Weather this evening was not suitable for the tests, although I did try. I set up the QRSS3 beacon pointing out of my bedroom window using the local windmill as the aiming point. This is on the top of our small hill which rises about 15m. I then drove to a spot 3.6km away over the hill to look for the signal with my sensitive RX and 100mm optics using Spectran to display the trace. Unfortunately this time the slight drizzle and murk was just too bad and no signal was copied, although I've had good results in the past at a very similar spot.
In daylight I need to recheck my beam alignment at the RX location as it was sufficiently murky to not see the local landmarks used to help aim the RX last time. Despite panning across 45 degrees of aim nothing at all was copied of my signal. I shall repeat the test in better optical conditions.
For those interested, the 1W 10mm diodes are available from http://www.ebay.co.uk/itm/350347623711. You get 10 pieces for £9.26 with free postage and they are very BRIGHT.
Showing posts with label nlos. Show all posts
Showing posts with label nlos. Show all posts
26 Feb 2013
481THz optical tests over the horizon tonight
This evening I am doing my first "over-the-horizon" optical test this year. The main aim is to check performance with the new receiver and to see how I get on using the iPod Touch 4g running SpectrumView software as the way of seeing the QRSS3 signal. I shall also be taking the laptop running Argo or Spectran.
The receiver circuit is the one in Practical Wireless this month by Stuart Wisher G8CYW. This is simple but works well in darkness. I've added an interface to the iPod Touch 4g (a capacitor and a resistor needed to enable the external mic input) and changed the coupling caps and op-amp gain. Using just MPF102 and 2N3904 devices the results look good. The low noise op-amp may be overkill unless one uses super low noise FET and transistor stages too.
After the tests I'll post results in the blog.
Latest receiver that seems more sensitive than my older RX |
After the tests I'll post results in the blog.
Labels:
g8cyw,
nlos,
optical 481THz
19 Feb 2013
Nanowave over the horizon tests - nearly ready
Original optical beacon |
Optical beacon capable of continuous subcarrier (choice of freqs) or QRSS/CW |
SpectrumView in action - it's brilliant |
I also want to optimise the use of the iPod Touch 4g as a handheld audio spectrum analyser. I have used it for this sort of test before using an excellent package available free called SpectrumView (see screenshot) available from Oxford Wave Research. With a laptop PC, running Spectran, the problem is the brightness of the screen which emits an interfering optical signal. With a tiny iPod Touch it is much less bright and can be held in the hand. Unfortunately the bandwidth can't be screwed down as narrow as with Spectran on the PC, so there will be S/N limitations. One test will be to see how far away I can detect my beacon (about 0.5W into the LED) over the horizon using just the optical receiver and the iPod Touch.
The beauty of 481THz (red light) work is the kit is simple: everything that matters is at audio frequencies and can be built and tested with the simplest of test gear.
Labels:
481thz,
nlos,
optical,
oxford wave research,
spectrumview
6 Oct 2012
Over-the-horizon on 480THz
My order for 3 off 12W red LEDs known as PT54 Phlatlights has arrived. These are VERY VERY bright LEDs mounted onto substantial heatsinks which emit a strong signal on 480THz. They were originally intended for portable projection systems. One of mine is going into my QRO optical beacon running continuous carrier, CW, DFCW, QRSS3 or QRSS30 to use in further over the horizon (non line-of-sight) beaconing tests using the scatter from particles in clear air and the reflection off the base of clouds. Last winter my own simple beacon running at around 300mW was detected several km over the horizon using QRSS3. G4HJW's optical beacon using a Phlatlight LED was detectable in my village some 8-9km over the horizon. In neither case could the red glow from the TX be detected by eye. This week I also received some SFH213 10 degree half angle PIN photodiodes which should be considerably more sensitive than my BPW34 detectors currently in use. Estimates suggest at least 6dB more sensitivity.
