WCVT (101.7 Stowe, VT)

Dave Doherty dave@skywaves.net
Sun Dec 11 17:55:31 EST 2011

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

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.


-----Original Message-----
From: boston-radio-interest-bounces@tsornin.BostonRadio.org
[mailto:boston-radio-interest-bounces@tsornin.BostonRadio.org] On Behalf Of
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

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