Optical communications in the 19th century

With the recent upsurge in interest in long range optical communications it is easy to forget that optical data communications over long distances predates radio communications by many years. In those far-off days the data was morse code and the light came from the sun in the form of a heliograph mirror that reflected the sun's rays over long distances in daylight. Keying was usually by tilting the mirror or  by keying a grill placed in front of the mirror. See http://www.modulatedlight.org/Modulated_Light_DX/Heliograph.html . Best DX achieved in the 19th century was well over 200km using these methods!

Infra-red "over the horizon" tests?

Reading Stuart G8CYW's article on the history of optical communications in the latest RadCom, I am considering repeating my recent NLOS optical test using infra-red (IR) rather than visible light as there may be some advantages with clear air forward scatter propagation by going to lower near optical frequencies. At least IR beams are not visible to the casual viewer, so are less likely to create problems.  However, IR can be more dangerous than visible light because the blink reaction that occurs with visible light does not happen. When using high power IR LEDs it is therefore even more important not to look into the beam and to take care where the beam is aimed, especially at close range. Never ever look into the beam at close range.

A suitable IR PIN diode is the SRH203-FA from Osram, widely available on eBay.  As you can see from the image, the PIN diode detector has IR filtering (black colour) , so may be usable in daylight with less degradation than would be the case with red LEDs.  I already use the SRH213 PIN diode for visible red optical comms.

I am looking for a suitable 1W-3W IR LED and they are available, but I have yet to find one in the 10mm "fat" standard LED package that I use currently on 481THz.

There are 3W IR LEDs available from China that should be suitable. See eBay item 370784927290 for example in the star package. This would be some 10dB more output than I currently use, although I am not sure of the beam divergence which may be greater than with the 10mm package.

Nanowave over-the-horizon experiments are very much like microwaves, except that the test equipment is a GREAT deal simpler!

13.8V distribution board

http://www.hamradio.co.uk/sysimages/origimages/PW-100-1_pr5198_1.jpg

If you are like me, you'll have several pieces of equipment in the shack that run off 12-13.8V supplies and only one PSU that is used for everything.  This results in a very untidy arrangement.

I see that Martin Lynch sell a Mydel PW-100 4-way distribution board with fuses on each output. Although a similar unit could easily be built, this is not a bad price for a ready-made unit complete with spare connectors at around 30 pounds.

When arranging my new shack I shall have to either buy one of these or make up something similar.

A walk in the sunshine with the Ventus GPS tracker

As the weather was so beautiful this afternoon (full sun and around 13 deg C) I decided to do a country walk and track my progress using the Ventus GPS data logger bought from Martin Lynch and Sons.  The walk was 10.7km and took about 2hrs 34 minutes with a couple of relaxing breaks for a drink and a snack.  No ham radio gear was taken this time, because I forgot to charge up my VX2 handheld. Next time, HI.  Incidentally Quy was where my optical beacon reached (over the horizon) a few weeks ago. When you walk that far it seems a VERY long way away!

This is a plot of the walk taken with the low cost GPS tracker  then plotted with Google Earth.

Today's walk in the Cambridgeshire countryside

My wife's choral concert next weekend in Cambridge

Concert Poster

My wife sings with the Cambridgeshire Choral Society (guess who does their website!) and next weekend (Sat April 27th 8pm) her choir performs in St John's College Chapel in Cambridge. Both the Vivaldi Gloria and the Faure Requiem are great pieces. If you live in the area, may I suggest you come along? Tickets are available on the door as well as in advance (see poster).  I shall be on the door acting as a steward.

Loopy on 10m - first results

This afternoon I managed to catch 10m open and got some excellent spots from 4X1RF with reports as good as -5dB S/N using 2.5W to the small magnetic loop taped to the chair in the bedroom shack. Without doing too scientific a test, the impression I get is the loop is every bit as good as the external longwire end-fed antenna in the garden.

I may move the magnetic loop up into the loft in the coming days to see how it performs there, pre-tuned to the WSPR frequency. Based on results in the bedroom, I would expect it to work well.

