It's been years since we've changed any transmitters or exciters. Are proofs still required when changing transmitters, exciters, or when making IPA modifications? How about when changing out an FM transmitter coax switch?
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Proof of Performance tests
- Thread starter Brian Bowers
- Start date
The broad interpretation seems to suggest ANY change to a transmission system requires measurements to be taken to insure the station is "in compliance"....
As a former broadcast engineer (having been retired for nearly 10 years)....my gut says if I've installed a new/different transmitter, I'm DEFINITELY going to do a proof - leaving NOTHING to chance...
Since exciters/IPA are an integral part of a complete FM transmitter....if changes are made to these, again....I'd err on the side of caution....and do at LEAST a "skeleton" proof to verify those "modified" sections meet specs....
Antenna coax switch??? IMHO, a simple check for insertion loss/minimum VSWR, noted on the engineering log, should satisfy "Charlie"!!!
RE: Proofs....My mantra has always been: "If in doubt....JUST DO IT!!"
Stay Safe!
As a former broadcast engineer (having been retired for nearly 10 years)....my gut says if I've installed a new/different transmitter, I'm DEFINITELY going to do a proof - leaving NOTHING to chance...
Since exciters/IPA are an integral part of a complete FM transmitter....if changes are made to these, again....I'd err on the side of caution....and do at LEAST a "skeleton" proof to verify those "modified" sections meet specs....
Antenna coax switch??? IMHO, a simple check for insertion loss/minimum VSWR, noted on the engineering log, should satisfy "Charlie"!!!
RE: Proofs....My mantra has always been: "If in doubt....JUST DO IT!!"
Stay Safe!
Thank you very much for confirming. That's what I thought too.
After doing a transmitter installation I typically do an RF proof, but not an audio proof. For example, I crank up the spectrum analyzer and take frequency measurements, including second and third harmonics. I include the spectral shots and narrative in the station public file under Station Technical Documents.
If your path is AES digital there is not much to measure for audio. Maybe clip levels, jitter, linearity, etc. but the traditional noise/distortion/freq response is no longer needed with an all digital path. That is making a big assumption that all the pieces in that path are designed, installed, and operated correctly.
I would always get a third party RF Proof to prove facility compliance. Same for the yearly NRSC measurements for AM.
I guess I should have been more specific, as I was referring to RF Proofs. Thanks for the replies. We already have an outside source doing AM NRSC studies when needed. I'm sure that we could hire the same company to do an RF Proof (if corporate recommends, desires, or approves, it), as we don't own a spectrum analyzer for our local radio station clusters.
As a matter of fact . . . yes, there are still "proof" requirements in the Rules.
"Proofs" need to be done when replacing the exciter and/or adding or changing the stereo generator. I don't think measurements are needed when changing a un-tuned passive device like a transmission line switch, but that harmonic filter or "mask" filter is a different story.
Here's the verbiage:
§73.1590 Equipment performance measurements.
(a) The licensee of each AM, FM, TV and Class A TV station, except licensees of Class D non-commercial educational FM stations authorized to operate with 10 watts or less output power, must make equipment performance measurements for each main transmitter as follows:
(1) Upon initial installation of a new or replacement main transmitter.
(2) Upon modification of an existing transmitter made under the provisions of §73.1690, Modification of transmission systems, and specified therein.
(3) Installation of AM stereophonic transmission equipment pursuant to §73.128.
(4) Installation of FM subcarrier or stereophonic transmission equipment pursuant to §73.295, §73.297, §73.593 or §73.597.
(5) Installation of TV stereophonic or subcarrier transmission equipment pursuant to §§73.669 and 73.1690.
(6) Annually, for AM stations, with not more than 14 months between measurements.
(7) When required by other provisions of the rules or the station license.
(b) Measurements for spurious and harmonic emissions must be made to show compliance with the transmission system requirements of §73.44 for AM stations; §73.317 for FM stations and §73.687 for TV stations. Measurements must be made under all conditions of modulation expected to be encountered by the station whether transmitting monophonic or stereophonic programs and providing subsidiary communications services.
(c) TV visual equipment performance measurements must be made with the equipment adjusted for normal program operation at the transmitter antenna sampling port to yield the following information:
(1) Field strength or voltage of the lower side-band for a modulating frequency of 1.25 MHz or greater, (including 3.58 MHz for color), and of the upper side-band for a modulating frequency of 4.75 MHz or greater.
(2) Data showing that the waveform of the transmitted signal conforms to that specified by the standards for TV transmissions.
(3) Photographs of a test pattern taken from a receiver or monitor connected to the transmitter output.
(4) Data showing envelope delay characteristics of the radiated signal.
(5) Data showing the attenuation of spurious and harmonic radiation, if, after type acceptance, any changes have been made in the transmitter or associated equipment (filters, multiplexer, etc.) which could cause changes in its radiation products.
