There are a couple of new Finnish 70/50 MHz beacons coming up
with dual polarization. Some of these will be research beacons
with a scheme on the phase-shift between the polarizations in
order to extract propagation information of the path involved.
For the casual operator these will be identifiable like any CW
beacon. Antennas will be stacked turnstiles (X-dipoles) in two
(2 dBd omni) or four layers (5 dBd omni). Vertical polarization
will be an omni J-pole, or a 6 - 8 dBd yagi with the main lobe
into 220 degrees azimuth, depending on how crowded the top
of the mast is. Ground reflection gain is more efficient for
horizontal polarization. Main lobes tend to converge for the same
maximum field for both polarizations below the Brewster angle,
i.e. toward the horizon, below 5 degrees take-off. These will be
potent ionoscatter beacons (mainly on 50 MHz, as ionoscatter
weakens rapidly with the 5th power relative to the frequency
Due to a fortunate coincidence related to the NEW 50 MHz beacon
band, milli-hertz precision carriers for these beacons can be derived
from a single LeoBodnar GPS-locked frequency reference.http://www.leobodnar.com/shop/index.php ... f5b059f0b8
When Output 1 of the Bodnar-unit is set for 50 MHz, there are not
too many options for Output 2. But fate wants it, that 50.400 MHz
projects to 84 MHz, which (divided by six and multiplied by five),
yields 70.000 MHz. In practice this can be achieved by an ACMOS
/6-divider, and by filtering out the 5th harmonic of the resulting
waveform (an XOR-gate function can be added for a part of the
sequence to add more spectral content to the 70 MHz component).
Due to the fixed relation of frequencies, 50.418 projects to 70.025
and 50.436 projects to 70.050, which is the limit of the Finnish 70 MHz
beacon band. This means that OH1SIX/b 50.412 projects to 70016.666
for OH1FOUR/b and correspondingly OH9SIX/b 50.417 to 70023.611
for OH9FOUR/b. I do not have info about the OH7SIX/b project and
whether there is a plan for a 70 MHz beacon there, but 50.433 would
yield 70045.8333 with the Bodnar-unit. Of course a separate unit
could be taken for each beacon if a dead-on round kHz frequency on
70 MHz is wanted (but it is the most expensive part of a beacon project).
ACMOS (5V or 3.3V) output levels (+13 dBm) suffice to steer out a 7 W
M67743L-module to full power. For OH9FOUR/b - the two polarizations -
2 x 7 watts is considered appropriate. For OH1FOUR/b two 50 watts
stages can be added (each having 2 x BLV80/28 running at a lower
voltage for long endurance in a harsh Arctic beacon environment).
Each PA-module will include notch-filters for the other band in order
to avoid reciprocal mixing of 50/70 MHz signals in the output units.
We hope to have some of this new technology running before the
commencement of the 2017 Es season. There is a perfect location
for the OH1FOUR/b + OH1SIX/b combo on a 200 m asl KP11TX hilltop,
with an isolated shack, grid power and 20 m of aluminum tower already
on the site, waiting to be immersed in beacon RF-signals. We have
some surplus 50 Ah telecom batteries to function as a primitive but
fool-proof parallel "UPS", during rare power grid breaks.
Cheers/73, "Zaba" OH1ZAA/OH2MZA/OH3BCX/OH4BCS/OH5ZA (OH0MZA)
P.S. There will be no beacon for OJ0 Märket reef (JP90NH), but the
good news is that we will do a 70 MHz dx-pedition to OJ0/Märket
in May 2017. The 6-el LFA with a 4.9 m titanium boom and 10 mm
solid aluminium rod elements is tested and ready to ship (there is
already a small/light 70 MHz 4-el yagi on the island). A LDMOS-PA is
in preparation for 100 watts: will mount at antenna feed-point. Solar
buffer: 48 volts, 660 Ah nominal (12x 12V 220Ah, not just for radio).