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KA9LCF > NEWS 15.09.12 16:04l 80 Lines 3276 Bytes #999 (0) @ ALLIN
BID : 38453-KA9LCF
Read: GUEST
Subj: ARN: That Final Item
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Sent: 120910/0426Z 38453@KA9LCF.#NEIN.IN.USA.NOAM [169527]FBB7.01.35 alpha $:38
From: KA9LCF@KA9LCF.#NEIN.IN.USA.NOAM
To : NEWS@ALLIN
THAT FINAL ITEM: CONTROLLED CARRIER AM -SOMETHING OLD IS
NEW AGAIN
And finally this week, an old modulation technology is
making a comeback for A-M broadcast stations in a new and
money saving way. Amateur Radio Newsline's George Bowen,
W2XBS, has the details where something old is new again:
--
Back in the days of full carrier A-M transmission one very
popular and low cost way to put ones voice onto a carrier
wave was to modulate the final power amplifier's screen
grid. A variation on this that required no heavy modulation
transformer was to vary the output power of the transmitter
at an audio rate by varying the final amplifier's screen
voltage at an audio rate. This system was called controlled
carrier A-M and it was made very popular on the ham bands in
the 1940's, 1950's and 1960's in such budget priced
transmitters as the Heathkit DX-35, DX-40 and DX-60 to name
only a few.
With the advent of single sideband transmission, full
carrier A-M fell out of favor in the ham radio world but it
has remained a staple in the broadcast industry and other
services that want to get their message to the public. And
now, carrier control modulation is making a comeback among
broadcasters but not in the way it was done by radio
amateurs of the past.
For broadcasters who spend 10's of thousands of dollars a
year paying for electric service, the ability to raise and
lower power levels can be a major cost cutting factor. And
because of this a number of stations have received waivers
from the FCC to experiment with several new forms of carrier
control technology.
In one instance, transmitter manufacturer Harris Broadcast
and New York City powerhouse WOR-AM say they have had
success with a power-saving Modulation Dependent Carrier
Level algorithm. This with no effect on Arbitron Portable
People Meter data encoding/decoding, the stations H-D Radio
signal coverage or digital audio quality.
Harris engineers worked with Tom Ray, W2TRR , who is the
Corporate Director of Engineering WOR AM in New York, to
test the compatibility of two Harris Modulation-Dependent
Carrier Level algorithms. Amplitude Modulation Companding
provided the largest reduction in transmitter power
consumption, by saving 37 percent in average AC power input
to the transmitter. WOR estimated this translates up to a
$3,000 per month savings on the electric bill at his New
Jersey transmitter site.
So will this new form of Amplitude Modulation Companding
bring back full carrier AM to the ham bands? While a tiny
segment may decide to experiment with it more than likely
SSB will remain the preferred voice system among ham radio
operators world wide. At least until it's replaced by a
digital voice system at sometime in the future.
For the Amateur Radio Newsline, I'm George Bowen, W2XBS, at
the North East Bureau in Albany New York.
--
Nautel, another transmitter manufacturer has estimated that
a 50 kilowatt AM transmitter using this technology and
operating 24 hours a day, 7 days a week could easily save
$20,000 a year or more in electricity costs. This based on
modest electricity rates of 10 cents per kilowatt hour.
The complete story can be found on-line at
tinyurl.com/harris-modulation (RW)
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