Before the end of the weekend I intend,weather permitting, to make changes to my small 500kHz antenna. These changes will be:
Mike Rainey AA1TJ has pushed his DX up to 1329kms on 80m using his Code Talker TX (see left) which uses only the energy derived by shouting into a loudspeaker to power the transmitter - no external DC power sources at all. He worked W4OP at 0133z. Just visible is the tin can used to focus the shouts into the LS cone! I am beginning to think Mike will work some serious DXCC countries in the years to come using his "voice powered" TX. Imagine this rig into a beam on 10m when the sunspots are high.
We have two lovely grandsons. This is a picture taken last month when they both came to stay for a few days.
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
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!
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.
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.
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.