(d) The data required by paragraphs (b) and (c) of this section, together with a description of the equipment and procedure used in making the measurements, signed and dated by the qualified person(s) making the measurements, must be kept on file at the transmitter or remote control point for a period of 2 years, and on request must be made available during that time to duly authorized representatives of the FCC.
From that, and from §73.1660 Acceptability of broadcast transmitters, specifically (a)(1) it would seem that that little sticker with the FCC ID Certification Number (formerly Type Acceptance Number) doesn't have any meaning because you still have to "Verify" the operation of each individual installation.
But as to what needs to be measured and documented (other than what may be stated on the license) . . . that takes a little (actually a lot) more research. Part 2 has most of the answers but you will also need to have a look at the Part of the Rules that applies to your particular service. Generally, conducted bandwidth occupancy and conducted spurs and harmonics to the 10th for every station is a starting point. (Good luck with doing radiated measurements outside a chamber, but it IS possible and sometimes necessary as some FM's that are alleged to be causing interference to new LTE operations have found out recently). Carrier frequency is on that list too.
And for you AM guys don't forget the "proof" requirements for directional antennas in addition to that annual NRSC measurement set. Even if you've "proofed" the antenna using MoM the performance of the elements in the sampling system still has to be checked periodically.
"Proofs" need to be done when replacing the exciter and/or adding or changing the stereo generator. I don't think measurements are needed when changing a un-tuned passive device like a transmission line switch, but that harmonic filter or "mask" filter is a different story.
Here's the verbiage:
§73.1590 Equipment performance measurements.
(a) The licensee of each AM, FM, TV and Class A TV station, except licensees of Class D non-commercial educational FM stations authorized to operate with 10 watts or less output power, must make equipment performance measurements for each main transmitter as follows:
(1) Upon initial installation of a new or replacement main transmitter.
(2) Upon modification of an existing transmitter made under the provisions of §73.1690, Modification of transmission systems, and specified therein.
(3) Installation of AM stereophonic transmission equipment pursuant to §73.128.
(4) Installation of FM subcarrier or stereophonic transmission equipment pursuant to §73.295, §73.297, §73.593 or §73.597.
(5) Installation of TV stereophonic or subcarrier transmission equipment pursuant to §§73.669 and 73.1690.
(6) Annually, for AM stations, with not more than 14 months between measurements.
(7) When required by other provisions of the rules or the station license.
(b) Measurements for spurious and harmonic emissions must be made to show compliance with the transmission system requirements of §73.44 for AM stations; §73.317 for FM stations and §73.687 for TV stations. Measurements must be made under all conditions of modulation expected to be encountered by the station whether transmitting monophonic or stereophonic programs and providing subsidiary communications services.
(c) TV visual equipment performance measurements must be made with the equipment adjusted for normal program operation at the transmitter antenna sampling port to yield the following information:
(1) Field strength or voltage of the lower side-band for a modulating frequency of 1.25 MHz or greater, (including 3.58 MHz for color), and of the upper side-band for a modulating frequency of 4.75 MHz or greater.
(2) Data showing that the waveform of the transmitted signal conforms to that specified by the standards for TV transmissions.
(3) Photographs of a test pattern taken from a receiver or monitor connected to the transmitter output.
(4) Data showing envelope delay characteristics of the radiated signal.
(5) Data showing the attenuation of spurious and harmonic radiation, if, after type acceptance, any changes have been made in the transmitter or associated equipment (filters, multiplexer, etc.) which could cause changes in its radiation products.
(d) The data required by paragraphs (b) and (c) of this section, together with a description of the equipment and procedure used in making the measurements, signed and dated by the qualified person(s) making the measurements, must be kept on file at the transmitter or remote control point for a period of 2 years, and on request must be made available during that time to duly authorized representatives of the FCC.
From that, and from §73.1660 Acceptability of broadcast transmitters, specifically (a)(1) it would seem that that little sticker with the FCC ID Certification Number (formerly Type Acceptance Number) doesn't have any meaning because you still have to "Verify" the operation of each individual installation.
But as to what needs to be measured and documented (other than what may be stated on the license) . . . that takes a little (actually a lot) more research. Part 2 has most of the answers but you will also need to have a look at the Part of the Rules that applies to your particular service. Generally, conducted bandwidth occupancy and conducted spurs and harmonics to the 10th for every station is a starting point. (Good luck with doing radiated measurements outside a chamber, but it IS possible and sometimes necessary as some FM's that are alleged to be causing interference to new LTE operations have found out recently). Carrier frequency is on that list too.
And for you AM guys don't forget the "proof" requirements for directional antennas in addition to that annual NRSC measurement set. Even if you've "proofed" the antenna using MoM the performance of the elements in the sampling system still has to be checked periodically.
Awesome. Thank you!
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