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In Reply to: Signal change when I move the coax wire why ? posted by legarem on December 2, 2006 at 04:40:26:
therefore you will get a little (antenna) gain by having it between the tuner and antenna. This is especially true if the length happens to be a multiple of the wavelength of the station you are trying to recieve. This affect is most often known to and exploited by hardcore DX'ers.Since you are essentially moving a piece of the antenna, ie reorienting it in the EM fields that is the station you are recieving by moving the coax, it doesn't suprise me that you would hear differences in reception especially on weak stations.
Follow Ups:
Re coax as antenna, take a look at Brian Beezley's FM page, you can make a coiled portion of the coax act as a current balun, to limit RF pickup by the shield. Might help. Probably a good idea to keep the line as short and direct as possible, and nail it to walls, etc. so it doesn't move around. It does have inductance and that well change with loops, etc., in it.
Dale
It could also be a break in the cable. RF can jump small breaks because the ends couple capacitively. It could be that when you bend it just wrong you decrease the capacitive coupling and hence the signal strength. RG-6 is certainly beefy stuff; your problem should not be attenuation (in a good cable). So my guess is that you have a defective cable.The only way I can figure to test it is to remove the cable, test for continuity and shorts. It might be that when you jiggle it just right, you get a continuity failure. In the same position, you should get some kind of capacitive reading through the cable. If you do, that would confirm the problem. If that's the case, you're out a cable. Good luck!
it only happens on weeak stations and not strong stations. A cable break would affect both weak and strong stations equally badly, ie they would both disapear during the broken wire conditions. Also the broken wire pieces are not going to have enough capacitance between them to pass enough signal to drive the recieve, no matter how strong the station.
The coax needs to be clear of all metal for 6-12" around it. Metal objects close to it may affect the impedance, and cause more mismatch.I'd also check the cable shield to F connector resistance. This is a common area for corrosion and problems on old cable, especially homebuilt cables. I've had good luck with the twist on gold F connectors from Radio shack, but you must get preceisely the correct one. Forget about crimp connectors unless you have the expensive crimping tool. The cheap crimp tool just creates problems down the road.
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