[Lowfer] Big sig on 17.8 kHz

[mikea]

On Thu, Jul 29, 2010 at 09:43:47AM -0500, Robert M. Bratcher Jr. wrote:
> I wonder how much RF power they put out? And what is MSK?

MSK is Minimal Shift Keying; Google will point you to places that
explain it well. 

About the TACAMO: 

>From <http://www.navy.mil/navydata/policy/vision/vis02/vpp02-ch3d.html>:

"E-6A/B can deploy a 28,000-foot trailing-wire antenna and a 5,000-foot
short trailing-wire antenna for VLF communications."

>From <http://oldtacamo.com/blog>:

"TACAMO VLF SYSTEM HISTORY
by Dick Buckner, former Collins VLF Engineer
(We are honored to have this expert contributing to the history record
of the community. Thanks, Sir.)

When the TACAMO III PA (with 25 kW output) was judged to be underpowered
(for coverage reasons), 200 kW output was specified, and this level was
selected because the limiting factor was available power from generators
to be added to each engine. But this resulted in two design problems:
1) The then-single trailing wire antenna, when driven at 200 kW,
generated excessive voltage at the driving point. (Antenna input voltage
was already about 35 kVpk with the original 25-kW PA.) Collins solution
was to design a dual-trailing wire antenna, with the feedpoint at the
aircraft frame, thus tapping down on the total antenna. The short-wire
antenna was then fed at a voltage below 25 kVpk, even at the 200-kW
power level. This design also saved weight, since now the heavy
long-wire reel could be grounded to the airframe.
2) The older TACAMO III operated with a PA conversion efficiency of 70%
or less, and the new 200-kW requirement forced higher efficiencies if a
practical PA input power could stay within the engine-generator limits.
Collins designed a new vacuum-tube PA that operated at a Class D
efficiency of about 90%, thus achieving 200-kW within the generators
limits. Unlike the experimental TACAMO IVA solid-state PA, which
generated 200-kW before its antenna coupler losses, the TACAMO IVB PA
was rated at 200 kW at the antenna input, so the actual PA output was
higher. The TACAMO IVB PA also contributed to weight and noise reduction
by using only two vapor-cooled vacuum tubes in the new PA. Anode
dissipation of about 20 kW was removed through a vapor-to-oil heat
exchanger, and then exchanged to the outside air by another heat
exchanger in the wheel well area.

Semper Orbitus, Vern
"

It appears that the new TACAMO puts even more than 200 KW on the wire.
It's no wonder that it shows up strong. 

>From <http://www.globalsecurity.org/wmd/systems/e-6.htm>:

"The High Power Transmit Set replaces the existing 200 kilowatt VLF High
Power Amplifier and Dual Trailing Wire Assembly, providing increased
capabilities (including low frequency transmission spectrum) with
significant reliability and operability improvements."

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin