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The translator recently moved it off of the Holiday Inn (formerly Crown Plaza) in downtown Pittsfield, MA to the WBEC AM tower. In order to make that move, we needed to do several things;<\/p>\n\n\n\n
\n“sufficient measurements shall be made to establish that the operation authorized in this construction permit is in compliance with the spurious emissions requirements of 47 C.F.R. Sections 73.317(b) through 73.317(d). All measurements must be made with all stations simultaneously utilizing the shared antenna.”<\/p>\n<\/blockquote>\n\n\n\n
These are intermodulation products, or third order products, between the two signals being transmitted, in this case W277CJ on 103.3MHz and WUPE-FM 95.9 MHz. The antenna side mounted on the AM tower serves as a back facility for WUPE-FM.<\/p>\n\n\n\n
WBEC-FM backup and W277CJ connected to Bext FDCSDC-2 combiner<\/figcaption><\/figure>\n\n\n\n Those measurements are as follows:<\/p>\n\n\n\n
\n
- (F1-F2) + F1 or (103.3 MHz \u2013 95.9 MHz) + 103.3 MHz = 110.7 MHz<\/strong><\/li>\n\n\n\n
- F2 \u2013 (F1-F2) or 95.9 MHz \u2013 (103.3 MHz \u2013 95.9 MHz) = 88.5 MHz<\/strong><\/li>\n\n\n\n
- F2 +F1 or 95.5 MHz + 103.3 MHz = 199.2 MHz<\/strong><\/li>\n<\/ul>\n\n\n\n
In order to make those measurements, I used two Microwave Filter Company MFC-6367 notch filters to attenuate the carriers on 95.9 and 103.3 MHz. This keeps the spectrum analyzer from overloading, thus lowering the analyzer noise floor and giving better results.<\/p>\n\n\n\n
Various tools for proofing FM installations<\/figcaption><\/figure>\n\n\n\n Over the years, I have collected various parts to assist in getting good measurements for FM proofing. Going clockwise and starting at the top, the Rhode Schwarz NRP-Z11 power sensor, the MFC-6367 FM notch filters, directional couplers with power extractor element, various attenuators including the HP 255C variable 0-12 dB unit, and in the middle are two Mini-Circuits NHP-200+ high pass filters. The high pass filters are great for measuring harmonics.<\/p>\n\n\n\n
W277CJ – WBEC-FM test setup<\/figcaption><\/figure>\n\n\n\n To measure the third order products noted above, I first measured the carrier without the filters and an appropriate pad to get a carrier reference level. Then installing the MFC-6367 filters to measure the third order products. In addition to that, harmonics of both FM transmitters out to the 10th harmonic. Of particular importance is anything in the cellular or mobile data bands. All of these measurements were well below the -80 dBc threshold required by the FCC.<\/p>\n\n\n\n
All of these measurements were well within the limits established by FCC part 73.317.<\/p>\n\n\n\n
Also, because this is mounted on an AM tower, there are some AM things that needed to be completed:<\/p>\n\n\n\n
\n“The AM station identified below may be affected by the facilities authorized by this construction permit. Pursuant to Section 1.30004 of the Commission\u2019s Rules, at least 30 days prior to commencement of construction of the facilities authorized herein, the permittee must provide notification of the construction to the AM station licensee. As part of this notification, the permittee must examine the potential impact of the construction of the authorized facilities on the AM station using a moment method analysis. The analysis shall consist of a model of the AM antenna together with the potential re-radiating tower in a lossless environment. The model shall employ the methodology specified in Section 73.151(c) of the Commission\u2019s Rules, except that the AM antenna elements may be modeled as a series of thin wires driven to produce the required radiation pattern, without any requirement for measurement of tower impedances. If the AM station was authorized pursuant to a directional proof of performance based on field strength measurements, the permittee may, in lieu of the moment method analysis, demonstrate with measurements taken before and after construction that field strength values at the monitoring points do not exceed the licensed values.”<\/p>\n<\/blockquote>\n\n\n\n
Since this station was proofed several times, we did about ten readings along the monitor point radials, both before and after.<\/p>\n\n\n\n
The new isocoupler was properly mounted:<\/p>\n\n\n\n
Kintronic broadband AM isocoupler<\/figcaption><\/figure>\n\n\n\n This is simply a large coil of 7\/8 Coax wound inside of a PVC form.<\/p>\n\n\n\n
These AM antenna systems are a regulatory nightmare. Although the Moment Method is an improvement over the system of field measurement proofs, it is still complicated. Part of the issue with AM in general is the expense of the the antenna systems, particularly anything that is directional. <\/p>\n\n\n\n
No real research into Medium Frequency antennas and propagation has been done since the 1930’s. Perhaps we know all there is to know about it, then again, perhaps not. I am currently working on a project which will study Medium Frequency propagation, which I feel, is the first step into revisions of antenna design.<\/p>\n","protected":false},"excerpt":{"rendered":"
W277CJ, Pittsfield was originally a translator for WUPE-AM 1110 KHz. Since that license has been surrendered to the FCC, it is now a translator for WBEC-FM HD2 which is simulcast of WUPE-FM, North Adams. Confused yet? Don’t worry, it is a reshuffling of signals because the land under the 1110 KHz transmitter site was sold … Continue reading After 10 years, it is time to move<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":8612,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[337,4],"tags":[87,82],"class_list":["post-13556","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-installations","category-tech-stuff","tag-am","tag-fm"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/13556","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=13556"}],"version-history":[{"count":23,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/13556\/revisions"}],"predecessor-version":[{"id":13628,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/13556\/revisions\/13628"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media\/8612"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=13556"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=13556"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=13556"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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