Meteor detecting

Assuming the spectrum is ~145 MHz, surely not ATC radar? I think they are all up at microwave.

Going back to my earlier observation, are there no signs of reflections off aircraft? Or are they flying too low for the range to the Graves radar?

My maths is poor but assuming Dijon to be about 1100km away from me:

1. For both sides to see an aircraft mid-way the effective horizon distance is 550km (ie the aircraft has both sides in view.
2. From this calculator the effective height needed to get a horizon distance of 550km is about 25km
3. The ceiling of a Boeing 747 is about 13km

The closer you get to Graves the more likely you are to see aircraft. But from this distance from the ground station we can only see things more than about 25km high.

Last night the moon might have been detectable, but the distances require a better antenna than mine:

Yes that is a dustbin, old drain-pipe and second-hand plumbing. The rotary drier isn't part of the installation

Dave

Apparently they show as traces with small, constant doppler shift, but are mostly too low to be detected.

Meteors are roughly 4-5 times as high up as airliners.

But it looks more impressive

www.britastro.org/radio/projects/Antennas_for_meteor_radar.pdf

Edited By Neil Wyatt on 22/06/2018 17:02:12

Dave,

you say that you should only see objects above 25km but do temperature layers in the atmosphere play any part in what could be visible below that 25 Kms. I ask because back in the 60’s when stationed in what was Trucial Oman, on guard duty at night out on the airfield in the desert, we could listen to Radio Caroline but only for about an hour or two before dawn because the atmospheric temperatures created conditions for the signal from Caroline to skip the 4,000 miles or so.

Dave W

Yes, there are several things that alter the range of radio signals, some common, others exotic. The Graves Radar transmits VHF which mostly goes in straight lines. Normally most of the signal disappears into outer space rather than following the curvature of the earth, but there are conditions in which the atmosphere can reflect round the curve possibly getting bounced several times. I believe the distance record for communication in the nearby 144MHz amateur band is about 6000 miles, but that's very unusual.

Short Wave transmissions bounce very easily off the ionosphere, sometimes going all the way round and back. Medium Wave signals tend to behave like VHF during the day but they too bounce long distances as ionisation drops overnight, which is how you could hear Caroline. It's remarkably complicated and 'Quite Interesting' : listening to radio playing odd tricks is a full time hobby in itself.

Dave

Edited By SillyOldDuffer on 22/06/2018 18:50:08

I read (and promptly forgot most of) the entry for 2m band on Wikipedia which explains/links to several long distance modes. I say explains but I think a few are still a bit of a mystery.

Some are so short and flaky they can only be used to send bursts of CW morse code that are so fast they have to be decoded by computer.

Neil

Neil - why can't your pics be clicked on to open them? I've noticed this before - some pics can be, some can't, including the "For Sale" pics. On this page, SOD's pics can be clicked but none of yours can. Somewhat puzzling - and annoying.

Murray

I just found a test report ona radar using taht ferquency - but it seems it is used for 'stealth defeating' military radar.

Neil

Because to save clogging the net I've just linked to images I've uploaded on another site. Use right click 'view image'.

Here are some recent ones in a different programme that I've managed to persuade to log meteors and cature images of the bigger ones.

Time and frequency have swapped axes, but they each show one or both of the doppler shifted 'meteor head' and the static ionisation trail. The first one lasts around12 seconds.