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Parade
Posts: 32


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OT: Interferance Problem
« on: September 01, 2003, 12:02:44 PM »

I have this problem with interferince sometimes when I play my guitar.

My dad has a Ham Radio which is similar to CB Radio, anyway when he is on that thing it always comes across my amp and it sounds terrible. He seems to have lots of power too cause over the years the interferrince is getting stronger.

SO my question is, is there anything I can do to block it or cut down on it alot?

This is off topic but this is the only place I know to ask, Yahoo is not giving me anything good.
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It takes a strong man to carry a bolder across a thousand miles, but an even stronger man to carry a burden for all eternity.
The Tone God
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Posts: 5289


Maggie


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OT: Interferance Problem
« Reply #1 on: September 01, 2003, 12:15:42 PM »

You may not be the only one affected by your fathers radio. Your neighbors might have something to say as well. Your father should have a pass filter on his radio output before either antana or antana tuner. If he doesn't he should get one as not to be a nucesnce to others. You can also use a torroed on your power line as well. That should chase it away.

Andrew
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Nasse
Posts: 2308

Eagle eats a piece by piece


OT: Interferance Problem
« Reply #2 on: September 01, 2003, 12:49:57 PM »

Few links

http://www.epanorama.net/links/radio.html#rfi

(in the very end)

Cool announcment in an old Finnish magazine, probably in 1930´s some bloke had an "Radio Interference Removing Office", he must have been a  private eye for radio frequencies

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Peter Snowberg
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Posts: 4898


OT: Interferance Problem
« Reply #3 on: September 01, 2003, 01:04:34 PM »

You do have yourself a pickle there.... But legally it is your father's responsibility to insure he does not interfere with your playing. That's all part of Ham radio. You can't interfere with others.

Ham output can be up to 1500 watts and depending on how good and centered his transmitter is, he may be bleeding over a good range to either side of the center frequency.

What's his TX power, how big of an antenna does he have, and what band(s) does he use?

Your best bet is probably going to be the use of torriods or some other shape of ferrite filter. The idea here is that you don't need anything in your guitar signal above say 50KHz (to be really sure) so you need a low-pass filter that scrubs the RF.

Ferrite filters come in a variety of shapes, the most popular being a cylinder of one form or another. There are "clip-on" ferrites that you just clamp over a cable, but you should loop the wire through the ferrite a few times if you can. The other standard style is a ferrite doughnut in a torriod shape. Same applies here... wrap your guitar cable through one a few times.

Your problem is that at least one of your cables is acting like an antenna. If you place the filter in the middle of the cable, you change the frequency and hopefully stop the interference. Play with the placement for best results. Also keep in mind that you could have the pickup in ANY cable in your setup including the power cable!

Ferrites are made of different materials for different frequencies.
Material Attenuation Range
75 or J = 0.5 - 10 MHz (160, 80, 60, and 40 meters)
72, 73, 77 = 1 - 40 MHz (160, 80, 60, 40, 30, 20, 17, 15, 12, and 10 meters)
43 = 20 - 400 MHz (15, 12, and 10 meters)
31 = 1 - 500 MHz (all HF Ham bands)
61 or 64= 200 - 2000 MHz (VHF ONLY)

I use 73, 75, or 77 material for filtering HF Ham traffic in the 160-40 meter bands. Type 43 material gets useful for people operating in and above the 20 meter band. I've never used 31 material, but just because I don't have it available off-the-shelf. You can always use multiple filters. Once you find a combo that works, toss a little more filtering in to be sure.

Your amp has an input resistor, which is there to remove broadcast RF. In Fenders, you see 34K from two 68Ks in parallel at the input jacks. You can insert a torroidal choke (with material selected for frequency) in series with that resistor. Get a torriod 2-3cm in diameter and wrap a dozen or so turns of wire through it and presto. You could also try a shield around your 1st preamp tube if you don't have one now (assuming a tube amp :wink:).

If the noise if coming through the power lines, try adding a good "hash" filter to the power in. These often come as sealed metal boxes with solder tabs for ins and outs. They are also called EMI/FRI filters.

If your interference is being picked up by a high gain pedal, you have a much tougher task. Put some filter between the guitar and pedal.

You could always line your room with copper mesh and make a Faraday cage to play in.  :wink:

I have a friend with a 100 watt rig and a ~250 foot long antenna. His PC speakers picked things up loud and clear. One clip-on ferrite later, problem gone. Same problem with the external amp on his Ham rig. Another ferrite, another solution. Similar problem in his mobile at 100 watts except that it caused the in-dash radio to blurt out noise at volume 11 even with the radio off when he used a section of the 40 meter band. Same cure... two clip-on ferrites near the in-dash radio. Problem solved.

This is a good test for your Father. According to the rules, it’s his responsibility to supply you with the proper filtering. I wouldn’t push that too far though. Smiley

Good luck!
-Peter

73 and clear Cheesy
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Peter Snowberg
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Posts: 4898


OT: Interferance Problem
« Reply #4 on: September 01, 2003, 01:10:23 PM »

Also..... a couple questions about your Father's rig come to mind:

What style of antenna is he using?

How good is his *** RF *** ground?

Grounding is funny with radio. If you use the wrong LENGTH of ground cable you can actually have an UN-ground. This is much more of an issue if he does not use a balanced antenna.

For more, look here:

http://www.arrl.org/FandES/field/regulations/


If you want to know more, the definitive source for all this jazz is The ARRL Handbook for Radio Communications. It's probably the best $35 you will EVER spend on a book. (also available on CD-ROM for $40)

http://www.arrl.org/catalog/?item=1921   (2003 softcover)
http://www.arrl.org/catalog/?item=1956   (2003 CD is sold out Sad )
http://www.arrl.org/catalog/?item=1905   (2002 CD is almost the same)

I hope your father already has a copy. Excellent book!!!!

73 and clear
-Peter
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Rob Strand
Posts: 572


OT: Interferance Problem
« Reply #5 on: September 01, 2003, 03:15:42 PM »

You have the choice is stopping it at the source, or at reducing the effect at the receiver (ie. your guitar amp/whatever), or attack it on both fronts.  You really need  to identify what is causing the problem - that isn't an easy task.  The problem is guitar amps work with low level signals and this promotes RF problems, the fact you are close to the rig and the antenna adds to the problem.  There's plenty of dogmatic solutions like power supply filters, adding chokes on the RF cables, adding RF filters to the audio signal path.  If the problem is the direct radiation from the antenna getting into your guitar/amp then many of those solutions are pointless,  the only way to stop the RF going out is to stop transmitting and that's not an option - so where does that leave you?  Well you have to make your amp more robust to RF.

The first place to start is to see if it gets into the amp directly.  Get your dad to start transmitting and create a problem situation.  Now the guitar lead out of your amp but leave all the controls as is.  If you dad is still breaking through the audio then it's getting into you amp directly (if it's getting in but not as bad then it's getting in the input as well as the amp).  The next step is to add an RF filter to the power cord, if the RF reduces then you are on the right track.  Next try a choke on the speaker lead.  You have to get the amp RF free before you even bother trying it ut with your guitar.  If the line filter worked but isn't good enough then there a chance adding a line filter to your dad's stuff will improve things too.

Just chip away at it and see what is important and what is not, eventually you will develop a picture of where the problems are then you can attack them.
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