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Author Topic: Short RG8X jumper with low pass filter and LMR400?  (Read 3649 times)
W6UX
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« on: January 20, 2012, 08:16:39 AM »

I'm going to be purchasing a low pass filter, probably the Bencher model.  My HF antenna is fed with LMR400 Flex.  I have a short (3') jumper made of RG8X.  I've used this jumper with band pass filters connected to a feed of 9913 without issue.

Is it worth the time and trouble to make a jumper out of LMR400? (I don't have any parts at the moment, nor do I have an adequate soldering iron handy).

Thanks for your opinions/advice.

-Jeff
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WB2WIK
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« Reply #1 on: January 20, 2012, 08:56:36 AM »

Why would you need to do that?

RG8X should work fine for this.
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W6UX
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« Reply #2 on: January 20, 2012, 09:07:07 AM »

Why would you need to do that?

RG8X should work fine for this.

Still learning about this stuff; didn't know if going from LMR400 down to a short run of RG8X was going to cause an issue.  But thanks for confirming it's not a problem!

-Jeff
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W0FM
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« Reply #3 on: January 20, 2012, 11:14:49 AM »

Hi Jeff,

Can I ask what specifically caused you to want to install a low-pass filter?  With today's cleaner rigs and no more TV Channel 2, many hams found the LP filters unnecessary and have opted to go without them.  I took mine out of several antenna runs years ago.  Just a thought.  Others will chime in, I'm sure.

73,

Terry, WØFM

« Last Edit: January 20, 2012, 11:21:19 AM by W0FM » Logged
WB2WIK
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« Reply #4 on: January 20, 2012, 02:13:06 PM »

Hi Jeff,

Can I ask what specifically caused you to want to install a low-pass filter?  With today's cleaner rigs and no more TV Channel 2, many hams found the LP filters unnecessary and have opted to go without them.  I took mine out of several antenna runs years ago.  Just a thought.  Others will chime in, I'm sure.

73,

Terry, WØFM



Darn you, Terry, I'm trying to sell one! Cheesy
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W6UX
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« Reply #5 on: January 20, 2012, 02:17:59 PM »

Hi Jeff,

Can I ask what specifically caused you to want to install a low-pass filter?  With today's cleaner rigs and no more TV Channel 2, many hams found the LP filters unnecessary and have opted to go without them.  I took mine out of several antenna runs years ago.  Just a thought.  Others will chime in, I'm sure.

73,

Terry, WØFM

I'm emulating the grounding and filtering system used by N6PEQ, a friend in my club who has one of the cleanest sounding/RFI-proofed stations ever assembled.  At full legal limit, the most he's ever had to do for a neighbor is donate a few ferrite beads.  I've never had problems with my neighbors, and only after I got the hex up did my good neighbor next door start to hear some garbled audio coming out of her PC speaker.  I'm going to do everything I can on my end to make sure I've got good clean RF coming out of my QTH.  Last thing I want to do is find out I've caused TVI to some stranger down the street.

-Jeff
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W0FM
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« Reply #6 on: January 24, 2012, 02:33:19 PM »

If you really want the low-pass filter Jeff, then buy the one that WB2WIK's trying to get rid of.  It's probably really clean, cause Steve wouldn't have transmitted any junk through it.  Grin

Take it away, Steve! 

Terry, WØFM
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KA5N
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« Reply #7 on: January 24, 2012, 03:32:24 PM »

A low pass filter is to help eleminate any harmonics of the basic signal.  Interference to
things like computers or audio systems is usually just RF getting into the troubled device
where it can be rectified (detected) and be heard or seen.  Getting rid of harmonics is unlikely
to make any difference.  The use of ferrite cores or snap-ons will be just as effective for any
harmonics as for the primary signal. 
Save your money  (anyway Steve already has plenty unless his  bevy of beautiful daughters
is eating him out of house and home)

Allen
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W0FM
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« Reply #8 on: January 24, 2012, 04:20:06 PM »

Allen, I think Steve's selling off ham equipment in anticipation of the cost of all those weddings!   Wink

Terry
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W8JI
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« Reply #9 on: January 24, 2012, 05:20:11 PM »

I'm emulating the grounding and filtering system used by N6PEQ, a friend in my club who has one of the cleanest sounding/RFI-proofed stations ever assembled.  At full legal limit, the most he's ever had to do for a neighbor is donate a few ferrite beads.  I've never had problems with my neighbors, and only after I got the hex up did my good neighbor next door start to hear some garbled audio coming out of her PC speaker.  I'm going to do everything I can on my end to make sure I've got good clean RF coming out of my QTH.  Last thing I want to do is find out I've caused TVI to some stranger down the street.

