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Thread: RM Italy 27/586 Low pass filters

  1. #11
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    Quote Originally Posted by JesseJamesDallas View Post
    I doubt your going to have any problems with the neighbors running those amps with/ or without the filters...It's not like it was back 30-40 years ago when just a stock CB Radio could mess up a TV set...since just about everything now has gone digital, CB's and amps don't hardly mess with anything...

    -=UNLESS=->>>>You have a radio that's had several golden screwdrivers stuck in the back of it to squeeze out every last drop of watts the radio is capable of squirting out! That's where you run into problems is with radios that splatter all over the place...Run a splatter-box radio into a amp, and harmonics will be flying everywhere and getting into everything...

    That 300A you have shouldn't bother anything either...Those guys saying your about to blow their windows out, are just complimenting you on how well your radio sounds is all...

    I talk on my Cobra 2000 that's hooked to a 300A, with my TV on, and the computer all at the sametime and the radio and amp doesn't get into anything...and the TV is less than 15' away, and the computer's monitor is actually sitting on top of my Cobra 2000!

    Another thing! I have a RCI 2980wx sitting next to the Cobra, it has it's own amp, a XForce 1x4 base amp, which is sitting literally "side-by-side" next to my computer and there's no affects there either!

    bottom line...don't worry about ol' Uncle Charlie....

    Thank JJD for the vote of confidence! LOL

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    Rack'em and stack'em. I used three separate filters, a low-pass filter on the output of the radio (loss of -.2 db) and the amplifier. The other two were on the output of the amplifier, one of which was a five band adjustable filter. All were installed, and the band adjustments made with the help of a spectrum analyzer. This was done with 100 watts, AM, on 27.495 into a dummy load. Then the final stage of the 100 watt amp was adjusted for the cleanest signal with as much of the harmonics tuned out. It can get complicated, tuning each stage, checking the SWR at each point to insure a clean signal to the final stage. It is important to stress that like lightning arrestors, surge suppressors, wall outlets and power supplies are properly grounded. Without a proper ground to the filter, the "bad stuff" gets filtered to the outside of the coax, radiating even more. I was able operate an AM/SSB station in a huge metro area where TV CH 3 was in use and I didn't interfere with my own TV. Clean signals are the gold standard.

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    whiteastro (02-11-2020)

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    Quote Originally Posted by mjd420nova View Post
    Rack'em and stack'em. I used three separate filters, a low-pass filter on the output of the radio (loss of -.2 db) and the amplifier. The other two were on the output of the amplifier, one of which was a five band adjustable filter. All were installed, and the band adjustments made with the help of a spectrum analyzer. This was done with 100 watts, AM, on 27.495 into a dummy load. Then the final stage of the 100 watt amp was adjusted for the cleanest signal with as much of the harmonics tuned out. It can get complicated, tuning each stage, checking the SWR at each point to insure a clean signal to the final stage. It is important to stress that like lightning arrestors, surge suppressors, wall outlets and power supplies are properly grounded. Without a proper ground to the filter, the "bad stuff" gets filtered to the outside of the coax, radiating even more. I was able operate an AM/SSB station in a huge metro area where TV CH 3 was in use and I didn't interfere with my own TV. Clean signals are the gold standard.

    Thanks for the info! Just like any field you go into it can get very technical and requires a lot of study. I was a licensed Waste water treatment plant operator and was required to do constant study to keep my license active. The chemistry and math was staggering. I was a certified welder at one time and there is a lot more to welding than people realize. The USAF taught me to be a AirFrame Repairman which can get technical. I'm glad I'm finally retired and can shift into Neutral! LOL

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    Quote Originally Posted by mjd420nova View Post
    Rack'em and stack'em. I used three separate filters, a low-pass filter on the output of the radio (loss of -.2 db) and the amplifier. The other two were on the output of the amplifier, one of which was a five band adjustable filter. All were installed, and the band adjustments made with the help of a spectrum analyzer. This was done with 100 watts, AM, on 27.495 into a dummy load. Then the final stage of the 100 watt amp was adjusted for the cleanest signal with as much of the harmonics tuned out. It can get complicated, tuning each stage, checking the SWR at each point to insure a clean signal to the final stage. It is important to stress that like lightning arrestors, surge suppressors, wall outlets and power supplies are properly grounded. Without a proper ground to the filter, the "bad stuff" gets filtered to the outside of the coax, radiating even more. I was able operate an AM/SSB station in a huge metro area where TV CH 3 was in use and I didn't interfere with my own TV. Clean signals are the gold standard.
    Just wondering..."when did you have this set-up?"


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    whiteastro (02-12-2020)

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    Name:  filter connect.jpg
Views: 18
Size:  175.2 KB This is RM Italy's instructions for the filter between the antenna and amp.

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    Turboomni (02-12-2020)

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    Was in use from 1974 until 2016. As a field service engineer, with military electronics experience with radio transmitters and antennas, radar and passive and active ECM. A spectrum analyzer is the best tool for locating and eliminating interference signals. Harmonics are a big part of what needs to be filtered out but a good clean main emission goes a long ways to reduce interference.

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    whiteastro (02-12-2020)

  11. #17
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    Quote Originally Posted by mjd420nova View Post
    Was in use from 1974 until 2016. As a field service engineer, with military electronics experience with radio transmitters and antennas, radar and passive and active ECM. A spectrum analyzer is the best tool for locating and eliminating interference signals. Harmonics are a big part of what needs to be filtered out but a good clean main emission goes a long ways to reduce interference.

    I'm sure you know your stuff and it is all over my head! LOL I've had no training in electronic just a interest! Thanks for the incite. PS. What do you think of RM Italy's instructions posted above?
    Last edited by whiteastro; 02-12-2020 at 07:08 PM. Reason: Add to

  12. #18
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    Quote Originally Posted by mjd420nova View Post
    Was in use from 1974 until 2016. As a field service engineer, with military electronics experience with radio transmitters and antennas, radar and passive and active ECM. A spectrum analyzer is the best tool for locating and eliminating interference signals. Harmonics are a big part of what needs to be filtered out but a good clean main emission goes a long ways to reduce interference.
    Figured you had that for the 70's...Bit different now days...With everything digital, you would have to be spitting out thousands of watts worth of harmonics to get into anything...

    Plus electronics now days have better filtering than what was available 40-50 years ago...So far about the only thing I have ran across that my station got into was my daughters headphones...snap-on ferrite choke onto the cord took care of that problem tho.

    I have more problems with my TV interfering with the radio, than the other way around...Damn Plasma TV's are noisy.


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    whiteastro (02-13-2020)

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