14.9km on 136kHz QRP (earth electrode antenna)

This morning I did some more tests using my little 136.93kHz 2W QRSS3 beacon feeding into the 20m spaced earth electrodes. The TX end was unchanged, but this time on receive I used my 30t 80cm loop resonated with about 700pF and fed straight into the high impedance input of my E-field probe. Results were as follows:

• At 2.4km good copy by ear (12wpm CW would have been very solid)
• At 8.6km good copy using Spectran
• At 14.9km clear copy of my callsign and locator in QRSS3 with Spectran on the Gog Megog Hills near Cambridge (see screenshot)

All these locations are more or less in the line of the earth electrodes that run NE-SW from the home QTH (JO02dg).  Another RX test some 11km to the south of the QTH  resulted in no visible trace, suggesting the TX earth electrodes are behaving as a loop antenna with some directionality. This was not the case when the same earth electrodes were used at 0.838kHz some weeks ago and when the mode was mainly conduction through buried utilities. Remember, this is ultra simple stuff:

• 2W out crystal controlled QRP 136kHz beacon TX on a 5 x 5cm board (see picture)
• Invisible ground "antenna" that can't be seen, even when a few metres away from it.
• No attempt to match the TX to the earth electrodes.
  
• Simple loop + FET impedance matching circuit and deaf FT817 at the receiver end.

It would be interesting to work out what the ERP must be and interesting to speculate what would happen with such a system at 73kHz. Pity there is no allocation there today.

DK7FC's 6th VLF kite TX experiment

Stefan DK7FC is testing his 600W VLF transmitter into a 200m high kite supported vertical today (Aug 1st). He expects to radiate about 10dB more than in his last test (on 8.97kHz) and may transmit at a slightly lower frequency today (around 6.5kHz) depending on where the antenna is best matched. You can check progress on his grabber at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html .  Results from his last tests were amazing with reception across Europe in DFCW600 mode (dual frequency slow CW). For a summary of the reports (screen grabs) see http://abelian.org/vlf/ss100321/.  To copy his signal you will need a decent low noise/high dynamic range receiver (E-field probe or loop with preamp and filters) at VLF feeding into a PC running a package like Spectrum Lab, Argo or Spectran using narrow 3...5 mHz FFT settings and about 1 minute per pixel running speed. You also need to know precisely where to look, so calibration will be very important.

136kHz QRP QRSS3 beacon video

This is a video showing the 2W QRP beacon for QRSS3 on 136.93kHz. Using a 20m spaced earth electrode transmit "antenna" it has been copied 8.6km away using an E-field probe antenna.

2696km on 10GHz - new record

A new DX record for terrestrial (non EME) communication has been set with a QSO between D44 and CT on July 10th over an incredible 2696km. See http://www.hyperatlantica.ch/ for more information.

136kHz with QRP and earth electrode antenna

Today I increased the power from my QRSS3 136.93kHz beacon to 2W out of the PA into the 20m spaced earth electrodes. Another "ride about" test locally with the deaf FT817 and E-field probe RX antenna gave the following results:

At 2.4km good copy on the Spectran display

At 4.6km clear copy on the Spectran display.

At 8.6km the signal was detectable, but weak (see picture attached from Spectran screen).

These reports are roughly "end on" to the electrodes and I've yet to try other directions such as orthogonal to them. No attempt was made to match the PA output to the impedance presented by the earth electrodes which are around 40-60 ohms below 10kHz; I've not measured it at 136kHz yet.

Even with true QRP it looks like a range of at least 10km should be possible on QRSS3 (and probably WSPR) with a half decent receiver (better than my crude set-up) using just a 20m earth electrode TX antenna on 136kHz.  I'll leave the QRSS3 beacon running over the weekend on 136.93kHz from my QTH in Burwell, Cambs (JO02dg) and any reports and screen shots would be much appreciated.

Class E MOSFET PA for 136kHz

I'm trying to optimise an IRF510 MOSFET PA for use in the 136kHz beacon and later transverter design. Alan Melia G3NYK has a very useful page on practical approaches to class E designs for 136kHz at his page http://www.alan.melia.btinternet.co.uk/classepa.htm together with a useful Excel worksheet to come up with practical values for the output network. Class E using square wave drive on the input can produce very good efficiencies, thereby reducing heatsink requirements.

136kHz PA progress

Today I started to modify my 136kHz QRP beacon to increase the power from 250mW to around 5W using an IRF510 MOSFET PA. I've still work to do to optimise the design but hope to complete this tomorrow.

More on time travel

A rather long, but fascinating article on the possibilities and issues with time travel is on Wikipedia.

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 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

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?