-Jeff

I'd like to see Steve sell his filters, and I'd like to sell some, too. But I have to be honest....

1.) Low pass filters have nothing to do with a neighbor's speaker problems, or how a signal sounds on the air

2.) Grounding has nothing to do with RFI, unless the antenna system is a mess with common mode. In that case it is better to fix the antenna than to band-aid it with a ground. If a ground to equipment makes a difference, you have an antenna system or station wiring problem

3.) Most TV systems are now cable, and now UHF digital if they are not cable. This almost always precludes the need for a low pass filter, although in cases of fringe off-the-air signals and amplifiers you could need a low pass filter.

4.) If beads fix something, a low pass filter on the transmitter would not make a difference

5.) Most external RFI problems are fundamental overload, which neither a transmitter ground or low pass filter affects

I share Steve's opinion. A low pass is one of the least useful things these days. But if you want to use one, any short 50 ohm cable of reasonable quality will work.

More important, how do I get a 14% tax rate?

73 Tom
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W6UX
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« Reply #10 on: January 24, 2012, 06:03:00 PM »

Yeah, the ferrite beads will be going on the neighbor's computer speakers next time she mentions any interference.  I did end up buying a Bencher YA-1 filter anyway.  The homes in this area are 30 years old, and some of the original residents are still here.  Some even have the old aerial antennas.  So if anything, it makes be sleep easier knowing I've gone the extra mile to reduce my footprint on legacy electronics.

-Jeff
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WA9YSD
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« Reply #11 on: January 24, 2012, 10:47:27 PM »

What is the highest frequency are you passing through the filter?
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W8JI
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« Reply #12 on: January 25, 2012, 09:00:24 AM »

Yeah, the ferrite beads will be going on the neighbor's computer speakers next time she mentions any interference.  I did end up buying a Bencher YA-1 filter anyway.  The homes in this area are 30 years old, and some of the original residents are still here.  Some even have the old aerial antennas.  So if anything, it makes be sleep easier knowing I've gone the extra mile to reduce my footprint on legacy electronics.

-Jeff

It doesn't matter if the electronics is "legacy".

The FCC moved off-air TV channels mostly to UHF, and they are now digital. What small amount remains on VHF is mostly high band, and not lower channels that are susceptible to harmonics from HF.  It is the move of nearly all stations to UHF and the digital mode, plus the fact modern radios and amplifiers are pretty clean compared to stuff from the 80's and earlier, that make low pass filters nearly valueless.   
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WA9YSD
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« Reply #13 on: January 26, 2012, 10:48:58 PM »

I had no luck with low pass filters on my radio equipment.  Junk! They were good back in the tube days now we have chips with thousands of diodes. We use to make a crystal radio with diodes just think about it.

Low pass filters are commonly in stalled in most transceivers these days.  They are as good or better than any external one out there. I had a Drake R-7 line. It went bananas when I put a low pass filter on the out put of the transceiver it went into self oscillation, cause of RF Feed Back. Not sure how modern day radios with react to another one.

Usually if you have an RFI problem some thing with your station set up is wrong or a multiple of things wrong.  Common modes chokes seam to work best to cut off current loops on your ham radio equipment. This is a good place to start.

Jim K9TF
If you do not have any issues why get the filter?

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WA9YSD
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« Reply #14 on: January 27, 2012, 11:06:28 PM »

I looked at your reference of the station you liked his Low Pass filter.

Several things re going on here. He has multiple antennas out side so the terminated them on a copper plate, probably has lightning protection. On the back side of the plate is not shown. If there is a coax switch or 2 that would be the place to put them. He eliminated all sorts of current looping by doing this.

You now want to ask your self what does his ground consist of? Is it per NEC? If he tied the station ground to the electrical ground and did he isolate the line with a common mode choke or ferrite beads slipped over the electrical ground wire or what to prevent RF loop back through the ground, or what? Most important, where, how and what did he tie the plate to electrical ground, station ground what?

Did he use common mode chokes on various cable on the radio equipment?  Does he have a ground strap on the back of the operating table where he tied down the chassis from each radio equipment?

How long is the wire from the ground buss behind the radio gear to the station ground? Did he use a shielded ground?

You see how complexed it can get when taming the beast, RFI?

Remember grounds do radiate. The trick is to keep the station ground from radiating and let it absorb or dissipate the RF.

Jim K9TF
« Last Edit: January 27, 2012, 11:20:02 PM by WA9YSD » Logged
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