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elements' lengths as they were putting these together, and that the positions on the on the boom are fixed, there just isn't anything length-wise, separation-wise to go wrong, especially if you are using separate feeds. Several items keep coming up: 1) Use of analyzer devices (MFJ 259, etc) that are being biased off proper readings by broadcast station interference. 2) Measuring at the transmitter end of a feedline and/or balun that has problems. 3) Unknowingly operating too close to a conductor that is detuning the beam. ...and this one I don't hear much about, but ... 4) Using too much goop in one of the joints of just about any of the elements and effectively making a no-contact or high-resistance joint. I assume there is a reason why we are instructed to keep the Noalox coating very *THIN*. I have heard of people DIPPING the element ends and rivets in Noalox. Here, MORE ISN'T better. I have been through #1 myself. Goes away when you use a Bird at the joint between coax and the balun and have a buddy in the shack hit the key. This is also the answer for #2. Never assume the coax is good. PROVE it's NOT the coax before anything else. As to #3, an op who shall remain nameless was trying to tune a beam on a sawhorse four feet off the ground. He complained that he got different readings depending on which way he oriented the antenna. First thing, he wasn't far enough from ground. Next thing, the previous owner had buried some #12 UG out to where he had an above ground pool and filter. It wasn't real deep (6 inches) and the beam was coupling it, except when the elements were perpendicular. PROVE it's NOT conductors in the vicinity. On #4, I have heard of people DIPPING the element ends and/or rivets in Noalox. Here, MORE ISN'T better. It will not take much at all to become a poorly or non-conducting SEPARATOR at the signal levels found on the analyzers. Power may bridge over the gap, but it will get worse over time. The person who took three inches off each end of a DE may have been compensating for an open element elsewhere in the beam. If you suspect this, get a 35' piece of wire and put alligator clips on each end. Zero the lowest range on an ohmmeter with each end of the wire clipped to an ohmmeter lead. Then clip one end of the wire to the far end of the element, and the other end of the wire to one lead of the ohmmeter. Touch the remaining ohmmeter lead to the near end of the element and measure the resistance of all the elements in the beam this way. (This is not all that bad an idea when putting them together in the first place.) If the resistance isn't very low (an ohm or so), then disassembly, cleaning, and reassembly with THIN noalox coating may be in order. If the reading is high, also try bringing the element under some bending stress and see if the reading changes. If so, that is a dead giveaway. Some have tried assembling with pop rivets NOT supplied by F12. They are NOT all the same. See an extensive discussion in the TowerTalk archives on rivets, which includes some long posts from N6BT. If one guy gets great results, and another has problems, and all the elements are the correct length and in the right order on the boom, it HAS to be something like the above. Nothing else left. Best of luck in any event. - - . . . . . . - - . . . . - - . . - . . 73, Guy k2av@contesting.com Apex, NC, USA ----- Original Message ----- From: Herb Rosenberg <herbr@netcom.com> To: <force12talk@qth.com> Sent: Thursday, June 08, 2000 1:37 PM Subject: Re: [Force 12 Talk] C31XR "tuning" > Natan: > > I would be very interested in hearing the tuning recommendations for > those of us haing problems on 15 with the three feedlines. > > Thanks. > > Herb - KG6OK > > herbr@netcom.com > > On Thu, 8 Jun 2000, Natan Huffman wrote: > > > Dear Friends, > > > > As there appears to be somewhat of an "urban legend" growing concerning the > > tuning of the C31XR, I thought a few comments might be helpful, even though > > you may find it repetitious. > > > > The C31XR uses a combination open and closed feed system to excite the three > > bands by a single feedline. The feedline arrives at the 10 meter driver and > > through a closed sleeve comprised of two wires, the energy makes it way to > > the 20 meter driver. The 20 driver and the 15 meter driver form an open > > sleeve to facilitate 15 meter excitation. > > > > Some installations have trouble getting the 15 meter resonance within the > > band. We have found that this is easily corrected by bringing the two wires > > of the closed sleeve in close proximity which then raises the 15 meter > > resonance to within the band. This method will preserve the lengths and > > geometries of the sleeves and therefore is strongly recommended over any > > element length changes. The manuals of recent vintage have the following: > > > > _____3) The next part installs the parallel driver wires between the 10 mtr > > driver feedpoints and the 20 mtr feedpoints. > > _____a) Locate the two, long wires with lugs on each end. > > _____b) Slip the lug from one end of each of these two wires to the 10 mtr > > driver feedpoint screws. > > _____c) Add a #10 flat washer, split lockwasher and a nut - leave loose at > > this time. > > _____d) Place a flat washer on each of the 20 mtr feedpoint screws and slip > > the other end of each wire over the 20 mtr screws. > > _____d1) Please be sure the wires are parallel (not crossed). > > > > _____d2) It is recommended these two wires be taped > > together with widths of vinyl tape spaced every three inches. Do not > > cross these wires. > > _____e) Add the 20 mtr hairpin coil across the 20 mtr feedpoint screws. > > _____f) Slip on a #10 flat washer, split lockwasher and nut. > > _____g) Align the wires and matching coil, then tighten the nuts on BOTH > > the 10 AND 20 mtr drivers. > > _____h) Adjust the turns on the 20 mtr hairpin coil for a small space > > between turns (1/8"). > > > > Any antenna installation is unique. Many factors affect all our antennas > > including ground topography and conductivity, structure, and of course other > > antennas. the presence of these objects are responsible for variations in > > the "tuning" of the C31XR. > > > > I've written about this subject previously on the Tower Talk reflector, so > > you can search the archives for more information if you like. As always, if > > you have questions or comments, please just write. The E-mail volume has > > been overloading me, so my response may be delayed, but it will come! > > > > Thanks, > > > > Natan W6XR > > Force 12 East > > Ithaca, NY > > FN12sk > > force12@qth.com > > > > > > > > -------------------------------------------- > > Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. > > Force 12 Web site: http://www.qth.com/force12 > > > > Submissions: send to Force12Talk@qth.com > > To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com > > Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk > > For problems with the list, contact force12@qth.com > > > > > > > > > -------------------------------------------- > Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. > Force 12 Web site: http://www.qth.com/force12 > > Submissions: send to Force12Talk@qth.com > To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com > Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk > For problems with the list, contact force12@qth.com > > > -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Submissions: send to Force12Talk@qth.com To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk For problems with the list, contact force12@qth.com |
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