[TransAtlantic] K6EDX #4

[k4mhz at aol.com]

Lots of perspectives... good tutorial on the duct.  

Headed to the airport for a trip Phoenix for our Renewable Energy Forum. There is a major effort to reduce communications facility power consumption and dependancey on secondary power grids... Cox Communications has a data facility running 150kw of solar to offest air conditioning peak...plan to build 450kw in 2010.

More comments to come on this note, need to jump on a plane...
Mark
K4MHZ

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I 


-----Original Message-----
From: Bob Cooper <skyking at clear.net.nz>
To: transatlantic at mailman.qth.net
Cc: Mike Bugaj <mbuga46 at gmail.com>
Sent: Mon, Nov 30, 2009 4:01 pm
Subject: [TransAtlantic] K6EDX #4


K6EDX #4 Post
There seems to be some misconception of what a 'duct' is or does. Think of an 
lmost lossless piece of large (HUGE! in fact) diameter coaxial cable, extending 
rom your QTH to one hundreds, thousands of miles distant. Now give that 'cable' 
n elevation above sea/ground level (ASL/AGL), a physical vertical dimension 
height) and a physical horizontal dimension (width). If your transmit/receive 
ntenna is at the correct height (ASL/AGL) your transmit energy 'couples' into 
he duct and it transports your signal with very small incremental attenuation 
ver whatever length as the duct exists to a receiving terminal (1) along the 
ay, or, (2) at the terminus of the duct (end) - provided the station at the 
pposite end of the 'path' (imaginary cable) ALSO has their receive (and 
ransmit) antenna at the height required (ASL/AGL) to ALSO be inside of the 
uct's vertical height parameters.
My apology for the basics here but based upon email responses, it is apparent 
ot all, who should, understand the physical properties at play here. If you are 
at either end of/OR along the duct) above OR below the duct's physical 
arameters (height or vertical thickness) no reasonable amount of energy on the 
ransmit end will 'couple' (connect) you into this invisible-to-the-eye 
waveguide."
Ducts tend to have a "resonant frequency range" and for us it is fortunate 
00-200 MHz fits the "typical" duct resonance. I have experienced 50 MHz signals 
rom Hawaii into California on ducting and 55.25 signals from Boston to the 
urks and Caicos Islands (approaching 1,400 miles) but on average anything below 
he FM radio band in frequency (88 MHz not to be specific but as a class of 
ignals) is non-resonant in a duct. So you can miss out on the high energy 
ransfer efficiency of a duct by being (1) at the wrong height (too low or too 
igh ASL/AGL), (2) the wrong north-south/east-west coordinate; simply beyond 
here the duct has formed), or, (3) on the wrong frequency. A percentage, fairly 
igh in fact, of ducts 'resonate' well at say 400-900 MHz but not so good at 
00(144) MHz. TV DXers can recount endless examples of this; signals at 600 
iles on UHF, nothing unusual on VHF (including FM). The reverse also happens; 
M (88-108 MHz or the weather radio channels in the 160-1
65 MHz band) are 'hot' and UHF is "dead." It pays to have a variety of 
eceivers and the skills to monitor more than say only 144.300. 
All of this leads to my own attention to ducts from at least 1970 onward. In 
974-1979, it was my good fortune to be associated with CATA (the Community 
ntenna Television Association; and its monthly journal CATJ) within which 
everal members including CATA head Kyle Moore owned their own two engine 
rivate plane. Kyle, and I, made dozens of short (under 1,000 mile) trips out of 
iley Post Field (Oklahoma City) and as he was a TV guy (operating cable TV 
ystems) he understood when I climbed aboard with a battery or 12V operated 
olor TV set and stuck a whip antenna to the Plexiglas window on his Bonanza. I 
an recount (will not) perhaps a dozen incidents when we lifted off the Oklahoma 
urf and he very slowly - much slower than he had been instructed by ground 
ontrol - climbed through 400-600-1,000-2,000 feet to his assigned cruising 
ltitude. The distance to, say, Lexington, Kentucky was just over 600 miles as 
e lifted aloft. "Stop - slow the climb down" I would instruct 
and for several tens of miles I could fine tune Lexington's channel 18 or 27 to 
llow him to fly and me to measure the duct's height. The answer was plus or 
inus 300 feet much of the time and with some skill he would drift up and down 
o allow me using his altimeter to define where the duct boundaries occurred 
typically VERY sharply defined). Of course traveling to Ohio at say 800 feet 
levation would have been a violation of (1) air traffic rules, and, (2) fuel 
