Message-ID: <005801bf2131$5c95d2a0$c396b38f@w8k3f0>
From: "Dick Rollema" <d.w.rollema@gironet.nl>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Subject: LF: Calculating transmitter power from field strength measurements
Date: Thu, 28 Oct 1999 12:43:01 +0200
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To All from PA0SE,

It is interesting that the Millington method used by that Vaino to calculate
Reino's  power seems to produce more realistic results than the CCIR
Recommendation 386-7.  Why is that so?
Is the Millington method newer than the CCIR method? What is it like?
Perhaps Vaino can tell us a bit more about it.

As I see it the CCIR curves and presumably the Millington method produce a
relation between the power fed to the antenna and the field strength of the
ground wave (surface wave).

Using an aircraft obviously  measures the field strength of the sky wave.
This makes sense as it is the skywave that is used by an aircraft
approaching a locator (part of an Instrument Landing System).  But the CCIR
curves and presumably the Millington method cannot be used for this
situation I think.  How the power radiated by a locator can be found from
measurements using an aircraft is not clear to me.


>From Vaino's figures for locators it seems that  the power in the sky wave
is very much higher than in the surface wave.
The 500 W TX power and a top loaded antenna  of 14 m as quoted by Vaino for
Finnish NDB/locator beacons  is not unlike the situation at several amateur
stations in our LF-band. But they certainly do not radiate 8 - 15 W in their
ground wave! The somewhat higher frequency of the beacons, resulting in a
higher radiation resistance, cannot explain the difference.

73, Dick, PA0SE


Vaino wrote:

>Hi folks,
>
>This is just a comment. I recently wrote a short story
>for the Finnish SRAL magazine about Field strength
>measurements - which we have been doing for over 40 yrs.
>
>We have been flight measuring most Finnish NDB/Locator
>beacons and all Finnish and Swedish DGPS beacons.
>Most powerful I've ever seen in N. Europe is Tallinn
>"LK" 386 kHz radiating abt 30 W. Of 105 Finnish NDB
>/Locators most (Tx=500W) radiate between 8-12 W,
>some even 15 W, using a 14 m high top loaded monopole.
>
>I made some EMRP calculations for OH1TN who is located
>152 km from my place. Can hear him daily as ground wave.
>For 136 kHz sigma I use 0.5 mS/m, for 300 kHz 1 mS/m.
>Reino's EMRP can be anything between 10 mW and 50 mW.
>Hope some day we can make some real field measurements.
>I have at home an old Anritsu Field strength meter but
>its sensitivity / selectivity is not good enough.
>Can only estimate that his real Fs is less than 10 dBuV/m.
>---------------------------------------------------------
>     GROUND WAVE FIELD-STRENGHT, MILLINGTON METHOD
>
>     OH1TN -> OH2LX,  Ground distance = 152 km
>
>          FIELD-STRENGTH DB ABOVE 1 MICROVOLT/METER
>
> EPS =10.0   SIGMA = .5 mS/m   FREQ = 136. kHz  POWER = .05 W
>
>                      DIST. (KM)    F-S (DBU)
>
>                        1.0            66.3
>                        2.0            60.2
>                        3.0            56.5
>                        4.0            53.9
>                        5.0            51.9
>                        6.0            50.2
>                        7.0            48.8
>                        8.0            47.5
>                        9.0            46.4
>                       10.0            45.4
>                       30.0            33.9
>                       50.0            27.2
>                       70.0            22.6
>                       90.0            18.8
>                      110.0            15.7
>                      130.0            12.8
>                      150.0            10.2
>                      170.0             7.8
>                      190.0             5.6
>                      210.0             3.5
>END OF CIRCUIT
>------------------------------------------------------------
>
>----------------------------------------------------------
>V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
>------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
>E-mail: vaiski@dlc.fi - alias: oh2lx@dlc.fi & oh2lx@sral.fi
>
>