[TowerTalk] Takeoff angles - some practical experience

[n4kg@juno.com]

On Wed, 20 Dec 2000 "i4jmy@iol.it"<i4jmy@iol.it> writes:

> One should always consider that relatively short time openings with 
> anomalous conditions are not very much considered in studies that 
> have  been developed with the final purpose to establish how a P to P
link 
> or a broadcast transmission can be realized at best and with a safe 
> margin.   (I4JMY)

	Good point.  I use the MUF predictions to tell me
	when the peaks are likely to occur, and check
	bands ABOVE the posted MUF to 'stretch' the
	openings over the pole into Asia and other remote
	places on 10, 12, and 15 Meters.   Remember,
	the HF Broadcasters and Military / commercial
	traffic handlers (who sponsored propagation
	prediction development) are looking for LONG term 
	openings and not narrow windows into remote corners 
	of the world.  N4KG

> Amateurs that use low power and generally marginal antenna systems, 
> more than often base their traffic just on those peculiar conditions 
> (i.e sunrise and sunset or summer E layer multihop) that are not of 
> primary importance for other kind of traffic that uses larger power 
> and  available antennas.   > 73,  Mauri I4JMY
> 

	Yep.  This is especially true on the LOW Bands
	where most simplistic propagation predition programs
	are very misleading (if not useless) at predicting the
	significant pre-sunset and post-sunrise enhancements
	that are very consistent and reliable on 30, 40, and 80M.
	(160M is a special case and does not correlate well 
	with any other band.)  

	Unfortunately, many DXpeditions use these inaccurate
	prediction programs to make their band plans, missing
	their brief opportunities to provide polar path contacts
	during the critical openings on the low bands (and
	sometimes even the higher bands).

	Example 1:  Except for some 80M LP QSO's with the
	West Coast, VK0IR had ZERO  80M NA contacts 
	until day 6 when they finally agreed to stay on after
	their sunrise.  (Ref:  VK0IR by KK6EK - note 160 and
	80M QSO data tables are reversed).  Unfortunately,
	conditions were more disturbed after day 7 and the
	openings were quite brief vs. the 90 minute opening
	enjoyed on day 6 when conditions were still quiet.
	Approximately 80% of their midwest contacts on 80M
	were made after their sunrise.
	
	Example 2:
	Another DXpedition to XW used computer propagation
	predition to determine their low band plan.  They appeared
	sequentially on each band, 80, 40, and 30M  BEFORE  
	east coast sunrise, moving up just as each band was 
	opening to the USA and wondered why they had NO
	contacts with N.A.  Shortly AFTER their premature
	appearances, QSO's were easily made with stations
	in DU, HS, XX, etc.

	To my mind, the BEST propagation tool for the Low
	Bands is a SUNRISE / SUNSET indicator, whether
	computer program, plastic DX Edge, or simply a 
	set of tables AND the knowledge that the enhancements
	require daylight, on the order of 0 to 20 minutes on 80M,
	15 to 45 minutes on 40M, and 30 to 60 minutes on 30M,
	with reduced signal levels holding in up to twice that long.

	de  Tom  N4KG

   

> > It appears to me that there is really a pretty good fit between 
> theory, as embodied in VOACAP predictions, and practical experience.  
> You  can't oversell the former, but neither should you ignore it in
making 
> station design decisions.
> > 
> > 73, Pete N4ZR
> > 
> > Contesting is ... Extreme Radio
> > 
>
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today!  For your FREE software, visit:
http://dl.www.juno.com/get/tagj.

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com