Message-ID: <001f01c24bf7$599c0e40$4e6152d5@it>
From: "Giulio Scaroni" <scaroni@phoenix.it>
To: rsgb_lf_group@blacksheep.org
References: <000001c24c38$ea026420$f976073e@main> <002001c2513c$a9f3a5c0$4bdf7ad5@j1r9b7>
Date: Sun, 25 Aug 2002 07:22:02 +0200
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Subject: LF: Re: Re: E-field antennas
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Hi and many thanks to all that have answered to my question about E-field
antenna.
Many different design, but the best seems really the Amrad pubblished in
QST.
So i'm planning to made an Amrad antenna, i have send a request at
Crystalonics for high current FET.
Many thanks Derek, for the really good job that you have done testing the
antenna alltogheter in the same times!!!!
Here i have during summer times only a ferrite antenna with a J310
preamplifier with 28 mA of idle current, and work very well, but i want to
compare soon it with performance of the E-field antenna.
73 and thanks all again.

de Giulio Scaroni IK2DED.


> Hi all,
>
> Re Alan Melia's posting on E-field antennas (Aug. 25th), I confirm his
> comment that I did carry out a number of tests on two E-field active
> antennas each having roughly a 3m whip, one an ex-Decca Navigator design
> using op-amps, and the other an AMRAD high dynamic range design using a
> Crystalonics high current FET and published in QST in September last year
(I
> think it was).Both of these designs feed DC up the coax to the active
> element.
>  I compared these with a 50m long inverted 'L' antenna with a 15m vertical
> section (resonated with a base loading coil) and also with a large
> rectangular loop approx 8m per side in a very noisy urban environment.
This
> was at a time when I was experiencing interference on 136kHz radiated from
a
> hi-speed data cable which also coupled into local CATV distribution cables
> (not connected to my QTH!).
>        The main findings were :
>
> (1) Both E-field antenna designs performed in a similar fashion and when
> mounted reasonably in  the clear, ie more or less above roof-top height,
> produced a signal to noise ratio  similar to the inverted 'L' antenna.
> Generally anything I could hear on the inverted 'L' , I could hear on the
> active antenna but the active antenna appeared less susceptible to the
cable
> interference than was the wire antenna. Under conditions of radiated
> interference which appeared to be primarily in the H-field from the local
> data cable, the loop was virtually unusable which meant that I could not
use
> it for Loran cancellation!
> (2) The slope of the variation in absolute signal strength at the output
of
> the E-field antenna with variation in height above ground was initially
> fairly constant and surprisingly high at around 2 to 3dB per metre up to
> about 12m. Above that the rate of change flattened off but the received
> signal strength still continued to increase up to at least 20m which was
as
> high as I could measure.
>     The flattening off in signal strength increase at around 12m I assume
is
> as a result of the active antenna becoming less 'E-field shadowed' as it
> rises above roof-top height.and local trees.
> (3) It is strongly recommended that the coax feeder from the E-field
antenna
> should be allowed run more or less vertically downwards to ground level
and
> the outer of the coax then earthed at some point underneath the antenna.
At
> the shack end of the coax, noise currents on the outer of the coax should
be
> suppressed by passing the signal through an isolating 1:1 transformer (eg.
a
> bifilar winding of a few turns on a suitable small toroid). Without the
> isolating transformer I found the performance of both the E-field antennas
> very disappointing in a noisy environment. The transceiver in the shack
> should be separately earthed
> (4) The above results confirm those outlined AMRAD article in QST.  I
think
> that Wallter G3JKV would also confirm that at his QTH, the results from an
> active receiving antenna mounted at 20m+ above ground are similar to those
> obtained from a large well-sited wire antenna.
> (5) There is little advantage to be found in extending the whip much
greater
> than 1 metre or so - cross-mod then potentially becomes more of a problem.
A
> bandpass filter between the output of the active antenna and the RX input
is
> also strongly recommended to minimise the risk of  intermod problems from
> broadcast stations.
>
>                               Regards to all,  Derek Atter, G3GRO