Hi Roger that sounds reasonable, my estimate for 45 degrees of would be more
like 6dB down, assuming a loop pattern, but there is "cut in" at ground
level due to ground loss and that could reduce the signal more from your
transmitter. Most ground level measurements underestimate the ERP by 4 to
5dB (see Jim's work)
Well done interesting experiment
Alan G3NYK
----- Original Message -----
From: "Roger Lapthorn" <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 2010 12:41 PM
Subject: LF: ERP calculation (revised)
> Today I managed, I believe, for the first time to *accurately* measure the
> ERP of my QRPp system on 137kHz.
>
> This is the method used:
>
> - Using the E-field probe, FT817 (AGC off, gain backed off as far as
> possible and a 10dB pad between the EFP and the FT817) and Spectran I
went
> to my usual test site 1.5km away from the QTH, 45 degrees off the main
lobe
> of the TX loop/earth electrode antenna.
> - Measured the signal level of DCF39 on 138.83kHz
> - Measured the signal level of G3XBM on 137.675kHz
> - Repeated this three times to reduce errors.
> - Noted the difference in FS level.
>
> Difference in signal level = *44dB *. I feel pretty confident this is an
> accurate figure now and *not* effected by AGC and overload. Assuming DCF39
> is 1mV/m here (info from Alan Melia) then my FS at the test site
is*6.4uV/m
> *. Using the formula ERP = (E*d)^2/49 where E = 6.4*10E-6 and d=1.5*10E3
> gives an *ERP = 1.9uW* giving an antenna efficiency of *-63dB* using the
> earth electrode antenna with the elevated feed and 4W from the PA.
>
> The test site is about 45 degrees off the main line of fire of the
antenna,
> so in the best direction it could be 10dB (?) stronger, i.e. *20uW
> ERP*giving an antenna efficiency of
> *-53dB* in the best directions. Frankly I'm amazed that anyone can copy
this
> signal at any distance, so full marks to G3XIZ (48km) and G3XDV (62km).
>
> Next stage is to try this arrangement for a few more days using QRSS3 and
> WSPR before swapping to a full "in the air" loop and repeating these
tests.
>
> Great fun and I'm leaning as I go, which is the whole point of ham radio.
>
> 73s
> Roger G3XBM
>
> --
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> http://www.youtube.com/user/g3xbm
> G3XBM GQRP 1678 ISWL G11088
>
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