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| To: | [email protected] |
|---|---|
| Subject: | Re: VLF: ERP calculation (was: dj8wx on 8970.022Hz) |
| From: | [email protected] |
| Date: | Wed, 09 Mar 2011 17:35:46 +0100 |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
|
Hi Markus,
thanks for your instructions.
Ill try this substitute mothode one hot day in the month of august.
Thanks for the link to the US grabber.
vy 73 Uwe/dj8wx
Von: [email protected] Gesendet: 08.03.2011 20:33 An: [email protected] Betreff: VLF: ERP calculation (was: dj8wx on 8970.022Hz) Dear Uwe, LF,
my usual method for ERP measurement is as
follows:
1. Build a simple nonresonant loop of known area A,
eg. 50 cm x 50 cm x 4 turns = 1 m^2. Do not connect a capacitor.
2. Using a selective voltmeter or soundcard,
measure the voltage Vloop induced by a strong transmitter in the far field (eg.
DHO). Note that the main Marconi antenna should be disconnected (ie. grounded
via 1 megohm) during this measurement to decouple it from the
loop.
3. Calculate the magnetic fieldstrength B (for
DHO) using Faraday's induction law:
B = Vloop / A / omega
4. Derive the undisturbed electric field from this
transmitter:
E = Zo * H = B * Zo /
µo = B * c
5. Series resonate your Marconi for DHO, connect a
high impedance voltmeter, and measure the
open circuit voltage Vmarconi.
7. Derive the effective height of the
Marconi:
heff = Vmarconi / E
8. Calculate the radiation resistance at your
transmit frequency:
Rrad = 1579 ohm * (heff /
lambda)^2
9. Connect your TX and loading coil, measure the
antenna current I, either at the cold end of the coil or in the ground
line, and calculate radiated power:
EMRP = Rrad * I^2
10: If you want, you can convert radiated
power to ERP referenced to a halfwave dipole:
ERP = EMRP * 1.83
You do not have to absolutely calibrate the
voltmeter because the result depends only the ratio between the loop and Marconi
measurement. This is handy with the soundcard, as you will only need to
read a dB difference.
The method also correctly includes the shunt effect
of nearby objects (eg. trees) on the radiated power. It measures the disturbed
electrical field, and compares it to a reference based on the undisturbed
magnetic component.
Best 73,
Markus (DF6NM)
From: [email protected]
Sent: Tuesday, March 08, 2011 7:27
PM
Subject: LF: VLF dj8wx on
8970.022Hz
Hi all,
Im doing some measurements trying to find out how low
(high?) the ERP of my system is.
the test lead of the oscilloscope in use has a resistor
of 10Mohm. The oscilloscope advise text says that I have to multiply the result
by 10.
OK. I added two other 10Mohm in series multiplyed
the result by 1000 and got 40000Vpp
using the twentieth of max TX power. 40kV? Is that
possible?
the current from the coile foot into the radials was
0.145A (3 A with max power).
I cant measure the Tesla voltage when the power is
raised because the oscilloscope or other
instruments indicate results without connected to the
object under test.
the station is on the air in mode QRSS3600 on 8970.022Hz
since today 1640UTC.
current into the radials: one
Ampere.
who will try to calculate the ERP?
the aerial in use can be seen at
fourth pic on the site. The shown 23m long wire has been
lengthened to 43m.
best regards
Uwe/dj8wx
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