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LF: Re: Chaff and LF

To: <[email protected]>
Subject: LF: Re: Chaff and LF
From: "Alan Melia" <[email protected]>
Date: Tue, 24 Jul 2012 00:48:51 +0100
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Hi Laurence, I didnt thinkanything as crude as "chaff"was used in ECM these days :-))
A couple of thoughts..... it was probably dropped from 30000ft altitude 10km. the effective path length for reflection off that would be quite short around the same as VHF and microwave aircraft scatter. This has a rangel limited to arounf 700milesmax (I think some of that isdue to tropo bending too, which is not available at LF 
 
The original "chaff" was cut to half wavelengths but that was when radar was using vhf/uhf. At LF the effect would probably be one of scattering. I think the cross-section of a jumbo even, at 136khz would be quite small. Geo effects tend to make man's efforts look a bit puny :-))
 
Alan
----- Original Message -----
Sent: Monday, July 23, 2012 10:45 PM
Subject: LF: Chaff and LF


One of the most interesting weather reports this week was from Hawaii - when a radar image showed a broad swarth of radar returns some 15 miles long and 1 mile wide gradually moving South with the prevailing wind. I first thought it was a a weather gust front or rain squal but the weather chappy says it was from the ongoing military exercises and they had dropped a large amount of the chaff stuff (radar sized/reflective) and it was causing the X band radar to show it in detail.
 
I was pondering - as I sat on the beach on Maui the next day whether this form of chaff can actually produces anomolies below the frequency engineered - as a lot of the new type of chaff has to cover a load of GHz and MHz channelling - if the area is large enough, as this was, and the drop density of reflective material is large enough whether it would cause some effects as it appeared to be dropped from 30,000ft or so...even down to LF...?
 
Another anomoly was seen this morning when I was returning from Honolulu back to Anchorage - I was approx 1200 miles South of Anchorage and a Blue glow started to appear - firstly I thought it was just a band of Green/Blue Auroral light we get fairly often but  as we got closer it was the Notchtilucent clouds way way above us - banded, stripes and globs of thin cloud being illuminated by the sun which was way below our horizon and actually not even a pre glow. Now - this isnt a normal radio thing either but on reading up on these clouds it appears they too are radio reflective up to a point given the ions that attach to the nulceous and given they appear to be sub-polar or polar, and mostly a summer thing, when the temps are coldest at that altitude Im wondering if some of the oddities we see on MF and HF are caused by these clouds too...
 
 
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