Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, FORGED_RCVD_HELO,HTML_MESSAGE,SPF_PASS autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u38AVlkh030956 for ; Fri, 8 Apr 2016 12:31:47 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aoTdz-0003Ja-Kp for rs_out_1@blacksheep.org; Fri, 08 Apr 2016 11:28:03 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aoTdz-0003JR-60 for rsgb_lf_group@blacksheep.org; Fri, 08 Apr 2016 11:28:03 +0100 Received: from rhcavuit01.kulnet.kuleuven.be ([2a02:2c40:0:c0::25:129] helo=cavuit01.kulnet.kuleuven.be) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.87) (envelope-from ) id 1aoTdw-0001hO-Q2 for rsgb_lf_group@blacksheep.org; Fri, 08 Apr 2016 11:28:02 +0100 X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-KULeuven-Scanned: Found to be clean X-KULeuven-ID: E5F2B138097.A7DAB X-KULeuven-Information: Katholieke Universiteit Leuven Received: from icts-p-smtps-1.cc.kuleuven.be (icts-p-smtps-1e.kulnet.kuleuven.be [134.58.240.33]) by cavuit01.kulnet.kuleuven.be (Postfix) with ESMTP id E5F2B138097 for ; Fri, 8 Apr 2016 12:27:57 +0200 (CEST) Received: from ICTS-S-HUB3.luna.kuleuven.be (icts-s-hub3.luna.kuleuven.be [10.112.9.17]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by icts-p-smtps-1.cc.kuleuven.be (Postfix) with ESMTPS id E3A9B403B for ; Fri, 8 Apr 2016 12:27:57 +0200 (CEST) Received: from ICTS-S-MBX1.luna.kuleuven.be ([fe80::edaf:341f:90e:f70e]) by ICTS-S-HUB3.luna.kuleuven.be ([fe80::a470:76b3:406d:2b1a%27]) with mapi id 14.03.0224.002; Fri, 8 Apr 2016 12:27:57 +0200 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Thread-Topic: LF: Re: RE: Field Strength Measurements Thread-Index: AQHRkRla540uMhdjIEKJdTBCfWFp/59/E+kngAATdPWAAIlBAIAAJqkTgAAJMDQ= Date: Fri, 8 Apr 2016 10:27:56 +0000 Message-ID: <7E7DFBB4D102A04DB5ADC88D66628A4A444EBCA7@ICTS-S-MBX1.luna.kuleuven.be> References: ,<747224627.2437401.1460108208360.JavaMail.yahoo@mail.yahoo.com> In-Reply-To: <747224627.2437401.1460108208360.JavaMail.yahoo@mail.yahoo.com> Accept-Language: nl-BE, en-GB, en-US Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mimectl: Produced By Microsoft Exchange V14.3.123.2 x-originating-ip: [10.112.11.16] MIME-Version: 1.0 X-HELO-Warning: Remote host 2a02:2c40:0:c0::25:129 (rhcavuit01.kulnet.kuleuven.be) used invalid HELO/EHLO cavuit01.kulnet.kuleuven.be - verification failed X-Scan-Signature: 4547f2cca70c75b03fc1ebaed398eea1 Subject: RE: LF: Re: RE: Field Strength Measurements Content-Type: multipart/alternative; boundary="_000_7E7DFBB4D102A04DB5ADC88D66628A4A444EBCA7ICTSSMBX1lunaku_" X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.56 on 10.1.3.11 Status: O X-Status: X-Keywords: X-UID: 7617 --_000_7E7DFBB4D102A04DB5ADC88D66628A4A444EBCA7ICTSSMBX1lunaku_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hello Chris, a lazy-L of 9m by 40m should have a radiation resistance (Rrad) of +/- 0.25= Ohm. If you know the antenna current (I) you can calculated the EIRP =3D G*I^2*R= rad where G =3D the antenna gain (referred to an isotropic antenna). The theoretical gain of a short vertical monopole is 3 (4.77dBi), but this = assumes a perfect ground and no obstructions. A non perfect ground will aff= ect the antenna pattern and gain. Whereas the max. takeoff angle over perfect ground is 0=B0 it will rise ove= r non perfect ground. In addition the gain will slightly drop. I simulated your antenna using Mmanagal: Over perfect ground the max. takeoff angle is 0=B0 and the antenna gain is = 4.7dBi. With a "real ground" of 20mS/m and Er=3D 5 the max. takeoff angle rises 17= =B0 and the antenna gain drops to 4.2dBi (at 17=B0). At a low angle of 1=B0= the gain has dropped to -4.3dBi, thus 8.5dB below the max. gain. The fact that maximum gain is not at 0=B0 takeoff makes is difficult to mea= sure E(I)RP at ground level (cfr. Alans suggestion to go for higher grounds= , if possible). Just out of curiosity a prediction of the antenna current based on the numb= ers above: with an ERP of 0.38W (=3D EIRP of 0.62W) and a gain of 4.2dBi th= e antenna current should be close to 1A, assuming a takeoff angle of 0=B0. = Now taking into account a 8.5dB low reading (due to the higher takeoff angl= e) the real antenna current should be 2.6 A. 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: vrijdag 8 april 2016 11:36 Aan: rsgb_lf_group@blacksheep.org Onderwerp: Re: LF: Re: RE: Field Strength Measurements 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 fl= at 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 g= round system. Making measurments of G4GIR's transmissions with his 260 watts at 16 km ret= urned a value of 0.88 watts ERP 73 Chris G3XIZ On Friday, 8 April 2016, 0:24, Alan Melia 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) amat= eur short aerials measure around 5 to 6 dB low.(that is a 136kHz observatio= n.) Often a better reading is taken say a mile away on slightly elevated gr= ound to the aerial site. Jim Moritz did tests in a field adjacent to the Pu= ckeridge 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 =3D 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@yah= oo.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 PA0= SE and published in the LF Experimenters' Handbook. I've modifed it to measure signals in the MF band and have calibrated it wi= th a home made Helmholtz coil arrangement. This question may have been raised before but PA0SE gives the formula for d= eriving the transmitter power as P =3D 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 =3D (Ed)^2 / 30 i.e. 0.0333 (Ed)^2 . . . . (2) My calculated radiated power seems rather low so I'm wondering whether I sh= ould be using formula (2) Any clarification would be most welcome. 73 Chris G3XIZ --_000_7E7DFBB4D102A04DB5ADC88D66628A4A444EBCA7ICTSSMBX1lunaku_ Content-Type: text/html; charset="iso-8859-1" Content-ID: <9C4D894DEF78C74AA6887109930458FD@luna.kuleuven.be> Content-Transfer-Encoding: quoted-printable