VHF/UHF take-off at new QTH

This evening I went up to our new, well being newly renovated, bungalow on top of our local "hill" immediately next to the Burwell windmill.

Currently the roof is being re-tiled and there was scaffolding everywhere, so I took the opportunity to climb up a ladder to the roof level to judge the VHF/UHF take-off.

Well, the good news is that even at just above the gutter level there is an excellent virtually unbroken (clear of houses) take-off from the north west all the way around to the south. With an antenna a few metres above the roof apex height, it should have a pretty good take-off in most directions.  It just begs me to get some better gear for the 2m, 70cm and possibly 23cm and 3cm bands. We'll see.

I was also checking out optical communications possibilities. At lower heights, the horizon view is obstructed, but I should be able to arrange my optical beacon for cloud-bounce and clear air forward scatter, non line-of-sight, tests with the beacon firing up at around 20 degrees up from horizontal in many directions out towards Cambridge and beyond.

Loopy results on 15m

WSPR results today with 2.5W to 80cm loop in the bedroom on 15m

Well never mind the theory - my loop WORKS well. On 15m, with the loop taped to the chair in the bedroom shack, I have already been spotted on WSPR in Japan when using just 2.5W from the FT817 at  9474km.  So, my first attempt with an indoor HF magnetic loop in the bedroom has left me very impressed.

Loop antenna in the bedroom (notice the grandchildren's toys!)

Current set-up is about 80cm diameter 6mm copper pipe inductor tuned with a small 365pF air spaced variable cap. Matched with a coupling loop 1/5 the size of the main loop made with RG58 coax. With the 365pF variable it tunes from 40m-10m, but the variable cap needs padding out as tuning is extremely sharp.

I should have tried magnetic HF loops long ago.

UPDATE 1600: Just QSYed to 14MHz with the loop in the bedroom and power reduced to 500mW and still getting plenty of WSPR reports out to 2600km or so so far.

Going loopy on 10m

Prototype 10m TX loop using 6mm copper pipe

Today I've made a small TX loop for 28MHz CW/WSPR using an odd piece of 6mm copper pipe I had around the place. As I don't want to move the frequency much and the maximum power out will be 5W (usually far less) I have used a small length of twin core mains cable, trimmed to resonance, as the capacitor to resonate the antenna. The loop is matched to 50 ohms with a small coupling loop made out of RG58 coax. Bandwidth is quite sharp suggesting the loop is working as expected.  At the time of writing (early evening)  I've only copied one signal EK6RSC at 3586km earlier in the day and am still awaiting some reports on TX. The loop is mounted on a PVC pipe taped to the back of a chair in the shack.

If successful, the idea will be to put this up in the loft at the new bungalow and use it with WISPY and a small dedicated netbook PC to run 10m WSPR.

Simple, fool proof 1296MHz transverter?

Thinking about my new QTH on top of our East Anglia "hill" (aka 20m bump) I am wondering if I should consider 1296MHz operation for the first time, if only to monitor/try the band in UKAC contests with relatively local stations. Although I have listened (briefly) on 23cm years ago with a borrowed RX converter, I've never transmitted on the band with any mode.

What I am looking for is a SIMPLE transverter for the band, either a no-tune kit or a simple ready built unit. I have no test gear for this band, which is why I've not really considered the band before. The driver would be the FT817, so any suitable band could be used for the IF.

The Down East Microwave 1296MHz transverter may be a possibility. See http://croatia-microwave.blogspot.co.uk/2010/12/w1ghz-rover-transverter-for-1296-mhz.html for a report of one built.

Incidentally I remember the 23cm antenna I used back in the 1970s with the borrowed converter: it was a 4 element yagi made with 2.5mm silver plated wire. The whole antenna sat in the palm of the hand, but worked well, even indoors mounted on a piece of bamboo cane as the mast! If I remember correctly, the design was in an early edition of VHF Communications, a magazine I subscribed to back in the 1970s.