Just a short real-time overview of the effectiveness of the VHF Low Loss Helical Band-Pass Filter for 145 Mhz. To be short - this filter works as claimed by the Mile Kokotov Z33T. Before connecting the filter I scanned the 2m band for local interference in the Mossel Bay area. I was not surprised to receive interference/break through by commercial users in the amateur radio band while scanning the band without the filter for a lengthy period. My station is close to a few commercial repeaters and telemetry transmitters. I ran the scan function with the filter connected to a VHF radio again for a lengthy period. Both tests with and without the filter was recorded only when there was activity. Well the final result is that this filter at my QTH resulted in a 99% success rate. The 1 % that caused the radio's squelch to open is attributed to the local authorities telemetry transmitters. After a call to the local electricity department it was confirmed that they experienced problems and that it will be solved promptly by their service provider. I can confirm that it has since been resolved. Does this mean that I do not have any interference anymore. No, from time to time a get a carrier that opens the squelch on 145. 525 Mhz. To solve this I will be adding CTCSS that will prevent the COS from being activated by this carrier. An update on adding CTCSS to the GRHub Network 145.550 Mhz Link Radio will follow in the new year.
Finally: A word of warning!! There is high RF voltage present when transmitting and as stated by Mile RF voltages can be in the kV range. This I can confirm. When I transmit the top lid of the filter gets warm to hot. So be carefull!! I am very happy with this build and the performance of the filter. A added bonus is the 1:1 SWR with full 25 Watts output power.
