| |
AE5ME > ARES 29.03.16 03:56l 16 Lines 4776 Bytes #999 (0) @ WW
BID : 3HQXHAC7U96H
Read: GUEST
Subj: Digital Emergency Communications Series by AD5XJ (SAT
Path: IZ3LSV<F1OYP<IK2XDE<DB0RES<DB0EEO<DB0GOS<ON0AR<VK6HGR<ZL2BAU<7M3TJZ<
HG8LXL<N0KFQ<AE5ME
Sent: 160329/0209Z 34478@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
A good way to get a look at PSK31 is to use the audio output from your radio acoustically coupled to your
computer internal mic and/or, connect your rig audio output (headphones, ext. spkr or aux audio output) to the computer sound cards' line input with a simple adapter cable made or purchased. Download from the Internet, multi-mode programs like FLDIGI, Digipan, MultiPSK, or MixW. With little time spent on setup and some practice receiving you will begin to receive PSK31 text on your computer. All that is left to do to get on the air, is to connect the speaker output from the computer to the mic input or audio input of your rig or (with some manual difficulty, key the mic with the PTT button, and acoustically couple the mic to the computer speakers). If you are really frugal, you don't even need to spend the money on an interface box. Simple adapter cables with the proper plug types at each end may work. With at least one rig I have even been able to rubber band the microphone to the computer speakers and manually switch to transmit with the software, as it turns on the microphone when the PTT line is activated. Many QSO sessions have been made this way and there is nothing wrong with it. This works fine with PSK31, and other keyboard modes that do not have fast turn around times. It will not work with semi-automated modes like WinLINK, AMTOR, PACTOR or any other ARQ (Automatic Repeat Request) or synchronous mode due to the fast turn-around T/R times and much lower audio quality, higher noise, of acoustical coupling vs direct connection.
Often there is a problem with direct connection of the computer soundcard to the radio because it introduces what is called “common modeö noise, i.e. hum. When this is the case, the only solution is to use a computer interface to isolate the radio from the computer.
For those of you who prefer Linux you may want to check out LinPSK as seen in the image below:
(BTW this IS Linux and Not Mac OS X. I am just running a Mac-like theme in the window manager.)
RTTY adapted from the FLDIGI documentation by W1HKJ
This is one of the oldest digital modes around. Even before modern computer software solutions were available, RTTY was used by construction of discreet audio components for tone generation and detection. Terminal equipment was generally available wire-line teleprinter equipment as surplus on the commercial and military surplus markets. My first encounter as a ham was by way of a veteran ham and MARS operator who was very proud of his Teletype Model 40 and a homebrew detector / modulator to operate RTTY for MARS. That was decades ago.
Today, computers replace the discreet components and software does the job of detection and transmission.
The RTTY modulator and demodulator have been extensively changed with version 3.21.67 of FLDIGI. The new design was a cooperative effort of Stefan, DO2SMF, and Dave, W1HKJ with extensive testing performed by Ed, W3NR, and Dick, AA5VU. Chen, W7AY, was a silent contributor to the design by virtue of his excellent technical papers on RTTY modulation and demodulation, which he so generously placed in the public domain.
FLDIGI can operate on a wide range of RTTY symbol rates and bandwidths. The selection of symbol rate and bandwidth is made on the RTTY configuration tab. The three most common in amateur radio use can
be selected from the mode menu. These are:
Mode Symbol Rate Typing Speed Bandwidth RTTY 45 45.45 baud 6.0 cps (60 wpm) 270 Hz RTTY 50 50.0 baud 6.6 cps (66 wpm) 280 Hz RTTY 75 75.0 baud 10.0 cps (100 wpm) 370 Hz
These modes were a result of mechanical and electrical designs of the early TTY machines. The 45.45 baud and 75 baud machines were for the US / Canadian market and used 60 Hz synchronous motors. The 50 baud machines were for the European market and used 50 Hz synchronous motors.
FLDIGI can encode and decode many other symbol rates and bandwidths. "Custom" combinations are set up on the RTTY configuration tab. You probably will never have to do that unless you like experimenting with unusual RTTY modes.
All of the modem signals that FLDIGI produces are audio signals. That includes the RTTY signal. FLDIGI can encode and decode an RTTY signal that is anywhere within the passband of the sideband transceiver. It is not limited to the traditional tone pairs around 2100 Hz. Each of the generated Mark / Space signals are on-off-keyed (OOK), bandwidth limited signals. The resultant waveform is not an FM type signal of constant amplitude. Therefore the transmit audio and RF amplifiers must be linear, just like the requirement for PSK signals. There are performance gains using this approach. The principal being a reduction in inter symbol interference which gives much improved performance by the receiver.
Read previous mail | Read next mail
| |
