[Fwd: LF: Re: Re: E-field antennas]

[Andre Kesteloot]

Giulio Scaroni wrote:

> 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