FCC FM Query Data Base

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jthorusen
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FCC FM Query Data Base

Post by jthorusen » Wed Jul 10, 2019 1:06 am

I just ran into a little problem concerning the license for an LPFM station that I am helping. Their antenna is considerably lower than it could be for its location and they would like to be higher. Unfortunately, there is a little hitch in the git-along. The FCC FM query data base entry for the station (KWPB-LP) if you wish to look it up for yourselves) shows the antenna HAAT as 18 meters. Right next to this line in the record, the FCC has helpfully provided a link to a HAAT calculator. When you click on that link, the HAAT comes back not as 18 meters as shown in the license record, but 14 meters.

Further, the HAAT calculator states that the height of the antenna radiation center is 57 meters above mean sea level. I looked up the height of the ground above mean sea level as close as I could get to the published antenna coordinates using an internet calculator. This gave me 48 meters. The problem is that if I subtract 48 meters from the FCC's HAAT calculator height of radiation center value (57 Meters), I get an antenna height above ground not 8 meters as the FCC license says, but 9 meters.

I have sent an E-mail to the powers that be to the effect that we need to accurately measure the antenna mast height, building height, etc. so that we can find out which number (if either) is correct. In the meanwhile, since we want to go up to the maximum permitted antenna height at which we can still run 100 watts, do we use our current HAAT as 18 meters (in which case we go up 12 meters) or do we use 14 meters, in which case we go up 16 meters? And do we subtract one from either or both values to account for the 8 versus 9 meter discrepancy? Do we need to file something with the FCC to correct the current license (assuming the HAAT calculation is valid)?

I intend to place a call to the FCC and see if I can get some answers to these questions, but I am also frightened of waking a sleeping giant, as it were. Therefore, I thought I'd ask here first and see if anyone has run into any similar discrepancies in the past and if so, what was done to resolve the situation.

Thanks,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

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Re: FCC FM Query Data Base

Post by radio_guru » Wed Jul 10, 2019 6:51 am

Don't confuse the FCC's use of HAAT and AGL/ASL. The latter two are absolute. Rarely does the AGL/ASL match the HAAT. HAAT is a derivation of an average of 8 averaged radials 10 miles long. In fact, there are many instances where the HAAT is a negative number. Such as when a site is located in a valley or on flatlands bordered by a mountain range.

Also, be careful about using the FCC's calculators as an absolute determination. The FCC places the responsibility of calculating and providing accurate technical data on the applicant/permittee/licensee. The FCC's tools are simply handy estimators and guides. Until you do the calculations yourself (or hire a consultant with the right tools), do not presume the data to be wrong. Especially if done by a professional consultant.

RG

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Re: FCC FM Query Data Base

Post by TPT » Wed Jul 10, 2019 7:08 am

This is a low power station--most consultants are probably beyond their budget.

The reason for the different HAAT's is that the Commission uses 8 radials (every 45 degrees from true north) to determine AHAAT for licensing purposes. The AHAAT link in FM query uses 360 radials. I did the calculation using the FCC's AHAAT program ((fcc.gov/media/radio/haat-calculator) for 8 radials and I get 9 meters for AHAAT. This uses the coordinates in the license.

Check the actual coordinates using Google Earth. You can also check the site elevation from a topographic map (trails.com has them, look under the trail finder tab). Then, as you suggested, double check how high the present antenna is.

Based on the information in the license you could increase antenna height to almost 70 feet above ground while keeping ERP at 100 watts.

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Deep Thought
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Re: FCC FM Query Data Base

Post by Deep Thought » Wed Jul 10, 2019 9:06 am

You've got a couple problems here.

First, whoever did this application used NAD83 and not 27 data for the coordinates so the antenna is not at the licensed location.

Second, according to the USGS topo for that location the elevation is 155 feet (47.2 meters).

Looking at that antenna from Google Street View 9 meters AGL is about right.

Plugging this into the FCC HAAT calculator you get 16 meters HAAT. They could raise that another 14 meters and stay at or below 30 meters HAAT.

I'll help you get this fixed/antenna height increased for the princely sum of $0.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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RGORJANCE
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Re: FCC FM Query Data Base

Post by RGORJANCE » Wed Jul 10, 2019 9:27 am

Deep:

You work too cheap! You need a "standard fee structure" like I have. My standard fee for "stuff" is a cup of coffee, payable next time we meet.

Fossil

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jthorusen
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Re: FCC FM Query Data Base

Post by jthorusen » Wed Jul 10, 2019 6:18 pm

I'll be happy to send both of you gift certificates to Starbucks if I can get some help on this. I'd hate to lose the license by doing something wrong.

