Hajo
Although this type of antenna works I am not sure how because it seems odd
that the outer braid of the coax has to be connected to Earth at the base of
the antenna mast, therefore altering the design properties of the active
antenna. You say no other Earth connection is permitted in the shack, how is
this possible when the RX in the shack has already an Earth connection
except an Isolation transformer is always used.
My logic would say that an Active antenna as described should be mounted on
a pole preferably in a quiet location and the coax connection should go
directly to the RX in the shack, also height of mast should make no
difference, but some say the signal is better the higher the active probe,
why is that the case ?
It would be interesting to just have a small vertical antenna mast, with an
amplifier and compare against a probe type.
Perhaps I should build one of these miniwhip antennas and compare it against
an inv L on 137. I did this with with a small commercial active loop and
found although it worked it was well below the sensitivity and signal
capture of my inv L system.
My 40 metre RX vertical quad loop resonated for 137 is not as good as the
inv L. One strange observation is that late afternoon early evening I
cannot detect DX signals on this loop whereas the inv L system is excellent
all the time, but late evening and night time the DX signals start to appear
using the loop, this must have something to do with Angle of arrival of
signals at night time.
73 de mal/g3kev
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, August 10, 2011 9:58 AM
Subject: Re: LF: HB9ASB...
> Dear all, Mal in special,
>
> if the cable to the rx would really be the antenna for the active
> aerial, only local qrm would be received! The screen of the cable has to
> be grounded bfore entering the house, as Roelof has stated, but avoid
> any additional grounding within the house.
>
> Especially at VLF an 1:1 isolation or separation transformer having an
> inductivity of 10 mH or higher is needed for active aerials before the
> receiver to break currents in the screen which the cable has picked up
> from the environment. And on an ordinary toroid the polarization of the
> transformer has to be optimized for real noise-free performance.
>
> Just by this method I got rid of qrm from a nearby solar panel
> installation and its 300 Hz spectrum up to 20 kHz which has plagued me
> since autumn 2010. For my inductive aerials, this interfering field ist
> still existing. But copy of SAQ last Friday using the active aerial (in
> my case using an LT1252 as amplifier just needing 10 mA) has been ufb
> again.
>
> 73 Ha-Jo, DJ1ZB
>
>
> "mal hamilton" <[email protected]> schrieb:
> > Minto
> > Get rid of fluorescent strip lights from your house, only QRM generators
for
> > radio amateurs.
> > It seems MINIWHIP antennas work better the higher they are installed
above
> > ground which makes me think that the cable connecting the probe to the
RX is
> > in fact the REAL antenna. !!!!!!!!!!!!!!!
> > A probe antenna should work equally well at ground level in the clear as
in
> > an elevated position.
> > G3KEV
> >
> >
> > ----- Original Message -----
> > From: "Minto Witteveen" <[email protected]>
> > To: <[email protected]>
> > Sent: Tuesday, August 09, 2011 8:44 PM
> > Subject: Re: LF: HB9ASB...
> >
> >
> > > .. And he is even visible on my grabber!
> > > I raised the miniwhip from +4 to +11 meters (large fishing rod in the
> > > backyard).
> > > Signal levels increased by 15 dB. Noise level was raised too, but the
QRM
> > > from my fluorescent lights in the house no longer show up. so there
must
> > be
> > > some improvement.
> > > Tomorrow I will again measure de DCF39 to noise ratio.
> > >
> > > 73's
> > > Minto pa3bca
> > >
> > >
> > >
> >
> --------------------------------------------------------------------------
> > > Ceterum censeo Carthaginem delendam esse
> > > -----Original Message-----
> > > From: Stefan Schäfer
> > > Sent: Tuesday, August 09, 2011 21:10
> > > To: [email protected]
> > > Subject: LF: HB9ASB...
> > >
> > > ...now joins in at 137.695! 25 dB SNR here.
> > >
> > > Looking forward to a opening band tonite...
> > >
> > > 73, Stefan
> > >
> > >
> >
> >
> >
>
>
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