305 BROADCAST AKG/7M Посібник користувача - Сторінка 6

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FM Antenna User Manual

Some Criteria For Evaluating Antennas

b. Network Analyzer/Spectrum Analyzer with Tracking

Generator?

(These devices do not rely upon the site's transmitter as a signal source.

They can produce more accurate and meaningful results but do not

subject the antenna to full power where arcing or flashover would occur).

c . Time Domain Reflectometer?

(Occasionally, a technician will use a "TDR". This is not an industry

recognized instrument for antenna testing, and many manufacturers will

not respond to these measurements because the equipment uses

pulses rather than RF and does not measure beyond band limiting

devices. See Nov/Dec 1996 Microwaves & RF Magazine Article entitled

"Identifying Transmission Line Faults" on page 40 forexplanation of TDR

misapplication).

3. Did you perform the measurement directly at the

antenna's connect or?

The technician may have chosen not to perform this test because it requires

climbing the tower. This procedure should be done to eliminate jumper cable or

down-lead cable factors. These cables could be either defective and cause the

problem or be fine and absorbing the reflection which masks the problem.

4. What is your operational frequency?

Check to see if the antenna was ordered for the correct frequency. The

manufacturer may have mis-marked the antenna or carton. Several methods

can be used to determine an antenna's frequency. If the technician has swept

the response of the antenna he will know the frequency of best match. That

should be its designed frequency. The technician may also measure the

physical length so that we may compare it to a cut chart.

This is a crude method. If the antenna is of relatively new and the model

number is known, the factory may still have the production test data sheet

which will identify its frequency by Serial Number.

Website

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