[Boatanchors] WRNO's transmitter.

[Sheldon Daitch]

The GE 250kW units at Greenville also have a modulator driver section
off ground by a few kV, and please don't hold me to the correct number.

There was a substantial  audio transformer feeding the driver deck, not
large from a audio power issue, but from a voltage insulation concern. 

I don't know if I still have any manual excerpts on the transmitter which
discuss why GE engineers when this way, but they must have had some
good reason.  This transmitter has a modulator driver cabinet, right side
cabinet and had at least four tubes on the off-ground deck.  Now that
I think about it, I can't remember if that chassis was positive or negative
to ground.  Wonder if someone had stock in an insulator company?

Seriously, however, considering the low numbers of this unit in
production, there must have been some technology-based
decision path.

The P-P modulators and single PA were in the classic high-level
modulation scheme, modulation transformer and modulation choke
layout, very popular in virtually all higher power systems.

We've converted many of our HF transmitters, replacing the typical
P-P modulators and associated iron with Continental Solid State
Modulators.  The modulator system replaces the entire audio system
originally installed in the transmitters and the existing PA plate voltage
power supply with a new power supply with nominally
50 series switches feeding the PA tube.

Continental does a much better explanation at their website:

http://www.contelec.com/SSM.html

Most of our higher power AM broadcast band transmitters are
versions of Harris' DX series, although there are some Marconi
and Thomson transmitters in the network.  Totally transistorized.

Harris has a sales brochure on their newer Destiny line
which does a block diagram of how they achieve power to
the antenna.

http://www.broadcast.harris.com/product_portfolio/prod_media/dx-destiny.pdf

At the 1 megawatt level a Harris transmitter would have over 800
RF power amplifiers in 5 power amplifier systems, running 200 kW each.

I was at the Harris factory in Quincy some years ago and they were testing
a 2 MW system, DX-2000, which consisted of two 1 MW DX-1000
transmitters feeding a combiner.

The DX-1000 system itself used five 200 kW power blocks feeding a five input
combiner and then the output of those two combiners was fed into the bigger
2-input combiner.

Lots of changes in the way the high power transmitters have changed,
driving mostly by power costs and tube costs over the life of the 
transmitter.


73
Sheldon





Sandy wrote:
> The old Hariis rig WRNO had was very troublesome.  It was a pulse 
> modulation scheme rig.  Parts of it had chassis on big standoffs at 
> very high potentials.  Very dangerous to work on.  Very 'iffy' to get 
> adjusted.
>
> I did not see the CCA rig nor did I pass by there after they had it 
> installed.  I relocated from Metairie, LA to Hammnd, LA area before 
> that came about and did not run into town to see what was going on.  
> The transmtter site is about 90 miles from where I am now. (roughly)
>
> 73,
>
> Sandy W5TVW
>
> -