R: Topband: How to orient the receive antenna?

[Maurizio Panicara]

Beverage antennas start to have a rather sharp forward pattern when their
lenght exceed three wavelenghts.
It's not usual to have such lenghts for 160m, but since beverages are not
single band antennas the same beverages are conveniently used on 80 where it
might be needed to have more antennas to cover all headings.
Concerning the small receiving antennas it's wise to be aware none of them
approach a good beverage result.
Small receiving antennas are basically phased verticals (better to say a
notch is developed) or magnetic loops and they work somehow when they don't
couple to trasmitting antennas.
In spite of the created notch, the phased verticals are still electrical
antennas and suffer two main problems. One is the response to ground wave
that lead to catch all the electrical local noises (off the notch
direction), another gap is the vertical polarization that inherently has no
rejection to atmospherical noise.
Small loops have the advantage to be magnetical antennas with rejection of
atmospherical and local noises but, opposed to (long) verticals they have a
small rejection of higher wave angles. Since reception is a matter of S/N,
to have a big response to nearby strong station is not a good feature at
all.
Both small verticals and small loops (expecially the not resonant ones) are
fractionally efficient antennas and someone uses preamplifiers to overcome
this bad feature (and complicating his life).
Althought 160m ground floor is high, when the antenna efficiency is very
poor the preamplifier needs to have a noticeable gain and a good NF to
deliver receiver at a convenient level the weaker signals.
High gain and low NF devices are very prone to IMD distortion, and as is
well known intermodulation is the S/N havoc.
Moreover, in case of broadband loops or verticals, higher HF bands signal
are not rejected at all, but their amplitude is enormously bigger than 160m
signals. Opposed to beverages with preamps where bandpass filters are mainly
a need against local MW, with small antennas the band pass filters are
mainly against the signals belonging to the higher part of HF spectrum.
In case of restricted space, a reversible beverage only one wavelenght long
does (in a simpler way than small phased receiving antennas) a quite decent
job into a pair of quadrants, concerning small antennas where no beverage is
permitted my point is in favour of large tubing resonant loops (single or
phased) whose dimension is big enough not to require preamplifiers.

73,
Mauri I4JMY





--
FAQ on WWW:               http://www.contesting.com/FAQ/topband
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com