Dave, What complex Z value do you get after running NEC at 1835 kHz? Can you attach the .NEC input file?
Phil, Does your MFJ analyzer give you complex Z results in a R+jX format, rather than just Z magnitude? Not sure if the 259B model will do that or not. Anyway, with complex Z info, it's easy to design either a low-pass or high-pass L network using TLW software. Paul, W9AC ----- Original Message ----- From: "DAVID CUTHBERT" <[email protected]> To: <[email protected]> Cc: <[email protected]> Sent: Monday, February 06, 2012 12:06 PM Subject: Re: Topband: Help With Vertical Antenna Matching > Phil, NEC shows that shortening the radials to 110' will resonate things > at > 1.8 MHz. The ends are 10' from ground. The radial length can be used to > adjust the antenna to resonance. > > The input impedance is 100 ohms. > > A balun having a lossy 400 ohm impedance is needed to reduce the worse > case > feed line shield current to 20 dB below the total radial current. > > Dave WX7G > On Feb 5, 2012 3:49 PM, "Phil Clements" <[email protected]> > wrote: > >> I need the help from one of the Guru's here on the group.... >> I need to know how to match the 160 meter vertical ground plane here. It >> worked fine for years until I removed 80 meter 4-square from the tower. I >> have no modeling capabilities here. >> >> The set-up is this: >> A 200 foot Rohn 25 tower, with insulators at the 60 foot level. >> Three elevated radials at the 60 foot level; sloping down to about 10 >> feet >> off the ground at the far ends. They are c. 110 electrical degrees long. >> The vertical radiator is c. 140 feet long. >> There is a large 1:1 balun at the feed point. >> The feed line is 450 feet of 7/8 helix to the ham shack. >> >> >> The reading on the 259B at the feed point is c. 3:1 VSWR, with a slight >> dip >> to 2.7:1 at 2.45 mhz. >> >> I am at my wits end here; several trips up the tower produced no good >> results. There are many systems on Google and YouTube, but the matching >> systems are for antennas shorter that 1/4 wave length. >> The old matching system when the 80 m 4-square was co-located was a 600 >> pf >> series capacitor from the center of the coax to the base of the vertical >> element. The three radials are joined together at the feed point, and >> connected to the coax shield. >> The VSWR back then was 1.25:1 @ 1835 khz. , and was a "killer" antenna on >> 160! >> >> Any help will be greatly appreciated; my old knees have about two more >> climbs left in them! >> >> Thanks in advance. >> >> (((73))) >> Phil, K5PC >> >> >> >> _______________________________________________ >> UR RST IS ... ... ..9 QSB QSB - hw? BK >> > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
