Optical DXing - mirages

Andy Young has an excellent page about optical mirages which is worth reading. Land has been seen hundreds of kms over the horizon as a result of this phenomenon. Indeed there is some evidence that the discovery of Greenland may have been as a result of a mirage off the coast of Iceland. I'm not aware of radio amateurs exploiting fleeting mirages for optical frequency laser DXing.

Our grandchildren

We have two lovely grandsons. This is a picture taken last month when they both came to stay for a few days.

New 500kHz ERP calculation

Some weeks ago Jim Moritz M0BMU made an estimate of my 500kHz ERP based on received signal strength levels at his QTH 69kms away. As I've recently increased my ERP, I asked Jim if he would kindly do a recalculation. These are his latest estimates.

Well, repeating the original calculation, taking your "best" signal level as -12dB on a noise level estimated at 3uV/m in 2.5kHz, your received field strength at my QTH is 0.75uV/m. At a distance of 69km, and assuming only "geometric spreading" propagation losses (i.e. an inverse relation between FS and distance), your ERP is

ERP = (Ed)^2 / 49 , with E = 0.75u, d = 69000, ERP = 55uW

Then we have to consider what additional propagation losses exist; originally I suggested 3dB, which would increase the ERP to 110uW. However, looking at G4FGQ's grndwav4 program, and the ground resistivity around this area, the "ground type" in the program might be 6 - 8, making the ground wave propagation losses between 4.2 and 8.5dB. This would make the ERP between about 140uW and 390uW.

Obviously there is a lot of uncertainty in this kind of estimate - the two main things are the possible variability in noise levels between when I estimated the noise level and now, and the propagation losses. Both these could contribute several dB variation, so the ERP estimate should only be regarded as "order of magnitude" accuracy.

Still, your signal is certainly much stronger now - one of my nearer-term projects is to make some more accurate FS measurements by injecting a calibration WSPR signal into the loop antenna, which should give a more direct and accurate measurement of the signal levels.

Cheers, Jim Moritz
73 de M0BMU

500kHz - two new reports and a new country

M0DUO (104kms away) spotted my 500kHz WSPR beacon late this evening. Then in the middle of the night my first report from The Netherlands from PA3FNY (JO22nc at 330kms). So, 22 different reports in 11 grid squares and 5 countries with best DX remaining 896kms. Not bad for a 6m long antenna and less than 1mW ERP!

AA1TJ's Code Talker TX

Mike Rainey has now added a schematic to his page on the New England Code Talker CW transmitter powered and keyed only by audio derived from his whistling into a loudspeaker. Mike is hoping to span the Atlantic with a similar TX on one of the HF bands in the years to come, knowing that others have "crossed the pond" with powers as low as 1mW or less when conditions were very good.

LC Meter - a nice kit

Some months ago I bought a PIC based LC meter kit from the Cambridge Radio Club (CDARC). This was a club project and the unit allows very accurate measurements. The kit had remained unbuilt until today when I decided to build it. I'm impressed: it went together well and worked first time. The quality of the kit is first class with a custom case, silk screened PCB and good instructions on the club website. This little box will measure from low pF and nH right through to uF and mH. I can see it being used almost daily. I believe CDARC is to make these kits available more widely. Go and buy one for £50.

20th station hears me on 500kHz

Last night M0WKR (IO94 at 237kms) reported my 500kHz WSPR beacon bringing the total number of unique reporters up to twenty.

The 500kHz ATU

This is a close up picture of my 500kHz ATU which consists of a ferrite rod with thin copper wire tapped at various points to which the antenna and TX are connected. The TX connection is about 5t from the ground end. Also in view are the current transformer (the small toroid with 50 turns secondary) and the small meter used to measure the antenna current.

AA1TJ's "Code Talker TX" - all voice powered

Mike Rainey continues his work on purely voice powered transmitters, in which just the energy in his voice is used to power the RF circuits i.e. no batteries or PSUs at all. He's achieved well over 100kms on 80m this way using a form of CW derived by whistling into a loudspeaker to generate the energy needed. Here is an example of his signal received 109kms away. He can clearly be heard "keying" (actually whistling!) the words of "Mary had a little lamb" in CW.

A good evening on 500kHz QRPp

This evening my 500kHz WSPR beacon has been running from 1700-2300z, still with less than 1mW ERP. As the map shows, this is not preventing 8 stations in 4 countries copying me and many at considerable distance. There has been some transatlantic propagation this evening with SM6BHZ and OR7T being copied in Canada already. These are distances I can only dream of with my tiny station!