[BC] Re: Skywave reception, big potential......

[Al Wolfe]

    Has anyone done any practical work with NVIS (all skywave) antennae in 
the AM band? I have played a bit with them on both 1.9 and 3.9 mhz and am 
surprised at how well they can work, even in the day time. I recall 73 
magazine had an article or two back around 1967 regarding using very low 
dipoles on 40 meters for communications out to about 400 miles in the 
daytime. Also cut down greatly on interference from foreign broadcast, low 
angle stuff.
    This may be the newest savior for AM radio. Eliminate the ground wave!

Al (retired),
AKA K9SI


> Date: Sun, 24 Jul 2005 07:20:09 -0500
> From: "Richard Fry" <rfry at adams.net>
> Subject: [BC] Skywave reception, big potential, under-utlized , was
> Re: Daylight Savings Time changes?
> To: "Broadcast List" <broadcast at radiolists.net>
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>
> Rich Wood:
>>I really think the only way nighttime AM radio can continue to exist
>>is to reduce skywave that's going to wipe out a lower powered local
>>signal. IBOC stations have admitted anything beyond their protected
>>contour isn't important. Let's take them at their word and reduce
>>their interfering signal
> __________________
>
> Effectively reducing the skywave is much easier said than done.
>
> Even radiation at low elevation angles (from just above zero to, say, +20
> degrees) eventually becomes a skywave, and can provide nighttime secondary
> service under the right conditions.  Nighttime radiation directed at +20
> degrees elevation returns to the earth after one reflection from the
> ionosphere at a point about 500 km from the transmit site.  Lower 
> radiation
> angles serve greater distances, so it can be seen that the part of the
> radiation envelope most useful for generating usable secondary coverage is
> contained at these low elevation angles.
>
> There is no practical way in the MF band to build an antenna system that 
> can
> generate a groundwave of 100% relative field, and at the same time produce
> very low relative fields at all elevation angles that produce a useful
> nighttime skywave.
>
> RF