{"id":2488,"date":"2011-03-07T08:19:29","date_gmt":"2011-03-07T12:19:29","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=3928"},"modified":"2023-04-30T14:39:16","modified_gmt":"2023-04-30T18:39:16","slug":"the-burned-contactor-fingers","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2011\/03\/the-burned-contactor-fingers\/","title":{"rendered":"The burned contactor fingers"},"content":{"rendered":"\n

This is a set of burned contactor fingers on a Harris HS-4P<\/a> 30 amp RF contactor:<\/p>\n\n\n\n

\"Harris<\/a>
Harris HS-4P RF contactor with burned finger stock<\/figcaption><\/figure>\n\n\n\n

The back story is this:<\/p>\n\n\n\n

The contactor in question is at the base of Tower #3 of the WBNR<\/a> (1260 KHz, Beacon, NY<\/a>) antenna array.  This is the tallest of all the towers, at 405 feet.  As such, it gets struck by lightning often.  There was at least one occasion where one of the inductors in the ATU got “sucked in” due to the huge magnetic field of a high current strike.  It is not at all surprising to me to find other component issues in this ATU.  Because of the burned contacts, I’d suspect that the station was switching modes under power, but I didn’t see that happening today.<\/p>\n\n\n\n

The problem manifested itself in very high SWR after changing over from day pattern to night pattern. \u00a0This did not occur every time, in fact, it only occurred once in a great while at first. \u00a0Then, over the last couple of months, it began occurring more and more often. \u00a0Since the snow drifts are now down to a manageable six to eight inches, it was a good day to go out and do some exploring.<\/p>\n\n\n\n

First of all, I put the station into nighttime mode just to confirm that there is still an issue. \u00a0The transmitter, a Broadcast Electronics AM1A showed very high SWR and carrier fold back. \u00a0Left it in night pattern, but turned it off and took a walk, not a drive, to Tower #4 which is all the way at the bottom of a hill, near the old City of Beacon landfill. \u00a0I figured that I would check that one first, then look at Tower #3 on the way back. \u00a0When I got to Tower #3, I found the issue right away.<\/p>\n\n\n\n

Fortunately, I was able to salvage a set of contact and contactor bar from another relay in the same ATU that was not using them.<\/p>\n\n\n\n

\"Burned<\/a>
Burned RF contactor bar<\/figcaption><\/figure>\n\n\n\n

The night pattern is only 400 watts, but these are tall towers, 225 degrees, therefore current and voltage are high at the base. \u00a0In fact, the slightest change at the base of the nighttime towers will greatly upset things.<\/p>\n\n\n\n

\"Burned<\/a>
Burned RF contactor fingers<\/figcaption><\/figure>\n\n\n\n
\"Harris<\/a>
Harris HS-4P contactor repaired<\/figcaption><\/figure>\n\n\n\n

This is the repaired contactor.  I will say, the EF Johnson RF contactors are easier to work on.  Those are the ones with the big rocker bar across the top and two solenoids on either side.  All of the wiring, status switches and contacts are exposed and easy to get to.  This one, not so much.  This is the BE AM1A transmitter<\/p>\n\n\n\n

\"Broadcast<\/a>
Broadcast Electronics AM1A transmitter<\/figcaption><\/figure>\n\n\n\n

It is not a bad unit, compact, sounds good, is reliable, etc. \u00a0In order to work on the power supply or anything in that top cabinet, the whole thing needs to be removed from the rack and taken down. \u00a0I suppose that is my only gripe about the thing.<\/p>\n","protected":false},"excerpt":{"rendered":"

This is a set of burned contactor fingers on a Harris HS-4P 30 amp RF contactor: The back story is this: The contactor in question is at the base of Tower #3 of the WBNR (1260 KHz, Beacon, NY) antenna array.  This is the tallest of all the towers, at 405 feet.  As such, it … Continue reading The burned contactor fingers<\/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":[17,4],"tags":[33,32],"class_list":["post-2488","post","type-post","status-publish","format-standard","hentry","category-maintenance","category-tech-stuff","tag-am-towers","tag-am-transmitters"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/2488","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=2488"}],"version-history":[{"count":6,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/2488\/revisions"}],"predecessor-version":[{"id":11857,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/2488\/revisions\/11857"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=2488"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=2488"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=2488"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}