How far is to far for a filter and preamp from antenna?

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nmelfi

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I have a ST2 on 30 feet of mast and want to install a Par162 filter and a Ramsey preamp. I would like to put them in a weatherproof box under my eve about 15 feet from the antenna. I run Belden RG6 quad swept at 3 gigs for my feedline. Is that close enough for the filters and amp or should I figure a way to make a box at the antenna? Thanks in advance, Nick
 

n5ims

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As a rule, a filter should be as close to the radio as possible while the preamp as close to the antenna as possible. The reason for this is you will want to filter out not only what is picked up by the antenna, but also any junk picked up by the feed line as well.

The preamp works best with maximum signal levels to amplify. If you don't place it at the antenna the signal you're trying to amplify will start out smaller (and with more noise) and often there may not be enough signal left for the preamp to amplify. A preamp will not only amplify the signal, but also the noise. If you place it away from the antenna you'll get an increase in the relative noise level.

That said, the preamp will also amplify what signals may be filtered out by the filter and therefore cause the filter to be less useful. Remember that an antenna is not just the antenna itself, but an entire system (that you're adding parts to with the preamp and filter). You should tune the antenna as a system and not as individual parts and be prepared to make adjustments as you go. It might be best to place the filter at the antenna ahead of the preamp as well, but only trying different combinations will say for certain what will actually work best in YOUR installation.

I'm sorry that this gives you some conflicting answers, but that's just how an antenna system works. There's not a single hard-and-fast answer to how to make it work best everywhere. One thing you can take away from this is that the middle of the feed line isn't the best place for either.
 

prcguy

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You generally want the preamp as close as possible to the antenna and any filter in front of the preamp to keep junk out.

If you need a PAR162 to cure a problem, adding a preamp will make it much worse and especially with a Ramsey wide band preamp.
prcguy
 

zz0468

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Adding a preamp and a filter are usually done as a response to solve a particular problem. What is it you're needing to accomplish that a decent antenna and feedline alone can't solve?
 

nanZor

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That 162 filter is for trying to notch out the 162mhz NOAA broadcasts. Are you sure that is your problem, or are you hearing pagers etc or other forms of interference? On a side note, what scanner are you using - just checking here also in case you are running into image issues with a dual-conversion IF type scanner...
 

nmelfi

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The local NOAA tower is about five miles from me and my BCT15 picks it up all the way into the 2 meter band at times so I want to block it if possible.I wanted the amp for milair scanning but I may be better off without it due to the towers on Paris mountain being so close. See attached picture for my problem. Thanks.
 

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zz0468

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The local NOAA tower is about five miles from me and my BCT15 picks it up all the way into the 2 meter band at times so I want to block it if possible.I wanted the amp for milair scanning but I may be better off without it due to the towers on Paris mountain being so close. See attached picture for my problem. Thanks.
A pass filter for mil air in front of a preamp might work ok. But I'd try the filter in front of the receiver first and see if your results are satisfactory. A notch filter for NOAA weather will take that out, but it'll still let everything else in, and that won't do a preamp any good.
 

nmelfi

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On top of that mountain is NOAA, SCETV,TV Channel16 and a few FM radio stations.I recieve most of what I want to hear without too many problems,but I think you are right a notch filter may be the way to go.Can I move it downstream enough to be able to tke it out when I don't want to filter everything else out?
 

zz0468

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Yes, you can put the filter inside near the radio. Just don't put a preamp in before any filtering.
 

gewecke

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On top of that mountain is NOAA, SCETV,TV Channel16 and a few FM radio stations.I recieve most of what I want to hear without too many problems,but I think you are right a notch filter may be the way to go.Can I move it downstream enough to be able to tke it out when I don't want to filter everything else out?
I feel your pain. :( I have a NOAA transmitter less than 2 miles from me. The top of the tower is in direct line of sight with my antennas. I have intermod from noaa all the way into the 220mhz. band.

73,
n9zas
 

nmelfi

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Heck I heard NOAA competing with Greenville County SO tonight on VHF 460.250. That mountain peak is about 4 miles from me and about a thousand feet higher with a clear line of sight. Oh well at least I will never miss a storm warning no matter what band I am listening to!
 
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