Together, the QRO optical beacon running from home, focussed with a 100mm lens (gain about 24-30dB), and a portable high sensitivity 100mm lens based detector should allow plenty of scope for innovative NLOS tests on dark winter evenings.
Just realised: 5W out (for example) into a 30dB gain lens "antenna" is equivalent to 5kW of light power in the beam. That is SOME bright light. Clearly great care is needed in siting and aiming such a system to ensure safety.
Together, the QRO optical beacon running from home, focussed with a 100mm lens (gain about 24-30dB), and a portable high sensitivity 100mm lens based detector should allow plenty of scope for innovative NLOS tests on dark winter evenings.
Just realised: 5W out (for example) into a 30dB gain lens "antenna" is equivalent to 5kW of light power in the beam. That is SOME bright light. Clearly great care is needed in siting and aiming such a system to ensure safety.
Labels:
beacon,
nlos,
optical,
phlatlight
14 Mar 2012
Further 481THz G4HJW reception "over the horizon"
G4HJW received on 481THz over an 8.63km non line-of-sight path |
On 3 attempts copying G4HJW's optical signal it has been (1) 30dB S/N, (2) no copy and (3) today 20dB S/N in 0.67Hz bandwidth over an 8.63km NLOS path. I am still using the BPW34 detector in 100mm optics.
26 Feb 2012
Successful 481THz NLOS test (8.63km)
8.63km non line-of-sight reception of 481THz optical beacon |
Both on Bernie's RX kit and my own we got solid copy by ear of the beacon at a distance of around 8.63km NLOS using 100mm optics. Once found, the signal was solid. I then set up the optics on the tripod and fed the signal into Spectran where the signal was 30dB over noise in a 0.17Hz bandwidth. Listen here for a recording (best played back using Spectran with 0.17Hz bandwidth settings)
G4HJW's beacon TX |
This was very gratifying as it is the furtherest NLOS signal I have copied and it verified my RX kit is now working at good sensitivity.
When I got back home I did try to copy the beacon by ear out of the bedroom window but the tree cover and lights made copy not possible. However I will try again later in the week with Spectran running and narrow bandwidth.
23 Feb 2012
Failed cloudbounce 481THz optical test (7.6km)
Possible weak 481THz reception at 7.6km NLOS |
The best I can say is reception was very doubtful: the screen capture above shows a signal at the correct subcarrier frequency in the right direction, but too weak to identify CW characters. The recent 3.6km NLOS test produced good 10dB S/N signals in 0.67Hz bandwidth - much easier.
With a largely clear sky, few clouds and a slight haze, not ideal conditions for cloudbounce testing. This test will be repeated when cloud cover is better and visibility is clearer. QRSS30 would give me another 10dB so this may be worth a go if QRSS3 doesn't work on a second try. There are several variables that make weak signal forward scatter detection difficult: (a) what vertical angle to use at both ends, especially with few clouds (b) amount and height of cloud cover, (c) horizontal direction of aim. With QRSS3/30 modes it is a case of small aiming increments and wait to see if a signal appears on the screen. It is quite hard work.
The result is disappointing, but there will be plenty of other occasions to repeat this test and do others. All good fun.
17 Feb 2012
Optical cloudbouncing (stage 2)
With my QRSS3 success last weekend over a 3.6km non line-of-sight path at 481THz (red light) I've been looking at other possible NLOS cloudbounce paths that start from my home QTH where I can set up my 100mm optics 0.7W input beacon pointing out of a bedroom window.
There are several different paths out to around 8km away that will be tried shortly. I need to do a quick check at the RX locations to see that there are no issues e.g. trees very close and that I can safely park the car off the road at night. The tests can't start for a few days as I have grandchildren with us over the weekend. Maybe the first test will be on Tuesday evening.
There are several different paths out to around 8km away that will be tried shortly. I need to do a quick check at the RX locations to see that there are no issues e.g. trees very close and that I can safely park the car off the road at night. The tests can't start for a few days as I have grandchildren with us over the weekend. Maybe the first test will be on Tuesday evening.
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