[ARC5] LDE

[Dennis Monticelli]

George,

Thank you for the info and excellent article.  I definitely learned some
things.

Dennis AE6C


On Mon, Jul 22, 2013 at 11:32 AM, George Maier <george at maiergroup.com>wrote:

> Great subject.......The possibility of a monster trans global duct exists,
> but it's pretty doggone low on the probability scale.  Having spent decades
> in microwave systems engineering, the idea of ducting is pretty much a
> routine exercise in some areas.  Surface ducts appear when the refractive
> index drops into the cellar and traps radio signals close to earth's
> surface
> over the length of the duct.   An elevated duct can occur when signals are
> trapped between different layers with opposite indicies.  Again, not
> impossible but really unusual, especially at HF frequencies where the duct
> size would be really big and would have to remain stable long enough to
> allow enhanced propagation.  GTE Lenkurt published a good book microwave
> propagation decades ago; I still have my original 1972 second edition:
> Engineering Considerations for Microwave Communications Systems by Robert
> F.
> White.   There's a good on-line explanation of ducting by VK3KAQ here:
> http://vhfdx.radiocorner.net/docs/GTPaper2004V2-1.pdf
>
> I should think the HF OTH radar guys would have a really good handle on
> this, based on years of observations.  Personally, I think that one, or
> even
> a series of tall and coincident surface ducts could have been be the
> mechanism that Dennis is referring to.    BTW - one trip around mother
> earth
> at radio (light) speed is a bit more than 130 milliseconds, so 1/2 second
> echos are taking a pretty unusual path!
>
> 73, George - W1LSB
>
>
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net]
> On
> Behalf Of D. Platt
> Sent: Friday, July 19, 2013 6:14 AM
> To: ARC-5 Maillist
> Subject: Re: [ARC5] LDE
>
> Gents,
>
> A number of yeasr ago, I worked for a lab (ITT-EPL) that was in the
> forefront of Over-the-Horizon Radar (OTH) and ionospheric sounding
> development.  We used frequencies up to the lower VHF region, but primarily
> in the HF spectrum, of course.  The thing is, I don't recall return delays
> into the multi-second region?  Many return signals appeared to be mostly to
> be "extensions" of the original pulses, to the human ear.  Of course, those
> signals coming back from Eastern Europe and the Middle East and Asia were,
> of course, predictably longer.  That I never heard very long dalay signals
> indicates nothing as I would have had to be at one of the sites at the
> exact
> time one of these phenomena occurred.  The power we used was in the 3-10
> KW.
> My first S-Line transmitters were much-modified 32S-1's the company
> surplussed out.....
> That was in the early days, of course.  I recall we used Rhode &Schwartz
> programmable signal generators, later.
>
> Jeep - K3HVG
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