DC Feedback

jakj1234 · 04-30-2009, 08:13 PM

Okay I got my converter fixed, and now I need to move on to my next project. My RV dealer tells me I have DC Feedback but he never explained what it was or how to take care of it. I will explain whats going on. I am plugged in with a shoreline. I have 2 TV's one in the LR area and one in the bedroom. When the furnace kicks on I get a light snowy effect on the TV in the bedroom. The one in the living room plays fine and has now snowy effect. I have had this problem since I bought the camper so my repair to the converter had nothing to do with because it did it before and it still does it after the repair. The only time I have the snowy effect is when the furnace runs. When it shuts off it goes away? Could this be an outlet problem in the bedroom? Or can someone tell me whats going on and possibly how to correct it?

Thanks
Jerry

W4RLR · 04-30-2009, 09:38 PM

DC feedback?

More than likely it is a faulty connection or a bad cable on your antenna feed to the TV with the snowy picture. If the connectors are not on tight, or there is a nick or cut in the coax, the RF hash thrown off by the furnace motor can mess up your signal.

The F connectors on the ends of the coax cable should be tight, and crimped or soldered. If the connectors on your cable are the screw on type, replace them. They are total junk.

Paul R. Haller · 05-01-2009, 09:24 AM

The Furnace motor is putting out noise and the picture is affected. I would guess, as others have said, that it's your coax cable. Check all connections and if you cant find it, run a separate RG6 cable back to your TV just to test and then try it. If the noise is still there when you turn on the furnace you'll have to put on a RF choke. Is the TV 12 volts or 110?
-Paul R. Haller-

jakj1234 · 05-01-2009, 10:34 AM

The Tv is 110. What is a RF choke, is that something that goes on the TV line? and where would I get one.

Jerry

**Hitchhiker** · 05-01-2009, 11:02 AM

RF Choke = Radio Frequency Choke.

Paul R. Haller · 05-01-2009, 11:38 AM

Yes, RF choke is device used to filter out unwanted radio frequency. But before doing that go out and buy or borrow a 50 length of RG6 coax and run it from the TV signal source to the affected TV. Turn on the furnace. If the problem goes away it's your existing coax in the trailer. RG 6 is a better quality coax with a full shield around the lead wire and a full braided ground around the inner core. It will shield out most any RF noise. Do not use RG59 which was probably what was used in the trailer. It can be of very poor quality depending on the manufacturer. Look for signal amplifiers built into the trailer. They usually are located in the wall next to the coax plate beghind the TVs. They will have an on/ off switch on them to boost the signal. Generally they also have a LED to signal they are ON but not always. These are are notoriously troublesome devices. Look behind the cover plates behind the trailers coax plates and RF amp plates and look for bad connections at the amps or in the coax splitters. Go to the incomming coax and find where it spits off to the second tv. Remove the coax going to your TV thats affected and screw in your lengh of RG6. Check again to narrow down where your trouble is located. Do this until you have located the bad coax run or found that a connection is loose, a splitter is bad, or amp is bad. It will take some time. Turn on and off all amps to see if they make any difference. An amplifier does no good if you are amplifying a noisy signal.
-Paul R. Haller-

wa8yxm · 05-01-2009, 12:35 PM

Just so you know, Many (If not all) RV makers take bids on the assorted parts

Now not all Coax is created equal. I mean really good RG-6 will be full shield and very very low loss.. Good RG-59 is also full shield and about 4 times the loss of RG-6

Cheap RG-59 may be as little as 30% shielded and ... Well, it makes a good attenuator (Makes the signal LOTS weaker)

Paul R. Haller · 05-01-2009, 12:59 PM

I also forgot to mention that if the RG6 coax hooked up to bypass your trailers coax does not fix the snowy picture, you need to check all your 110 grounds especially around the furnace and TV and all your 12 volt neutral wires again around the furnace and TV. Many RV 110 outlets are really cheap Chinese made junk and the 110 leads ore just slipped into the outlet. Not good! Replace them with good quality household screw down connector outlets. Use a VOM meter and check Ohms resistance between the ground of the 110 outlet at the furnace and TV and the frame with the line cord to shore power unplugged. It should be 0 or very low resistance. If its high or infinant, you have a ground fault. Check all battey connections from the - side (white wires, rarely but sometimes green) to the frame and check all 110 grounds (bare wires or green) to the frame. Also check to see if your ground at the shore power cord is also connected to the frame using a VOM. Check within your ac service entrance within the trailer to see if all grounds are connected together and run electrically back to the frame using a 8 guage solid copper wire or some other cable. Most trailer manufacturers connect all 12 volt - wires back together at the fuse box and from there back to the battery and onto the frame. Sometimes they even have a separate bare #8 copper wire from the 12 volt negaive side at the fuse box going directly to the frame along with a heavy guage white wire back to the battery. This is GOOD. Other manufacturers, in an effort to save wire, just run all negative wires back to the nearest frame point and screw them down. This is bad because all the returns to the battery and frame are separated and many can have a poor connection leading to ground faunt nightmares. Often no one knows where they are secured leading to hours of frustration. I hope your 12 V negative wires are all hooked together and then run back to frame and negative battery post.

Lets hope your problems here are on the coax side of things not on the 110 ground system. Finding a ground fault can be very tricky and often impossibe without running another separate ground back to the battery or frame to solve the fault. They are often associated with weird electrical gosts that are hard to pin down. good luck youi have some basic diagnostic work to do.
-Paul R. Haller-

jakj1234 · 05-01-2009, 01:09 PM

We found out what was wrong. When I removed the TV Booster outlet and inspected the coax cables it appears the screw they used to attach the booster to the wall pierced one of the coax cables I also replaced the splitter and the problem is solved. Paul I did do what you said and ran a bi-pass wire from my TV supply to the problem TV and it worked fine. What that told me was that the problem was between the booster and the bedroom TV and between the the screw in the coax and changing the splitter it took care of the problem. Thanks for every ones advise and thanks for taking the time to help me out your a great bunch of people and I am proud to belong to iRV2.

Jerry