I presume that we will have to file something to correct the NAD 83 versus 27 problem and correct the HAAT to a real value before we can file FCC 318 to change the height. Or maybe, we can put all the changes in one 318 filing and thus "move" the antenna to where it is now as well as change the height?

Anyway, let me get accurate measurements of the structure first. I'm not sure how to measure height above ground... what should I use for a datum? The flower bed at the end of the building near the antenna? Or the driveway that goes right past it? Or some average? Egad! What a can of worms we have opened!

Many Thanks,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

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Deep Thought
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Re: FCC FM Query Data Base

Post by Deep Thought » Wed Jul 10, 2019 6:38 pm

jthorusen wrote:
Wed Jul 10, 2019 6:18 pm
I presume that we will have to file something to correct the NAD 83 versus 27 problem and correct the HAAT to a real value before we can file FCC 318 to change the height. Or maybe, we can put all the changes in one 318 filing and thus "move" the antenna to where it is now as well as change the height?
You can do everything on the same 318. It is much neater that way.
Anyway, let me get accurate measurements of the structure first. I'm not sure how to measure height above ground... what should I use for a datum? The flower bed at the end of the building near the antenna? Or the driveway that goes right past it? Or some average? Egad! What a can of worms we have opened!

Many Thanks,
Try to use a solid flat surface like the driveway or sidewalk. The FCC tolerance is +2/-4 meters for antenna heights so you don't have to get it to the inch.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Deep Thought
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Re: FCC FM Query Data Base

Post by Deep Thought » Wed Jul 10, 2019 6:38 pm

RGORJANCE wrote:
Wed Jul 10, 2019 9:27 am
Deep:

You work too cheap! You need a "standard fee structure" like I have. My standard fee for "stuff" is a cup of coffee, payable next time we meet.

Fossil
Yeah, and you're horrible at collections. I still owe you one from about five years ago. :mrgreen:
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Dale H. Cook
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Re: FCC FM Query Data Base

Post by Dale H. Cook » Fri Jul 12, 2019 10:12 am

RGORJANCE wrote:
Wed Jul 10, 2019 9:27 am
My standard fee for "stuff" is a cup of coffee, payable next time we meet.
Fossil -

What? You don't even bill a kringle?
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

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RGORJANCE
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Re: What? You don't even bill a kringle?

Post by RGORJANCE » Fri Jul 12, 2019 11:46 am

Now, that is a classic description of what old age can do to a formerly sharp mind. I'm going to have to re-do my :roll: "standard fee invoice"

Fossil

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Dale H. Cook
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Re: FCC FM Query Data Base

Post by Dale H. Cook » Fri Jul 12, 2019 12:07 pm

When I was a kid I enjoyed the occasional Scooter Pie in my brown-bag school lunch. It wasn't until I moved south in 1984 that I encountered the real deal - the Moon Pie from Chattanooga Bakery. It became part of my standard fee invoice until I had to drop it after developing diabetes a decade ago. I haven't yet found a satisfactory diabetic-friendly replacement.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

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RGORJANCE
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Re: FCC FM Query Data Base

Post by RGORJANCE » Fri Jul 12, 2019 5:41 pm

OMG!!! RC and a Moon Pie-------wow! Used to do them a lot back in the 50's when I lived in Tulsa. The other delicacy was SPUDNUTS and a good cup of coffee. Yummmm.

Kinda hijacked this thread.....ooopppsss.

Fossil

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jthorusen
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Re: FCC FM Query Data Base

Post by jthorusen » Fri Jul 12, 2019 9:34 pm

Well, I went down to the station (KWPB-LP) today with my GPS. Did a few quick chores like check the carrier frequency and confirm that the TFT 723 mod monitor is still working (don't know whether to be surprised or pleased... maybe both). I put the GPS on the window sill which is only about 3 feet North of the base of the antenna mast (facilities are on the second floor). Based on Mark's very observant catch of the wrong NAD having been used on the original app, I came up with the following numbers:

If we convert the numbers in the FCC data base to NAD27, the difference between the converted numbers and the GPS position (also converted from NAD83 to NAD27) works out to be a little over six inches in Longitude and a little under three feet in latitude.... which is about how far North I was from the base of the antenna. Which is not bad considering the GPS accuracy at the time was reported to be 19 feet.

The GM is all wrapped up in the forthcoming national EAS test, so it may be a while before I can get a work party together to measure the antenna height parameters correctly. However, the GPS reported my altitude as 170 feet, which is also about right, considering I was on the second floor. The HAAT study places the antenna at 57 meters above mean sea level. If we subtract the 8 meter height above ground in the data base, we get 49 meters or 161 feet. Add 10 feet for being on the second story and we are pretty close to the GPS value of 170 feet.

It's nice to know that SOMETHING checks out, at any rate. Very nice catch on Mark's part concerning the standards error.

Thanks to all,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.

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