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Six Meters (50mHz), the Weak Signal World and Digital It seems the digital world of weak signals is the fastest growing segment of our hobby. Each month that passes sees new operating modes and new software. The purpose of this section is to try as best we can to keep readers aware of what is happening in this segment, to show you examples, and where to find more information. Rocks a Flying Dave Moore, N7RF, March & April, 2018. With yagis up now, I found time on March 18th to check
out the 6 meter meteor calling frequency (50.260). I immediately
started hearing strong bursts of raspy MSK144 signal. I started up
the WSJT-X software and then logged in to the Ping Jockey web site to
see what was happening (https://www.pingjockey.net/cgi-bin/pingtalk).
As it seemed pretty busy, I announced on PJ that I would be calling CQ.
Almost immediately, K8LEE came back. The QSO exchange was rapid
since the meteors were hot and heavy. During the final
"73" exchange, I saw an uncommon 4-1/2 second burst from Wayne
in Indiana. Here's the record of that burst on the 15-s long
waterfall trace. Wow.
After that, I conducted QSO's with KE5RV (Arkansas),
K2DRH (Illinois), and W5TN (Texas). The next morning, I added
WB4JWM (Georgia), and W8BYA (Indiana). March 24th update: Another good morning for
meteors. I called CQ and was called by two stations, one after the
other, WB4JWM again (Georgia) and K0TPP (Missouri). Several times,
I saw bursts from 2 or 3 stations within the same 15-second frame.
At 1427Z, I worked AK5QR (Alabama), and then was cold-called by XE2YWH.
My first new country on meteor scatter. Jose is 535 miles south of
here in Zacatecas, Mexico. Here's the "Roger" and
"73" transmissions at 1430Z and 1431Z:
And, finally, I asked W5LDA to give it a shot via the
PingJockey web site. We connected within 3 or 4 sequences.
Big signal from Oklahoma City! March 31 update I turned on the 6m station this morning and immediately decoded a meteor CQ from XE2JS in Chihuahua (449 miles). After calling him for several minutes, someone broke in on SSB. It was XE2OR in Coahuila, 151 miles away, with a 59+ ground wave signal. After that QSO, I returned to calling XE2JS, and we finally connected. He is my second Mexico QSO on meteor scatter. A few minutes later, I worked N0LL in Kansas (693 miles). I switched over to 2 meters to see what I could see. On 2m, I'm only running 60W barefoot until I get the PTT cable made up for the linear.. The first decodes I received were from XE2AT in Aguascalientes, Mexico (689 miles). I pointed the beam south and, after 10 minutes or so, I worked him, my first 2m meteor QSO (of recent times), and my first 2m DX entity at the same time! American Meteor Society Meteor Shower Calendar Meteor
activity picks up a bit during April as the Lyrids become active during
the month. They are active from the 14th through the 30th, with a
pronounced maximum on the 22nd. Sporadic rates during April are steady as
seen from both hemispheres with southern observers enjoying twice the
activity that can be seen from the mid-northern hemisphere. During
this period the moon will reach it’s full phase on Saturday March 31. At
that time it will be located opposite the sun and will remain above the
horizon all night long. As the week progresses the waning gibbous moon
will rise later in the evening but will still hamper the more active
morning hours making meteor observing difficult at best. The estimated
total hourly meteor rates for evening observers this week is 2 as seen
from mid-northern latitude (45N) and 4 from the southern tropics (25S).
For morning observers the estimated total hourly rates should be near 5 as
seen from mid-northern latitudes (45N) and 8 from the southern tropics
(25S). The actual rates will also depend on factors such as personal light
and motion perception, local weather conditions, alertness and experience
in watching meteor activity. Rates are reduced during this period due to
interfering moonlight. Note that the hourly rates listed below are
estimates as viewed from dark sky sites away from urban light sources.
