License question

[E5911]

Did not know where to post so here goes.....
Poking around the ULS I ran across 2 that have ERPs significantly LOWER than their authorized power output
One for example had a repeater authorized 100 watts but only authorized 29 watts ERP
I'm not sure but I think that means they have to turn the tx down to 29 WATTS or calculate the total loss and adjust the Tc accordingly.
This particular lic. was for a Air medical helo service.
What gives? This location (mountain top) has many transmitters in the same band with 200 or 300watt ERP authorized Transmitters

 

[nd5y]

What gives?

The difference between 100 W and 29 W is -5.376 dB.
You would need to know the antenna gain and system losses to understand what is going on.
It could be a typo on the application & license or something else.
Can you post a link to the license?

 

[mmckenna]

I'm not sure but I think that means they have to turn the tx down to 29 WATTS or calculate the total loss and adjust the Tc accordingly.

No, could be running 100 watts at the repeater, ~6dB of feed line loss, 0dB gain antenna.

This particular lic. was for a Air medical helo service.

Pretty common for air type service. You'd likely find the aircraft end is only licensed for 10 watts. Just not that much power needed for really good coverage when airborne.

 

[E5911]

No, could be running 100 watts at the repeater, ~6dB of feed line loss, 0dB gain antenna.



Pretty common for air type service. You'd likely find the aircraft end is only licensed for 10 watts. Just not that much power needed for really good coverage when airborne.

No, could be running 100 watts at the repeater, ~6dB of feed line loss, 0dB gain antenna.

Yeah but licensed like that ? I figure the coordinator would take that into consideration, but I guess when you factor the coverage area, who you are talking to (aircraft) and the minimum power necessary power to make it happen, 29 Watts is what you get

I always figured you told the coordinator "I would like 100watts erp" but most business owners don't know from anything radio, they just say "I need to talk to my guys in this whole town, or county" or whatever

 

[mmckenna]

I always figured you told the coordinator "I would like 100watts erp" but most business owners don't know from anything radio, they just say "I need to talk to my guys in this whole town, or county" or whatever

Depends on what you are looking for. Last time I did this, you can put in the power level you want to run, but you also have to supply requested coverage area. The coordinators are supposed to look at what you are asking for versus what you actually need to get the coverage and adjust accordingly.

Frequency coordination is done to limit interference and allow reuse of frequencies. It's done plotting coverage using ERP, location and looking at the contours of coverage and making sure it doesn't overlap with co-channel users.

 

[AM909]

Used to be that the vendors, users, and co-ordinators used pretty rough guesstimates as to required ERP or, more often, what they had or were going to order to build it with, adjusting downward if they really had to for channel re-use. In recent years, it seems they feed all the parameters into their system design software, including coverage and terrain maps, required S/N ratio, fudge factor, etc., and that's the ERP that gets submitted and licensed.

I see a lot of these oddly small and precise ERP values on large multi-site trunks, but also others, like the CHP's 2 UHF conventional (access/interop?) channel licenses, like KYJ339, which has a 60W TX on Snow Peak with 14W ERP and a 100W TX on Chuckwalla Mtn. with 22W ERP.

 

[speedway_navigator]

Ran into that in TX a few years ago, looking through my notes from 2016 but I think it was 100 W TPO / 45 ERP. We figured they were over 100 with the gain antenna so the FD has their local radio shop come out and lower the power. We told the FD they should not have to pay because the engineer or tech didn't pay attention and had put them in place of getting an NOV.

See KNAI770 for 200 / 120 but site 2 has 10 / 20.

 

[freddaniel]

In the case of KNAI770 cited above, the 10 watt ERP station was a CONTROL station as a FX1 class code and the higher power repeater as a FB2 class code. See FCC Station Class Codes - The RadioReference Wiki for explanation. The power of Control stations is limited to avoid causing interference to adjacent service areas.

The FCC also limits the ERP of newer base and repeater stations in most services, depending upon the Height Above Average Terrain, so the service area is limited to a prescribed radius. This could be the city or county boundary or the asked for operating radius, but rarely more than 50 KM or 35 miles. Some exceptions exist, such as older grandfathered stations, along a road or river or some stations also used for paging. However, the FCC is trying to make fewer exceptions by harmonizing the rules between services.

Besides FCC rules, there is loads of FCC policy which is not organized into books, but is available in the language of prior rule-making decision documents.