Re: WGBH dismissal, and an array sizing question.

[Dan.Strassberg@att.net]

High-gain antennas cause a weak signal close to the 
transmitter. A friend who built an FM says that in 
addition, the vertical radiation pattern becomes 
frequency sensitive, so that as you deviate the carrier, 
the Chinese hat that represents the pattern in 3D waves 
up and down (becomes flatter or more conical--depending 
on whether you deviate the carrier up or down. Thus, the 
waving effect occurs at audio frequencies). He says that 
most FM receivers have far more AM sensitivity than you 
might think and this modulation of the vertical pattern 
causes AM at the receiver. The result is nasty audio-
frequency distortion. He thinks that the gain of FM 
transmitting antennas should be limited to 3 as a 
maximum and less is better.

My guess is that Viacom found something more lucrative 
to do with the space on the Channel 4 tower and 
told 'GBH that the rent would be higher than GBH had 
figured, so GBH said, "no thanks."
--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367
> Looks like all that discussion a bit ago regarding WGBH changing their 
> HAAT/power/location is moot:
> 
> MA  BPED-20000303ACI	WGBH  70510	WGBH EDUCATIONAL FOUNDATION		
> 		    P	89.7 MHZ	BOSTON, MA				
> 
> Minor change in licensed facilities.
> 21 kW ERP, 323 meters HAAT, 42 18 37 NL, 71 14 14 WL.										
> Application dismissed 8/28/2002.
> 
> Good thing, too - from what I could calculate, indeed it would have been a 
> great deal less signal than what they have now.
> 
> If the big problem is terrain shadowing Back Bay, why don't they put in a 
> booster? Is the concern there that too many receivers don't have the 
> capture ratio to deal with the two same-frequency signals, especially 
> where they're close in strength?
> 
> Oh - and a re-query to the (more advanced than I) engineers on the list.  
> What is the downside of higher-gain arrays in FM broadcasting? Obviously,
> the savings on the electric bill is an upside, but what do you give up?  
> I've visited sites with 10-bay Shively arrays, and yet I don't typically
> see that - usually 3 to 6 bay arrays are what I'll see.  Does that more
> sharply focused (towards the horizon) signal produced more marked
> shadowing when terrain gets in the way?
> 
> Thanks much for any info.
> 
> Peter Murray (N3IXY)
> Pittsburgh, PA
>