Observers viewing from urban areas will see less activity as only the
brighter meteors will be visible from such locations. The
radiant (the area of the sky where meteors appear to shoot from) positions
and rates listed below are exact for Saturday night/Sunday morning March
31/April 1. These positions do not change greatly day to day so the listed
coordinates may be used during this entire period. Most star atlases
(available at science stores and planetariums) will provide maps with grid
lines of the celestial coordinates so that you may find out exactly where
these positions are located in the sky. A planisphere or computer
planetarium program is also useful in showing the sky at any time of night
on any date of the year. Activity from each radiant is best seen when it
is positioned highest in the sky, either due north or south along the
meridian, depending on your latitude. It must be remembered that meteor
activity is rarely seen at the radiant position. Rather they shoot
outwards from the radiant so it is best to center your field of view so
that the radiant lies near the edge and not the center. Viewing there will
allow you to easily trace the path of each meteor back to the radiant (if
it is a shower member) or in another direction if it is a sporadic. Meteor
activity is not seen from radiants that are located far below the horizon.
The positions below are listed in a west to east manner in order of right
ascension (celestial longitude). The positions listed first are located
further west therefore are accessible earlier in the night while those
listed further down the list rise later in the night. These
sources of meteoric activity are expected to be active this week. Details of each
source will continue next week when lunar interference will be much less.
FT8 Digital Mode Dave Moore, N7RF, March, 2018 On a separate note, I have worked quite a bit of DX on
FT8. To me, it seems a lot easier than fighting the CW and SSB
pileups you hear when a rare one comes on. It's hard to compete
with the super stations with multiple towers, stacked beams on every
band, and full legal limit amplifiers. There is a distinct
advantage when the DX station can pull your weak signal out of the noise
and get a perfect copy in the presence of lots of other stations.
Software has now replaced the human ear. Yeah, it almost sounds
like cheating, but you can't look at it that way. Technology keeps
improving the hobby. I bet very few of you run vacuum tube radios
anymore, nor are most of your solid state rigs without modern Digital
Signal Processing. Think of it this way: instead of aspiring
to be like the muscle stations and overpower everyone on frequency, you
don't need to any more. IMHO, this opens up the door for many,
many more hams to make more contacts rapidly without the mega-buck
expense. Nevertheless, as the popularity of FT8 grows, we are
starting to see DX pileups. The problem is, you can have dozens of
signals spread across the 2 kHz wide FT8 channel and the software
decodes and displays all of them every 15 seconds. A DX station
sees all the stations calling him but the software only lets you respond
to one station at a time. Until now. The ARRL reported that
a beta version of a new FT-8 contest mode software was tested recently.
A DX station (the Fox) can now conduct multiple QSOs simultaneously.
Fox can select the number of responses (Hound stations) he wants to deal
with. He can also call region-selective CQs. When Fox
responds, his transmission consists of multiple simultaneous signals
sent to selected Hound stations, each on their own frequency.
Sounds crazy. And it's not simple. Users are encouraged to
study the operating guide and not try to wing it (http://physics.princeton.edu/pulsar/k1jt/FT8_DXpedition_Mode.pdf
). Contest mode will never be used in established FT8 channels,
rather a specific frequency to be announced beforehand. On 20m, the FT8
channel is 14.074-14.076 MHz. During the recent beta test of
contest mode, they used 14.105 MHz. The test results were
positive. Expect to see this used by real DXpeditions. But
get some some conventional FT8 time in before you try it.
Updates,
N7RF, May 2020 – New FT4 contest mode and other useful how-to
information
The
above was written over two years ago.
A lot has changed. The
interest in low signal-to-noise digital has not waned at all.
FT8 seems to be the de facto go-to mode of choice now.
DX stations use it in abundance, DXpeditions use it as their main
mode as they can handle a large number of QSOs in a short period of
time.
FT4 Contest Mode: FT8
frame times are still 15 seconds long, and 5 or 6 frame are still
required to complete a QSO. Not
fast enough for you? Now
we have FT4, a 4-tone MFSK modulation with a faster baud rate and is
designed for contest operations. Here
is how Joe Taylor, et al, describe the new mode:
Introduction:
FT4 is an experimental digital mode designed specifically for radio
contesting. Like FT8, it uses fixed-length transmissions, structured
messages with formats optimized for minimal QSOs, and strong forward
error correction. T/R sequences are 6 seconds long, so FT4 is 2.5 ×
faster than FT8 and about the same speed as RTTY for radio contesting.
FT4 can work with signals 10 dB weaker than needed for RTTY, while using
much less bandwidth.
Basic
parameters:
FT4 message formats are the same as those in FT8 and encoded with the
same (174,91) low-density parity check code. Transmissions last for 4.48
s, compared to 12.64 s for FT8. Modulation uses 4-tone frequency-shift
keying at approximately 23.4 baud, with tones separated by the baud
rate. The occupied bandwidth (that containing 99% of transmitted power)
is 90 Hz. Threshold sensitivity for 50% decoding probability is S/N =
–16.4 dB, measured in the standard 2500 Hz reference noise bandwidth.
A priori (AP) decoding can push threshold sensitivity down to –18 dB
or better.
REF:
https://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf
Bottom line:
FT4 is 10 dB better than RTTY at the same baud rate.
By comparison, the decoding threshold for FT8 is about 4 dB
better. FT8 is better for
DXing and working weaker stations, but FT4 is perfect for racking up
high contest scores.
Try
it out! FT4 can be found any
time of day or night, but not on every band.
Although there are nominal frequency channels suggested for FT4 (ie,
they are programmed into the WSJT-X software), most of the daytime
activity is found on 20m (14.080 MHz). In the evenings, 30m, 40m, and
80m become more active as the propagation changes.
Meanwhile, FT8 rules on every band, when its open, including 6m
(watch for summer sporadic E propagation, 50.313 MHz), and even 2m
(morning tropospheric ducting, 144.175 MHz)
Current WSJT-X software
version:
Be sure you get the latest. Today
it is Version 2.1.2. Go to
Joe Taylor’s web site to download the one for whatever computer
platform you are using (for most people, it is Windows):
https://physics.princeton.edu/pulsar/K1JT/wsjtx.html
How to Digital Ops.
I have purposely not tried to get into how to connect up a
station for digital operation. With
the variety of radio types out there, the “how” is “it depends.”
But here are the basic requirements:
1.
A
2-way audio interface between radio and PC (or iMac. Or
Linux computer. Or even a
Raspberry Pi3). This can be:
a.
An analog cable pair from
radio speaker/mic to the audio port of a computer (uses the internal
CODEC of the computer).
b.
A third-party CODEC
interface such as a SignalLink USB device (they also sell custom cables
that connect up your specific radio port).
c.
Or a single USB cable
interface to the later generation of radios that handle both CAT and
audio. My FTDX-3000 does
this and most other new generation radios (Icom 7300, FT101, etc.).
But my older FT950 requires use of a SignalLink USB.
The newer the radio, the easier it is to make it happen.
d.
Or buy a FLEX radio.
The radio IS the computer.
2.
A
CAT (Computer Aided Tuning) connection between radio and computer.
WSJT-X software can control the frequency of the radio, although
this is not a hard requirement. But
it is a nicety. A new
generation of USB-serial port cables actually makes this pretty easy.
But be sure you order one that specifically says it uses an FTDI
chip set, under $15 on Amazon (Other cables use a Prolific chip set, but
Windows has a hard time with these - ask me how I know).
3.
A
means of executing PTT.
The best way is to do it through the CAT control.
But, again, not necessary, as most radios have a VOX mode that
will key the transmitter when an audio signal presents itself. (Webmaster
note: If SignaLink to Icom, one must use VOX.)
4.
A
computer system clock that is synchronized to a time standard.
Usually this means installing free Network Time Protocol software
on the computer that and “disciplines” the PC system clock.
You can check your time synch by typing time.is
in a browser window and it will tell you how close you are to real time.
Having
your clock more than a few tenths of a second off time can result in
lost QSOs. I use the free
Meinberg NTP:
https://www.meinbergglobal.com/english/sw/
Logging QSOs.
If you still insist on writing down contacts in a logbook, then
maybe digital isn’t for you. You
cannot possibly keep up with all the QSOs you will make without using
click-and-go logging software to expedite the process.
What
does logging software produce? There
is a standards committee that decides the proper format for digital ADIF
QSO files (ADIF = Amateur Data Interchange Format).
They are found here:
https://www.adif.org/ along with the latest ADIF
format description, currently version 3.1.0.
In
theory, this common file structure allows different platforms to pass
information back and forth. For
example, if you are striving to obtain the various operating awards that
ARRL issues, you want your resident logger to be able to send new QSO
ADIFs to ARRL’s Logbook of the World (LOTW) to get credit for Worked
All States, DX Century Club, etc. Depending
on how and what you are doing, make sure you always have the latest
version of software. I had
some initial problems logging FT4 contacts until I installed v.2.5 of
LOTW tQSL, and v.6.7.0.277 of Ham Radio Deluxe.
When a QSO completes on
WSJT-X, a small logging GUI pops up on the screen.
When clicked, it saves ADIF data in a master file on your hard
drive, and sends the same data to whatever logging software you told it
to use. In my case, Ham
Radio Deluxe. Here is a map
showing what happens to digital logging data and the results of
submitting it:
HRD
Logbook is the main repository of my QSO information.
At the close of an operating session, I manually highlight all
the new QSO’s of the day and send the ADIF information to LOTW, QRZ
and eQSL. There are other
destinations possible too, like Club Log or HRDlog. LOTW is probably the
most used logging service. The
stations you contact will be sending their data in to their favorite
services too. Each service
compares your data to their data and confirms the QSO if there is a
close match. This is how you
collect credits for operating awards.
eQSL is a bit different – confirmed contacts allow you to
download an image of a real QSL card and print it for display in the
shack.
Of
course, you may not wish to collect awards, or digital QSL cards.
There is still U.S. Mail!
Hope
you try out FT4 or FT8. You
will enjoy it!
100
Year-Old Digital
mode?
By
Mark Rosier,
KE5GL
Lately, I’ve been looking to experiment with
different digital modes. Did you know there are more than a hundred
different types of digital modes?
Many are variants of Frequency Shift Keying (FSK) incorporating
several methods of error
correction. Others
are unique
in their
own rights.
A couple of months ago I was looking for digital
contests and ran across a mode I had seen listed in my Ham Radio
Deluxe/DM 780 software but knew nothing about – Feld-Hell.
I quickly requested membership in the FELD-HELL
club, received my membership number, and began contesting.
I made several QSOs during the contest and was
genuinely intrigued.
I did
some research and discovered Feld-Hell
mode is derivative
of something
called “Hellschreiber,
which is
a method where a small selection of alphabetic characters is
“painted” onto a screen instead of being decoded in the
true sense of digital communication; very similar to a FAX. It
reminded me of Slow Scan TV signals my grandfather,
K4LBF (SK) experimented with back in the early 70s.
I remember eagerly waiting for the small CRT tube to finish painting the
screen as
we received signals from
other Hams.
What I found most fascinating was that this method
was developed in the 1920s!
“Hellschreiber” was patented in
1929 by Rudolf Hell, a German Electrical Engineer.
Before WWII, it was used commercially by newspapers over
copper wires
in the
days before more modern facsimile
transmissions were invented.
Its use can also be considered a precursor to dot
matrix printing because of the methodology.
It uses a single tone,
on-off keying,
to represent a
dark “dot” or
a white “dot”.
This is
accomplished with a
single pair
of sidebands spaced
122.5 hz
either side
of the carrier wave, to create
a matrix at
a rate
of 122.5 dots
per second.
Duty-cycles are relatively low too and operate much like CW. The speed isn’t
fantastic, about 35 wpm, but bandwidth is also very
conservative at
only 75
hz.
Is Feld-Hell truly a digital mode? Well, you decide! In 1998, Murray Greenman, ZL1BPU coined the
phrase “Fuzzy Mode” and said “These
Fuzzy modes have unusual characteristics and some very real benefits…
Hellschreiber, and related
modes... are generally digitally transmitted, but are analogue, human
readable, uncoded, direct viewing or
printing modes, and so are truly
'Fuzzy'”.*
*Article
reviewed by
Murray Greenman,
ZL1BPU.
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