Re: LF: Re: RE: Field Strength Measurements

[Chris Osborn <g3xiz@yahoo.co.uk>]

Many thanks for the rapid replies gentlemen; they are very much appreciated.

Rik, thanks for the explanation of the two formulae and I've inserted that ERP formula into my spreadsheet now - excellent !

Alan, I take measurements in open fields to the south of Biggleswade and at about 1 - 1.5 km distance from the transmitter.

Noted about the advantages of higher ground measurement but we're fairly flat around here - HI !

I'll look at the O/S map and see what I can do.

Transmitting 56 watts my ERP was calculated as being 0.38 watts which just seemed rather low.

My aerial is a 40 m long inverted 'L' at 9m mean height with a reasonable ground system.

Making measurments of G4GIR's transmissions with his 260 watts at 16 km returned a value of 0.88 watts ERP

73

Chris G3XIZ

On Friday, 8 April 2016, 0:24, Alan Melia <alan.melia@btinternet.com> wrote:

Chris two other points

1.  How far from the aerial are you taking the measurement .....you need to be at least 300 to 500 metres away

2   Because of ground loss problems even the best (fully in the clear) amateur short aerials measure around 5 to 6 dB low.(that is a 136kHz observation.) Often a better reading is taken say a mile away on slightly elevated ground to the aerial site. Jim Moritz did tests in a field adjacent to the Puckeridge Decca mast, with a 10m high inverted L.

 

Alan

G3NYK

 

 

----- Original Message -----

From: Rik Strobbe

To: rsgb_lf_group@blacksheep.org

Sent: Thursday, April 07, 2016 11:24 PM

Subject: LF: RE: Field Strength Measurements

Hello Chris,

 

(1) will give you the EMRP (Effective Monopole Radiated Power)

(2) will give you the EIRP (Effective Isotropic Radiated Power)

The formula P = 0.0203252(Ed)^2 will give you the ERP (Effective Radiated Power)

 

73, Rik  ON7YD - OR7T

 

---

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Chris Osborn [g3xiz@yahoo.co.uk]
Verzonden: donderdag 7 april 2016 23:58
Aan: LF Group
Onderwerp: LF: Field Strength Measurements

LF,

I've recently resurrected my old RF field strength meter as designed by PA0SE and published in the LF Experimenters' Handbook.

I've modifed it to measure signals in the MF band and have calibrated it with a home made Helmholtz coil arrangement.

This question may have been raised before but PA0SE gives the formula for deriving the transmitter power as

P = 0.0111 (Ed)^2  . . .   (1)

where E is the electrical field strength and d the distance

I've read in other places that the power from an isotropic radiator is

P = (Ed)^2 / 30

i.e.  0.0333 (Ed)^2  . . . . (2)

My calculated radiated power seems rather low so I'm wondering whether I should be using formula (2)

Any clarification would be most welcome.

73

Chris G3XIZ