Introduction

This reference has been written to provide aid to the technician performing the required Federal Communications Commission Proof-of-Performance testing, the data entry personnel who must compile the gathered data, and those individuals interested in the results of the tests. Therefore, the reader will find information on basic testing procedure, data compilation, and what the results may indicate The cited FCC rules are current as off May 2, 2012.

ATTENTION! This reference is intended only as an accessory in compiling and understanding the FCC Proof-of-Performance Report. While every effort has been made to be as current and as accurate as possible, no claim is made as to its completeness. Alternate reference materials should be consulted as necessary. No connection with the FCC is implied or claimed by this material.

General POP Testing Procedures

By FCC rules, all systems over 1000 subscribers must be tested twice a year for certain performance benchmarks. This testing is a generally a cable television system level responsibility. For the plant, a minimum of six test points is required with one third of those points being the most distant from the system input in terms of cable length. More test points may be required depending on subscriber count and the use of "non-mechanical" connections (microwave) as described in part 76.601(b)(1) of the rules (all rules quoted in hyperlink pop-ups are from the 10-1-2001 edition of 47CFR).

Although not required by FCC rules, systems under 1000 subscribers can be tested based on company policy and local franchising needs. Less stringent standards can be negotiated with the local franchising authority.

Depending upon equipment, the 24 Hour tests and the Noise & Distortion tests may require different input levels. The 24 Hour tests are to be done with typical subscriber levels (no less than 6dBmV recommended). For the best accuracy and range, the Noise tests are to be done at the maximum input levels (typically 15 - 25dBmV) recommended by the equipment manual. If this exceeds the maximum recommended levels for a given channel load on the Distortion tests, either the input levels can be lowered for those tests or pre-selection filters can be used. It may be desirable to have two test points at a given location - one typical tap output for 24 Hour testing and one "hot" tap output for Noise and Distortion testing. If inconvenient, the test point drops do not need to be located on the same pole. If they are on the same pole, they must be marked to prevent confusion. A second method might be to feed a small "apartment" directional coupler with a single drop from a hot tap. The through leg would provide high output for noise and distortion while the loss leg should provide subscriber levels typical of that test area. For a third method, an amplifier may be used to bring the output of a normal tap up to the desired input, but please be aware that the noise contribution of the amplifier will appear more significant as the trunk cascades draw shorter. Do not temporarily adjust the plant distribution amplifiers for the test! Finally, it may be necessary to locate the test point a few spans from the last active to avoid a tilt and present a flatter response for test.

Before performing any tests, be certain all equipment is properly calibrated.

Headend Tests

-Visual Carrier Center Frequency

Although part 76.605(a)(2) of the FCC rules require only the aural subcarrier difference frequency to be reported, it is considered good engineering practice to test the visual frequency as well. For those systems without automated test equipment, this visual carrier frequency would be needed in order to calculate the visual-to-aural intercarrier difference. It is also recommended that all channels be tested rather than a select few. The frequency testing is required at both the output of the modulating and processing equipment (headend) and at the subscriber terminal. Since only a baseband converter may change the intercarrier difference (although AML microwave and Fiber Optic conversion may alter visual carrier frequency, respective aural subcarrier differences are maintained), direct drop testing is not necessary. The baseband converters, however, should be sampled and reported as such.

A frequency counter or an analyzer with a built-in counter known to meet accuracy requirements may be used.

-Aural Carrier Center Frequency

This test is to be performed at the headend and at the converter. Although the FCC specifies we need only perform this test on selected channels, as a good engineering practice, it should be done on all channels at the headend. A frequency counter or an analyzer with a built-in counter known to meet accuracy requirements may be used. In addition, the test must be done at the subscriber terminal (converter output). Recording a sample measurement of each converter type and keeping those measurements on file may satisfy the latter requirement. Check with your test administrator.

The software reports the frequency difference and any failure.

Color Video Tests

In accordance with FCC rules Part 76.601(b)(4) the cable system (generally the headend) must be tested every three years for compliance with video limitations as outlined in Part 76.605(a)(11). Care must be taken that modulation levels do not exceed limits as this will produce inaccurate and failing results for differential phase and differential gain.

Take note of whether the modulator in use incorporates pre-correction (also known as pre-distortion) filtering. Many "economical" modulators do not have pre-correction. The pre-correction advances the chrominance information with respect to the luminance information to account for the chrominance delay that will occur in a demodulator. The test for Chrominance-Luminance Delay assumes pre-correction is present. Please note that it may be advisable to simply add "out-board" pre-correction filters to those modulators lacking it. Greater confidence can then be held in presenting superior pictues as well as passing any inspection.

24-Hour Tests

The 24-Hour test concerns itself with maintaining channel carrier levels within certain limits.

For the 24-Hour test, meters should be calibrated prior to the test. This test requires the use of 100 feet of cable loss to approximate a typical subscriber drop. The technicians performing this test should either carry a long drop cable or one can be coiled and attached to each test point.

