Charles
Your geometry which led you to believe that the reflecting layer for radio
aurora is at 200-400 km must not be correct in some way. 200-400 km is more
like an F layer phenomenon and auroral radio contacts are made by reflection
[more accurately backscatter] off ionization in the E layer. Thus the
maximum height for auroral reflections should be no more than 110 km. That
height defines the distance limits for auroral contacts at ~2400 km in an
East/West direction and at about 1000 km in a North/South direction. Emil
Pocock W3EP once did the geometry for single hop contacts off the E layer
and determined that it was limited to ~2400 km or a little more for a
refraction height of 110 km. Thus one would think that the furthest away
the auroral curtain could be and still scatter a radio signal would be half
that distance or about 1200 km [~700 miles] unless there is some error in my
thinking - always a possibility. That is the equivalent of an entire grid
field. For example, if the curtain were at 59N degrees directly north of
N1BUG at FN55, it would be at FO59 - still some 4 grids or so beyond where
Paul could reach IF my calculations are correct. That said, Paul is
absolutely correct that many possible AU openings are missed at least in
great part because of lack of activity.
If you want to learn more about the formation and properties of making
contacts via AU, I have found Charlie Newton's [G2FKZ] book "Radio Auroras",
published by RSGB and perhaps still available via the ARRL bookstore, to be
a great source of information. See pp.43ff for distance limits of auroral
contacts and p. 39 and Fig 3.12 for the formation of radio reflections in
the E layer.
73 Gene W3ZZ
----- Original Message -----
From: <Charles.Morrison@apcc.com>
To: <vhfcontesting@contesting.com>
Sent: Wednesday, October 20, 2004 3:38 PM
Subject: [VHFcontesting] Distance away from AU (expressed in degrees
ofLatitude) to predict RF-VHFaccess to AU.
>
>
>
>
> Aurora range question:
> Q: >>>>
> How far away from the visual Aurora can VHF QSOs be made ? <<<< By
> degrees or miles/km.
> Distance away from AU (expressed in degrees of Latitude) to predict
> RF-VHFaccess to AU.
>
> The noaa.gov site states :
> " ( Keep in mind that aurora can still be viewed when it's position
> is 4 to 5 degrees of latitude away from the viewer,
> although it will appear [at ] about 20 degrees
> above the horizon.)"
>
> According to the link on the N1BUG page, there was some aurora
> down to about 59 degrees latitude last night.
> But, no spots were found for NA VHF QSOs.
> =====================================
>
> More de N1RR:
>
> We all now that the radio horizon is 4/3 of the visual horizon. So,
> that roughly translates to 6.66 degrees
> for a 20 degree take-off at RF. But this doesn't give the maximum range
to
> AU at RF-VHF.
>
> It's probably the same one half the maximum skip distance for a
> signal which is reflected off a 200-400km, the
> highest of AU depending on intensity of disturbance. Another way may be
to
> determine the maximum skip distance
> for an RF short skip when the atmospheric reflection/refraction occurs at
> an altitude of 200-400km.
>
>
> Charles Morrison
>
> Amateur Radio callsign: N1RR
>
>
>
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