{"id":3620,"date":"2011-09-13T07:50:03","date_gmt":"2011-09-13T11:50:03","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=3928"},"modified":"2023-04-29T13:44:58","modified_gmt":"2023-04-29T17:44:58","slug":"the-malfunctioning-stl-antenna","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2011\/09\/the-malfunctioning-stl-antenna\/","title":{"rendered":"The malfunctioning STL antenna"},"content":{"rendered":"\n

Right after Tropical Storm Irene, it was noted that the STL signal strength at the WHUD transmitter site was low. Normally it was 300+ \u00b5V, but now reading around 100 \u00b5V, which is a problem. Upon further investigation, it was revealed that the STL transmitter on the intermediate hop had higher than normal reflected power.<\/p>\n\n\n\n

Time to call the tower crew.<\/p>\n\n\n\n

The STL transmit antenna for WHUD’s STL (WPOU464) hop is a Scala Paraflector (PR-950<\/a>), mounted at the 280-foot level on this tower:<\/p>\n\n\n\n

\"Scala<\/a>
Scala PR-950 on a guyed tower<\/figcaption><\/figure>\n\n\n\n

The fact that it happened after a major storm and the transmitter was showing higher than normal reflected power indicates a problem with either the antenna or the jumper between the 7\/8″ Cablewave coax and the N connector on the antenna.  A measurement with a spectrum analyzer shows very high return loss:<\/p>\n\n\n\n

\"WHUD<\/a>
WHUD STL antenna return loss<\/figcaption><\/figure>\n\n\n\n

This shows the distance to fault 413 feet, with a return loss of -7.4 dB. \u00a0That distance is either near or at the antenna and -7.4 dB indicates a lot of reflected power. \u00a0We had the tower climber take apart the jumper connections and terminate the jumper with a known good 50-ohm load. \u00a0The return loss did not change. \u00a0We then had him swap out jumpers and reconnect to the antenna. \u00a0That did the trick:<\/p>\n\n\n\n

\"WHUD<\/a>
WHUD STL antenna with new jumper<\/figcaption><\/figure>\n\n\n\n

Much better, most of the power is now being radiated by the antenna, the VSWR is 1.02:1.  The impedance bump at 51 feet is a sharp bend in the coax where it is attached to an ice bridge.  Reconnecting the transmission line to the transmitter and turning it on confirms that all is normal again.  The problem with the jumper was found in one of the connectors, it was full of water.<\/p>\n\n\n\n

\"Water<\/a>
Water-contaminated Andrew flexwell connector<\/figcaption><\/figure>\n\n\n\n

I cut away the boot, water had entered the connector from the back because waterproofing and tape was not applied all the way to the coax. \u00a0This was installed in 1998 when the station moved from Peekskill to its current location in the town of Fishkill. \u00a0The fact that it happened now in the nice weather when Mt. Beacon is still accessible and not in the middle of winter means the radio gods are smiling on us.<\/p>\n","protected":false},"excerpt":{"rendered":"

Right after Tropical Storm Irene, it was noted that the STL signal strength at the WHUD transmitter site was low. Normally it was 300+ \u00b5V, but now reading around 100 \u00b5V, which is a problem. Upon further investigation, it was revealed that the STL transmitter on the intermediate hop had higher than normal reflected power. … Continue reading The malfunctioning STL antenna<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,1],"tags":[46,62],"class_list":["post-3620","post","type-post","status-publish","format-standard","hentry","category-tech-stuff","category-uncategorized","tag-repair-work","tag-stl"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3620","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=3620"}],"version-history":[{"count":8,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3620\/revisions"}],"predecessor-version":[{"id":11721,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3620\/revisions\/11721"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=3620"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=3620"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=3620"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}