I'm always reading about folks trying to improve their scanner reception by adding preamps to their wide-band antenna systems. Most folks rightly comment that preamps will generally make the situation worse by amplifying undesireable signals such as FM radio transmitters, TV, paging, etc. that then desense the receiver. Some others suggest using filters to eliminate the powerful signals overwhelming the receiver.
Wouldn't it be cool if some manufacturer made an integrated, tower/mast-mounted preamp that included a series of band-pass filters for the desired bands, say 138-174, 450-512, and 850-861. That way, your preamp is only passing signals down the feedline in the bands you want to monitor, and eliminating all the other junk that you don't want to hear. At the receiver end there would be a variable gain control to allow for optimized amount of gain on the preamp.
Take this a step further, and suppose that they could make a preamp/filter device with multiple antenna feeds, so you could optimize your antenna system with, for example, a dual-band VHF/UHF antenna and a separate directional 800MHz antenna. The device would put the appropriate filter in line with the correct antenna and "di-plex" the signals onto a single feedline. In theory, they could make models with 3 or 4 inputs (1 for each band), or they could make models that only support a single band, and a user could have a separate antenna, amp/filter and feedline for each band, hypothetically with each routed to a receiver dedicated to a particular band.
The manufacturer could even package the device with an antenna of choice and decent low-loss coax. Pick your band or bands and purchase the appropriate model as a turn-key package.
So, aside from the extreme cost of such an animal, what's the technical reason(s) that would make something like this impratical? Can you make a filter or filters do pass multiple banbs with an acceptable insertion loss?
Wouldn't it be cool if some manufacturer made an integrated, tower/mast-mounted preamp that included a series of band-pass filters for the desired bands, say 138-174, 450-512, and 850-861. That way, your preamp is only passing signals down the feedline in the bands you want to monitor, and eliminating all the other junk that you don't want to hear. At the receiver end there would be a variable gain control to allow for optimized amount of gain on the preamp.
Take this a step further, and suppose that they could make a preamp/filter device with multiple antenna feeds, so you could optimize your antenna system with, for example, a dual-band VHF/UHF antenna and a separate directional 800MHz antenna. The device would put the appropriate filter in line with the correct antenna and "di-plex" the signals onto a single feedline. In theory, they could make models with 3 or 4 inputs (1 for each band), or they could make models that only support a single band, and a user could have a separate antenna, amp/filter and feedline for each band, hypothetically with each routed to a receiver dedicated to a particular band.
The manufacturer could even package the device with an antenna of choice and decent low-loss coax. Pick your band or bands and purchase the appropriate model as a turn-key package.
So, aside from the extreme cost of such an animal, what's the technical reason(s) that would make something like this impratical? Can you make a filter or filters do pass multiple banbs with an acceptable insertion loss?
