Support with Engineering tabulation or calculation for Translator 2nd. Adjacent protection and waiver

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TopNotch
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Support with Engineering tabulation or calculation for Translator 2nd. Adjacent protection and waiver

Post by TopNotch »

I use FM Commander to allocate or modify a translator, but I don't know how to make the tabulation or calculation regarding the 2nd. adjacent channel protection. The study is almost completed I just need to make the calculation regarding the interference contour that does not reach the ground.

Can some expert help me teaching me more about it? I am not engineer but use relatively well the software to allocate a translator.
TPT
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Re: Support with Engineering tabulation or calculation for Translator 2nd. Adjacent protection and waiver

Post by TPT »

Well, start with the rule See ECFR.Gov, then you are looking for Title 47, Section 74.1204. Depends on where you are, different protections for different classes of stations.

Let's say your 2nd adjacent is a Class A station. The interfering contour of the translator is 100 dbu to the 60 dbu contour of the protected station.
The loophole or rule waiver occurs in "unoccupied areas." Now we go to subsection (d):

"The provisions of this section concerning prohibited overlap will not apply where the area of such overlap lies entirely over water. In addition, an application otherwise precluded by this section will be accepted if it can be demonstrated that no actual interference will occur due to intervening terrain, lack of population or such other factors as may be applicable."

Let's use a real example. Haven't played with the software you use, I do these calculations manually using tools on the FCC's stie. Class A with an ERP of 3800 watts 10.47 KM from the translator site at a bearing of 347 degrees. We use the Commission's AHAAT calculator to determine the AHAAT on this bearing is 123 meters. Using the propagation curves calculator the 50/50 projected contour at the site is 77.3 dbu. Thus the translator's interfering contour is 77.3 + 40 or 117.3 DBU. The translator's AHAAT at 167 degrees is 121 meters, so the 50/10 contour is .157 meters away from the tower.

In this case the translator's antenna is 170 feet AG, and the licensee of the Class A really doesn't care--since the translator is for their co-owned AM station. And I collect the tower rent...But we go back to the loophole at (d). We own 16 acres at the transmitter site, using Google Earth, most of the area 157 meters out is on my land, where this 117 dbu contour goes off my land it is just forested hill side--only other structure is a transmitter hut for two other Class A stations 95 meters out.

Once you've done this analysis--here comes the tricky part. Let's assume you don't have a lot of land around the tower, is the proposed translator still in compliance? You will need to know the downward radiation characteristics of the antenna you are going to use. In my example the translator uses a NIcom BKG-77, Nicom had some charts on-line showing this--but I don't see them now. You would then have to use the actual amount of radiation at a downward angle, let's say 45 degrees, to determine where this interfering contour falls. (This close in the propagation calculator gives you a free space number, unrelated to AHAAT). So, using numbers picked out of thin area, let's assume the actual erp at a 45 degree downward angle is more more like 175 watts instead of 250 watts, and the antenna is 50 meters AG--then the interfering contour falls at 131 meters instead of 157 meters. If there are no structures or roads within 131 meters, then you've met the criteria for the waiver.
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Re: Support with Engineering tabulation or calculation for Translator 2nd. Adjacent protection and waiver

Post by TopNotch »

its 62.2 dbu +40 dBu resulting in 102.20 dBu interference contour, the software calculated the distance and height above the ground and from the tower, but it produced a graph but does not generated in words and explanations. take a look in the attachment specially in the 2 first pages, it is completed? or needs explanation?

if so, could you make this calculation for me and teach me with those numbers, so I learn and can do it for future analysis.

I am sending you the attachment to your inbox.
Last edited by TopNotch on Fri Jun 11, 2021 11:01 am, edited 1 time in total.
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Re: Support with Engineering tabulation or calculation for Translator 2nd. Adjacent protection and waiver

Post by TopNotch »

I think the explanations I provided are not proper or missing some or incorrect information?
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