Since the available frequency resources are limited, different military units need to share these resources. For frequency hopping radio systems, this generally means that different units share a common pool of frequencies. When several military units in the size of batallions or brigades are co-located within areas that are geographically limited, interference from frequency collisions may not be avoidable. The impact on communication performance depends on a number of factors, such as the number of available frequencies in the shared pool and the propagation conditions within the area. The main objective of this work is to analyze the performance of frequency-hopping narrowbanded VHF-networks that are affected by interference caused by out-of-band emissions and jamming. Three models for out-of-band-emissions of varying suppression ability are used. Performance during active jamming is also investigated, where a jammer with 5 kW power is jamming the frequency hop band. The evaluation is performed using Monte Carlo simulations, where the transmitter, receiver and interfererers are randomly positioned in a brigade area. The radio systems are generic and modelled using a number of parameters such as the number of frequency hops per packet and the number of available frequencies. The results show that the effects of frequency hop collisions and out-of-band characteristics are important to consider when planning the tactical networks of a brigade. Interference from the orthogonal battalion networks can not generally be ignored in the evaluated cases. The number of available frequency channels necessary in order to achieve an acceptable packet error rate vary depending on the out-of-band model. When including the orthogonal networks of the entire brigade, a sizeable part of the available VHF bandwidth is necessary in order to obtain a low error rate. The results shows the effects of out-of-band emissions and the importance of setting sufficient requirements in procurement of new radio systems. Interference from the brigades own networks enables the jammer to achieve the same error rates at further distances.