Balanced Combiners can be connected together to realize Chain-Combiners, also mixing different Cavity Sizes and Number of Poles, in order to optimize the Combiner chain.
A chain of n Balanced Combiners has n Narrowband inputs and one Wideband input port, which can be used to further extend the combiner combination capability, adding new or existing combiners, also with other techniques (Starpoint, Manifold):

Wideband Port Use Extended Combination
Not used, Terminated with Load 0 channels added (can be added at a later stage).
Filter, Starpoint or Manifold Combiner
(or existing Combiner)
1, 2 or more extra channels added. Cheapest Solution.

Balanced Combiners also allow to be extended at a later stage. The new channels can be added inserting a new combiner in two possible different positions into the Combiner chain:

Position Requirements, Advantages and Disadvantages
On the Output (antenna) side The new Combiner must be Balanced. The integration requires major mechanical work, and the new Combiner is generally bigger. The new Balanced combiner can be optimized to accept the existing channels.
In the Wideband Input Requires the existing combiner to have its Wideband port unused (terminated with a load), able to accept the new frequencies and withstand the increased power. The new Combiner can be Starpoint, Manifold, Balanced (or a single Filter). The integration requires minor mechanical work, and the new Combiner is generally smaller.

Adjacent-Channel/Block Combination

COM-TECH has exploited the Adjacent-Channel/Block Combination thanks to innovative techniques: DualCross and XLine Filters, MultiStep Hybrid Couplers, and an improved Manifold combination.
The combination of Adjacent-Channels/Blocks requires Manifold or Balanced Combiners, together with a Mask-Combiner configuration; it is generally not possible with Starpoint Combiners (which require at least 1 Guard-Channel/Block Spacing):

Manifold Starpoint Balanced
4-Pole Adj.-Channel (<10 W) 1 Guard-Channel  (>10 W)
5-Pole Adj.-Channel
6-Pole 1 Guard-Channel
4-Pole A.N.T. Adj.-Channel
6-Pole XLine 1 Guard-Channel Adj.-Channel
7-Pole XLine 1 Guard-Channel Adj.-Channel
6-Pole DualCross 1 Guard-Channel Adj.-Channel
8-Pole DualCross 1 Guard-Channel Adj.-Channel
7-Pole (DAB) 1 Guard-Channel Adj.-Block
6-Pole DualCross (DAB) 1 Guard-Block Adj.-Block
8-Pole DualCross (DAB) 1 Guard-Block Adj.-Block


  • Adjacent-Channel/Block Combination can be implemented independently of the required Mask (e.g.: Critical), it does not necessary require 8-Pole Filters
  • Adjacent-Channel/Block Combination involves an increased dissipation for the filters reflecting the adjacent channel; for these modules, Narrowband power ratings must be consequently reduced
  • No-Mask-Combiner configuration, and Starpoint or Stretchline Combiners do not allow the combination of Adjacent-Channels/Blocks

Combiner Request Guidelines

The system engineering of a Chain-Combiner requires several data to be collected from the Customer.
When requesting a quotation please specify as much information as possible, completing the following guideline table:

Data Values
Operating Band, Standard, Bandwidth Please include as much information as possible on the standard
Eg.: UHF DVB-T2 8 MHz
Channel List Channel list with: ch. numbers or frequencies, with RMS or S.P. input power of each one.
If a preferred order is requested, please list it from the farthest to the nearest to the output (antenna)
Eg.: 21 (1.5 kW RMS) – 23 (1 kW RMS) – 24 (2 kW S.P.) → [ANT]
Adjacent-Channel Combination Requires Mask-Combiner configuration, together with Manifold or Balanced Combiners.
In case of FM Combiners specify minimum frequency distance.
No. of Poles required (if specified) Adjacent-Channel/Block Combination does not necessary require 8-Pole Filters
Constant Impedance requested Requires a Balanced Combiner, with its Wideband port unused (terminated with a load)
Existing Combiner to be added Requires a Balanced Combiner, with its Wideband port connected to the existing combiner
Existing channels to be added (if any) Channel list with: channel numbers or frequencies, with RMS or S.P. input power of each one
Eg.: 31 (2.5 kW RMS) – 33 (1.5 kW RMS) – 44 (2.5 kW S.P.)
Inputs: Connectors and Directional Couplers Connectors type for each Input. If Directional Couplers are required, please specify the number of probes
Eg.: 3x EIA 1+5/8” Flanged, 3xDirectional Couplers with 1xFWD and 1xRFL
Output: Connector and Directional Coupler Connector type for the Output. If a Directional Coupler is required, please specify the number of probes.
Eg.: EIA 3+1/8” Flanged, Directional Couplers with 2xFWD and 2xRFL
Forced Air Cooling or Liquid Cooling accepted Liquid Cooled Combiners require transmitters to have a liquid cooled system, connected to the Combiner
Environmental Conditions Please specify transmitting site altitude, room temperature, expected maximum combiner body temperature, etc.
Eg.: 2700 m, 35°C, 60°C

Wideband Power and Peak Voltage

Wideband Input Power
COM-TECH Balanced Combiners have been dimensioned to withstand the overall output power even in Wideband mode (the Wideband input power having a double impact on hybrid couplers), thus making the calculation of the Wideband Input power extremely easy:

WB Input Power = Maximum Output Power – Sum of NB Input Powers

Voltage Peaks
The composition of several digital signals undergoes to a complex statistical process, which deviates from the theoretical voltage composition. COM-TECH Balanced Combiners have been dimensioned to widely sustain the increased voltage peaks caused by the vector composition of several signals (up to 10 channels).

Wideband Tuning Optimization

The Return Loss on the Wideband port can be optimized either for the best value on specific channel(s) (at the expense of reducing the performances outside the given frequencies), or to reach the best tradeoff value on the whole band.

Wideband Tuning Features
Channel Optimized Best Return Loss values on the specified channel(s). Reduced performances outside
Whole-band Optimized Best Return Loss tradeoff on the whole band

Combiners with MultiStep technique have unparalleled performances, allowing an almost optimal Return Loss value on the whole band.

Return Loss

Tuning data reported on the Datasheets refer to one single Balanced Combiner module.
The combination of several Balanced Combiner modules involves a derating of the overall Return Loss, influenced by the number of combined channels, channel order and assortment, and adjacency. For basic reference, and in case Channel-Optimized Wideband tuning (see above), the following table is provided:

No. of Modules Overall Return Loss (VSWR)
1 26 dB (1.11)
2-5 25 dB (1.14)
6-8 24 dB (1.16)
9-10 23 dB (1.18)

Insertion Loss

Tuning data reported on the Datasheets refer to one single Balanced Combiner module.
The overall insertion loss of a Balanced Combiner Chain is the sum of the insertion loss of the single module, increased by the sum of the Wideband insertion losses of the following modules:

 I.L. (Overall) = I.L. (Single Module ) + n x I.L. (Wideband)