Notes About Operating a Station with Four Transceivers

Notes About Operating a Station with
Four Transceivers, Four Computers
and Four Antennas.
With Four ‘complete’ stations in one I am able to monitor
and operate multiple modes on the HF frequencies at the same time.
Any combinations of modes and frequencies are possible. For example,
I can receive SSTV images at 14.230 using one radio, watch Digital (drm)
SSTV images at 14.233 on another, look for JT-65 DX at 7.076 on the
third, and follow a 15 meter PSK-31 QSO with the fourth. Engagement
in any QSO can be started at once. When needed, a second radio with a
different antenna is utilized to assist copy of weak signals using dual
diversity reception (more about this later). Normally, each radio
remains matched with its own designated antenna to facilitate quick
tuning changes between different bands.
My station added radios over time. The expense of my four
transceivers (two new, two used) may have been equal to or less than
the cost of one very well equipped top-of-the-line model. The radios
are normally set to my favorite operating modes (SSTV, digital SSTV, JT65, and PSK), but can be quickly adjusted to monitor with dual diversity
or operate any other digital mode, SSB, or CW if the need arises.
Station transceivers (clockwise from top left) : Flex-Radio 3000 SDR, Kenwood TS-480 sat,
Yaesu FT-950, and Ten Tec Omni-7. All can be used for SSB, CW, and Digital HF operation.
Each antenna performs well on multiple HF bands. I use two
horizontally polarized antennas: a Cushcraft MA5-B 3-element
rotatable beam and MFJ-1775 multiband rotatable dipole, and two
vertically polarized antennas: a Cushcraft MA5-V vertical, and Gap Eagle
vertical. All are reasonably priced, small, lightweight, and not overly
conspicuous, so the expense and appearance of the classical ‘antenna
farm’ dwarfing the house was minimized. I have (fortunately) not
experienced ‘detuning,’ signal ‘overloading,’ or ‘SWR issues’ by
installing them in relatively close proximity to each other. The Comet
GP-6 is used for satellite/ISS and local 144/440 contacts.
Transmitting with low power (5-75 watts) on the digital modes and
CW has returned lots of DX contacts from these antennas. I am
expecting even better performance in the upcoming solar cycle. The
Ameritron AL-811H amp (@600 watts) is often used for SSB, SSTV, and
digital SSTV contacts.
Because of wind issues at my QTH (near Lake Ontario, NY), a
compromise between safe antenna elevation and good signal radiation
was made at a height of approximately ½ of 20 meter’s wavelength
(approx. 35 feet), with the beam placed several feet higher. At that
elevation, the lowest signal take off angle (favorable for favorite 20
meter DX) occurs at 8 degrees above horizon. Antenna SWR is
improved using internal/external tuners when necessary.
About the computers? Each radio is connected to a separate
computer. I purchased three (used) 2-4 year old laptops for $45.00 each
and a tablet PC for $75.00 from a friend when his business office
upgraded to new units. All have average RAM and ROM, between 1.66
and 3.00. Before connecting to my radios, I proceeded to erase the
memories and old software and then reloaded the original operating
systems (two computers are running Microsoft windows XP Home and
two are running Vista 32 Home). All are working well and are
compatible with favorite amateur radio software.
I find using a dedicated computer with each transceiver
provides me the greatest freedom, speed, and stability for each radio,
operating mode, sound card, and antenna. It makes set-up, software,
soundcard configuration, and (if any) trouble shooting easier to
manage. Computers and software are not absolutely necessary to run
SSB or CW with the radios, but CAT software (Pegasus Plus) is always
running on multiple instances if I want station mouse/keyboard (or
remote) control.
Separate LCD computer screens allow me to see and operate
the programs controlling each radio at a glance. One LCD screen on the
desktop is dedicated to each laptop. The screen on far right displays the
rotator controls for Yaesu DMU, and far left is cable TV. For the digital
modes, each radio can be controlled instantly by mouse commands on
its respective software screen. To avoid clutter, I only use one mouse
and keyboard to access all the computer screens.
“Synergy” is a freeware program that installs in one computer and
functions as a ‘server’ to all four computers. It allows seamless,
independent mouse and keyboard activity to flow between all four
systems. As a backup, I can access each laptop with an extra installed
mouse that can be used to call upon a Windows on screen keyboard
should the need arise to enter data or reboot.
Separate Sound Card Interfaces assure full independence for all
four radios. External units are used for the Digital Modes on 3 of the 4
radios (two Signalink USB’s and one Ten Tec). The Flex-3000 SDR uses
VAC (virtual audio cable) software as an ‘interface’. Individual sound
card interfaces can be adjusted quickly and easily, and provide stable
and non-volatile interference-free connections between radio and
computer. Shielded connecting cables and effective grounding
minimizes RF interferences within the shack.
Multiple Antennas Assist Reception
It is customary for HF radio transmissions to be sent in a mostly
horizontal or vertically polarized fashion, but due to refraction angles,
interference, and other ionizing layer effects during propagation, the
signal may become distorted or differently polarized at distant
reception sites.
Weak signals often succumb to fade, or cannot be copied clearly. One
way to partially compensate for this problem is to compare reception
with separate radios connected to antennas of different polarity or
design. I often enlist the help of a second radio connected to an
antenna of different polarity (horizontal vs. vertical), design, or
directivity when copying marginal signals.
The concept has been recently revisited and defined in an
excellent article by Joel Hallas, W1ZR, which appears in his May 2011
QST Magazine column “The Doctor is In.” He answers a question from
Lance Elliot, KF0HC, who inquired about ‘dual diversity reception for
weak signal work.’
Joel states: “Diversity reception has been around since
before WW2, so it does not require fancy new equipment. The basic
idea of HF diversity is that as the ionospheric geometry changes with
time, the arrival angle and polarization of incoming signals will change.
With a single antenna and receiver, this generally results in the fading
that we all have observed. By having two antennas – perhaps one
vertical and one horizontal, or at two different heights, or in two
locations – the chances are that while one experiences a fade, the other
will not. So the first requirement is for two independent antennas and
feeds. The two antennas need to be connected to separate receivers so
each can operate independently.” (1.)
Signal reception on the HF bands is enhanced by the ‘dual
diversity’ technique described herein using different antennas
connected to separate receivers. It is especially helpful when cocopying the imaging modes including SSTV, digital (drm) SSTV, and KGSTV and comparing the image clarities side-by-side as they appear on
the desktop screens, and when listening to weak CW or SSB signals
surrounded by interference.
Example of how Dual Diversity can help reception: SSTV images from PZ5RA (Suriname, SA) on
14.230 using my MA5-V vertical on the right vs. the MA5-B beam directed South on the left.
(1.) Joel R. Hallas, QST Technical Editor, “The Doctor is In” page 55,
QST Magazine, May 2011. jhallas@arrl.org