{"id":10173,"date":"2019-07-01T20:20:21","date_gmt":"2019-07-02T00:20:21","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=10173"},"modified":"2023-03-19T09:06:53","modified_gmt":"2023-03-19T13:06:53","slug":"more-am-retuning-work","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2019\/07\/more-am-retuning-work\/","title":{"rendered":"More AM retuning work"},"content":{"rendered":"

Working on another old AM station, this one is a simple Class C one tower on 1230 KHz.<\/p>\n

\"Broadcast<\/a>
Broadcast Electronics AM Output Tuning Network<\/figcaption><\/figure>\n

The main problem today was this BE AM output network unit between the BE AM1A and the ATU.\u00a0 This site has had some dirt difficulties over the years and the internal parts of this tuning unit arc at full power.\u00a0 I attempted to drive the ATU directly with the transmitter, which was a no-go.<\/p>\n

\"Gates<\/a>
Gates Radio 1 KW AM ATU, circa 1947<\/figcaption><\/figure>\n

I took a look at the ATU, which is a pretty standard Gates 1 KW ATU from the late forties or early fifties.\u00a0 I have seen perhaps dozens of these things.<\/p>\n

My first thought was that over the years, likely due to changes in the ground system, the base impedance has shifted away from its licensed values.\u00a0 However, a quick measurement of the base impedance shows it to be exactly at the licensed value, 17.3 ohms.\u00a0 The tower is 67 degrees tall so the impedance value is right in the theoretical norm.<\/p>\n

I\u00a0 measured the input to the ATU, which showed 38 ohms with about 7 ohms of capacitive reactance.\u00a0 I can only surmise that it has always been this way.\u00a0 The transmitter in use before the BE AM1A was a Harris\/Gates Radio BC-1G.\u00a0 That model transmitter will drive anything including an open transmission line.<\/p>\n

\"Retuned<\/a>
Retuned ATU input; 49 ohms resistive, 0 ohms reactance<\/figcaption><\/figure>\n

Having the bridge on hand, I decided to retune the ATU for a better match. I put the bridge on the input terminals of the ATU and set it to 50 j0.\u00a0 Using the remote control, I turned the transmitter off and on while making small adjustments to the output strap on the coil until the resistance was 49 ohms with zero reactance.\u00a0 I would have gotten it to 50 ohms, but the strap on the output side of the coil would not stretch far enough to reach the proper spot on the coil.<\/p>\n

Now the transmitter will run into the ATU directly at full power with about three watts reflected. \u00a0 The BE AM output matching network unit has been removed for cleaning and repairs.\u00a0 I will reinstall it once those repairs are completed.<\/p>\n","protected":false},"excerpt":{"rendered":"

Working on another old AM station, this one is a simple Class C one tower on 1230 KHz. The main problem today was this BE AM output network unit between the BE AM1A and the ATU.\u00a0 This site has had some dirt difficulties over the years and the internal parts of this tuning unit arc … Continue reading More AM retuning work<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":10195,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[87,284],"class_list":["post-10173","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tech-stuff","tag-am","tag-am-tower"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/10173","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=10173"}],"version-history":[{"count":10,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/10173\/revisions"}],"predecessor-version":[{"id":11071,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/10173\/revisions\/11071"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media\/10195"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=10173"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=10173"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=10173"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}