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LF: Re: TR

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Subject: LF: Re: TR
From: "Alan Melia" <[email protected]>
Date: Fri, 27 Jan 2006 19:40:01 -0000
Delivery-date: Fri, 27 Jan 2006 19:41:49 +0000
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Hi Mal, this is a fairly common case in most parts of the cycle I have looked at so far. I can only surmise what I think causes the effect.  I believe that as the daytime absorption dies away  and the D-layer electron density drop the "reflection heaght" for long distance signals moves up from 50 to 60 km to around 100km. This means a greater distance can be covered in one hop and the received signals increase in strength. As the night progresses I think it may be that higher angle signals are propagated so around the 0200 to 0330z period you will see quite deep fading on long distance signals as the differnt paths cancel each other out (or sometimes reinforce each other) I notice that the centre part of the night does not normally show lower levels but it does seem to have more dips which carve the QRSS signals up. Why this should change again towards morning is a mystery still, but over all I agree with you that the best times are around an hour to 90 minutes before dawn. 
The effect oftent mentioed of signals continuing until after dawn is fairly common at "quiet sun" times, and particularly in the morning. In Europe the noise is mainly from the east (the land mass). The sunrise sweeps over eastern europe up to a couple of hours before the dawn reaches the UK. This can mean that there is a quieter period in the morning just before UK dawn, this is good for looking to the west but not so good for the Russian stations. The important cut-off is the time that the darkness shadow reaches the region of the "reflection" at the height of the "reflecting layer"  ( I keep putting reflection in quotes to save myself hassle from the purists who say it is not a mirror-like reflection but a gradual bending or refraction). Tis reveals some interesting  ideas, although geometrically the maximu, rage on LF for a one-hop signal is about 2200 to 2500km, my suspicion is that the first signals to reach the NA coast from the UK may do so in just one hop (!!) They are quite weak but at this time half the Atlantic at 100km altitude is in sunlight. It is possible that there is some "daytime" propagation but there are strong reasons related to the "tea-time dip" that suggest this is not the case. Daytime signals were often visible from CFH, usually in winter when the solar radiation was weaker and probably the attenuation was less. These often peaked at about 1500z when the mid-atlantic point was getting the highest dose of UV. I did copy Joe at daytime in 2004 (I think) around 1300 in summer, but I think the reason for that was a very high concentration of electrons in the D-layer due to a geomagnetic storm. Normally the summer radiation levels with wipe out daytime propagation at that distance.
I do have ARGO signal traces from Joe John Dex and Warren (when active) through most of the last week or so. The suffer fading in the middle hours and come up quite strong before dawn. It is interesting to see the way that the fade at different times due the phase differences on the different path lengths. The same effect  occurs at the receive end, different station will see the fades at different times and one station may report excellent  signals (beacuse of addative effects) whilst another will moan of poor signals because the fading at his site as not been favouable. The distance between such widely varying reception can be as little as 50 km.
Its fascinating stuff (to me who is well adicted anyway !) and more effects are appearing during these quiet years which may help to harden up on some of my "flights of fancy".
Cheers de Alan G3NYK
----- Original Message -----
Sent: 26 January 2006 09:12
Subject: LF: TR

Hi All
Stns observed during the night. VO1NA, XKO and XES.
XKO strongest sig last nite and vy good around 0800z, XES not as strong as usual and VO1NA only visible at times but a good signal when he popped up. There were a couple of others that I could not make out *MJ
My observations indicate that the best time for TR to my QTH is late morning 0700 - 0900z other time is 0001 - 0200z approx and little or no propagation  the rest of the time during night time.  ie my sunrise seems best and sunset at the USA end. This is the RX situation at my end, TX could be different from here. I am surprised that there is no propagation during the majority of the dark hours at both ends.
What does Alan think about that.
73 de Mal/G3KEV/IO94SH/Scarborough
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