Re: [IRCA] QSL request

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> As an AM TX and general domestic AM dummy, what does all this mean, about
> not being able to put a 1kW signal into some type of tower? What does the
> power and or tower have to do with not being able to feed full power into
> the antenna?

Different classes of stations are required to have a minimum efficiency from
their tower.  Put a kilowatt in and the signal strength at a kilometer away
should be a specific number or more.  Clear channel stations have the
highest minimum.  Regionals are lower.  Locals like 1340 are the least.
When a station is licensed at a specific power and tower height (efficiency)
it's given an effective radiated power.  When a station puts a kilowatt into
a 5/8 wave tower it is about the same as putting 3+ kilowatts into a 1/4
wave tower.  So, many times a station using a taller tower has to reduce
transmitter output to keep the coverage the same.  One of my clients on 1110
was originally a kilowatt non-directional into a 1/4 wave tower.  They put
in a much taller tower to add an FM.  So, they had to drop transmitter power
to around 680 watts.  Same coverage on groundwave.

5/8 wave is the best height for a local station that isn't looking for
coverage beyond 40 miles or so.  There is a secondary high-angle lobe that
comes back down from skywave and causes interference about 70 miles out.
That's why the sweet spot for tower height for the big guns is a bit over
half wave, 195°.

Low band stations can reach the minimum with a shorter tower.  For example,
local WDDZ-550 has 1/6 wave towers but still meets the groundwave efficiency
requirements.  There are other problems with short towers, but that's a
subject for another chat.

WNBH is lucky in that they are grandfathered in for a full kilowatt into a
tower that's effectively around a half wave.  For a local channel station,
they do cover well.  And the fact that they are not far from the coastline
gives some pretty interesting DX reports now and then.  As I mentioned, this
is the third report from Scandinavia in the past couple of years.  The
previous two were quite easily identified.  Probably have the .mp3 of those
around somewhere.

Yeah, I probably ought to schedule some sort of DX test out of that station.
Let me see what I can do...

Again, thanks to all for the help.  My ears aren't anywhere as good as they
used to be...

Craig Healy
Providence, RI


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