Hello Chris,

 

a lazy-L of 9m by 40m should have a radiat= ion resistance (Rrad) of +/- 0.25 Ohm.

If you know<= a target=3D"_blank"> the antenna current = (I) you can&nbs= p;calculated the EIRP =3D G*I^2*Rrad whe= re G =3D the antenna gain (referred to an isotropic antenna).

The theoretical gain of a short vertical monopole is 3 (4.77dBi), but&nb= sp;this assumes a perfect ground and no obstructions. A non perfect ground<= a target=3D"_blank"> will affect the ante= nna pattern and gain= .

Whereas the max. takeoff angle over perfect ground is 0=B0 it will<= a target=3D"_blank"> rise over non perfec= t ground. In addition the gain will slightly drop.

I simulated your= antenna using Mmanagal:

Over perfect ground the max. takeoff<= a target=3D"_blank"> angle is 0=B0 and th= e antenna gain is 4.7dBi= .

With a "real= ground" of 20mS/m and Er=3D 5 the max. takeoff angle rises 17=B0 and the antenna gain drops to 4.2dBi (a= t 17=B0). At a low angle of 1=B0 the&nbs= p;gain has dropped t= o -4.3dBi, thus 8.5dB below the max. gain.

The fact that maximum gain is not at 0=B0 takeoff makes is difficult to measure E(I)RP at ground le= vel (cfr. Alans suggestion to go for higher = grounds, if possible= ).

 

Just out of curiosity a prediction of the antenna current=  based on the numbers above: with an ERP of 0.38W (=3D EIRP of 0.62W) and a gain of 4.2dBi the antenna current sho= uld be close to 1A,&= nbsp;assuming a takeoff angle of 0=B0. Now taking into account a 8.5dB low reading = (due to the higher takeoff angle) the real<= /a> antenna current should be 2.6 A.

 

73, Rik &nbs= p;ON7YD - OR7T

 

Van: owner-rsgb_lf_group@blacksheep.org [o= wner-rsgb_lf_group@blacksheep.org] namens Chris Osborn [g3xiz@yahoo.co.uk]<= br> Verzonden: vrijdag 8 april 2016 11:36
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: Re: RE: Field Strength Measurements

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

Rik, thanks fo= r the explanation of the two formulae and I've inserted that ERP formula in= to my spreadsheet now - excellent !

Alan, I take m= easurements in open fields to the south of Biggleswade and at about 1 - 1.5= km distance from the transmitter.
Noted about th= e advantages of higher ground measurement but we're fairly flat around here= - HI !
I'll look at t= he O/S map and see what I can do.

Transmitting 5= 6 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.<= /div>

Making measurm= ents 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 y= ou taking the measurement .....you need to be at least 300 to 500 metres aw= ay
2   Because of ground loss p= roblems even the best (fully in the clear) amateur short aerials measu= re around 5 to 6 dB low.(that is a 136kHz observation.) Often a better read= ing is taken say a mile away on slightly elevated ground to the aerial site. Jim Moritz did tests in a field adjacent to the Pucker= idge Decca mast, with a 10m high inverted L.
 
Alan
G3NYK
 
 
----- Original Message -----
Sent: Thursday, April 07, 2016 11:24= PM
Subject: LF: RE: Field Strength Meas= urements

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 =3D 0.0203252(Ed)^2 will give you the ERP (Effective Rad= iated 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 publis= hed in the LF Experimenters' Handbook.
I've modifed = it to measure signals in the MF band and have calibrated it with a home mad= e Helmholtz coil arrangement.

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

P =3D 0.0111 = (Ed)^2  . . .   (1)

where E is th= e electrical field strength and d the distance

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

P =3D (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 clarifica= tion would be most welcome.

73
Chris G3XIZ









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