Doesn't this suggest that there is a role here for cut and try? Take a set of clip leads to the base of the tower and experiment?
73, Pete N4ZR The World Contest Station Database, at www.conteststations.com The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots at telnet.reversebeacon.net, port 7000 and arcluster.reversebeacon.net, port 7000 On 6/20/2012 3:45 PM, Herb Schoenbohm wrote: > Tom, > > This is not encouraging news for those of us with towers already ground > and are either shunt fed or cage fed. Even though they are not > resonate, although top loaded and approaching resonance, it seems that > even with some elaborate decoupling arrangements, and I hope I am wrong, > not to much can be gained by even trying to get them "detuned". This is > crucial for me to know, and I would assume many others that have > Beverage terminations or feed points 100 feet away, > > Thanks for the warning as this summer I was going to install a HV relay > on the shunt cage to ground....but as you point out it may not help as > the grounded shunt or cage fed tower is already a noise source for close > proximity RX antennas. > > > > > On 6/20/2012 2:09 PM, Tom W8JI wrote: >> There are two potential problems with this. As general rules: >> >> 1.) Grounding any antenna which is dependent on a ground system to be >> resonant will maximize reradiation. >> >> 2.) Resonant elevated radials, even without an antenna connected, are >> resonant and re-radiate. >> >> 3.) Things that are not resonant can still re-radiate. >> >> To minimize coupling from a resonant radial, the radial has to be >> disconnected from ground and from other radials. >> >> Different systems can be different, and in some cases re-radiation can >> actually cause a null that reduces noise, but the general rule is >> self-resonant antennas with a ground (Marconi), or nearly self-resonant >> antennas when grounded, should be floated. Other antennas can be terminated >> in an inductor, capacitor, or opened, depending on the system. >> >> My 220 ft insulated tower, in the center of a four square, is "opened" by >> shorting a specific length of coax to the "L" matching network. It has much >> more radiation when open or grounded. radiation is minimal when detuned by a >> proper impedance. >> >> 73 Tom >> >> >> >> > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
