2712 Bandpass Filter
Small footprint, up tp 15kW with blowers
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Branched & Starpoint FM Combiners
Shively Labs Model 2530, 2630 and 2930 branched combiners are designed to combine the signals of two, three, or four stations over a single antenna. These combiners provide superior performance in the smallest space possible, and are fully IBOC-compliant. All Shively Labs combiners use bandpass filtering, providing higher spectral purity, flat in-band frequency response, and typical isolation values of 50 dB or higher – even for frequencies 0.8 MHz apart – and ensuring conformance to the most stringent regulatory specifications.
Each Shively Labs branched combiner consists of bandpass filters (one for each station), a matching section. An optional a precision single directional coupler for the output is available upon request. Shively Labs branched combiners do not require system reject loads.
Each bandpass filter is sized according to the output power of the transmitter it is paired with. For most applications, three-cavity bandpass filters are the optimum choice. Two-cavity filters can be used where the frequency spread already provides a good deal of isolation, and where space is at a premium. For three- and four-station combiners where the frequency spacing is 1.8 MHz or closer, four-cavity bandpass filters may be required for the middle station(s). Feedback loops are used on any combiner with 1.8 MHz or closer spacing.
Combiners can be designed from any combination of bandpass filter designs. Because of the large number of possible combinations, most of the data on this website were developed assuming that all filters in a combiner system are of identical design.
However, we have just developed a new data sheet with specifications for some combination iris-coupled and interdigital combinations. Please consult the factory for the specifications of other systems with non-symmetrical filter designs.
The matching section is sized to accommodate the combined average powers of all the transmitters. The design of this matching section is customized for each system; therefore, the size, weight, and location of the output will vary between systems.
In-Line vs Starpoint:
Two-station and most three-station systems will be provided as in-line systems unless requested otherwise by the customer. All four-station systems are provided as starpoints. Because the layout of a starpoint system is determined when the system is electrically tuned, it is impossible to provide typical footprints of these systems. Please consult the factory for more information on specific starpoint systems.
Interdigital vs Resonant Cavity:
Models 2530 and 2930 combiners use resonant cavity style bandpass filters. Model 2630 combiners use interdigital style bandpass filters. It is possible to combine the two different styles. In general, systems using interdigital bandpass filters will have a smaller footprint, but slightly higher insertion losses than resonant cavity based systems.
All Shively Labs branched combiners can be mounted on their sides, or in a number of other custom orientations (for example: around corners). Because the design of the matching section is electrically significant, these custom orientations have limitations. Please consult the factory for information and advice regarding specific systems. Each custom-oriented system must be tested at the factory in its final installed configuration, and it is not recommended that the system be installed in the field in any other configuration than that for which it was tested.
All Shively Labs combiners and bandpass filters except the 29xx series are fabricated using modern temperature-compensation materials and techniques. These filters are designed to operated at temperature ranges exceeding 160°F (71° C). Forced air cooling is used to keep the units operating at typical transmitter room temperatures. However, should the forced air cooling fail on the filter for a specific station, the filter is designed to continue operating at rated power. A slight increase in VSWR may be experienced on some closely-tuned filters, but this increase should not generally cause any foldback in the transmitter.
Shively Labs branched combiners should be maintained and operated at 60% or less relative humidity.
Configuration Changes and Expansion:
Branched combiners are designed as systems and must be operated with all bandpass filters in place. If a combiner will be operated without a transmitter attached, the input of the unpowered bandpass filter should be terminated with a small dummy load. Please contact the factory for help in sizing this load.
Branched combiners can be expanded by adding a balanced combiner module for each new station, between the branched combiner and the antenna. The output of the branched combiner is plumbed into the wideband port of the last balanced module in the chain. Please note that this will eliminate the use of the wideband port as a second antenna feed.
Last updated: 11/22/17