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> Date: Wed, 24 Nov 2010 20:51:29 +0100
> From:
[email protected]> To:
[email protected]> Subject: LF: new VLF antenna at DK7FC
>
> Dear VLF,
>
> Full of euphorism i want to tell you about my new VLF RX antenna.
> You know my active antenna for VLF which is in use at my grabber:
> http://www.iup.uni-heidelberg.de/schaefer_vlf/8,97kHz%20active%20E%20field%20antenna%20by%20DK7FC.jpg
>
> I have had the idea to separate the E field active antenna into a front
> end and the rest of the circuit can be left in the shack!
> The front end consists out of the first JFET, the 1MOhm and 10 MOhm
> resistor, the electrode(wire) and the C=20 nF. The diodes can be left
> away. The rest of the circuit is now placed inside the shack.
>
> This has the following advantages:
> -The gain and or filters can be adjusted and optimised in the shack!
> -There is no need for a (separate) power supply on the top of the antenna
> -No need for a (metallic) box on the top of the antenna
> -the electronic parts can be shrinked together with the wire(s) by
> shrink tubes (waterproof)
> -No need for a coupling-decoupling network at the antenna for the power
> supply
> - If the use of batteries is an advantage, they can easily be
> replaced/charged/measured in the shack!
> - A single twisted pair cable (e.g. 1/4 of a CAT5 cable) can be used
> -When a tiny fishing rod is used to keep the active antenna apart from
> the house, the distance can be increased due to optimised lightweight
> :-)
>
> I just have used a single twisted pair cable out of a CAT5 cable (now
> unshielded) at almost 30m length between the front end and the amp stage
> in the shack. This allows me to get more distance to the tram line which
> causes strong QRM on VLF on my grabber antenna. Now, this new antenna is
> on the other side of the house.
>
> See the difference between the 2 wideband captures: Old system, bottom
> capture of
> http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html
> and the new system, bottom of
> http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
>
> So, at least on VLF this is a great chance to reduce the local noise.
> Maybe some others can do the same since a very small twisted pair cable
> is almost invisible and cheep (i've used a 10m cable and soldered the
> pairs in series). No matter what the maximum distance might be but i can
> imagine 100m will be not the problem! I will check to do the same on LF.
> Since the length is still << Lambda i do not expect much trouble.
>
> 73, Stefan/DK7FC
>
