View Full Version here: : 31 meter band
05-11-2010, 10:18 PM
Hi all, I was just browsing a 1929 Popular Mechanics where I came across the story of a Dr. Carl Stormer who had broadcast into space on the 31 meter band. His signal was bounced back from a distance of + 1 million miles.
Anyone have an idea of 'what' would have been responsible for the bounce?
06-11-2010, 12:30 AM
Although I was not around in 1929, it is unlikely that it was Moon bounce. One million miles is about 1600 900 km if memory serves me right and we are talking about same miles. That would make return signal to take about 10.7 seconds. That means it would have to bounce from some comet or astroid in vicinity of the Earth. Iím not sure if they had technology to actually do and accurately measure this in those times
06-11-2010, 12:54 AM
The article claims it took 15 seconds to return so they felt that it had to be bounced by something further away than the moon. Apparently he was not aiming at any particular object.
06-11-2010, 01:27 AM
I have reset my planetarium program to 1929.As far it goes there were not any significant comets or asteroids that could bounce radio signal.That is visible from southern hemisphere. I think that in those times the radio spectrum was much quieter then it is today.So some radio observations that would be very difficult today were possible in those times
It may be that the Enterprise was passing by ;)
06-11-2010, 01:41 AM
15 seconds - that would place object from which the radio signal bounced at 22 50000km from the Earth
06-11-2010, 10:54 AM
You would need to understand the propogation characteristics of RF to explain the reason. The signal would most certainly not be eminating from a reflection in space.
It would have been the return echo of a signal bounded by the troposphere that has circumnavigated the earth many times before being picked up again.
In 1929 there would hot have been so much spurious emmission at 31 metres to mask the return echos of these occasionally happenning phenomenae that did and still do occur.
If you listen to short wave broadcasts you will often notice the effect of signals circumnavigating the earth by the echos and often multiple echos that accompany the direct signal.
06-11-2010, 11:46 AM
Would have had to beam it straight up and at night time otherwise as Barry mention would have wizzed around the world a few times.
I remember even at Hi-band VHF frequencies when working for Water Authority, we have a complaint from a radio user in Collie could hear conversation from Kunnunurra. This is slightly different called Tropospheric ducting. Similar principle. Hi-Band VHF has a range of 25km depending on height. The range on 31 meters is so variable.
Need to apologise, I am only an industrial radio tech I am having trouble using wavelengths in standard conversations :)
06-11-2010, 12:34 PM
At higher frequencies reflections from the E layer can extend coverage thousands of miles on signals that are not bounded by the ionsphere. This was noticeable on "low band" TV from Europe being picked up in Australia. Hams in the six meter band use this for long distance communication when the condition is favourable. At the higher VHF frequencies extended range is often had by "ducting" caused mainly by temperature inversion.
As the frequency increases the effect of signals being reflected off dust, Aurora, aircraft, balloons etc becomes more noticeable. In fact reliable communication can be had at UHF over hundreds of miles using High power digital techniques from back scatter reflections.
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