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Thanks John,
and Duh. The ferrite beads are in the truck, but not in the mind. Would have been easy. Not an integral antenna, problems started when we changed antenna. Our antenna is about 15' below the TV antenna, about 5' above where the TV coax enters the house. The radio is an early Deliberant 1300, plastic baseplate, no ground lug. If the beads don't do it, I will probably change out the radio. Scott Reed Owner NewWays Wireless Networking Network Design, Installation and Administration www.nwwnet.net ---------- Original Message ----------- From: John Scrivner <[EMAIL PROTECTED]> To: WISPA General List <wireless@wispa.org> Sent: Mon, 03 Oct 2005 22:39:40 -0500 Subject: Re: [WISPA] TV Interference > RF Interference was my job for some time in my old CATV days. Here are > some tips. First, is this an integrated radio/antenna? If it is then you > may have RF interference traveling along the Cat 5 cable. If so then > snap a ferrite bead onto the cat 5 cable near the antenna and POE ends > of the cable run. This may fix the trouble. RF ferrite beads are good to > keep around whether they fix this particular problem or not. > > Channels 2 thru 5 are much more susceptible to electrical interference > than higher VHF channels. There is actually quite a bit of band space > between channel 6 and 7. Cable channels 14 through 22 and 98 and 99 are > actually between channels 6 and 7 when incrementing by frequency up the > band. I know that seems weird but it is true. This could explain why 2 > thru 6 are more affected than channel 7 in your situation. Power > supplies are often the source of electrical interference. If you have a > second radio and/or supply to try then I would do this. Also you may > consider a ferrite bead on the output side of the power supply for your > radio. It could be the noise source. You have probably all seen the > cylinders inline with the outputs of commonly used wall wart power > supplies. These are ferrite beads integrated into the outputs of the > supplies for just this reason. > > Vertical separation is important in any RF environment. You may not need > 10 feet of separation but you may need at least a few feet of separation > between your TV antenna and you WISP antenna. RF signals (even from far > removed bands) can "swamp" receivers in other bands and cause a myriad > of problems, not the least of which could be the trouble you describe. > > One unlikely cause could be out of band interference where your wireless > radio could be actually radiating RF into the lower VHF channel bands > directly (which is not a common problem). It is easy to correct though. > It just requires the replacement of the bad radio. This may be a good > thing to try first as changing the radio is easy and isolates two > possible problems (power supply noise and out of band emissions) > Obviously you would want to change the wall wart power supply also if > the trouble does not go away with changing the radio. > > I have rarely seen grounding as a problem producing similar issues. I > have seen a proper ground either missing and leading to ground loops and > RF noise and I have seen the reverse where a ground of any kind caused > the interference. This is a really bizarre situation but it does happen. > I have usually found the grounding issue to be related to poor grounding > of the electrical service and/or tower. I once had a mobile home where > my CATV ground was carrying all unbalanced loads for all electrical > circuits for the entire home. When I unhooked it the ground lug sparked > and I received a shock. Needless to say I had the owner call an > electrician immediately. In this particular situation the cable > television drop line had a melted outer jacket from all the current > being carried by the outer cable sheath. I thought it had received a > lightning strike but it was actually just caused by too much current > through the cable line's shield. For those of you who do not know what > neutral or ground currents are in power electricity you may want to do a > little reading. Scary stuff! > > Order yourself some ferrite beads to keep on hand if you do not have any > now. Your local two way radio shop will have them if you need some > quick. Please do us all a favor and share what you had to do to make > this all work once you find a solution. > All the best, > Scriv > > Scott Reed wrote: > > > OK, I have dealt with TV interference before, but this one has me > > stumped. Installed customer 4 weeks ago. All is fine. Over last > > week, signal strenght started degrading. Customer complained about > > speed slowdown. Customer was out of town for weekend but we went out > > Saturday and RSSI was really bad. Did some testing. Replaced 15dB > > antenna with a 19. Raised about 4". Signal strength improved > > dramatically. Customer came home Sunday and there were dots/lines in > > channels 2 and 5. Channel 7 works fine. The 2 & 7 transmitters are > > not far from each other. Unplugged radio and dots/lines went away. > > Plugged it back in, dots/lines. So, why only channels below 7 and why > > only with the new antenna? > > > > Scott Reed > > Owner > > NewWays > > Wireless Networking > > Network Design, Installation and Administration > > www.nwwnet.net <http://www.nwwnet.net/> > > -- > WISPA Wireless List: wireless@wispa.org > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ ------- End of Original Message ------- |
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