[HCARC] OOPS Wrong Receiving Antenna Link

[Kerry Sandstrom]

Gary,

I wouldn't worry about a new Maunder minimum.  To say that scientists don't 
have a clue when it comes to predicting the sun is an understatement.  Our 
ability to predict what is going to happen is very limited.  There is some 
capability to predict the likelihood of a large flare 1-3 days ahead and 
usually the most likely sunspot group can also be predicted.  There is also 
some capability to predict in general terms what the next solar rotation 
will be like, 27 days, but that is about it.  The start of the next 
Maunder-like minimum has been postulated since the 1960's.  Hasn't happened 
yet, but what is 50 years in the overall life of the sun.

There are actually two things that one needs to do, and that is whether we 
have another long minimum or not.  The first is to be sure we have a station 
that does an adequate job on 160 through 40 m.  These bands require somewhat 
different techniques than the higher bands.  First, antennas with gain are 
seldom practical for normal people.  Second, the level of man-made QRN as 
well as atmospheric QRN is significantly higher and you need to know and 
practice how to operate your rig to minimize the impact of QRN.  Third, 
there will be a lot more activity on the lower bands so you need to know and 
practice how to operate your rig with high levels of QRM.  The second thing 
one must do if we enter another long minimum as well as when we enter the 
next minimum of the 11 year cycle is to know when conditions on the higher 
bands have momentarily improved.  Even during a solar minimum there are 
times when 10 and 15 meters are open for long distance contacts.  These 
openings may only last for a few minutes or a couple hours.  To some extent 
the openings depend on time of day and season and are somewhat predictable. 
They also depend on curreent solar-geophysical conditions.  The sun often 
has short bursts of activity which can enhance conditions on the higher 
bands.  There are also geomagnetic disturbances which may provide short 
openings using uncommon propagation modes.  One needs to be able to spot 
when these things are happening and know where to go and what to look for.

Any of the so-called receiving antennas need a preamp.  The reason they are 
called "receiving antennas" is because they are very inefficient, so 
inefficient that they can't be used as a transmitting antenna.  The nreason 
they are used is because they can be used to null out a noise source or they 
are less susceptible to noise pickup.  A vertical is a good transmitting 
antenna at low frequencies because it is an efficient radiator.  It is not a 
good receiving antenna because much of the low frequency QRN is vertically 
polarized and a vertically polarized antenna picks the QRN up better than a 
horizontally polarized antenna.  Unfortunately, if you want to work DX with 
a horizontally polarized antenna you have to get it well above the ground 
which is not easy to do.

The Beverage was originally designed for use in VLF trans-atlantic.  The US 
end of the circuit was in northern Maine.  The QRN was primarily from the 
south and southwest, while the signals from Europe were from the northeast. 
The Beverage did an excellent job of providing an improved signal to noise 
ratio for the signals received from Europe.  It was a good solution because 
the signals were all from the same direction and the noise was from the 
opposite direction.  By the way, the Beverage can be operated in either 
direction or both directions depending on how it is set up.  The original 
Beverages received vertically polarized signals and relied on the 
front-to-back ratio for the improved SNR.

I think the most practical low noise receiving antenna is a small rotatable 
loop as used in old DF systems.  The loop can be rotated to null out the 
interference and improve the signal-to-noise ratio.  The old 5-tube AC/DC AM 
broadcast receivers used a loop antenna and by rotating the radio you could 
improve the SNR of the station you wanted to listen to.  Early transistor 
ragios used a variation of a loop antenna called a loopstick.  My Sony AM/FM 
receiver comes with a small loop antenna for B/C band reception.

You can use these very inefficient receiving antennas on the low frequency 
ham bands because the signal strengths are very high as is the field 
strength of the QRN.  This is the only reason the AM B/C band was ever 
practical.  B/C band antennas, particularly automobile B/C band antennas are 
terrible antennas with very high losses, but the field strengths of the AM 
B/C transmitters are huge so it doesn't matter.  What matters is SNR.

Kerry