The objective of the activity is to develop a propagation model for the Very High Frequency band (VHF) that includes high latitudesand equatorial zones. The model will be able to predict signal impairment caused by various propagation effects. This model will beimplemented in a system and user modelling tool and is intended to be proposed to ITU-R for adoption. Targeted Improvements: Enabling the development of VHF telecommunication missions without the need for over dimensioning the system in both space and ground segment. Description: Current ITU models for the Very High Frequency band in ITU-R Rec 528 and 531 are mainly based and tested in L-bandsignals. However, their extrapolation to Very High Frequency band (VHF) provides very biased results. Having a representative VHF propagation model will improve the capability to design and operate Telecommunication missions in the VHF (and nearby) band and will allow satellites operators to accurately interpret and characterise the system performance. Operators are already flying satellites using this band (i.e., VHF Data Exchange System (VDES), Telemetry Telecommand, Air Traffic Management (ATM)) and they are encountering problems in the data which are not reflected in the ITU recommendations. In order to develop a VHF model, it is key to have appropriate data to be able to extend L-band models, or most probably to correct the description of these effects on the VHF domain. Thus, this activity will be focused on data gathering /collection and then developing a model and a software that is able to describe accurately the propagation effects in VHF band. The main tasks of the activity shall be as follows: To identify and study the propagation effects impairing VHF satellite systems and to develop a model to link such effects to signal degradation (power fading, scintillation, phase delay, etc.) To gather data of satellite signals in VHF and/or nearby bands from as many sources as possible (in-house, public and/or private) combined with a dedicated measurement campaign if necessary. To develop and test a SUMT (system anduser modelling software) for both downlink and uplink operating modelOutputs and SUMT will be available for ITU-R for adoption.Footnote: On Delegation Request activities will only be initiated on the explicit request of at least one National Delegation.

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