Wes, Only a guess...... If the feed line going to the inverted Vee was shorted at the shack end and the feedline was a halfwave long, that RF short would appear at or near the top of inverted Vee. Through mutual coupling from the tower to the inverted Vee could provide some additional top loading thus giving you different results.
Herb KV4FZ On Wed, Mar 7, 2018 at 2:07 AM, Wes Stewart <wes_n...@triconet.org> wrote: > Dave, > > First I see by my log that we've had two QSOs---35 years apart--- one on > 2-meter EME and one on TB. > > I'm no Beverage expert---antenna Beverage that is--- but it seems to me > that shortening the west antenna just decreased its sensitivity. If you're > pointing at one or more noise sources, there isn't much antenna > improvements can do. > > I can't recommend a tower detuning mode, however, you might at least > consider terminating the feedpoint on receive rather than leaving it open. > My system is quite modest on TB, a 55' vertical with an ~85' loading wire. > The separation between the vertical and a tower is 90'. The 85' loading > wire is attached (via an insulating rope) to the tower. The tower supports > a triband Yagi and a dual-band inverted-vee for 40-80. In doing some > feedpoint measurements on the vertical v. number of radials with a vector > network analyzer I saw a little anomaly on the Smith Chart. To make a long > investigation short, I discovered that either lowering the inverted-vee or > terminating the coax at the shack end, rather than having it open, > corrected the anomaly. I have no clue as to what this might have been > doing to the pattern. > > Wes N7WS > > > > On 3/6/2018 10:30 AM, David Olean wrote: > >> I have been putzing around trying to improve my 160 meter setup, and have >> run into a real problem. Most of the USA is covered by two directions from >> here in Maine. SW and W. My problem is that I have an excessively high >> noise level on both of the beverages that run in these directions. In the >> last six months it has gotten worse, and so bad that I cannot use either >> beverage. The wires terminate at the side of my barn where I have ground >> rods and the RG-6 goes through PVC conduit up to the shack on the second >> floor of the barn. During the day I see noise levels at -133 or -132 on >> the two wires, but at night the noise had climbed to levels around -100 or >> to -110 on a good night. I suspected that I was getting noise coupled in >> from my vertical which is rather close and on the other side of my barn all >> of 55 ft away. >> >> Yesterday, I modified the west beverage and shortened it so that it >> terminated about 150 feet away from the barn and I ran new coax back across >> the field. I kept the SW beverage as is to compare noise levels at night. >> Lo and behold, but the noise went to -110 on the SW beverage, but only >> about -120 dBm on the modified beverage. This is a 10 dB improvement. >> Other directions at night run at about -130, so I am now seeing a 10 dB >> extra hit in noise to the west. >> >> The vertical is a shunt fed Rohn 25 with a total height just over 90 ft >> with top loading from a 5 element long boom 10 Meter yagi. I am not sure if >> it is possible to simply un resonate this tower. Does anyone have >> experience with simple ways to decouple a shunt fed tower from the rx >> antennas? >> >> The extra 10 dB of noise that I get to the west and SW is mostly due to >> the location of a town about 7 or 8 miles away in NH. It is ripe with all >> sorts of power line noise. I still can't rule out re radiation from the >> vertical though! I spent many years fighting with the electric utility to >> quell the noise. I involved Riley Hollingsworth and later on, Laura Smith, >> his replacement. The effort was futile and I lost heart as the problem was >> just too big for one person to fight. I was hoping that the noise would >> not affect 160 meters as it had messed up my VHF exploits, and so far I >> only have this ten dB swath of noise that bothers me in two directions. >> >> Any help with un resonating a shunt fed tower would be appreciated. >> >> Dave K1WHS >> >> >> _________________ >> Topband Reflector Archives - http://www.contesting.com/_topband >> > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
