Pyramid Communications designs and manufactures a complete line of high selectivity Band Pass Filters and narrow bandwidth Notch Filters for use with the SVR Series Vehicular Repeater. The filters allow the SVR to be used in the same band as the mobile radio it is interfaced with, thereby allowing the users to utilize their existing handheld radios, giving them the same effective range as the higher power mobile. The Band Pass Filters are available in VHF (150-174), UHF (450-470), 700 MHz (764-776) and 800 MHz (850-870). Notch Filters are available as single or dual cavity VHF (150-174), and dual cavity UHF (450-470).
When operating vehicular repeaters in-band, certain rules must be observed. The SVR frequency should be as far away as possible from the mobile transmit and receive frequencies. A minimum of 2 MHz in VHF and 3 MHz UHF is required. At 700/800 MHz, the separation should be 30/45 MHz respectively. It is also important to locate the antennas as far apart from each other as possible (horizontal and vertically), and low profile narrow band antennas such as the Antennex Phantom Series are recommended.
Even with proper antenna placement and frequency planning, interference can occur between the high power mobile and the SVR. Pyramid Communications' filter products can further reduce the desense caused by the mobile transmitter. The high selectivity preselectors prevent the mobile's transmitter from overloading the SVR receiver front end. The filter is tuned to the SVR simplex frequency and rejects everything except a narrow band of frequencies centered around the SVR frequency.
The Notch Filters are tuned to the SVR frequency but are installed on the mobile's antenna cable to further reduce phase noise from the mobile transmitter that falls on the SVR receive frequency. The Notch Filter will be transparent to all frequencies except a narrow band centered around the SVR frequency. Since the Notch Filter is always present on the mobile's antenna cable, it is important that the mobile does not transmit on any frequency within 2 MHz of the Notch Filter's center frequency or damage to the filter and/or the transmitter may result.
For cross band operation, Pyramid offers a VHF and UHF High Pass Filter to prevent SVR front end overload from a high power Lo-Band or VHF mobile.