29 Jul 2010
More on time travel
A rather long, but fascinating article on the possibilities and issues with time travel is on Wikipedia.
Labels:
paradox,
quantum,
time travel
28 Jul 2010
Quantum time machine?
Researchers at MIT may have come up with a way of travelling through time (and space) using quantum closed timeline curves or CTCs. It has always fascinated me that in quantum mechanics one can describe things as wave functions that have existed in all space and all time, past present and future. It takes a leap of imagination to consider the possibilities. For an explanation see http://www.telegraph.co.uk/science/7904712/Quantum-time-machine-allows-paradox-free-time-travel.html
This is the abstract of the original MIT paper:
This is the abstract of the original MIT paper:
"This paper discusses the quantum mechanics of closed timelike curves (CTC) and of other potential methods for time travel. We analyze a specific proposal for such quantum time travel, the quantum description of CTCs based on post-selected teleportation (P-CTCs). We compare the theory of P-CTCs to previously proposed quantum theories of time travel: the theory is physically inequivalent to Deutsch's theory of CTCs, but it is consistent with path-integral approaches (which are the best suited for analyzing quantum field theory in curved spacetime). We derive the dynamical equations that a chronology-respecting system interacting with a CTC will experience. We discuss the possibility of time travel in the absence of general relativistic closed timelike curves, and investigate the implications of P-CTCs for enhancing the power of computation."Simple ??? See http://arxiv.org/abs/1007.2615
Labels:
quantum,
quantum mechanics,
quantum theory,
time travel
25 Jul 2010
136khz transverter
I'm getting ideas, and parts, together to allow me to build a small transverter for 136kHz. For the TX low pass filter I'll use either T68-2 or T157-2 (or something on between) toroids as these seem most suitable at up to 30W. For the RX input tuned circuit I still need to find a suitable inductor, preferably tunable. Any ideas?
Labels:
136khz,
qrp,
transverter
24 Jul 2010
Further 136kHz earth electrode tests
Later today I hope to do some more tests on 136kHz using 250mW QRP to the earth electrode "antenna". Last night I went out to look for the QRSS3 signal locally but realised the battery in my E-field probe was flat, so heard and saw nothing! I expect to see the signal to well beyond 5km.
UPDATE: Well a repeat of the test on July 19th gave less encouraging results. Reasonable copy on QRSS3 at 1.5km but no copy visible at the same spot 4.6km away from the QTH (within 20m). Not sure what has changed as the earth electrodes are the same. Maybe the soil is slightly more damp?
UPDATE: Well a repeat of the test on July 19th gave less encouraging results. Reasonable copy on QRSS3 at 1.5km but no copy visible at the same spot 4.6km away from the QTH (within 20m). Not sure what has changed as the earth electrodes are the same. Maybe the soil is slightly more damp?
Labels:
136khz
PW author Gordon King G4VFV now silent key
Practical Wireless author Gordon King G4VFV died yesterday from stomach cancer. Gordon wrote many radio and TV related books and contributed regularly to PW. He lived in Brixham, Devon.
Labels:
g4vfv
20 Jul 2010
Parts from Farnell - good service
For the first time I ordered parts from Farnell on-line yesterday. In the order were some 3C90 toroids (16mm and 42mm) to use in my 136kHz transverter. I cannot fault the service: parts were here the next morning with free delivery. Just remember the prices on the internet are shown less VAT. For on-line orders there is no minimum order quantity.
19 Jul 2010
4.6kms with earth electrode "antenna" and 250mW on 136kHz
Today I tried some more experiments with my 20m spaced earth electrode "antenna" and small QRP beacon TX on 136kHz. I switched over to QRSS3 and used the FT817, E-field probe and PC with Spectran to see where copy stopped. 1.5km from home and solid copy on QRSS3 when holding the E-field probe box as high as possible above the car roof. Then I drove on to a spot 4.6km from home and copy was again achieved, albeit not as strongly. I'm certainly getting a signal radiated beyond the near field. I'd like to check "antenna" directionality by looking for signal levels with the QRSS3 beacon at all compass points some 4-5kms away from the QTH.
In the meantime, if anyone near Burwell, Cambs wants to look for the QRSS3 signal near 136.93kHz I'll leave it running until about 8pm tonight when I have to switch off as my grandson is sleeping in the shack bedroom. Any reports would be amazing.
In the meantime, if anyone near Burwell, Cambs wants to look for the QRSS3 signal near 136.93kHz I'll leave it running until about 8pm tonight when I have to switch off as my grandson is sleeping in the shack bedroom. Any reports would be amazing.
18 Jul 2010
Simple 136kHz beacon TX
Francis F6HSI very kindly sent me a "divide by 26" module based on a small micro-controller. With this I've built a small beacon transmitter for 136kHz (QRSS3 or 10wpm CW) by dividing down from 3560kHz, the QRP calling frequency on 80m. At the moment it only puts out 250mW and, with the earth electrode "antenna" used, the ERP probably considerably below 1uW.
Using my 20m spaced earth electrode "antenna" on TX and with a PA0RDT designed active antenna with a 19 inch whip antenna feeding into the (deaf) FT817 I could copy the 10wpm CW at 0.4km across the fields.
Using my 20m spaced earth electrode "antenna" on TX and with a PA0RDT designed active antenna with a 19 inch whip antenna feeding into the (deaf) FT817 I could copy the 10wpm CW at 0.4km across the fields.
17 Jul 2010
New VLF DX record today: 5.6km on 838Hz earth mode
Today I resumed my VLF earth mode tests using 4W into 20m spaced earth electrodes. The aim of the test today was to determine the absolute maximum range possible by utilities assisted earth mode. Best result was 5.6km along Commissioner's Fen to the west of Burwell. Signals were just copied at this distance using the 80cm 30 turn loop and preamp into the PC running Spectran. A test a 6km resulted in no detectable signal.
Labels:
earth mode,
vlf
An amateur solar plane "satellite"?
Recently, Qinetic managed to keep a solar power plane aloft for 7 days using its onboard navigation to keep it over a fixed location and using solar cells to top up batteries to keep it flying at night. Could such solar powered flying devices could be used as "satellites" flying a few miles above the earth to support amateur VHF/UHF repeaters and experiments i.e. a more sophisticated version of balloon experiments? See http://www.bbc.co.uk/news/science-environment-10664362 .
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