Another members' post has me thinking about filters and how many I use for my main scanners. The antennas I use are a wideband discone and another that covers 800-925 MHz. A K&L (5IZ10-20/X1300-0/0) diplexer joins the two coaxial cables and then comes the filter fun.
Filters in no particular order:
A. 1-60 MHz ( I transmit on HF so this helps to some degree )
B. HF, AM & FM Broadcast bands ( Crazy strong RFI at my location )
C. NOAA Weather around 162 MHz ( The signal booms in here )
D. Two 152 MHz paging filters (It's really bad here and I need two)
E. Another FM broadcast 88-108 filter
A is made by Palomar Engineers
B is from ScannerMaster. HPN-30118 combined notch filter
C, D, and E are made by Dale Parr ( Par Filters)
I also monitor military aircraft and use the regular discone as well as an AT-197A/GR military air discone and a mil air 225-400 MHz filter made by Dale Parr too. They're connected to separate scanners/receivers and not both feeding together into one line.
I don't really monitor civilian air, so filter B works for my use. A more friendly filter for civil aviation that attenuates FM broadcast would be the Mini Circuits ZBSF-95+. It costs more, but if you enjoy monitoring civil air it should be in inline on your system.
* * * * * How did I discover I needed filters * * * * *
It started with garbled noise
I would receive coming in with other signals, or wiping them out. Using an inexpensive USB dongle I initially took a look around 440 MHz and watched the waterfall on the computer screen. When the noise started and stopped on a receiver, I noticed the noise floor would shift simultaneously. It turned out to be a simulcast paging system in my area way down near 152 MHz. There are four transmitters and they're using 100 and or 300 watts per my FCC search to find the culprit. Their intended targets are pagers that have compromised antennas, so they really blast the watts to reach them. Also, if you think you don't need a filter because you only monitor digital modes, well if they're really strong signals, you may be fine.
While the paging system is a nasty offender, I also have a NOAA weather station nearby around 3500' above me in the Sierra's that uses 300 watts. Then we get to the unfriendly RFI from AM and FM broadcast stations using infinitely more watts. Some of those transmitters are less than five miles away with most others less than 25 miles from me. Additionally, I use similar filters inline on my HF and VHF/UHF amateur radios as well to help block the RFI. Those filters are specially made to use with transmitters.
* NOTE: Not everyone needs a filter. If you monitor a strong nearby transmitter or systems that have clear signals you are fortunate.
* EXTRA NOTE: Due to the losses from the filters and adapters, I use a pre-amp inline between the filters and scanners/receivers. You may or may not need to add a pre-amp. Everyone's needs are different. I do not recommend a pre-amp more than 10dB. Your noise floor will become unfriendly.
Filters in no particular order:
A. 1-60 MHz ( I transmit on HF so this helps to some degree )
B. HF, AM & FM Broadcast bands ( Crazy strong RFI at my location )
C. NOAA Weather around 162 MHz ( The signal booms in here )
D. Two 152 MHz paging filters (It's really bad here and I need two)
E. Another FM broadcast 88-108 filter
A is made by Palomar Engineers
B is from ScannerMaster. HPN-30118 combined notch filter
C, D, and E are made by Dale Parr ( Par Filters)
I also monitor military aircraft and use the regular discone as well as an AT-197A/GR military air discone and a mil air 225-400 MHz filter made by Dale Parr too. They're connected to separate scanners/receivers and not both feeding together into one line.
I don't really monitor civilian air, so filter B works for my use. A more friendly filter for civil aviation that attenuates FM broadcast would be the Mini Circuits ZBSF-95+. It costs more, but if you enjoy monitoring civil air it should be in inline on your system.
* * * * * How did I discover I needed filters * * * * *
It started with garbled noise
I would receive coming in with other signals, or wiping them out. Using an inexpensive USB dongle I initially took a look around 440 MHz and watched the waterfall on the computer screen. When the noise started and stopped on a receiver, I noticed the noise floor would shift simultaneously. It turned out to be a simulcast paging system in my area way down near 152 MHz. There are four transmitters and they're using 100 and or 300 watts per my FCC search to find the culprit. Their intended targets are pagers that have compromised antennas, so they really blast the watts to reach them. Also, if you think you don't need a filter because you only monitor digital modes, well if they're really strong signals, you may be fine.While the paging system is a nasty offender, I also have a NOAA weather station nearby around 3500' above me in the Sierra's that uses 300 watts. Then we get to the unfriendly RFI from AM and FM broadcast stations using infinitely more watts. Some of those transmitters are less than five miles away with most others less than 25 miles from me. Additionally, I use similar filters inline on my HF and VHF/UHF amateur radios as well to help block the RFI. Those filters are specially made to use with transmitters.
* NOTE: Not everyone needs a filter. If you monitor a strong nearby transmitter or systems that have clear signals you are fortunate.
* EXTRA NOTE: Due to the losses from the filters and adapters, I use a pre-amp inline between the filters and scanners/receivers. You may or may not need to add a pre-amp. Everyone's needs are different. I do not recommend a pre-amp more than 10dB. Your noise floor will become unfriendly.
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