[BC] KKGM

[Bill Honigs]

I am sure you did not want that published...

Bill H. 

-----Original Message-----
From: broadcast-bounces at radiolists.net [mailto:broadcast-bounces at radiolists.net] On Behalf Of DANA PUOPOLO
Sent: Monday, July 18, 2005 8:03 PM
To: Broadcast Radio Mailing List
Subject: Re: [BC] KKGM

Craig,

Just a quick note to let you know that I'm moving (back) to Providence next month.

My address will be: 266 President ave.

Local phone number will be 410-454-1394.

Dana



------ Original Message ------
Received: Mon, 18 Jul 2005 07:31:56 PM PDT
From: "Craig Healy" <craig.healy at chowdanet.com>
To: "Broadcast Radio Mailing List" <broadcast at radiolists.net>
Subject: Re: [BC] KKGM

> Dan Strassberg wrote:
> 2. Is there a practical way to electrically shorten such a radiator? 
> For example, can you attach a skirt to the bottom and drive it so that 
> the skirted section (in this case something between about 40 degrees 
> and 100
> degrees) does not radiate?
>
> I've been trying for several years now to find someone who can comment 
> on electrically shortening AM towers that are too tall for a diplexed 
> station operating at a frequency higher than that of the station that 
> originally occupied the tower. KKGM is now the second case I've heard 
> of of a tall tower that proved to be too tall and provided very poor 
> efficiency. The other, in central New York State, did not, AFAIK, even 
> meet Class C
minimum
> efficiency (241 mV/m/kW @ 1 km) and defied the ministrations of 
> several well-known consultants. I don't know whether it is yet working 
> as the original consultant intended.

WNBH in New Bedford, MA has a tower about 3/4 wave at 1340.  Has a six-bay FM on top which probably provides a bit of top loading to boot.  What they did was put a skirt on top connected to the tower below the FM bays and going down somewhat less than 1/4 wave and insulated there.  That end is connected to a motor-driven vacuum variable capacitor between the skirt and the tower proper. The control is at the base.  There's also a sample loop in the skirt section.  What is done is the capacitor is tuned to minimum field on the sample loop.  That has that top section above the half or 5/8 wave point not radiating much at all.  In practice, it seems to work well.  WNBH has the full kilowatt into that tall tower, and covers pretty well for a local station.

One of these days I'll get an FIM out there and tune the capacitor for maximum field.  I'll bet it's close to where it is now.

I have often wondered how well an elevated feed point would work.  Find a point where the tower is between 180? and 225? down from the top.  Put a skirt feed above that.  Either use the existing radials as a counterpoise (sans insulators) or a detuning skirt below that.  I wonder how much the elevated feed would affect field strength?  It would be interesting to model in EZNEC, though it would take a while to enter the data.

Craig Healy
Providence, RI




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