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Re: LF: Re: MiniWhip antenna, fiber optic TEST SIGNALS NEEDED on 630m WS

from [Stefan Schäfer] [Permanent Link][Original]
To: [email protected]
Subject: Re: LF: Re: MiniWhip antenna, fiber optic TEST SIGNALS NEEDED on 630m WSPR
From: Stefan Schäfer <[email protected]>
Date: Tue, 16 Jul 2013 23:04:33 +0200
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MF!!!

Am 13.07.2013 14:56, schrieb pa3abk:

[...]
Do you see a difference in signal when you ground your TX antenna versus fully tuned on MF? 
In other words does the TX antenna has any coupling to the MW.

Jan/pa3abk
A few minutes ago i did another local test of the roof where the TX antenna is located. I run a spectrogram showing signals from the isolated short active dipole on 630m. To a certain time i detuned the antenna (there is no difference in my TX system between disconnecting the coax from the PA or disconnectinmg the coil from the wire. This is because i'm using an (isolating) transformer which is in series to the coil and acts as a L when the primary winding is open. The C of the coax is just 1 nF) and saw the difference! 
The difference is very big!!!
See that image: https://dl.dropboxusercontent.com/u/19882028/MF/ant%20disconnected%20from%20loading%20coil.png
When the TX antenna is connected, the WSPR signal (it was I5MXX) is nearly down in the QRM! The QRN is also nearly covered by QRM! The signal levels itselfe did not change dramatically, probably less than 3 dB.
This is a good example that the S/N of an active RX antenna can be much better than the S/N of the TX antenna when it uses a noisy earth :-) When using the "BIG" antenna for the RX (of course using a suitable attenuator to come out at the same signal level), which i have testes some time ago, i see the same vertical lines which lowering the RX performance. 

73, Stefan/DK7FC
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