Hi Roger you can calibrate your loop first using DCF39 on 138.83. This has a
field strength in our area of 1mV/m. Then you could work back your own ERP
by comparison...... 1W ERP produces 300mV/m at 1km, 100mV/m at 10km (from
memory ....I think that is correct....10dB per decade after 1km).  Doing it
that way removes as lot of the variables, and its a good thumbnail
calculation.

Alan G3NYK

----- Original Message ----- 
From: "Roger Lapthorn" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Tuesday, August 10, 2010 7:09 PM
Subject: LF: 136kHz ERP calculation


> *My last post didn't appear, so this is a retry...*
>
> About a week ago I recorded my 136kHz QRP beacon (2W from PA, QRSS3, using
> just 20m separated earth electrodes as the antenna) at 14.9km away from
the
> QTH using Spectran with a 30t, 80cm loop, Hi-Z matching into the FT817.
>
> I'm wondering if someone here is able to *work out the ERP* that I must be
> achieving please. These are the numbers I have:
>
> Spectran signal level     -42.5dB
> Resolution                    0.17Hz
> Sampling rate                11025
> Distance (Rx from TX)    14.9km
>
> It surprises me that the signal can be seen so well at this distance with
> such low power and with this "antenna" set-up.  Thanks in advance for any
> help and please excuse my ignorance.
>
> 73s
> Roger G3XBM
>
> -- 
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> http://www.youtube.com/user/g3xbm
> G3XBM   GQRP 1678    ISWL G11088
>