By: Steve Townes, WB4ILW<\/p>\n
I went up to the Mesa last Friday with Jonathan Cameron, KF6RTA, to evaluate the condition of the HF antennas.\u00a0\u00a0 Here is a short update.<\/p>\n
<\/p>\n
The Rohn HF tower with the 40 m and tri-band beams is definitely bent in the top segment.\u00a0 It looks like the combination of the weight of the two beams, the lever arm of the mounting pole and the wind put too much stress on the top-most supports.\u00a0 This also puts stress on the rotator and is likely why it quit working and was blowing fuses.\u00a0 It\u2019s not clear what the ultimate solution is but we may need to replace the top section of the tower and rethink the antenna mounting.\u00a0 It may be OBE but a drone inspection of the tower for confirmation could be useful. \u00a0If the top section is bent, that would probably mean taking it off and replacing.\u00a0 I\u2019m not sure exactly which tower it is but if it is a Rohn 45G class tower, a replacement section is under $300 from HRO.\u00a0 Note that one can apparently contract directly with Rohn, or likely one of their contractors, for assembly http:\/\/www.rohnnet.com\/tower-antenna-construction-services<\/a>.\u00a0 I\u2019m trying to find out if anyone knows the history of the tower.\u00a0 We\u2019ll probably need to look more carefully at wind loading.\u00a0 (Consensus is building that it is a Rohn 45G but I\u2019m trying to confirm)<\/p>\n We tried to crank down the tower section on the utility pole supporting the 160m inverted vee but it didn\u2019t respond as we expected so we need to do a bit more thinking on that.\u00a0 We\u2019ve requested Jan, WB6VRN, who has the most experience with this system, to give us some advice when he can.\u00a0 (Per Jan\u2014and Walt, there may be a locking mechanism that will need some attention.)\u00a0 A drone inspection of the tower for confirmation could be useful.\u00a0 I\u2019m not sure we could get a cherry picker in to this pole but we could get by with someone who can climb the standard wooden utility pole. \u00a0If \u00a0we can get this working, it does have potential for continued support of the 160m inverted vee (once the coax & connections are refurbished as needed) and maybe even a small HF beam with appropriate rotator.<\/p>\n The small tower down by the water tanks appears to be in good shape.\u00a0 We need to unravel the guy wires and crank it up to make sure.\u00a0 Once we do that, we should be able to put a rotator and beam on top.\u00a0 There will be lots of work to actually get to that point because we need to put in the junction box at the tanks, put connectors on the coax and control cables at both ends, refurbish\/buy a rotor and beam, get a \u201ccherry picker\u201d to lift the beam and rotor to attach to the tower, attach the coax and control cables, crank it up and test it\u2014doable but will take time and organization.\u00a0 The nice thing about this location is that it should be trivial to get a cherry picker in there to work on the antenna installation.\u00a0 I think Jonathan and I can handle getting the coaxes and cables fixed but we could probably use some help having a professional installation of the junction box (in the trailer, I think), grounding and cable supports like we have up by the big tower. \u00a0Once we get that ship shape, I\u2019m thinking of something like a Tennadyne T8 log periodic antenna that covers 13-30 MHz (good for MARS\/CAPS coverage) and hopefully isn\u2019t too big for the tower\/rotator combination.\u00a0 The T8 runs about $900 and a rotator and control box should be less than $500.\u00a0 (Note that the new T8 that goes 10-30 MHz is about 3 times the price and really big so I\u2019m not sure it would fit on the smaller tower in that location.<\/p>\n On another note, we\u2019ve found that the R-7000 vertical on the Mesa has an SWR that is too high for the ALS-606 amp. This currently limits our ability to use it on the 14 MHz NASA frequency.\u00a0 We should have an antenna tuner and Chris and I have talked about the LDG AT-600ProII as a possibility.\u00a0 There are likely others.\u00a0 In the meantime, I\u2019m attempting to refurbish an old manual MFJ tuner that we may be able to use until we can get an automatic one.<\/p>\n For operation in the 14-30 MHz band, a log-periodic antenna like the one above could ameliorate some of the requirement for an antenna tuner but it is a good idea in general to have an antenna tuner for non-ideal installations.\u00a0 We may also want to consider a wideband wire antenna(s) like the Tennadyne TD-SS120 or ones from B&W, etc., for operation between 1.8 MHz and 14 MHz.<\/p>\n","protected":false},"excerpt":{"rendered":" By: Steve Townes, WB4ILW I went up to the Mesa last Friday with Jonathan Cameron, KF6RTA, to evaluate the condition of the HF antennas.\u00a0\u00a0 Here is a short update.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-803","post","type-post","status-publish","format-standard","hentry","category-antennas"],"_links":{"self":[{"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/posts\/803","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/jplarc.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=803"}],"version-history":[{"count":9,"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/posts\/803\/revisions"}],"predecessor-version":[{"id":813,"href":"https:\/\/jplarc.org\/index.php?rest_route=\/wp\/v2\/posts\/803\/revisions\/813"}],"wp:attachment":[{"href":"https:\/\/jplarc.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=803"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jplarc.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=803"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jplarc.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=803"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}