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Re: LF: Re: RX3QFM

To: [email protected]
Subject: Re: LF: Re: RX3QFM
From: "Rik Strobbe" <[email protected]>
Date: Wed, 18 Sep 2002 16:10:30 +0200
In-reply-to: <[email protected] >
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Hello Alex,

Experiences have shown that antennas with a long horizontal section can produce strong signals on LF (ie. OH1TN and some DL stations), so Vlad has probably a good antenna. Regarding the determination of ERP (based on antenna current and estimated Rrad) one has to take into account that the real ERP in most cases is 2 to 6dB below the calculated ERP for low antennas, probably caused by local losses (trees, buildings etc...). In Vlad's case the theoretical Rrad is about 0.07 Ohm, so with 2.75A it comes to about 0.53W EMRP (calculated). Real EMRP is most likely in the range of 150 to 300mW, not bad at all - this should make him one of the stronger stations on the band it he were not so far away from the rest of us. But even at this distance he should have a good CW signal if QRN is low (and condx are good) and a clear QRSS copy at most nights.
73, Rik  ON7YD

At 21:06 18/09/2002 +0000, you wrote:

Hi, Group.

On Wed, 18 Sep 2002 [email protected] wrote:

> Just a thought, but isn't an antenna current of 2.75A a bit low for 0.5W ERP? > I recall running 8 Amps to a 300 foot wire with the top at 150 feet high and
> Jim measured it at 0.5W  ERP.  Or does Vlad have something really high up?

Vlad has Heff ABT 15 m (horizontal part of antenna is 150 m). So radiation
resistanse is:

Rrad = 1600*(Heff/lambda)^2=0.073 Ohm

P = I^2*Rrad= 0.56 Watts.

I do not know why your PWR is not high as follow:

Rrad = 1600*(45/2200)^2 = 0.67 Ohm

P = 8*8*0.67 = 43 Watts

If only one end of wire has H=45m then Heff=22.5 m and P=11 Watts

73 de RA9MB/Alex

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