WCVT (101.7 Stowe, VT)

[Dan.Strassberg]

I thought that HAAT was determined by subtracting from the height
above mean sea level of the antenna's electrical center the average
height above mean sea level of the eight highest radials starting at
eight miles from the antenna and ending I know not where. I also do
not remember how many points along each radial were to be used in
computing the height above mean sea level of the average ground level
along each radial, but it boggles my mind that HAAT could depend upon
the height of the ground above mean sea level of a single high point
at a specified distance from the antenna or even of eight points (one
point per radial) at the same distance.

-----
Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Dave Doherty" <dave@skywaves.net>
To: "'Dan.Strassberg'" <dan.strassberg@att.net>; "'Garrett Wollman'"
<wollman@bimajority.org>;
<boston-radio-interest@lists.BostonRadio.org>
Sent: Sunday, December 11, 2011 5:55 PM
Subject: RE: WCVT (101.7 Stowe, VT)


> Hi, Dan-
>
> It has to do with "reference distance" to the 60 dBu contour
> according to
> the f(50,50) curves.
>
> For Class C2 - 50 kW at 150 m AAT (not 152) - the reference distance
> is 52
> km.
>
> At 811 m AAT, the curves produce a reference distance of 52.0 km at
> an ERP
> of 1.05 kW.
>
> 1.75 kW produces a reference distance of 56.9 km, well above the
> limit for
> Class C2.
>
> -d
>
>
>
>
> -----Original Message-----
> From: boston-radio-interest-bounces@tsornin.BostonRadio.org
> [mailto:boston-radio-interest-bounces@tsornin.BostonRadio.org] On
> Behalf Of
> Dan.Strassberg
> Sent: Sunday, December 11, 2011 4:56 PM
> To: Garrett Wollman; boston-radio-interest@lists.BostonRadio.org
> Subject: Re: WCVT (101.7 Stowe, VT)
>
>
> The 50 kW at 152 meters and 1 kW at 811 meters claimed for WCVT seem
> inconsistent with each other. The curves that show height-adjusted
> max-allowable ERP (at the azimuth of peak ERP) vs HAAT show that the
> empirical curves are pretty close to the theoretical. For the Class
> C2 case, ERP (allowed) ~50 kW/(h/152)^2, where h is the HAAT for a
> partiular
> station. If h for WCVT = 811m, the formula reduces to peak ERP
> (allowed) ~50
> kW/(811/152)^2 ~50 kW/28.5 = 1.75 kW or 75% more than the 1 kW that
> somebody
> mentioned in an earlier post. Sure, 1.75 kW is a long way from 50 kW
> but
> it's almost twice as much as 1 kW.
>
> -----
> Dan Strassberg (dan.strassberg@att.net)
> eFax 1-707-215-6367
>
> ----- Original Message -----
> From: "Garrett Wollman" <wollman@bimajority.org>
> To: <boston-radio-interest@lists.BostonRadio.org>
> Sent: Sunday, December 11, 2011 1:29 PM
> Subject: Re: WCVT (101.7 Stowe, VT)
>
>
>> <<On Sun, 11 Dec 2011 11:21:47 -0500, Scott Fybush
>> <scott@fybush.com> said:
>>
>>> On 12/11/2011 9:36 AM, Bill O'Neill wrote:
>>>> The ERP will be 50 kW according to what the AM host, Brian
>>>> Harwood, said
>>>> recently.
>>>>
>>
>>> Well no, not exactly.
>>
>>> WCVT on Mansfield will be (is?) a class C2 station, which is the
>>> equivalent of 50 kW at 152 meters above average terrain. But the
>>> actual
>>> WCVT facilities are just one kilowatt ERP at 811 meters above
>>> average
>>> terrain. That combination of lower power and much higher antenna
>>> height
>>> results, *in theory*, in the same distance to the 60 dBu protected
>>> contour.
>>
>> This is a mistake that many non-technical people make -- and in
>> fact,
>> I made it myself when I was first learning about radio regulation.
>> The cause is that slippery word "effective", in "effective radiated
>> power".  In normal English usage, one would expect it to mean
>> something like "equivalent", but as a matter of engineering jargon,
>> it's actually much more restricted: take the transmitter power
>> output,
>> multiply by the transmission line efficiency, then multiply by the
>> antenna gain.  Nothing else enters into it.  (Normally, engineers,
>> who
>> are used to working in decibels, a logarithmic scale, would say
>> "TPO
>> in dB over a kilowatt, minus line loss, plus antenna gain"
>> instead.)
>>
>> The FCC then plugs the ERP and the height above average terrain
>> into
>> an empirically-derived formula to determine what the theoretical
>> coverage radius is, and station classes are actually based on the
>> area
>> covered -- even though they are specified in terms of prototypical
>> transmitters rather than the area.  So for a given class, there is
>> a
>> curve (which you can see in the FCC rules) which represents
>> permissible combinations of ERP and HAAT; at heights higher than
>> the
>> "standard", the power must be "derated" in accordance with the
>> curve.
>> However, the FCC does not allow applicants to compensate for a
>> lower-than-"standard" height by increasing power above the class
>> maximum; this is done to encourage stations to put their antennas
>> higher.  (Also, and for reasons not relevant here, there are many
>> ways
>> to compute HAAT, and applicants are permitted to use the one most
>> favorable to them -- possibly more than one in the same
>> application!)
>>
>> This method of licensing FM stations by coverage area goes back to
>> the
>> early 1940s, when the FCC started requiring applicants to specify
>> their service area in addition to the specific transmitter and
>> antenna
>> they planned to use.  At that time, there were four FM station
>> classes: A, B, C, and D in order of increasing coverage; the Yankee
>> Network stations WGTR (44.3) and WMTW (43.9) were both class-D
>> stations licensed to Boston.
>>
>> -GAWollman
>
>
>
>