It was recently desired to reactivate the 146.22/82 repeater on Mauna Loa after a 12 year absence. Interference from the 22 year old 144.170 beacon was strong. To solve the problem the following filter notch assemblies were fabricated. The dual notch/band pass filter for the receive port of the repeater duplexer provides about -90 dbc at the 144.170 beacon frequency. The band pass/notch on the output of the 144.170 beacon provides -55 dbc attenuation of any noise on the 146.22 repeater receiver frequency. New double shielded cables were also fabricated for the repeater receiver and the beacon. All close proximity RF equipment must have double shielded cables. The filters were installed in early summer 2004. The antennas will be positioned in their original location assuring adequate coverage of the mainland once again for the beacon. There will eventually be a 0.3 dB noise figure PHEMT preamplifier placed on the repeater receiver.
Single band pass and single notch for 144.170 MHz. Loss about 0.75 db
Paul installed this filter on the beacon in early June 04 and he is now getting 52 watts out of the beacon.
He will be normally using this filter when he operates his radio as well.
Above: Insertion loss and return loss plot of the
Paul and Fred W6YM installed the repeater filter assembly (shown below) on June 25th, repaired some poor coaxial connections on the repeater and it now works much better. Phase II complete..... still zero interference from beacon......one phase to go.....
Dual notch and single band pass filter for 146.22 MHz.
Insertion loss plot for the filter