Tower height adjustments

[joshzz]

We had to move our antenna slightly higher because of serious interference issues caused by the tower. We were told by an engineer that we were ok in doing so because of FCC allowances for variation and because we were actually lower than where we should be. Do you know what the exact FCC allowances are for height variation. Is there an easy method for securing an exact height as to our antenna height?



I read somewhere also that the FCC allows for a 5% power variation up and 10% down. I think there was one time where our power was below the threshold ( I think it happened last winter) and also another time we were slightly above 5%. Usually we're in range but it concerns me that there have been a couple of times that we were off by more than the FCC allowance. We're an lpfm .. I wonder if it could be because lpfm transmitters are just not as good as the big company stuff. Could weather affect it? thanks jj

 

[joshzz]

my email address is [email protected]

 

[tpt]

If the antenna center of radiation is changed by more than 6 feet up or 12 feet down, you need to file a form 301 for a construction permit & pay $800 filing fee. If the chance is less than that, you still need to file a form 302.

The "Center of Radiation" is the imaginary point half-way between the top bay and the lowest bay (for a three bay that's the center bay!).

As a practical matter, these minor changes have no real effect on anything, except perhaps to get the antenna away from guy wires. But the Commission's staff is increasingly anal-retentive, and, besides, everytime a commercial station files one of these things, they have to pay a fee.

After all, if we didn't keep sending money to Washington all these bureaucrats would have to get real jobs. That could be even more disasterous to the economy.

We had to replace our tower recently, Cost $800 to file for a CP to move the FM antenna 4 feet HORIZONTALLY (from the old tower to the new tower).

 

[billybee]

> I read somewhere also that the FCC allows for a 5% power
> variation up and 10% down. I think there was one time where
> our power was below the threshold ( I think it happened last
> winter) and also another time we were slightly above 5%.
> Usually we're in range but it concerns me that there have
> been a couple of times that we were off by more than the
> FCC allowance. We're an lpfm .. I wonder if it could be
> because lpfm transmitters are just not as good as the big
> company stuff. Could weather affect it? thanks jj
>

Most things you want to know are found on the fcc website: www.fcc.gov/mb/audio

Power upper/lower limits FCC Rules 73.840 You are allowed +5% and -10%, same for commercial stations.

Some transmitters are more stable than others, and some are self-adjusting. However, weather can affect the antenna tuning, which would affect the load impedance, which would cause a change in power output if the transmitter does not automatically adjust.

 

[talkers]

>
> Most things you want to know are found on the fcc website:
> www.fcc.gov/mb/audio
>
> Power upper/lower limits FCC Rules 73.840 You are allowed
> +5% and -10%, same for commercial stations.
>
> Some transmitters are more stable than others, and some are
> self-adjusting. However, weather can affect the antenna
> tuning, which would affect the load impedance, which would
> cause a change in power output if the transmitter does not
> automatically adjust.
>

I used to work at a radio station in Bellefontaine, Ohio that was next to a residential area and the power on the FM transmitter would fluctuate depending on how hot or cold it was outside because the hotter it was, the more power that was being used by the neighbors and would drop the power going into the building. I've seen that transmitter at 75% power and it's cranked up all the way. I don't know how they got away with that, but the station didn't have a dedicated line for power...it was from the same source as everyone else on the street.

 

[thebroker]

Two thoughts for you:

First, yes, you area allowed 5% over/10% under. However, this should not be taken to mean that you may regularly run your transmitter at 5% over. If an FCC inspector notices that you constantly run at 5% above licensed power, you'll get a fine. This is meant for minor/temporary fluctuations due to weather and power conditions. When you are over/under, make sure you note this in the log with an explanation if known. However, don't get busted logging 105% power over and over.

Second, be VERY careful when filing to adjust your antenna. I recently learned of new rules stemming from an agreement between the FCC and several tree-hugger-ish groups dealing with towers. If your tower was erected before 1994, you may well have to perform an environmental impact study before applying for any adjustment to your antenna, even though you plan no structural changes to the tower. This is time-consuming and costly, as it requires generally the hiring of an outside consultant to wade through the pages of crap required to be submitted. You'd be best to consult a very qualified FCC attorney before filing this.

 

[ajhenderson]

I would assume this is the same for AM, yet I've been at three 50kWs that can (according to documentation on their STL) and do run up to 55.3kW and down to 47.4kW. That's more than double the 5% allowed.

 

[ajhenderson]

> I used to work at a radio station in Bellefontaine, Ohio
> that was next to a residential area and the power on the FM
> transmitter would fluctuate depending on how hot or cold it
> was outside because the hotter it was, the more power that
> was being used by the neighbors and would drop the power
> going into the building. I've seen that transmitter at 75%
> power and it's cranked up all the way. I don't know how they
> got away with that, but the station didn't have a dedicated
> line for power...it was from the same source as everyone
> else on the street.

WBLL?

 

[skipspence]

> Note the $800 fee with the FCC is a COMMERCIAL fee and not subject to Non-Commercial Licenses or Construction Permits (Non-Coms or LPFM's)..... Keep that radiation center within a meter of your listed facility... Then make sure you fill out on line forms to correct the HAAT and ERP adjustments... Art Doak at the FCC would be happy to help if you email him.....Be honest and they will be honest with you.....