Prior to starting the test, the headend should be flattened although this was no doubt completed as part of the regular monthly maintenance program. The FCC test was reimposed, in part, to encourage system maintenance. This maintenance will aid in meeting FCC specifications. Do not, however, "tweak" the levels in any specialized manner to temporarily pass the test! The visual-to-aural carrier level difference should also be checked at this time. While part 76.605(a)(5) of the FCC rules allows 10 to 17 dB of difference, it is recommended that the headend be maintained with an A-V difference of 13 to 15 dB. This will allow a margin for error out in the field. Once the headend is flattened and adjusted for proper A-V, one reading can be recorded prior to starting the readings at the plant test points. This does not have to be repeated at each time interval of the other test points.

Once the 24-hour period has begun and the tester has arrived at the first test point, the time of the test should be recorded. All successive visits to that test point require the time to be posted as well. While performing this test, the rules set forth in part 76.601(b)(3) must be respected. The time can be entered as "military" time to avoid AM or PM designations.

While at the first visit to the first test point, the tester should record the aural carriers as well. All later visits to that test point need only the visual carriers to be recorded. All readings are to be taken through 100 ft. of drop cable. This could be accomplished with a 20 ft. pole riser and an 80 ft. coil of test drop or vice versa. Although part 76.605(a)(3) indicates a lower minimum signal level is allowable, it is recommended the typical subcriber drop produce 6 dBmV of signal or more. Check with the Chief Engineer in charge of your system.

Although some technical personnel prefer five visits to each test point in order to open and close an exact 24-hour period, the rules only stipulate that four visits spaced at six hour intervals are needed to fulfill the intent of the 24 hour test. That intent, of course, is to determine signal level variations during the cyclical changes in temperature and weather during the day.

Along with checking adjacent levels, minimum levels and 24 hour variations, it must additionally be remembered to compare level differences from test period to test period as set forth in rule 76.605(a)(4).

Noise, Distortion, and Other Plant Tests

Insure calibration of equipment prior to beginning tests. Consult the owner's manual for the spectrum analyzer in use to determine the desired minimum and maximum carrier signal levels for the channel loading in use.

Although the FCC rules part 76.601(b)(2) may require a minimum of 4 channels be tested in a small bandwidth cable system, it is recommended that a minimum of 6 channels be tested as a practical guideline. One additional channel should be tested for each 100 MHz bandwidth added beyond 300 MHz. While all these test are normally to be done at a system test point, exceptions as outlined below may be considered.

CHANNEL FREQUENCY RESPONSE

Under the FCC rules part 76.605(a)(6) a cable operator is obligated to maintain the individual channel frequency response within +/-2dB (4 dB peak-to-valley) across a 4.25 MHz bandwidth. The rules normally require this measurement to be taken out at the test point (with a converter) rather than at the headend. If automated equipment and programmer VITS are available, this can easily be done by one technician. If this measurement must be done manually, it is typically a two-person job. One technician is needed to inject the sweep or multi-burst signal in the headend while another technician measures the result at the test point.

CARRIER TO NOISE

In accordance with FCC rules part 76.605(a)(7) the allowable carrier to noise ratio has progressed to its present minimum level of 43 dB. The automated equipment of today can not only apply the necessary bandwidth corrections to the raw levels measured, but some can even test in a non-intrusive manner. Care must be taken when recording data with equipment that uses gated-sync technology. This equipment works by testing the video vertical interval "quiet lines". Any excessive noise generated by programmer souces may add to the total noise and not present an accurate reflection of the system noise contribution. This may be more evident the closer the testing is done to the headend where the added noise appears as a more significant percentage of the total noise. When using non-gated testing, it is recommended that either unmodulated carriers or carrier removal be used to increase accuracy. Otherwise, non-gated equipment can still be used non-intrusively by inserting a video notch filter to create a small segment of bandwidth in which programmer noise is removed and testing can occur. Alternatively, test equipment using gated-sync technology can be paired with "quiet-line inserters" installed in the headend. This will allow less channel interruption while testing only the system noise contibution and not that of the programmer.

Proper input levels must be made to the test equipment. False readings can be produced by improper input levels. The test equipment documentation should be consulted for a recommendation. Ideally, a "hot" tap should be set up to provide the necessary signal level. A pre-amp can be used if necessary, but should be avoided as it may appear as a more significant contributor of noise as the test points draw closer to the headend.

As a convenience, the same channels used in the individual channel response may also be tested for the carrier-to-noise. This is not a requirement, however.

>

COHERENT DISTURBANCES

Although the FCC rules may require the testing for distortion disturbances at the subscriber terminal, this may be an impossibility with AGC most converters. It is suggested that distortion testing can be done at the "hot" tap test point and converter specifications be attached to the report. Of course, through calculation it must be determined that the added converter distortion contribution does not cause the plant measurement to exceed the rule limitations.

When using an analyzer to test for distortion products, care must be taken not to overdrive the input of the device. Input levels should not exceed the manufacturer's specifications. If the analyzer is sensitive to a large bandwidth of carriers, bandpass filtering should be used. These measures may aid in passing Part 76.605(a)(8) of the FCC rules.

LFD

Low Frequency Disturbances (more commonly called Hum), is a simple test that needs only to be taken on one umodulated channel as outlined in FCC rule part 76.605(a)(10) .