You might be dealing with AM BCB being detected by the meter - and masking what you are looking for.
On Thu, Jan 30, 2014 at 9:14 AM, Tom W8JI <w...@w8ji.com> wrote: > I cannot get the inverted L to provide a dip on my MFJ 259 analyzer > anywhere in the 160 meter band. I get dips at 8.2 MHz (R=36 ohms X=0) with > reactance on each side of X=0. At 5 MHz R=40 ohms X=0 with reactance on > each side of X=0. I cant get any significant dips neat the 80 or 160 band. > However, when I approach 1.750MHz the resistance drops to 6 ohms and X is > off the scale...at 1.825 I'm at 10 ohms and X is off the scale. Its as if > my 140+ feet of wire is resonant on 8MHz.>>>>>>>>>>>>>>> > > Given you have dips on 8.2 and 5 MHz, the MFJ is working normally. > > With the tower so close to the Inverted L they are like one big coupled > system. I expect the "system" is resonant in the AM BCB, and that is why > you cannot find the low dip. > > I would look for resonance around 5MHz / 3 and or at 8.2MHz /5 MHz. So > look around 1650 kHz or. > > Another way to find the base frequency for Marconi resonance when a system > is out of band is to subtract the closest two dips and divide by two. (This > is what I use in the MFJ 259 firmware to find distance to fault.) > > 8.2 MHz - 5 MHz = 3.2 > > 3.2 / 2 = 1.6 > > So you have two different methods pointing to 1.6 MHz as the resonance. > This tells me your combination antenna is on 1.6 MHz. > It might not move like you think because the tower is fixed at a certain > frequency, and probably well down in the BCB, but you can try making length > 1.6/1.8 = .889 times what the L is now, or 129 ft. I wouldn't expect it to > move perfectly, but it should move. > > ***Ignore trying to determine resonance with a shunt wire. You are wasting > time, because that is a complex system. A shunt system consists of a > transmission line stub mode plus a common mode resonance, so you see the > combination of the two effects. It will NOT tell you where the tower is. *** > > > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband