FT-8 Digital Interface for use with Boat Anchor SSB Radios
A Digital Interface
By
Pete Juliano, N6QW n6qwham@gmail.com
So,
Ok, you are an entrenched homebrew, CW QRP, minimalist enthusiast and here is
this guy from California trying to lead you to the digital dark side. Yes, that
is exactly what I am doing but maybe only to share some of my experiences and
information with you. Disclaimer: upfront you must have an SSB rig tuned to USB
to have this work on the several digital modes that are mentioned.
I
have been at this hobby a long time and aside from doing the WSPR thing several
years ago with my Softrock V6.3, I am not deeply involved with digital
operations. But seeing as I have a few SSB rigs available for experimentation
coupled with some new digital modes I felt it time to once again test the
waters. Coincidentally a new program from K1JT, Joe Taylor, called WSJT-X has
many of the digital aspects rolled into a single program which are simply menu
selected. You must download this free program to the computer you will use.
Two
of the currently popular digital modes are WSPR (Weak Signal Propagation
Reporting) and FT8. WSPR has been around a long time and essentially has you
tune a specific frequency and listen for other stations. Periodically your
transmitter, under computer control, is turned on and other stations listen for
you. Most often stations run QRP power levels like 30 dBm signals (1 watt),
some even less. I have been spotted 10,000 miles away running 500 MW.
The
key feature to this program is the real time database where you can see who you
have spotted and who spotted you. Today 40 Meters is a DX band and spots
spanning great distances is often the common experience. WSPR uses a two-minute
time block and so you can watch your lawn grow during the two-minute intervals.
Thee 40 Meter WSPR frequency in 7.038600 MHz USB. Included on the WSPRNET
webpage is a world map which captures the spots specific to your station. I
learned a lot about my antenna as the spots are consistent NE SW
FT8
is a new addition to the digital array and this format is much quicker as each
pass is 15 seconds and is more QSO like. A station sends an CQ call and the computer
screen shows the station who sent it. Boom, double click on that call and the
computer takes over by responding and then listening for a return. The computer
will continue doing this until the person responds back OR another station
picks him up. Once the connection is made the computers on each end exchange
signal reports, confirm the reports and send 73’s. It is the latest craze; but
some naysayers have likened it to remote quickie sex. A variant called FT8CALL
now adds to the sequence by letting the operator add text and other
information, so it is more like a QSO. The FT8 frequency is 7.074 MHz USB.
When
I was using the Softrock V6.3 much of the interconnect to the rig and the
computer program was done entirely in software within the computer. With a
standalone rig, this requires some hardware to do the interconnect. A little
time with the Internet resulted in a configuration that will do that task.
Pre-made inexpensive circuit boards are readily available; but also, there had
to be some adjustments made to work with modern computers.
The
first board is a sound card interface kit from KF5INZ available on eBay for
around $7 USD. This board has a couple of 600:600 Ohm modem transformers and
some keying circuits that trigger and opto-isolator switch from either a DTR or
RTS signal via computer Serial Port. That is the first issue as most modern
computers don’t have a Serial port as everything has shifted to USB. That was
one of the first nuts to crack. Although initially I did use the Serial port on
an old Windows XP Pro computer; but then later shifted to the USB. Knowing what
I know today I would not buy the kit, but just build the modem isolation part.
Essentially, I have abandoned the Serial Port keying.
I
also have abandoned the XP Pro machine and now the system is running on a small
form factor Windows 10 NUC computer that is about the size of a CD case and 1
inch high. This computer has only an earphone output, so I added a plugin USB
Sound card Dongle from Sabrent (about $7) as that provides the audio in/out
capability. For the triggering of the PTT, Adafruit Industries makes a small
USB to Serial board that is quite small (CP2140). One of the outputs is RTS
–perfect. But the output logic is only 3.3 volts whereas the Serial Port is 10
Volts. So, I needed a way to trigger the PTT from 3.3 Volts. A simple 2N3904
transistor switch, a SPDT relay, isolating diode and one small resistor handles
that chore. I have successfully loaded an earlier version of WSJT-X on to a
Raspberry Pi3B but am having a bit of difficulty with the current version that
has the WSPR and FT8. Just need a bit more time. But think of the
possibilities.
The
WSJT-X has a settings tab that requires you to enter your call sign, grid
square and the method of keying (RTS) and the COM Port to be used. There are
some other items that require checking the block, like double click to
automatically respond to a CQ and to disengage the transmitter once your
computer sends 73’s. Spend a little time with this setup and look at all of the
tabs. I didn’t and then wondered why nothing worked.
Oh,
a cool feature of the WSJT-X –it is linked with hamlib. When you call a
station, it tells you the azimuth (like if you have a beam) and the distance
from you. Pretty cool
I
am happy to report that my interface box has been in operation for several years and works perfectly with vintage boat anchors. The KWM-1 was built before I was licensed in 1959 > 64 years ago!
73’s
Pete
N6QW
