Here is a couple more thoughts: Reduce power for testing to about 5 to 10 watts. This is a safety measure in case you are dumping power into something in the structure. House wiring, plumbing, downspouts, etc, can easily be accidently resonant on 15M. Your 10m of coax with a velocity factor of about 0.66 might be an electrical half wave to this system. That would show your transmitter an infinite impedance. If it is not too difficult, ADD about 5 meters of coax at the trasmitter end to assure that it is not performing as a half wave line. Be certain to not coil it so it becomes a choke. I assume the antenna feed point is difficult to get to. If it is not, take your dummy load to the antenna end of the coax and check the SWR. If that is good consider a matching stub across the antenna terminals. It is messy to set up because it takes a helper. I usually use twin lead tv antenna wire for matching and an open line is easier than having to short the stub again everytime you cut it. Test at low power for safety! Dipoles are theoretically 70 ohms Transmitters are usually 50 ohms Most coax in amateur work is 50 ohms AND all of these numbers only work when they are matched! John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" ----- Original Message ----- From: "Milan Pavlica YU7XW" To: Sent: Sunday, December 29, 2002 1:30 PM Subject: Re: [OT]: (Stupid) Antenna question.. > > John Ferrell wrote: > > > The math is all theoretical, a great place to start. Antennas, especially > > transmitting antennas can be humbling. > > Really? I didnt see that ;-) > > > My thoughts: > > Is the antenna location to close to the ground? > > Nope. This is the story. > It was 1/2wave 3.5MHz diple which resonated very well. > Now i wanted to build 21MHz dipole, cuted the wire - and it's doesnt work. > Antenna is located under roof of my house, and coaxial cable length is about > 10m - exactly above my room where radio is located is feed of antenna. > > > Is the coax shorted or open? > > open > > > Could you be coupling to something in the near field of the antenna that > > affects its resonance? > > i dont think so. > I just checked radio on dummy load and radio is OK > > > Sometimes drooping the ends of a dipole will help bring the match closer to > > unity. > > Baluns are more popular than effective. My Cushcraft A3S Multiband beam is > > fed directly but they specify that you use six turns of the coax on an 8 > > inch diameter as an rf choke at the antenna end. This discourages rf on the > > outside of the coax. > > > > How long is the coax run? It can make a difference. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics