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--- communication:piii_experience [2006/07/26 20:42] – rocketboy
+++ communication:piii_experience [2008/07/19 23:33] (current) – external edit 127.0.0.1
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-====== Pegasus III – The Radio Tracking Experience ======
+====== Pegasus III – The Radio Tracking Experience (by Steve Randall) ======
-Some time ago I did some path loss calculations to see if a 10mW 434MHz licence exempt transmitter was viable for balloon to ground communications. The maths indicated that narrow-band communication should be feasible over that distance using a modest sized yagi as a receive antenna. To prove my calculations I conducted some tests using a 10Km line of sight path – the results were very good.  I added a 20dB attenuator – thus simulating a 100Km path – the signal was still of respectable strength.  Finally I tried a further 20dB of attenuation (simulating a 1000Km path) – the signals was still audible. So much for the theory – when the opportunity of Pegasus III came up I offered to build and track a transmitter.
+Some time ago I did some path loss calculations to see if a 10mW 434MHz licence exempt transmitter was viable for balloon to ground communications. The maths indicated that narrow-band communication should be feasible over that distance using a modest sized yagi as a receive antenna. To prove my calculations I conducted some tests using a 10Km line of sight path – the results were very good - the signal as respectible stength.  I added a 20dB attenuator – thus simulating a 100Km path – the signal was still of respectable strength.  Finally I tried a further 20dB of attenuation (simulating a 1000Km path) – the signal was still audible. So much for the theory – when the opportunity of Pegasus III came up I offered to build and track a transmitter.
 The tracker was built using a standard licence exempt narrow-band 10mW 434MHz transmitter, a PIC microprocessor (to provide a modulating signal and power management) and a Photo-Lithium Battery (which should have been sufficient for almost a weeks operation).
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 I headed north on the M11 again – this was a mistake as after only a few miles the signal was completely lost.  I pulled of the M11 at J9 and found a place to park about 10:45 – but despite a sweep of the sky nothing was heard.  I headed south on the B1383 – stopping off here and there to take a sweep – nothing.  After a while the main balloon team gave me a call to say that it was down and had reported its position just south of  Stocking Pellham village.
-As I got close to the village I started to pick up the signal again and at one point It became very strong (this would have certainly be strong enough to carry data) so I parked up and started tracking with the yagi.  As I moved about I started to get some quite confusing direction readings – I tried attenuating the signal – but with little effect. After about 20 mins of  walking about I got a strong and clear reading and within a minute or so  I found PIII in the corner of a Oilseed-Rape field almost directly under some power lines.  I suspect it was the power lines had been carrying the signal form PIII that had given me the false readings. Fortunately PIII had landed upside down – which meant that the antenna was on the top side – had PII landed right way up the signal would have been a lot weaker.
+As I got close to the village I started to pick up the signal again and at one point It became very strong (this would have certainly be strong enough to carry data) so I parked up and started tracking with the yagi.  As I moved about I started to get some quite confusing direction readings – I tried attenuating the signal – but with little effect. After about 20 mins of  walking about I got a strong and clear reading and within a minute or so  I found PIII in the corner of a Oilseed-Rape field almost directly under some power lines.  I suspect the power lines had been carrying the signal away from PIII that had given me the false readings. Fortunately PIII had landed upside down – which meant that the antenna was on the top side – had PIII landed right way up the signal would have been a lot weaker.
 Frequency shift – most of the flight the frequency kept relatively stable – shifting a couple of hundred Hz. On landing the frequency jumped about 1KHz higher.