OH1ZAA's blog

According to WX-forecasts Summer will start tomorrow, so I took a head start
with some antenna construction. The intention is to have two fixed structures
that can be monitored on the same band by two separate receivers. The dual
dipole with anti-phase parallel elements (mentioned in a previous blog) is near
completion, and it will have about 3.5 dBd wideband rx-gain into the opposite
directions broadside to the dipoles. When mounted horizontally it will have zero
response toward the dipole ends as well as toward the zenith, or for signals

Winter is easing its grip, but it is not yet time for antenna work, so the
anti-parallel dipoles mentioned in the previous post will have to wait.

While the weather is warming up, the 85 watts dissipated by the IC-761
during WSPR-reception is a bit of a waste; soon the shack will need
additional cooling with all equipment running. Therefore a "hundredfold"
reduction in rx-power is very welcome. Presently 15 volts 40 mA is fed
to a 7812 regulator followed by a 7808 to provide 12 and 8 volts bias to
four 8-pin chips, namely a SA612A - NE592 - SA612A - LM318H string.

SA612A mixers have very low bias, so they are prone to overload and
IMD when fed with wide input spectra. In this prototype receiver some
risks are taken, but narrow pre-filtering is expected to minimize the IMD-
problem. Due to the availability of standard crystals for certain frequencies
the 10140.2 kHz band-center seemed within reach with a 4.000 MHz and
a 6.144 MHz crystal. Both had to be pulled down a little off their nominal
frequencies for WSPR action. So we are talking about a superhet.

The first SA612A has the 4 MHz crystal in its oscillator section so
6144 kHz is serving as the intermediate frequency. Actually another
6144 kHz crystal is used as the IF-filter in the NE592 stage between
pins 2/7. It is in fact not a straightforward filter: it kind of "shorts"
two emitters of the NE592 at X-tal series resonance, which peaks
the amplifier gain enormously at around 6140 kHz. Bandwidth is not
much more than the 200 Hz WSPR-band, so it is quite a remarkable
response for a single high-Q component in that particular circuit.

The second SA612A makes a 6144 kHz crystal oscillate round about its
nominal frequency, so both the 4 MHz and 6144 kHz crystal have to be
pulled down with a series coil to arrive at band-center 10140.2 kHz with
1500 Hz BFO offset, actually in LSB mode. As standard WSPR offers

Antennas used in WSPR-experiments may have very differing structures. As such I do not think
that there is any specific recommendation. One uses often an existing antenna originally built for
completely a different purpose. Personally I started my HF-career for this particular location
30 years ago with log-yagis (3-element log-cells with a parasitic reflector and director) at various
heights. With WSPR I have used these on the “wrong frequencies”, that is: hardly ever on the
14 - 28 MHz bands those have been designed for. Since I have operated WSPR mainly on 7 MHz
and 10 MHz, the elements of those log-yagis have been electrically “too short”, thus specifically
yielding poor pattern and efficiency in transmit mode. While WSPR is generally not intended for
point-to-point traffic, the described behavior has been actually often more welcome than operation
on the initial design frequency of the antenna. Simulations with horizontally polarized 3-element
off-frequency log-cell structures show best field strength toward the horizon, but not in a controlled
or optimized way. Additional uncertainty about the pattern is introduced through usage of the feed
point matching arrangement on an off-design frequency. A big burden on such an arrangement is the
presence of numerous local sources of man-made interference these days.

So the chase for better SNR is imminent, preferably with a structure that scales well with changing
frequency. Such an antenna cannot be an isotropic, though that would be an ideal antenna for WSPR-
experiments when aiming for a minimum number of variables. Isotropic behavior is a theoretical
concept though, especially when taking into account ground reflection effects. However, anything
of the perfectly round pattern of a free space isotropic that (by changing radiator layout) can
be shaved off from specific azimuths or elevations, can be steered to add increased gain toward

Tonight at 2054Z there was suddenly 35 Hz spread on one incoming
WSPR-signal. It returned at 2104Z starting with 30 Hz spread and
declining to 20 Hz at the end of the 2 minute period. Immediately
I checked the magnetogram at SGO Sodankyla (Northern Finland):

http://sgo.fi/Data/RealTime/magnetogram.php

and the spectrum widening correlated with the 60 nanoTesla spike in
the Y-component of the Earth Magnetic Field starting just before 21Z.

