures capacitors for this application ). it can be installed either phase to phase or phase to neutral . this is useful on long express feeders with laterals having few customers ( up to 200 or 15 km of express line length .) 3 . capacitive couplers : similar to the inline lateral coupler , this unit replaces the drop wire from the feeder to an existing bank of power factor correction capacitors . it must be used wherever there is a capacitor bank installed on any feeder — either express ( trunk ) or lateral ( branch ) feeder . 4 . split core couplers : these units are designed for underground , insulated cables and should be deployed wherever there are power factor correction capacitors . typically these units would be used for suburban subdivisions with underground distribution . 1 . a transponder / coupler must be installed wherever there are power factor correction capacitors . 2 . a transponder / coupler - 200 has a maximum capacity of 200 customers . ( except in cases of densely populated laterals , for example of 75 – 100 customers where one transponder / coupler would be installed for this subset of customers .) 3 . for every 15 km of express line length , a transponder / coupler likely will be required . 4 . a transponder / coupler is expected to traverse no more than 3 branches ( e . g ., express to lateral to sublateral , or lateral to sublateral to sub - sublateral ). 5 . no customer data can be transmitted through more than one transformer to the transponder / coupler ( this is very rare ). 6 . a coupler can serve as a block for a neighboring transponder / coupler to bypass a lateral and communicate with meters beyond that coupler . for example , transponder / coupler “ a ” communicates to a geographic area of 15 lightly populated laterals . within that area , there is one densely populated lateral ( 75 – 100 customers ) that requires transponder / coupler b . transponder / coupler b will not permit transponder / coupler a &# 39 ; s plc signal to run down its lateral (“ plc ” is power line communication ). therefore , transponder / coupler b allows transponder / coupler a to essentially ignore the densely populated lateral and bypass it to communicate with the remaining lightly populated laterals down the line . 7 . by careful engineering of each system , as each system is unique , utilizing the different coupling systems , it is possible to optimize communication integrity with a minimum of transponder / coupler sets , thus reducing reliance on costly , monthly fees from third party suppliers . 8 . coupler designs are available up to 35 kv , and all are for indoor or outdoor use on copper or aluminum . scu utilization : the overhead couplers are designed to allow install installation using live line techniques when used on lateral feeds or express feeders . this means that the couplers can be installed without disconnecting power . see fig5 and 6 . the split core may be installed this way on underground installations where the concentric neutral is stripped back or nonexistent . the coupler will also act as an upstream block to down stream signals making it a useful tool in plc communication design . as more than one coupler can be tied to a transponder / coupler they can be used to cross - communicate between two different laterals , in close proximity . transponder : the transponder module has the ability to handle bi - directional requirements for up to 200 metering units , and up to three modules can be ganged together to make a transponder unit that can service 600 metering units via plc . the transponder unit has the ability to output to a variety of communication media ( all via existing rs232 , rs485 , or pots plain - old telephone modem ): 1 . gprs 2 . pots telephone copper pair via internal modem ( 19200 baud ) 3 . cdma / gsm 4 . rs 232 5 . rs 485 6 . fiber ( via fiber to rs232 converter ) 7 . plc to master transponder via power lines the system has the ability to transmit on several frequencies and to have the communication timing planned and programmed so that large systems can be engineered to avoid communications and data collision issues . the transponder , in one embodiment , requires 3 phase power supply @ 60 hz . plc frequencies : when multiple transponders are installed on one feeder , the transponders will utilize the “ channel groups ” feature so as not to interfere with each other . the transponders are put on different frequencies . qlc &# 39 ; s plc has five bands each with 16 frequencies totaling 80 channels . each channel can collect daily metering information for 200 customers within the allotted time to perform this task . plc bandwidth : the qlc system operates at a high enough bandwidth to allow the collection of interval data from large meter populations . each transponder module is able to collect 200 meters programmed with hourly interval data within a 5 hour time frame so as to have data available for collection by 5am . although those skilled in the art will understand , from the above description , how to make and use the claimed invention , additional details regarding construction of a preferred embodiment are provided below . place two 0 . 50 ″ segments as sleeves over each prong of the u - shaped ferrite . slide both segments all the way to the bottom of the u . heat shrink the segment to create a snug sleeve . wrap two 7 ″ zip ties on the bottom side of each sleeve and tighten to secure each sleeve from sliding . repeat the process to create 10 pieces . stack 5 u - pieces together in parallel . sandwich a 0 . 25 ″ flattened segment at each of the four surfaces where the troughs of the u &# 39 ; s meet . fasten two 11 ″ zip - ties together , head to tail to make one double length zip tie . use this “ double - tie ” to hold the u &# 39 ; s together at the troughs . make two more double - ties to hold the u &# 39 ; s together at each prong of the u &# 39 ; s . repeat this process with the remaining 5 u - pieces to make another stack . designate one stack as the “ bottom stack ” and the other as the “ top stack .” on the bottom stack , glue 10 spacers , one on the surface of each end of each u . allow glue to dry . mate the two stacks together to create a closed rectangular block . the surface - ends of the u &# 39 ; s should meet , creating a stack of 5 - parallel rectangular frames . create 5 more double - ties . secure each of the five rectangular frames under tension with a double - tie . feed 16 turns of 14 awg wire over the top stack and leave excess length of 20 feet on both sides . twist the excess wire to create a twisted pair . 1 — connector terminal block 4 position 5 . 08 mm pcb ( phoenix contact : 1729144 ) while certain specific embodiments of the invention have been described herein for illustrative purposes , the invention is not limited to the specific details , representative devices , and illustrative examples shown and described herein . various modifications may be made without departing from the spirit or scope of the invention defined by the appended claims and their equivalents .