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Author Topic: Low Pass Filter for Flex-Radio 3000?  (Read 4566 times)
VE6ETP
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Posts: 19




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« on: May 17, 2013, 10:16:21 PM »

I'm getting interference on all the stereo speakers in my house. This includes the computer speakers connect to the PC I use with the Flex-Radio, the main stereo speakers a floor up connected to my TV, and the stereo speakers in a room 2 floors up.

I thought it might be the power I was using but it happens even at 25 watts. I'm using RJ-11 cable to supply my dipole (I know it's 75 ohm but it's very good coax and it was free).

I'm thinking a low-pass filter may be in order. I was looking at the Bencher YA-1. However on the product description of the flex 3000 a BCB Low Pass Filter is mentions to prevent out of band transmissions. However I can't find anything in the manual on how to turn it on so I assume it's just always on.

So, finally to my question. Would this Bencher low pass pass filter help? Or do I need to look at other possible problems?

Thanks for any insight. I'm guessing this has happen to a lot of other people so I apologize if it's been asked before.

Regards,

Pete
VE6ETP
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WX7G
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« Reply #1 on: May 18, 2013, 04:15:11 AM »

Pete, a LP filter will not help with your RFI problem.

It is simply the fundamental frequency getting into the stereo and TV audio system.

1) Reduce TX power until the RFI is cured
2) Add ferrite cores to the TV and Stereo until the RFI is cured

When adding ferrites it can help to reduce TX power until the problem is barely there. Then add ferrites and if the problem is cured at that TX power level increase the power until the problem is again barely there. Repeat until the RFI is cured.
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K5LXP
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« Reply #2 on: May 18, 2013, 01:00:19 PM »

WX7G is right, this is fundamental overload.

One other thing you can try is an unun (choke balun) on your dipole.  If you've got any common mode maybe these will help reduce some of the energy floating about.

It's possible a combination of cures will be reguired - choke balun, ferrites, bypassing.  Using the technique WX7G describes will help lead you to what method is having the most beneficial effect.

Mark K5LXP
Albuquerque, NM
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VE6ETP
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Posts: 19




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« Reply #3 on: May 19, 2013, 04:11:30 PM »

Thank you very much for the suggestions. I do have what I think is a choke balun on my dipole already. I made the ugly balun which I believe is a 1:1 choke?

Also I'm concerned how far reaching this RFI is. I'm worried I could be effecting my neighbours equipment. How far reaching could this be? I turned the drive way down and still could hear it on my speakers. I guess the only solution would be to put the antenna even higher or give ferrites to everyone around me so they can put them on their speaker wire?

I've read of other people using dipoles such as this in their attics or under an eaves. I would have to guess they've had the same issue?

Pete
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WX7G
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« Reply #4 on: May 20, 2013, 11:12:05 AM »

The easy fix for your speakers is to power them OFF when you are on the air.

I don't know about Canada but in the US a licensed Amateur Radio Operator is under no obligation to fix RFI problems if his signal is "legal." The burden is on the user of the affected equipment.
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K5LXP
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« Reply #5 on: May 20, 2013, 12:13:44 PM »

I made the ugly balun which I believe is a 1:1 choke?

Can't hurt, but an ugly balun is often not as effective as a ferrite one. 

http://www.karinya.net/g3txq/chokes/

Quote
Also I'm concerned how far reaching this RFI is.

It's not what you're transmitting, it's what the affected equipment is detecting.  How sensitive something can be to RF energy is dependent not only on the intensity of RF but also how well the item is shielded and isolated, and how the end user connected it.


Quote
I'm worried I could be effecting my neighbours equipment.

I wouldn't.  I suspect if it's ever a problem you'll find out about it.


Quote
I turned the drive way down and still could hear it on my speakers.

That just means you have especially sensitive speakers.  I have several sets of amplified speakers on PC's and a surround speaker set on my TV.  I've never bothered them.


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I guess the only solution would be to put the antenna even higher

That's a win-win for you.


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give ferrites to everyone around me so they can put them on their speaker wire?

Technically it's up to them to come up with and pay for any remedy.  You can be a nice guy and do that but that's a form of implied guilt.  First thing I do is point to the Part 15 notice that's on just about everything these days.  From there we can work on an amicable solution.

Quote
I've read of other people using dipoles such as this in their attics or under an eaves. I would have to guess they've had the same issue?

Any time you have an antenna that close to or inside a structure, the field strength will be that much higher plus there's more opportunity for energy to couple into power and signal wiring.


Mark K5LXP
Albuquerque, NM
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VE6ETP
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Posts: 19




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« Reply #6 on: May 20, 2013, 11:28:02 PM »

Thank you both WX7G and Mark (K5LXP).

You've definitely put my mind at ease. I will take the suggested steps to isolate my own equipment and continue on from there.

Any suggestions on where to get some ferrites? I see digikey has a bunch and I've always had good service from them (unbelievable service in fact.) So I will probably grab some from there but wanted to make sure I didn't miss a better place to get them.

Does the diameter matter? Or just any old ferrite that will give you enough space to wrap the wires a couple of times?

Thanks again!

Pete
VE6ETP
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K5LXP
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« Reply #7 on: May 21, 2013, 07:37:30 AM »


You're welcome.


Any suggestions on where to get some ferrites?

You can get them a lot of places online.  Depending on the exact mix/size Digikey is pretty good, and I note that DX Engineering also sells them.  If you're already a DigiKey customer you probably can't go wrong there.


Quote
Does the diameter matter? Or just any old ferrite that will give you enough space to wrap the wires a couple of times?

It matters when the wire doesn't fit through.  Getting multiple turns through multiplies the effect, but you may not want a softball sized lump hanging from back of the TV so putting a few in series would work too.  Having a selection of both fixed toroids and snap-on units in various sizes and mixes is a great asset to have when mitigating EMI/RFI problems.

Don't forget there's other avenues for remedy too, such as cable dress and bypassing.  The key is establishing the bands and power levels where the interference happens so you can know if whatever you're trying is having a beneficial effect or not.


Mark K5LXP
Albuquerque, NM
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VE6ETP
Member

Posts: 19




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« Reply #8 on: May 24, 2013, 12:23:17 AM »

Thanks again Mark. I'm looking at Digikey now.

I've finally gotten myself an antenna analyzer as well (RigBlaster AA-54). Looking forward to not only working on my interference but working on tuning my antenna properly rather than relying on my Antenna Tuner in my flex this weekend.

Again, thanks for all the help. Once I get the ferrites I'll see how it goes.

Pete
VE6ETP
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