FAT, April 5, 2011
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Why FAT is Cool!
Factory Acceptance Testing (FAT) is a must for the following reasons:
These are the justifications I use in order to get the FAT approved by employers. Conducting a FAT is a proactive way of protecting such a huge company investment. If I am to describe the relationship of the engineer to a transmitter he just bought, he should set up an eyeball meeting before taking his mail-order bride home.
Never go out without a checklist.
Study the claims of the transmitter manufacturer that made you buy it in the first place then jot down those claims and ask them to prove to you on your SPECIFIC transmitter.
First on your list should be the important specifications like total power output (TPO). Find out how the manufacturer tests the TPO and with what particular instrument set-up so that you can do something similar on site for FCC compliance. Verify the value of the directional couplers being used and the level of confidence on the reading (directivity of the coupler). Make sure that the front panel metering of the transmitter is tracking the power measurements. The TPO at 100% should correspond to your licensed TPO. If not, find out how to calibrate the meter.
Relative to the TPO is the AC to RF efficiency of the whole transmitter. You need to get a good grip on the actual power consumption and heat load to verify AC and HVAC requirements. Another parameter that you may want to see for yourself is the output spectrum of the transmitter. Have it printed out so that you have a reference when the proof is done after the site installation.
There are other important specifications that you may want to ask for, depending on whether it is FM or AM and if digital or analog. Signal Quality has never been a big issue since ALL manufacturers can satisfy that requirement so I did not waste my time on them. My other concern was if the protective circuitries are working right. I found out in some occasions that overload circuits were not tested during the assembly and the first time I found about it is when it was already working at the site. The manufacturer should be able to demonstrate to you if the RF output overload protection, for example is working on your transmitter. If there is a way to check the automatic power cutback, that will be great, too! The reason for this is for you to get that confidence that the overload protection are working like they should. Any discrepancy can be corrected right there at the factory. This will save you from a lot of frustration and coordination back and forth later on. Also, you don’t want to find out that the overload circuits are not working ONLY when you actually needed them during on-air operation!
For multiple modules, try pulling out one and see how the transmitter responds to a failed amplifier. My recent experience with a manufacturer was, the whole bank of 4 power amp modules died when I pulled out only one. This dropped the TPO to 32% which is tantamount to being off the air and definitely non-compliant with the FCC. It is good that I found it during the FAT and the manufacturer was able to trace the problem to a loose connection on a combiner load. I will be saddled with this problem if it showed up during on-air operations. Imagine what that loose connector problem will be after going through shipping and installation!
One of my concerns when the transmitter arrives on site is how to hook it up to my station’s remote monitoring and control system. It saves me from a lot of pain by knowing right away at the factory how to connect my monitoring system to the transmitter. Just where exactly is that terminal block? No wonder I can’t bring the power up without grounding that interlock! Don’t expect the technical manual to tell you all when you are in a hurry to get it on the air on site. I know how employers will want that transmitter on line as soon as possible when they see it delivered at the site. You can plan for the wiring and even custom label the transmitter connections while at the factory.
Most important of all, and not necessarily on your checklist, is getting to know the factory engineers face to face. You can connect a face to the voice on the phone should you need to call them later on.
Remember that even though there may not be a perfect transmitter, there is such a thing as a very supportive manufacturer. Nautel is one of them!
Romualdo “Rolin” Lintag, CSTE