Damien,
As a start, I would go to various books and online articles regarding the impedance of your antenna (resistive AND reactive components) considering its length, height above ground, AND the bands that you plan to operate. That will suggest whether 450 ohm or 300 ohm twin lead is more appropriate. Off hand, I would not expect a large amount of degradation due to the twin feed passing through pine trees. I have some antennas fed with 300 ohm window line, although I have used 450 ohm previously, and I have an 8 inch standoff where it passes close to the trunk of a tree BUT this is to prevent rubbing of the feedline against the tree. In addition, I have committed several sins with regard to routing of the twinlead. It goes through two 90 deg bends as it enters the house through some weatherproof quick disconnects (for when storms approach), another 90 deg bend when it first enters the house, follows water pipes and heating ducts spaced about 6-8 inches from the twinlead, three more sharp 90 deg bends as it goes from the basement, up through the wall, and into my shack, with yet another 90 deg bend as it enters another quick disconnect. This last couple of bends put the twinlead an inch or two away from a heating duct for about four inches. While I have two such feedlines they are spaced about a foot apart as they run through the house. Both feedlines have approximately one twist per each three feet of length. Inside, I use electric fence insulators to space the twinlead away from the floor joists. In spite of all these violations of preferred practices, the antennas work well to my satisfaction. It is not uncommon to hear unsolicited reports of "You're the loudest signal on the band" or "You are consistently putting in a good signal to my QTH." The installation is indeed a compromise but it is the best I have been able to do. Through experimentation, I see no interaction by having the feedlines about a foot apart for a length of approximately 50 feet inside the house. The two antennas are concentric loops, one for 40 meters at a height of about 12 ft and the other is a loop for 80 meters at a height of about 20 ft. Shorting the unused antenna, grounding it, etc. does not seem to affect the SWR on the active antenna in use; whether it affects the radiation pattern is another issue but it is of little concern since I'm pleased with the performance of the antennas and feedlines. As a side note, there are two reasons why I use 300 ohm transmitting style window line. (1) Analysis of my antennas indicated that the 300 ohm was a better match than 450 ohm although I could see no change in performance between the two. (2) The 300 ohm window line has a lower visual cross section and it pleases the xyl; happy wife, happy life. There is likely to be some pickup between the two feedlines but it seems to be minimal. Experimentation with antennas can be as much fun as it is educational. A compromise antenna in the air works a lot better than the perfect antenna design on paper. Enjoy the experimentation, and enjoy the hobby. Please share your experiences with others. 73, Evan, K9SQG -----Original Message----- From: Damien Mannix <[email protected]> To: drakelist <[email protected]> Sent: Wed, Sep 11, 2013 10:46 am Subject: [Drakelist] MN-2700/B-1000 use I have just been fortunate enough to obtain an MN-2700 with Balun. Sorry if this is slightly off topic, and I hope it is not a silly question, but if I feed an antenna 150 foot away with 450 ohm twin feed, will it matter if it passes through two mature pine trees whilst on its way? Also, if I want to feed two antennas can I run two 450 ohm twin feeds beside each other or will they interact? I have looked at endless antenna books but cannot find the answers. Regards Damien G3XER _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
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