Monday nights at 8pm on 144.575MHz FM

Every Monday evening a number of East Cambridgeshire locals get together on 144.575MHz FM for an hour between 8-9pm clock time. The usual stations on the net are G6ALB, G3KKD, G4NUA, M3YPZ and G3XBM.

Originally this started as a regular session between G6ALB and G3XBM on 144.55MHz AM. We managed to engage in some sort of QRP related experiment most weeks. We've worked each other on all bands from 1.8-432MHz with extreme QRP and had 1-way contacts on 8.97kHz, 136kHz and 500kHz QRP too. We are 3km apart, which is an ideal distance to try all sorts of things from listening to each other on crystal sets to trying to see how weak a signal can be copied on each band: you may be surprised how little signal can be copied at this range: it is no wonder we suffer from so much interference on HF these days as nanowatts go a long way.

These days the net conversations cover all manner of subjects but, sadly, Andrew G6ALB and I don't get to do experiments so often: this is a drawback of a larger net. At some point I think Andrew and I will find another spot to do experiments on another evening whilst letting the Monday net continue as it is. It is fun to simply chat.

Let me share a pearl from this evening:  Alex M3YPZ, who has a truly fascinating background going back to working on radar in WW2 and research in Cambridge University, mentioned he had a book on how to improve his memory.  He lent it to someone   ....but could not remember who.  The joys of getting a bit older!

If you are the area feel free to call in to the net.

10m across the pond

Late this afternoon I was very surprised when my 5W to the halo was spotted on 10m WSPR by K9AN 6505km west of me. It is unusual, I think, to get 10m transatlantic propagation at this time of the year by F2, so wonder if this was Es propagation? There were quite strong PY stations coming through earlier, so it could be F2 back-scatter. Incidentally, 4X1RF and I seem to have a pipe between us on 10m: we WSPR spot each other most days and I often copy him when his beacon is running 50mW.

Further to my earlier post, WSPR allows one to do "gentleman's DXing": you can see how far your signal is reaching whilst running QRP and a simple antenna and still do other things in the shack at the same time. Perfect.

DX Chasing (no thanks)

Chasing DX is just not my thing any more. For example, on 10m CW this afternoon there was one heck of a pileup of stations trying to work 7O6T in Yemen. This is a rare country but those who get through tend to be the stations with the BIG beams, high power and who call and call. Occasionally, a QRP station with good skills can manage it. On rare occasions I have found DX before the pileups or the DX cluster shows it's there and then a QSO is possible.

But basically I am past this stage in the hobby now. I prefer to explore new things, experiment and have fun. I know that if I had 400W+  and a big beam up high I could work the world if I was patient, but having amassed well over 100 countries worked with 5W SSB/CW it matters not to me that I don't work that rare DX.

On VHF and UHF it can still be fun though, and counting squares is still my answer to train spotting, HI.

AM lightbeaming down the street

With my wife manning the TX this afternoon and pointing it out of the landing window we managed a daylight speech test today with 100mm optics at both ends at 0.3km using the v.simple AM lightbeam TX described in the previous post. The LED was run with an 80mA standing current. Biggest problem was aligning the TX beam and the lack of talkback, but I managed to get 59+ copy of my wife saying, "I'm bored with this. Come home and have some tea" when I was aligned on the TX beam.

There is no doubt the simple circuit can be refined to improve audio quality when clipping, but it works. The RX is far more sensitive at night too.  I am now finding a way of replacing the XYL for these tests by using another source of speech such as a radio receiver or MP3 player. She is good at cooking and other things, but not at doing optical tests!

Later this week I'll begin experiments with a simple single LED AM 481THz transceiver.

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.