"I am not sure how a 40' tall vertical with 94' of top loading, models in NEC, but it seems like it might be close-ish(?) to resonating on 160m. (will I be in the ballpark?) What kind of matching will I need if any?"
Mike, I modeled a 40' vertical with 92' of top loading on 1.825MZ using EZNEC+ 5.0.66. EZNEC+ 5 uses NEC-2. NEC-2 does not like connections to ground with Real/High Accuracy ground. So I modeled two (2) 65' radials at 6 inches above Real/High Accuracy ground. The pattern looks very good with a deep overhead null. As for feeding the antenna, 40' of vertical and 92 ft of top loading is too short for 160M. The calculated feedpoint impedance is 16.22 - J 365.6 ohms. You can add a series inductor and use a 1:2 balun (50 ohm source to 25 ohm load) and get the SWR to about 1.5:1. The actual feedpoint impedance will almost surely be different than calculated. Before you order/wind a balun and wind an inductor, it might be a good idea to build the antenna and measure the actual feedpoint impedance. Then you will know for sure what you need to match. I would not count on an internal ATU to do the job. I hope this helps at least some. 73, Marsh, KA5M From: "Mike Smith VE9AA" <[email protected]> To: [email protected] Sent: Wednesday, March 25, 2015 8:57:18 PM Subject: Topband: ZS6BKW(G5RV) on 160m? I might have a chance to operate from a portable location this summer for a contest or two but at the location they have no antennas, nor is there room for any huge vertical, inverted L, guys ropes etc. etc. and no permission to climb roofs, chimneys, or put a bolt in the building, nor touch the trees. All very restrictive. I might be able to erect a 35' freestanding fiberglass mast with a ZS6BKW. Maybe. The ZS6BKW is basically a 94' dipole with a 40' downlead of 450ohm ladeer line..which will be sloped slightly, as I don't see a way to get the peak above 35' Suffice to say, the best I MIGHT be able to do is sneak in this low ZS6BKW(G5RV) as an inv. vee to run 10m-80m but I am looking for a way to ALSO be on 160m to make a few dozen contacts in a contest or two. I am thinking the peak of the ZS6BKW (G5RV like antenna) would be at max 35'. For 160m, could I short the 2 leads of the 450ohm ladder line together where they meet the coax run and sneak out 2 x 65' (bent) ground radials and attach them to the braid side of the coax? (maybe I'll even make up a switchbox so I don't have to be running around in the dark a few times a night reconfiguring bare wires in an unfamiliar location.) I've read 3830 contest reports where folks have done this type of thing, but of all the antennas I have ever had (many!_) I have never EVER tried this shorting of the ladder line or coax and feeding what is a G5RV as a T-Top vertical. with a couple of radials. I am not sure how a 40' tall vertical with 94' of toploading, models in NEC, but it seems like it might be close-ish(?) to resonating on 160m. (will I be in the ballpark?) What kind of matching will I need if any? I could maybe even add more coax or ladder line to the "vertical" section when on 160m, however it will also have to be sloped/bent and on or very near the ground (probably not good, eh?) I'll be using a modern transceiver with internal ATU. I am not looking to run pileups on 160m.(where I am going is not rare, just a nice summer place)..I just want to pick up a few 160m mults in a contest or two. Ideas? Remember, I am very restricted. Gotta have the ZS6BKW for my antenna.and I may not be permitted to have more than 1 coax run out to the antenna. I doubt adding a couple extra 65' legs is possible either. (no square footage for that. Thanks Mike VE9AA Mike, Coreen & Corey Keswick Ridge, NB _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