At least a 3 months break with WSPR at the OH1ZAA-location. In the meantime
we have been following it from the side at OH3MHA (mainly active on 7 MHz).

There are many reasons why from a particular location the reported
TX and RX signal-to-noise figures can be very different. One obvious
cause is a different transmit power level at the station on the other
end of a particular WSPR-path. The positioning of the RX-antenna
relative to noise sources is however often the most determining factor.
This is perfectly evident if there is only one major local noise source,
and if it is OFF intermittently (during round-the-clock WSPR-operation).

At OH3MHA and similarly on various other locations we have observed that
things are generally fairly balanced at 10 MHz and higher frequencies, but
7 MHz and 3.5 MHz very often expose computer hash, internet data transfer
spectra (e.g. HomePNA), PLC, switching power supply harmonics and the like.
I do not have experience on the lower bands (1.8 MHz / 500 kHz / 137 kHz),
but there may be a slight advantage due to the fact that there the geophysical
background noise threshold is higher to begin with (to make a fundamental
distinction as opposed to man-made noise: geophysics cannot be manipulated).

OH3MHA was temporarily active on 7 MHz where antenna SWR is optimum with
a perfect 1:1 match, but the incoming man-made noise is very high, so that often
only a few stations are received for upload, while dozens of OH3MHA-spots
are reported by others. OH3MHA transmissions are now back on 10 MHz where
the situation is fairly symmetric, with about even numbers of in/outgoing reports
for each 2-minute transmission slot... We are presently experimenting with
remoterig.com products (like the Webswitch 1216H) to have full TX-control
under all imaginable circumstances. Remote control could also be a solution
if one wants to install full WSPR-RX-functionality at a quiet remote location.

I will try to add figures and plots soon to my previous blog posting regarding the
analysis of the benefits of poor ground with vertical antennas for WSPR-traffic.

At OH3MHA we use for WSPR-communications presently a 4 x 3 m vertical (28/25/22/19mm Alu-tubing, totally 11.5 m in length) attached to a wooden fence support, with the fence's wires (cut for various lengths) functioning as the radials. SWR is excellent on 7 MHz. On the 10/14/18/21 MHz bands it can be forced to accept some RF-power with matching circuits. There is considerable loss in the long RG-58 cable. Finally it is the magnitude of the current in the vertical element that is forming the amplitude of the radiated field in cooperation with the properties of the surrounding soil.

The station is situated in an industrial area with poor ground (assuming a dielectric constant of ε = 5 and a conductivity of 5 mS/m). Pending future site improvements it was decided to run some simulations with a design frequency of 14.15 MHz using the free MMANA 1.2.0.20 simulator. To get rid of the radials, a J-pole structure seemed suitable, while the matching section is usable as a mechanical support to get the radiating part of the [vertical dipole] element up in the clear. Starting at 1 m elevation with the structure base the top of the structure arrives at 17.7 m height (guying ropes certainly needed, unlike with the first vertical).

The simulation was done for Ocean water (dielectric constant ε = 80 ; conductivity 4000 mS/m), Lake water (ε = 80 ; 1 mS/m), Good ground (ε =20 ; 20 mS/m), and Poor ground (ε = 5 ; 5 mS/m). Though the maximum intensity of the radiated far field does not change more than 1.5 dB between the cases, its dependence on the take-off angle is huge. Over Ocean water one is able to launch into a low angle of 5 degrees, but there is a -13 dB relative dip at 20 degrees take-off, and even a stronger wide maximum peaking at 44 degrees vertical elevation.

In earlier days while being new to operating it was fully satisfactory
to make the contact, log it, and move to the next one. Only much later
it became more interesting to search for what is behind it, what sort of
conditions, and to quantify signals or levels as a reality check for
the used technology. For some years I have advocated that a single
antenna is not enough on any band if one wants to optimize the use
of all possible propagation conditions. Actually, even two antennas

WSPR is quite an interesting mode for doing certain
(scientific) experiments. Data integrity is important
when digging into a database. I have been enjoying
reception of mainly 10 MHz WSPR-signals for 10 days.