481THz AM transmitter

This morning I took a step further towards making a complete 481THz lightbeam transceiver by breadboarding and testing a simple AM transmitter for use with a high brightness red LED. The circuit could hardly be simpler but works very well. The bias on TR2 is adjusted to give around mid-rail so the LED has a standing bias before audio is applied. Listening (without optics) on my modified KA7OEI receiver head and looking on a scope, the modulation looks good with around 150mA current into the LED.

Dual band 10m/6m halo erected

10m and 6m nested wire halos on the mast

The Homebase-10 halo is now a Homebase-10/6 with a second dipole within the first covering the lower part of 50MHz. After just minor adjustment both bands have a near unity VSWR over the parts of the bands where there is CW/DATA/SSB activity.

Since making the changes I have exchanged 5W WSPR reports with FR1GZ  on 10m, and got -19dB S/N on 10m WSPR from CX2ABP (11127km), so that is still working as before. I have yet to work something on 6m to be able to judge the omni-directivity of the 6m halo.

Dimensions for the inner 6m dipole were simply scaled down from the values at 10m: the outer sections are 564mm long and the folded dipole inner section 873mm long (these are the dimensions each side of the feed point). A single 50 ohm RG58 coax feeds both 10m and 6m sections.

Details of the original Homebase-10 were in my Practical Wireless article a few years ago and also on my webpage at https://sites.google.com/site/g3xbmqrp/Home/homebase10 .

Optical DXing and refraction

Although my own experiments at 481THz have so far been limited to around 9km non line-of-sight, the amateur experts around the world have been achieving remarkable ranges both line-of-sight (LOS) and over the horizon (NLOS). In the UK several groups are looking for longer line-of-sight paths up to around 147km.

Some interesting information is coming to light (no pun intended) about the refractive index of the lower atmosphere at optical frequencies. At radio frequencies the refractive index (K) is around 1.33 and I had always assumed that for lightwaves it was just over 1. But tests suggest this is NOT the case at lower levels such as over the near line-of-sight paths now being attempted. A recent paper by Barry Chambers G8ACN on the UKNanowaves Yahoo group suggests a much higher figure may be more appropriate for a lot of the time meaning that what may appear to be a non line-of-sight path actually is one. He cites some observations by G8CYW and others of distant factory chimneys and cooling towers that should not be visible over the distant horizon but frequently are clearly visible.

Many are familiar with optical mirages, but the fact that the optical refractive index is frequently in the 1.1-1.33 range surprises me. It suggests many more distant optical paths may be workable with suitable equipment than was previously thought possible without having to resort to clear air scattering or cloudbounce. With 481THz cloudbounce and clear air scattering the additional path loss (compared with a LOS path) can be in the 30-50dB range, so equipment for NLOS paths is much more demanding than for a quasi line-of-sight path.

May Projects

All being well I have a window of a few weeks before visiting grandchildren and the like, so I have a couple of new aims:

(1) Convert the 10m halo to a dual band 10m/6m halo
This should be a fairly easy task as I already have dimensions for the 6m halo and I've air tested it in the loft. All that should be necessary is to take down the 10m halo and change the feed and support arrangements so both the 10m and 6m halos are fed from the same coax. The pair of halos well clear in the air should prove an effective QRP antenna system for my 2 favourite bands.

(2) Complete my first optical speech transceiver
Strange though this is, I have made several quite sensitive optical receivers and a couple of reasonable power QRSS3 and CW optical beacons, but I've still not got around to making a complete optical speech transceiver. Locals hereabouts use baseband audio for TX, so this is what I should do if I want to work people like Bernie G4HJW. It would be good to get a few line-of-sight short range (up to around 10-15km) 481THz QSOs in the log-book soon. Based on my optical work so far this is not a difficult task, just one I need to crack on with.

Target for both projects is within 2 weeks i.e. by May 17th. We'll see.

New Granddaughter

Our granddaughter - just a few hours old

Not much amateur radio here these last few days as we've been to stay in Kent welcoming our newest grandchild into the world. She is our fourth grandchild. Mother and baby doing well. Not sure if I'll manage to get her interested in our hobby, but her brother is very keen on batteries and screwdrivers at the age of 3, so there is some hope there.

More 10m DX and some Es

500mW 10m WSPR results - ZS6BIM best DX

Today I ran my 10m WSPR beacon at 500mW into the wire halo antenna. Conditions were quite reasonable with some good DX reports. Later there was a first sign of sporadic-E propagation around Europe - a sign of things to come for the next few months. I did try beaconing at 50mW for a little while but propagation had deteriorated so no reports were received this time.

Amateur radio history DVD?

The ARRL has produced a DVD recently on the history of amateur radio in the USA over the last 50-60 years. See http://www.arrl.org/shop/The-ARRL-Film-Collection/ .  I wonder how much material exists on old film and video in the UK/Europe and whether there would be enough to make a DVD on the history of amateur radio on this side of the pond?

As I mentioned a few years ago, there was (once) a 78rpm sound disc made by G5UM of the last night of UK operation on the old 56MHz band back in the 1940s, but this appears to have been lost. Although there have been several books on the early history it would be wonderful to find and collate old film material on amateur radio in Europe.

Win XP PC - a full restore?

My main Windows XP laptop PC is now around 6 years old. It has a small 32GB hard drive and my own files occupy around 8GB of this, yet the PC says the C drive has only 3.8GB spare. There is a small back-up partition (about 3GB) and the rest must be program files and Microsoft bloat accumulated over the years. I've already done defrags several times and deleted all the files I know are safe to delete. CCleaner is also regularly run to sort out registry issues and I have compressed files where possible. McAfree anti-virus seems to do a decent job of keeping out the malware.

Although I hope to invest in a new PC soon, I'm considering doing a full system restore back to original factory settings in the hope of recovering all the lost/wasted space.  A full restore will need a few days of work to reload updates (SP2/3 etc) but there must be a lot of unnecessary rubbish there which would be cleared by a full restore.

My plan is to use this "old" PC to run WSPR and some VLF programmes and use a new PC for everyday tasks.

Apart from the usual back-up of any photos and data that are important, does anyone have any advice before I go ahead?

Better 10m conditions

Today I put my 5W 10m WSPR beacon on for a few hours during the day and was rewarded with reports from CX, PY, 5Z4, 4X, LB and G stations. Conditions appeared better than I have noticed in some while and this is proved by a look at recent sunspot activity. See http://www.solen.info/solar/ .

Google Drive (bye bye Dropbox issues)

With the introduction of Google Drive, an online storage facility, I can at last overcome my issues with Dropbox and my VLF grabber. With Google Drive one can store up to 5GB free and more for a fixed price. With the PC or Mac add-on, the drive appears as a file(s) on the computer into which documents can be saved in the normal way. These then appear/sync on any PCs when you sign in to Google Drive.

The bonus is that you can make any file public and get a URL that others can go to. This means that a saved .jpg screen shot of a VLF grabber can be saved to a unique filename on the PC which then is visible to the world if they know the URL. From a webpage I can point people to the URL and they can see the screen grab as it is updated regularly.

I could do all this with Dropbox until about 4 months ago when it started playing silly and refused to sync on my WinXP PC complaining of a registry issue. Despite trying all sorts of recommended fixes none worked and I gave up on Dropbox.

In the coming weeks I will be mounting a more permanent E-field probe which will be connected to the PC whenever it is running and the VLF spectrum view(s) will be available on my sub-9kHz website.