Is it legally permissible to increase the transmitter's power to well over 100 watts when using a single bay antenna (like a Nicom BKG-77) with 150 feet of LMR-600 cable and a lightning arrestor?
Once your station receives authorization, you'll be assigned an Effective Radiated Power (ERP). It's important to clarify that ERP pertains to the power emitted by your antenna, not the power generated by your transmitter alone. Various components along the signal path, such as your feed line (coaxial cable) and equipment like lightning arrestors, introduce some degree of loss.
In the case of a single bay Nicom BKG-77 configuration, it's essential to note that it operates with a gain of -3 dB, effectively causing a loss. To illustrate this further, let's consider a scenario where your feedline exhibits a loss of 0.8 dB per 100 feet, and the lightning arrestor contributes a 0.1 dB loss. With 150 feet of LMR-600 cable, you'll encounter a 1.2 dB loss from the cable alone, and when factoring in the lightning arrestor, the total loss amounts to 1.3 dB.
Additionally, the antenna itself introduces a 3 dB loss. When transmitting at 100 watts Transmitter Power Output (TPO), the resulting ERP is actually 38 watts, which falls below the legally required minimum.
To rectify this situation, you can set the TPO to 263 watts, which will yield an ERP of approximately 99.99 watts, ensuring compliance with regulatory minimums. This adjustment highlights the importance of selecting an appropriate transmitter when considering your station's specific setup.
If you decide to add an additional bay to the Nicom antenna, it will attain unity gain, meaning there will be no additional loss or gain from the antenna itself. However, you'll still need to account for feedline and insertion losses. In this case, setting the transmitter at 132 watts TPO would result in an ERP of approximately 100.13 watts.
In the U.S., LPFM (Low Power FM) stations are subject to specific power limits and technical requirements defined by the FCC. These regulations are designed to prevent interference with other stations and ensure the efficient use of the radio spectrum. Exceeding the authorized power limits for your LPFM station without proper authorization from the FCC would likely be a violation of regulatory rules.
Therefore, before increasing your transmitter's power, it is essential to consult with the FCC or a legal expert familiar with broadcasting regulations to ensure compliance and obtain any necessary permissions or waivers. Operating within the approved power limits helps maintain a fair and interference-free broadcasting environment.
When you're ready to make these calculations and file your Form 319, Nexus can provide assistance to ensure proper compliance with regulatory standards.