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Timebomb
Junior Member
Username: Timebomb
Post Number: 15
Registered: 2-2005
| | Posted on Wednesday, February 23, 2005 - 4:57 pm: | 
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I HAVE done some research on low pass filters, but if you had to choose ONE, which one would you choose?
Also, I've got some bleedover coming into stereo speakers in another room in the house. I'm hoping I'm not effecting the neighbors, no complaints yet...My question, would the low pass filter help clear up stereo speaker bleedover, or just TVI? I do have a bit of TVI on one TV with rabbit ears, but hardly noticable.
Last question, if I acquire a some bead ferrites, should I apply them to both ends of my coax, or which end is the right end to apply them?
P.S. I run an Antron 40 ft. to feedpoint using a tree to support the mast, to a barefoot(peaked) Cobra 2000. I've got a 150 watt amp I might use eventually, once I acquire the low pass filter, finish grounding EVERYTHING, and take all precautions to try to eliminate any interference. I know that alot of people believe that your NOT at fault for bleeding over neighbor's TV's, speaker's etc., but for me, it's part of the fun to make sure it's not happening. |
Racer_x
Junior Member
Username: Racer_x
Post Number: 27
Registered: 2-2005
| | Posted on Wednesday, February 23, 2005 - 8:33 pm: |
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Low pass filters only cure TVI, not RFI like you're experiencing with the speakers. At the power level you're currently using, the RFI in the speakers will probably be stopped by choking the coax because your antenna is pretty high and the power levels are pretty low. It's almost surely being caused by RF running back down the shield to the ground. You need to create a choke just below the feed point of the antenna. You can do it by either creating a coax coil or you can use ferrite beads. When you start using the amplifier you might need to do more because the near field radiation will greatly increase in strength.
TVI specifically creates interference on television channels. You generally see it on channel 2 or channel 6 as they are harmonics of the CB frequency. It's usually a herringbone pattern, but it can look like almost anything else. As part of the peaking did they adjust the 54MHz trap in the radio? If so, you might just want to get someone else to properly adjust it to 54MHz again. I suggest someone else because if they detuned the TVI trap, they didn't know what they were doing and probably won't know how to tune the trap properly. |
Kirk
Intermediate Member
Username: Kirk
Post Number: 279
Registered: 6-2002
| | Posted on Thursday, February 24, 2005 - 5:48 pm: |
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I would choose Bencher LP filter. I have an Oak Bay Technologies (don't think you can get those anymore) and a Vectronics LP 30. I do not care for the LP 30's construction....just my opinion. When I had an issue at another QTH with RFI, I used ferrite cores wound around the speaker wire and on the incoming AC. Through all of that I did get rid of it but I will say that I found more of an issue with my antenna placement. i.e. your tower in relation to your shack. |
Timebomb
Junior Member
Username: Timebomb
Post Number: 16
Registered: 2-2005
| | Posted on Thursday, February 24, 2005 - 5:52 pm: |
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Thanks Racer, your reply makes perfect sense to me. I plan on upgrading to an Imax 5/8 very soon, and will add chokes at that time. I would probably go with a 10K, but too many branches to get it up there!! but that's another story...
As far as the peaking on my Cobra goes, honestly I don't know what was done, took it to the local cb shop, and the tech there seems to do good work, never had any problems. I'm not quite ready yet to experiment with my MAIN radio, but after a bit more studying, I should know what I'm doing!!
Thanks again for the info. |
Timebomb
Junior Member
Username: Timebomb
Post Number: 17
Registered: 2-2005
| | Posted on Thursday, February 24, 2005 - 7:38 pm: |
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Kirk, the Benchers look like quality LP filters.
Are 1/2" ferrite beads the right size for RG8U coax? Are they supposed to fit snug, or do they need to be taped? Thanks again.
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Kirk
Intermediate Member
Username: Kirk
Post Number: 280
Registered: 6-2002
| | Posted on Thursday, February 24, 2005 - 11:18 pm: |
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Timebomb, I've used both and honestly prefer the cores (which look like donuts). You may need to wrap several turns of wires around them so get something like an inch in diameter (depending on your gauge of speaker cable). I don't know what Copper sells here, but I typically buy from Palomar Engineers. A 43 or 77 mix should work for you. I have and do use beads on my coax, but truthfully I don't think they will help your situation. |
Timebomb
Junior Member
Username: Timebomb
Post Number: 18
Registered: 2-2005
| | Posted on Friday, February 25, 2005 - 12:02 am: |
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Wow, quite a selection of RFI cancelling goodies! Thanks for the heads up.
I will probably end up using chokes on coax, and other devices that need it. |
Racer_x
Junior Member
Username: Racer_x
Post Number: 37
Registered: 2-2005
| | Posted on Friday, February 25, 2005 - 8:14 am: |
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Timebomb - For ferrite chokes I'd buy the computer type that zip tie onto video cables. They're cheap, so use a couple right below the antenna, and another couple a few feet farther down.
Ideally you'd loop coax through a toroidal core, or even just loop the coax into a choke itself, but I think the split beads will do the job for you.
And yes, they should be snug. The farther away from the shielding the less effective they will be. |
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