[TowerTalk] re Take off angles - especially for LF work

Peter Forbes prforbes@tbsa.com.au
Thu, 21 Dec 2000 19:14:27 +1100 (EST)


Hi Tom and others.

I hope you took my comments tongue in cheek!!!

A couple of extra comments.


(1)  Birds in VK twitter louder and longer than in the states!!!

(2)  I think the example that you keep quoting of VK0H is the exception to
the general rule, because it is not typical westward propagation at sunrise,
at that time of the year.

The short path to W3 is 250 degrees
The short path to W4 is 230 degrees
The short path to W6 is 143 degrees as it is long path propagation - hence
the interesting series of articles by Bob Brown about the W5 black hole
region for VK0H on low bands.  

If you look at the actual sunrise line at Heard Island in mid January it is
almost running at 220 degrees local bearing due to the extreme southerly
position of Heard near to the Antarctic circle.  Hence the signals are
actually running almost ALONG the terminator towards W3.   That is why I
said that propagation generally North/South (i.e. along the terminator, is
much more unpredictable.

The other issue with VK0H is that it is quite near to the South Geomagnetic
pole hence easily affected even at low SSN.

(3) What I do agree with you about VK0H is that they missed many excellent
openings to W6/W7 at their sunset 1500z - 1700z on 80/160 mx due to
inappropriate scheduling and plain pig-headedness.  We told them many times
but they just would not accept the advice.

(4) What I am trying to do, is look at what actually happens as the layers
develop in near real time when looking westwards at sunrise in our area.  I
have access to SYDNEY, CANBERRA and HOBART which are all within 500 kms of
my QTH.

We can access 45 minute apart IONOSONDES from IPS Australia which help to
give some insight into what happens locally in the developing layers, but
until we get down to 15 minutes and perhaps some oblique readings to
construct a 3D vision of the reflecting region, I feel that it is all
guesswork - just like fishing!!!


(5) Your comment about propagation being lousy just before sunrise I
entirely agree with - especially on 30 and 40 metres.  It is more difficult
to determine on 80/160, as static often masks the true signal strengths
until it begins to disappear from the east, as the D layer rises is strength.

Hence VK3QI's TIRED, TRIED and TRUE RULE !!!!!!


P.S.  Have you looked at any ACTUAL ionograms for your area during the VK0H
operation?  Perhaps they are archived at the NOAA, or whatever it is called
now that Bushy will be in?

 
Cheers

Peter  

>> 160 metre opening - once it is light enough to read the headlines on 
>> the newspaper outside, the band has closed
>
>	N4KG:  Usually true.  
>> 
>> 80 metre opening - once it is light enough to read the fine print on 
>> the newspaer outside, the band has closed
>
>	N4KG:  NOT  SO.  This the mistake VK0IR made.
>	My observations are that signals begin to rise at
>	sunrise (Sun on horizon, past first light) and peaks
>	to the West 10 to 30 minutes past SR. 
>
>	One SUMMER, I heard FR5DX on 75M LP an 
>	hour and a half past my SR (and about the same
>	amount of daylight before his SS).  MUF (and 
>	absorption) rises more slowly in summer months.
>
>	BTW, the hour BEFORE SR can be be the WORST
>	hour of the day, especially to the West.  Weaker
>	stations from the Pacific are often inaudible before
>	SR (working other stations to my east) but come up 
>	nicely at my SR.  I remember sitting on 3798? hearing
>	East Coast stations working XX9-- a their SR, following
>	the SR from W1 to W4 but not a peep here until my SR
>	at which time he came up enough to make contact and
>	disappeared a few minutes later as the W5's began 
>	working him.   de  N4KG
>> 
>> 40 metre opening - once the birds stop twittering the band has 
>> closed.
>> 
>	40M usually peaks from 30 to 60 minutes past SR.
>	I have heard Pacific / SE Asians as late as 3 hours
>	past my SR during low sunspot levels.  de  N4KG
>
>> 30 metres opening - add 1 hour for summer, 2 hours for 
>> spring/autumn, add 3 hours for winter to 40 metre times.


>> I am carrying out extensive scientific analysis on formulating a 
>> rule for
>> sunsets propagation to the east.  Findings will be released soon.
>> North/south paths present more problems such as what the hell is 
>> going on in the ionosphere/geomagnetic field !!!
>> 
>	Signals arriving perpendicular to the approaching 
>	Sunset terminator can be heard before SS (an hour
>	or more on 40M).  As the terminator gets closer,
>	signals from further south can be heard.  During
>	the twilight period, LP signals from East / SE Asia
>	can be heard.  These LP openings typically last
>	for 5 to 15 minutes on 80M, longer on 40M, perhaps
>	up to an hour.  de  Tom  N4KG
>
>


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