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Not so
sure about the balanced pre-amp, it doesn't makes double
balance, only one stage should be centered,
when the aerial is
balanced - the connection to once side is just as good as balanced connection,
the only
improvement you can
add is better linearity. The only result of a balanced amplifier is that it is
more
difficult to make,
but probably isn't so balanced after all.
As long as the
background noise without pre-amplifier is 10-20dB above the background band
noise
it is totally vaste
to use a pre-amplifier, it may only worsening the result.
73
LA8AK
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J
M Nøding, Datakvalitet, Kristiansand (Baneheia)
http://tts.telenor.no/orginfo.html?filterstructureid=13&parent=86&treetopid=86
Telefon 380-52660, 9077-7126
The first 136 kHz US receptions of
G3AQC and MØBMU made nearly two years ago were made with my 160 meter
dipole. The dipole is supported with a 1 meter side arm from the
95 foot level of a 100 foot, insulated guy wire tower. The home brew
open wire feed line was fed as a single wire with a series pot core inductor
to bring the antenna to resonance. Later test were made comparing the TA
signals received with this antenna to a 3.3 square resonant loop. This
loop was matched with a single turn pick up loop. The two antennas were
comparable for 136 kHz reception most of the time.
Last year I constructed a new receive loop, octagon in shape, twenty turns,
a little over 3.3 meters diameter. This loop is center tapped and feeds
a balanced preamp. Every comparison I made showed this balanced fed loop
to outperform either the old loop or the T vertical wire. I'm a firm
believer in the balanced loop design.
W4DEX
www.w4dex.com
[email protected] wrote:
Hi John and LF
group,
Just curious -- since the
signal to noise ratio in my receiving installation
appears to be limited by external (man-made and
atmospheric) noise, rather
than noise in my preamp/receiver, how would a 100 foot tower
improve that
situation?
John Andrews,
W1TAG
A big vertical does help a lot against
local noise-sources (neighbours' TVs and SMPSs), but with anything
originating further away than a couple of 100m, it makes absolutely no
difference.
However the directivity provided by a
magnetic receive loop can be valuable. If all of the noise was coming in
isotropically from the horizon, the figure-eight pattern would theoretically
have 3dB better SNR than a vertical, and a cardioid combination would gain
4.8dB. In practice, of course one can often null out a source of QRM or a
thunderstorm front and have far greater improvement.
The only problem I am having with small
loops is that they seem to be much more prone to local pickup than the
E-field antenna - at least in my suburban area which has underground mains
wiring. The 86cm-diameter pair in the garden is often swamped by notorious
100Hz-modulated carriers which at the same time I can hardly see on the
marconi.
73 de
Markus,
DF6NM
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