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LF: Re: Active antennas on 136kHz, additional wire needed?

To: <[email protected]>
Subject: LF: Re: Active antennas on 136kHz, additional wire needed?
From: "Alan Melia" <[email protected]>
Date: Tue, 29 Sep 2015 13:43:52 +0100
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Chris,
It should not be necessary. The E-field probe couples to the incomming wavefront capacitively and extra wire adds little to this. The secret is the "size" of the segment of wavefront you intercept.....between the capacitive plate and the ground connection. Thus the higher you can mount it the bigger the signal you will get from it. E=heff*Fs
The signal received on the plate is of course at very high impedance and the
active bit is an impedance transformer converting the signal to drive 50ohm
coax. The "voltage gain" is probably very close to one. Use the idling
carrier of DCF39 on 138.83kHz as a test signal. this has a daytime field
strength in the UK of approximately 1mV/m ...as measured several years ago
by Dick Rollema PA0SE at an RSGB Convention.
Alan G3NYK

----- Original Message ----- From: "Chris Wilson" <[email protected]>
To: <[email protected]>
Sent: Tuesday, September 29, 2015 1:13 PM
Subject: LF: Active antennas on 136kHz, additional wire needed?


29 September 2015


A friend bought me an active RX antenna, a PA0RDT clone, from Ebay:

http://www.ebay.co.uk/itm/111719689171?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

as  a  gift for sorting a car problem. It's built and working, but the
build  notes  suggest  an  additional wire on the PCB that acts as the
aerial  may  be  needed. What are people's thoughts on adding say a 12
inch wire poking out the PVC tube that it will be mounted high up outside
in? Necessary or not? Just use the PCB board antenna? Thanks.



--


Best regards,
Chris                            mailto:[email protected]



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