500kHz improvements - summarised

The spiral top-hat on the 500kHz antenna.

Since first putting a signal out on 500kHz a few months ago, I believe the ERP has increased by about 18dB. These steps were:

• Initial PA 500-700mW (0dB reference)
• PA output increased to 5W (+10dB)
• Additional grounds added (+2dB)
• Antenna spiral top hat added (+6dB)

No further changes are planned as I am close to fulfilling my original objectives of seeing how effective a small and simple QRP 500kHz station could be. The two remaining goals are to get reports from Germany and Sweden.

After that, it will be farewell to 500kHz and welcome to the next challenge!

ERP increased on 500kHz (6dB up)

Today I modified my 500kHz antenna introducing a spiral inductance/ top capacity hat consisting of around around 8 "spiralling in" turns in the space occupied by the original 28MHz halo. Seeing my initial reports from M0BMU I am some 5-6dB stronger than I was before, I guess because more of the antenna current is in the 6m long vertical section.

Three new 500kHz reports overnight: F4DTL, PA0AM and G4CAO. The improved antenna efficiency is definitely helping. Also my strongest report yet from GM4SLV.

Top Band WSPR

This evening I moved from 500kHz to 160m to see if I could improve my WSPR DX on topband. At first try, GM4SLV heard me up in the Shetlands. As for 500kHz, my ERP will be considerably lower as I am only using a short 5m long vertical tuned with a ferrite rod ATU. See John's screenshot, that also shows some digital QRM on the same frequency. At 2116z John was copying me on 160m when I was running just 100mW from the TX.

24 stations hearing me on 500kHz

This evening I received a WSPR spot report from F4EMV who is 433kms to the south of me. Yesterday I had one from F0DVZ. This brings the number of different stations reporting my signals on 500kHz to 24 (22 on the WSPR database and 2 others).

Planned 500kHz antenna changes

Before the end of the weekend I intend,weather permitting, to make changes to my small 500kHz antenna. These changes will be:

1. The 28MHz halo and 6m long feeder will be replaced by a spiral top capacity hat and a slightly longer vertical wire. The effect should be to increase the effective height of the antenna a bit.
   
2. Move my TV antenna away from the pole carrying the 500kHz wire. At the moment this is on the same pole, so is probably absorbing energy.
   

Taken together, I expect another 2-3dB improvement in antenna current and ERP. If these improvements work I'll give it an "on-air" test for a week or so. After this, I'm not planning any further 500kHz improvements as I'll have run out of "keep it simple" options.

More voice powered DX in the USA

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.

Mike tells me he is having a go at a 20m version now.

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!