| Index | Thread | Archive | Sep-2000 | Archive | Send |
 |
  |
  |
   |
|
  |
|
a C-19XR. The jumpers on the linear loading wires had been connected during assembly to be 15 inches away from the stand-off for the reflector and 25 inches for the driver. Initial tests after installation indicated that it resonated somewhere around 6.8 mhz, and had a VSWR of 2.75 at 7.010, rising to over 3.0 at 7.200. I could discern no F/B ratio on DX signals. This past Saturday we suspended the boom from a pulley on the mast, using a sling wrapped around the boom, so that the elements could be pulled in toward the tower. We then removed the jumper wire from the reflector, and one end of the coil on the driven element. This was to de-couple the elements. We then adjusted the jumpers on the linear loading wires while measuring the resonant point on the reflector using an antenna analyzer belonging to K5YA (don't know the model, but it is not the MFJ). We found that it took more than 4 inches of adjustment away from the stand-off for each end of the jumpers, on both sides of the boom. We tuned the reflector in this manner to resonate at 6.920, per the manual. We found similar large adjustments needed for the driver to make it resonate at 7.080. This makes me wonder about the original settings specified in the manual. I note that a single manual is provided for EF-240 standard, EF-240 heavy duty, and EF-240 X (long boom) models. The EF-240 model has a 16 foot boom, while the EF-240X has a 24 foot boom. Yet there is no difference mentioned in the assembly instructions as to the jumper settings. I would think that the difference in boom length would affect the coupling between the elements, and thus, the resonance points. To have identical jumper settings for the two models make no sense to me. After our adjustments, the antennas resonates at 7.080, with VSWR 1.0 at that point (after fiddling with the driver coil). At 7.000 VSWR shows 1.25, while at 7.250 is rises to 2. This appears to be consistent with the expected results. However, I still am not convinced that there is much F/B. Admittedly, I have had little time to observe it, but this morning I was listening to a loud JA pile-up for HO1A on 7.005, and it made little difference in signal strength whether the antenna was on the JAs or HO1A. Have others experienced similar problems in tuning the EF-240X by factory settings? Any comments appreciated. 73 de Chas W5DV -------------------------------------------- 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 n4zr@qth.com |
This Thread
|
This Author (Sep-2000)
|