onsumption common sense so my 'measurements' seldom lasted for more then a few 
inutes. After settling at say 12,000 feet I'd urge him to drop 'back down' 
very few hundred miles and we'd run smack dab into the duct at the logical 
eight virtually every time. "You are using up my fuel" was his usual chiding 
emark. Not to speak of why he was deviating from his 'assigned' altitude and 
eeded to request permission to 'drop down to 800 feet' over say Joplin, 
issouri!
Now move me to the 1980-1990 period. I now am VP5D and twice a month on average 
or ten years (200+ times) I flew in a Beechcraft D18 tail-dragger from 
rovidenciales to Fort Lauderdale, and return; +/- 600 miles x 2. The pilot was 
he last of the surviving WW2 fighter pilot guys, 'Crazy Ed,' and he would do 
nything you asked as long as you gave him cash. Crazy Ed paid absolutely no 
ttention to FAA/CAA rules, lied his way out of dozens (even hundreds) of 
fficial inspections with me standing beside him, and flying with Ed was akin to 
eing a Japanese Kamikaze passenger. Once over the Bahamas his HUGELY overloaded 
18 ("Weight and balance???" he would say to anyone stupid enough to ask; "If 
his sucker gets off the ground I pass!!!") with me in the co-pilot seat because 
he rear end was so badly overloaded with freight there were no seats left, we 
ost the entry door when the cargo bounced onto the loading door latch (only the 
argo net strung in the doorway kept the freight
 on board with a gaping hole now where the door had been). Someplace down there 
n perhaps Eleuthera there is a D18 door buried in the coral. Or he would take 
aying passengers and stick them into the one seat crapper/loo (toilet). Once I 
ried to get in there through an aisleway jammed with freight and discovered a 
ative Turks & Caicos lady with two kids crammed into the 'john.' You get the 
icture - Crazy Ed was totally off the wall. He 'loaded' each flight, especially 
rom Fort Lauderdale Exec Airport down to Provo, from the front; "You are 
o-pilot" he would assign and then from front to back the boxes and Caterpillar 
8 gears and foodstuffs and who knows what was jammed in until they reached the 
ear loading door. At that point a ground guy, after loading the 'john/loo' as 
ell, would use all of his force to shut the door against the protruding boxes 
nd freight. I cannot believe I did this - and still alive to relate the story - 
ver 200 times!
The good times were when I had enough 'room' to operate my 12" GE battery 
perated TV set using a whip antenna 'Crazy Ed' had 'graciously' allowed me to 
nstall on his top fuselage - mostly because I was his best (and cash paying) 
lient. I won't bore you with why he stopped in the Bahamas both to and from 
rovo but there were certain 'services' along the Bahamian chain which SOME 
assengers really wanted to use (read the book: "Television's Pirates" from 
mazon.com). Getting to ducting; Ed was reasonably accommodating as to my '800 
eet please' requests - subject ALWAYS to my promise to pay for the extra fuel 
hese diversions would cost him. I can tell you that over a decade I witnessed 
ozens - tens and tens - of ducts especially in March-June, where we would lift 
ff Exec Airport with me to tuned to a Fort Lauderdale or Miami UHF channel and 
00+ miles later (or 300 miles later when we let down on a Bahamian island for 
service') as we descended down to Providenciales runw
ay there it was - still there at about the same altitude but gone at sea level. 
hese two generic examples sort of illustrate my point; either you are "in" the 
uct or you are "out" and if you are below - well - no reasonable amount of ERP 
power) is going to get you in - or the other guy's signal out. Being inside the 
uct is paramount here - being below is to suffer a double whammy; first you are 
ot in, and worse yet, your signal is being shielded from getting in by the 
oisture/temperature parameters of the bottom (or top if you are well elevated) 
f the duct. Think METAL waveguide here - those inside are home free; those 
outside" (whether 'above' or 'below' ) might as well be in New Zealand; ducts, 
ike metal waveguide, keep signals 'out' as well as 'in.' 
So this effort - to reach Europe on 144 MHz or above, if by the troposphere, is 
EALLY all about wave propagation. It is not about red blobs on Bill's maps or 
hat happens between two distant points; it is about being conscious of what it 
akes to get 'inside the magic waveguide' (where power is not an ingredient; 
eing in the right place at the right time is!)
Bob Cooper K6EDX/ZL4AAA
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