[IRCA] Fwd: Noon-time MF propagation

[Phil Bytheway <phil_tekno@xxxxxxxxx>]

Some additional information on the "noon time" DX topic which was
discussed at this year's convention.

Anyone with any ideas, insights, let us know.

philb

--- SBJohnston@xxxxxxx wrote:

> From: SBJohnston@xxxxxxx
> Date: Tue, 31 Aug 2004 10:25:29 EDT
> Subject: Noon-time MF propagation
> To: phil_tekno@xxxxxxxxx
> CC: lynn@xxxxxxxxx
> 
> 
> Please share with other IRCA members... thanks!  Steve
> 
> - - - - - - - - -
> 
> Hello, I'm new IRCA member Steve Johnston, Interim GM and Director of 
> Engineering/Operations at Boise State Radio.
> 
> During my talk on Synchronous Detectors and HD Radio at the recent Boise
> IRCA 
> Conference, I mentioned in passing my observation that signals AM
> broadcast 
> stations and other MF communications can experience a remarkable change
> at 
> local high-noon.  Distant stations will sometimes jump up out of the
> noise right 
> around noon.
> 
> This has been a puzzle to me, but I've experienced it several times over
> the 
> years, and an old-timer once mentioned the same thing to me without
> knowing 
> I'd already encountered it.  It seems counter-intuitive since the
> D-layer should 
> be at maximum absorbtion at noon.  Several IRCA members were interested
> in 
> this phenomenon, but I did not have any further info at the time.  
> 
> A search on the web on this topic this evening revealed the following
> info 
> from the "KN4LF 7 Day Propagation Outlook #2003-17".  In this report
> Thomas 
> Giella, KN4LF, of Plant City, Florida wrote:
> 
> A Propagation Observation-
> 
> As an Amateur Radio Operator and 160 meter enthusiast I regularly
> monitor MF 
> propagation conditions. During daylight hours while I toil in my website
> 
> design business, I monitor a 10 kw expanded band broadcast station, WCNZ
> 1660 kc 
> from Marco Island, FL. The station is approximately 140 miles SSE of my
> QTH here 
> in Plant City, east of Tampa. I use my 160 meter 1/4 wave inverted L as
> the 
> listening antenna and the station puts in a decent signal of at least
> S9. But 
> throughout the daytime hours including at local noon time the station
> signal 
> arrives via skywave, with peaks at +20 over S9, fading down to S3 with
> phase 
> distortion. 
> 
> Conventional propagation wisdom holds that sky wave propagation on
> medium 
> frequencies does not occur at daytime due to total D layer absorption.
> The 
> D-layer, which is at an approximate height of 30-60miles in the
> mesosphere, totally 
> absorbs daytime medium frequency RF signals "most of the time". I say
> most of 
> the time because at high latitudes, during the winter season and
> especially at 
> the low part of a sunspot cycle, penetration of RF signals through the 
> weakened daytime D-layer and then refraction via the E-layer does occur.
> 
> 
> True to form during the Winter season of 2002-2003 I regularly observed
> sky 
> wave propagation on 160 meters at local noon time on 1845 kc and
> occasionally 
> WSM 650 kc in Nashville, TN. A group of stations here in Florida meet on
> this 
> frequency, the Old Florida Amateur RadioTransmitting Society! 
> 
> However one might expect a ground wave signal only in late Spring with a
> high 
> Sun angle here at 27-28 deg north latitude, especially during ahigher
> part of 
> Cycle 23. But as the daily solar flux level drops under approximately
> 110, 
> the skywave propagation continues to occur.  It will be interesting to
> see what 
> happens later this summer.
> 
> This confirms my observations and provides a very interesting hypothesis
> for 
> this noon-time enhancement - the E-layer reflection/refraction peaks at
> noon 
> and provides skywave propagation in spite of the D-layer absorbtion. 
> Verty 
> interesting...
> 
> Steve 
> 
> sbjohnston@xxxxxxx
> 
> 
> 

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