Simple local ragchewing rigs

The Sixbox 40mW AM transceiver for 6m. Maybe a Fourbox will follow?

The experiments last week by G6ALB and I confirm that to talk over a few kilometres, very little power is needed. Indeed, below 1mW is all that would be needed on any mode, at least on 144MHz. Andrew and I are now thinking about rigs that we can use to simply keep in touch whilst we get on with other QRP tests on bands from VLF to light. One idea is a 4m version of my Fredbox/Sixbox QRP AM transceivers to be called the Fourbox. This would be extremely simple to build and ideal for communication between a couple of stations in adjacent villages. Activity levels on 4m are not that great so we would be unlikely to suffer much interference issues if a super-regen receiver was used as on the original designs. A simple wire dipole in the loft would be fine for an antenna at each end. At 6m I was able to use T37-6 toroids, but at 70MHz I think these would be just beyond their intended design limits. Small airwound coils would probably be OK.

How little power do you need to communicate?

Last night G6ALB and I did a test on 2m to see how little power was needed to communicate between the two of us. Andrew is 3km from me. We both use V2000 triband vertical antennas. We started the test with Andrew using about 0.5mW pep from a simple DSB rig. We then switched to CW (from a decent low leakage signal generator) and G6ALB reduced power in 10dB steps. The lowest level I could still copy his signal was -55dBm which is around 1.8nW. The screenshot above, taken from Spectran, shows his signal at that level.

This sort of power level could be generated by power harvesting, even rectified RF from the HF antenna. Now there's a thought - a free power TX.

Non line-of-sight optical path profile

This is the path profile of my successful 3.6km QRSS3 cloudbounce non line-of-sight 481THz (red light) test on Feb 12th 2012. Sorry it is in feet and miles. The vertical scale is exaggerated, but it shows how non line-of-sight the path was. I used http://www.heywhatsthat.com/ to produce the data. This is a very useful site.  It is fascinating that such paths can be used successfully for optical frequency communications.

A new MF ham band agreed at last

472-479kHz was officially agreed as a new secondary allocation for radio amateurs at WRC-2012 today.  See http://www.arrl.org/news/amateur-radio-gets-secondary-mf-allocation-at-wrc-12 .

It may be some months, or even a year or so, before the band is available in the UK. I already have kit to use on the new frequencies (my 500kHz tranverter) but may update it with a better antenna and a bit more power.

7kHz doesn't sound much but it is much better than the 3kHz available by NoV around 500kHz currently. Also it is likely to be available in most countries with EIRP somewhere between 1 and 5W depending on footnotes and location.

Simple Home-Built Radio Projects page

The website of Rick Anderson KE3IJ is one of my favorites as it is filled with simple circuits, mainly simple receivers, that can easily be reproduced and that work well. See http://www.ke3ij.com/radios.htm. What I like is that on many pages there are little extra bits of circuitry that can be used in other projects too.  Lke me, Rick loves the humble 2N3904 transistor which is useful from audio to VHF.  They appear all over the place in his novel circuits.

The universal scale of things

http://images.4channel.org/f/src/589217_scale_of_universe_enhanced.swf

This quite wonderful website brings to life the scale of things in our incredible universe from the smallest strings and branes to the largest galaxies and nebulae in the cosmos. And we are somewhere in the middle of all this.  Zoom in both directions (smaller and larger) and be amazed.

Successful non line-of-sight 481THz test tonight by cloudbounce

QRSS3 signal at 3.6km by non line-of-sight cloudbounce

Armed with my simpler QRSS3/CW beacon (see earlier post) I did a very successful non line-of-sight (NLOS) cloudbounce test this evening using my 1W red LED in 100mm optics (run at 340mA). TX was my "G3XBM" message in QRSS3 (3 second dots CW) at 820Hz subcarrier.

With the beacon aiming out through the double glazed shack window at nearby Burwell windmill (as an aiming point) I set off for a road at Landwade which was 3.6km away "over the hill" and on a NLOS path from here. At Landwade I set up the 100mm optics and my variation of the KA7OEI head feeding into my laptop running Spectran. Immediately I got a good signal from the beacon 3.6km away. Signal was around 10dB S/N in 0.67Hz bandwidth. The signal was neither visible as a red glow nor audible in the earpiece despite listening quite hard and panning around for best signal.

This was my first proper NLOS test and it is extremely encouraging. I did try to elevate the RX to higher points in the sky but best reception was with the optics aiming at the lights of Burwell village in the distance i.e. as low as was possible in elevation. At the TX end I was aiming to just clear the slight rise in ground to the east of me near Burwell windmill.

Weather conditions were light patchy low cloud with pretty decent visibility. I did notice QSB as cloud cover varied.

I'm really lucky finding this test path as I can put the TX beacon on the bedroom shack windowsill and fire towards the windmill. In daytime I would be able to align the RX better as I was having to guess the best direction with only Burwell church visible. I had to tweek the alignment to what I thought was the right direction. I did not spend a lot of time trying to peak the signal and better copy is possible.  In all honestly I did not expect this test to be successful.

Simpler 481THz beacon TX

This afternoon I built a simpler CW/QRSS3 beacon for lightbeam experiments. Rather than use a crystal divided down in a 4060 IC I simply used my K1EL keyer IC's sidetone output to drive an IRF640 which drives the 1W LED. 10wpm CW or QRSS3 beacon message is therefore produced on an 800Hz subcarrier. The stability of the sidetone from the PIC keyer is quite sufficient for QRSS3 although not good enough for QRSS30 or 60.

Homemade 45rpm disc recording

Handmade disc recording made on a coffee tin plastic lid

Whilst clearing out a cupboard the other day I chanced upon a piece of my history in the form of a small 45rpm disc recording that an old school friend and I made in 1969. Using an old record turntable with a very large horn as the acoustic microphone we recorded me saying some words and poems onto the polypropylene lid of an old coffee jar. Shouting VERY loudly, the sound is imprinted onto the disc in just the same way old gramophone records were made back in the 1800s. The metal foil inner lids of cocoa tins were also quite good for this as I recall. Francis Wood, my school friend went the whole hog and put the record into a homemade sleeve (with suitable handwritten text) with inner cover and the disc finally inside. I did play this disc some years ago and it was still intelligible (just) but nowadays I have no 45/78rpm kit to play it on. I remember the first time we made such a disc back in 1962 how amazed I was that it worked.

Cambridge Club Talk - a good turn-out

This evening I gave my talk "VLF Amateur Radio" to the CDARC in Cambridge. The turn-out was excellent, especially considering the very cold weather here at the moment. It was -10deg C coming home in the car.  At the end of the talk there were plenty of interesting questions. It was fun to share my enthusiasm for VLF things with such an appreciative audience. Click on the link if you'd like to see a copy of the slides I used this evening.