{"id":2008,"date":"2016-04-05T17:47:09","date_gmt":"2016-04-05T17:47:09","guid":{"rendered":"http:\/\/www.tsgarc.uk\/?p=2008"},"modified":"2016-04-05T17:56:56","modified_gmt":"2016-04-05T17:56:56","slug":"strange-problems","status":"publish","type":"post","link":"https:\/\/www.tsgarc.uk\/?p=2008","title":{"rendered":"Strange problems…."},"content":{"rendered":"

So, for a couple of months I’ve had a growing suspicion that I’m not receiving as well as I am transmitting. \u00a0I first noticed the problem when observing the strength of signals from GB3VHF <\/a>which after one winter storm seemed much weaker than it had been. \u00a0However, there seemed to be no impact upon transmit as SWR remained negligible and stations some distance away where still receiving me well even\u00a0when my transmitter was generating about 0.5W PEP!<\/p>\n

Since first noticed I’ve worked many\u00a0stations and the signal reports always seem to identify that I’m not receiving as well as the remote station. \u00a0Establishing this pattern has taken some time. \u00a0It should be said at this point that its the same antenna and feeder used for both transmit and receive.<\/p>\n

Its been a wet Winter and not really suitable for removing weather proofing from exterior connections and outdoors work. \u00a0But now Spring has arrived things are finally starting to get dryer and warmer. \u00a0Alongside this I’ve taken down the mast and antenna for work to support an new PRO.SIS.TEL<\/a> 641D rotator. \u00a0This has enabled a detailed inspection and test of feeder and antenna.<\/p>\n

Before starting any work I thought about and identified the following possible causes:<\/p>\n

    \n
  1. failure of the receiver, possibly signal amplifer<\/li>\n
  2. damaged feeder, possibly a connector problem or water ingress<\/li>\n
  3. damaged feeder at the antenna feed-point. possibly also water ingress.<\/li>\n<\/ol>\n

    Problem (a) seemed possible but without a second receiver its very hard to be sure. \u00a0But its a quality Transverter <\/a>(Kuhne TR144H) and I’d be surprised if that had partially failed – remember signals are only 2 – 3 S points down on what I think they should be.<\/p>\n

    So, (b) or (c) seemed much more likely.<\/p>\n

    So with the mast down and everything removed back to a\u00a0dry, warm environment I removed weather seals – no sign of water or even the slightest amount of moisture ingress. \u00a0The coax was tested with a DC Ohm meter – no shorts or higher than expected resistances; with an antenna analyser and dummy load – again this looked perfect.<\/p>\n

    \"InnovAntenna<\/a>So attention shifted to the antenna feed-point, pictured before<\/strong> it went outside for the winter and before<\/strong> the connections where weather sealed. Note: Grey plastic tape overlays\u00a0amalgamating tape. \u00a0Again, there was no signs of moisture ingress into the coax, but there where signs of galvanic corrosion<\/a> between the aluminium driven element and the stainless steel (A2 grade) machine screws\u00a0to which the feeder connected. \u00a0Actually, to be more precise between the aluminium driven element and the flat washers on each machine screw.\u00a0 It was clear that the liquid rubber<\/a> sealant which I’d applied had not sufficiently covered these connections and thus water had been in contact between the different metals acting as an electrolyte.<\/p>\n

    To be clear, the machine screws where not showing any significant signs of corrosion<\/a>, just the washers. \u00a0So the feed-point was thoroughly cleaned and reassembled without using the washers then liberally coated in liquid rubber<\/a> to seal against\u00a0contact with water.<\/p>\n

    Now, at this point I don’t know if this was the problem, but it does make some sense. \u00a0Any transmit signal would\u00a0be of a much higher voltage\/current than a received signal so would probably cross a\u00a0mildly corroded junction with marginal attenuation. \u00a0But marginal attenuation of a much weaker signal would be more noticeable. \u00a0That’s my reasoning anyway.<\/p>\n

    The acid test will be when I erect the mast and antenna again in a few weeks and see if received signals such as GB3VHF <\/a>have returned to their earlier\u00a0strength. \u00a0When doing this I will also use new feeder, so if signals are stronger I’m never going to be absolutely sure the problem was galvanic corrosion<\/a>. \u00a0Of course the problem may still be present and it could be another cause such as the receiver!<\/p>\n

    For information, the antenna is an 8-element LFA Yagi from InnovAntennas<\/a>.<\/p>\n

    Andrew
    \nG0RVM<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

    So, for a couple of months I’ve had a growing suspicion that I’m not receiving as well as I am transmitting. \u00a0I first noticed the problem when observing the strength of signals from GB3VHF which after one winter storm seemed … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5],"tags":[32,9,17],"class_list":["post-2008","post","type-post","status-publish","format-standard","hentry","category-news","tag-2m","tag-antenna","tag-g0rvm"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/posts\/2008","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2008"}],"version-history":[{"count":7,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/posts\/2008\/revisions"}],"predecessor-version":[{"id":2018,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=\/wp\/v2\/posts\/2008\/revisions\/2018"}],"wp:attachment":[{"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2008"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2008"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tsgarc.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2008"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}