PS: Forgot to mention that you may also need to consider directivity: The broadcast station used for the measurement should preferably be close to one of the main lobes (ie NE or SW). If there is significant deviation, you could either correct the measurement using the cosine of the azimuth difference, or simply orient the reference loop the same way as your ground antenna.

 

73, Markus  

From: Markus Vester

Sent: Saturday, September 20, 2014 9:25 AM

To: [email protected]

Subject: Re: LF: DX with 472 kHz, earth electrode antenna, 25 Watts output :-)

Hi Piotr,

 

congratulations on those results from your ground dipole!

 

In my opinion, it is somewhat difficult to estimate ERP directly from WSPR SNR figures, because the variations in skywave sttenuation and receiver noise floor are difficult to predict. I would probably go about it by using a receiver to measure the effective loop area Aeff of the ground dipole. This can be done with some broadcast station in the lower medium wave band, comparing receive level with that from a simple nonresonant loop with eg. 1 square meter. Only the voltage ratio (dB difference) is required so you don't need an absolutely calibrated receiver. Thus

 

 Aeff = voltage on ground antenna / voltage on reference loop * 1 m^2

 

If the frequency of the used broadcast station was significantly higher than your transmit frequency, you can make a correction for the increased skin depth:

 

 Aeff' = Aeff * sqrt (f_broadcast / f_amateur)

 

Then, during your transmissions you'll only need to measure the current to your ground antenna, and calculate ERP as

 

 ERP = 1.83 * 62342 ohms * Aeff'^2 / lambda^4 * current^2

 

Best 73,

Markus (DF6NM)

 

From: Piotr Herko

Sent: Saturday, September 20, 2014 8:32 AM

To: [email protected]

Subject: LF: DX with 472 kHz, earth electrode antenna, 25 Watts output :-)

Hi,

I reached OH8HTG WSPR,  1414,  km with my earth electrode antenna! TX is M1GEO project, DDS RN3AUS, electrodes are 20 meters apart. Antenna is directly connected to 50 ohm tx filter with serial 2,2 nF capacitor. SWR is about 1,1 to 1.4 according to weather. Direction of the antenna is NE, 50 deg.

So far my WSPR was received in DL, OK, OE corner by DH5RAE,  DJ0ABR and  DC1RJJ, about 650 km far. Also closer by SP2OVY and SQ5KLN.

Who can help me estimate EIRP power? I declare now in WSPR beacon 5 mW.

2014-09-20 02:14	SP5XSB	0.475636	-30	0	KO02ld	0.005	OH8HTG	KP34	1414	12
2014-09-20 02:12	DK7FC	0.475684	-9	0	JN49ik	1	SP5XSB	KO02ld	911	66
2014-09-20 02:06	SP5XSB	0.475636	-33	0	KO02ld	0.005	OH8HTG	KP34	1414	12

Piotrek, sp5xsb