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Winter 2010 : Every first and third Monday at 9:00 p.m., NPARC members
try hold a "net" (on-air meeting) using digital
modes; all are welcome. This net is for anyone who wants to experiment with various digital modes including RTTY, PSK-31, and slow scan TV.
Most recently we've been experimenting primarily with RTTY. Dave Barr K2YG has been taking the lead in organizing the net
and anyone interested in activating the net should be in touch
with Dave. He writes:
"The frequency is nominally 14085 mark tone, in RTTY mode. This means if you are running FSK (frequency shift keying) your readout should be close to 14085.
For AFSK (audio frequency shift keying, which is actually
Lower Side Band,
LSB, using two audio tones generated by your computer, and is the more common and less complicated, but some say less desirable, method of transmitting RTTY), your readout should be somewhat higher, perhaps around 14087, depending on what audio tones your RTTY software is set to. (Note: most RTTY software mentioned below uses AFSK by default.)
In any event, with the longer days, there will still be some DX RTTY signals coming in from the west, so we may have to locate plus or minus QRM. Look around a bit before you assume the net is not there. I will be transmitting about 20 seconds of "RYRY" with 20 second pauses for about 3 minutes before 9pm
EST (0200z). Please wait to call until I ask for stations to send their calls.
If anyone needs help getting set up, please contact me. 73, Dave, K2YG"
The net is run in 'round table' fashion, meaning that every ham who checks in is given an opportunity to transmit usually in the 'check in' order. The transmitted reports are usually personal news or ham activities that might be of interest
to others on the net, or responses to comments made previously on the net. Transmissions do not need to be related to ham radio topics. The nets also allow for operating assistance and troubleshooting, typically by voice on 145.75 MHz (or perhaps the W2LI repeater 147.255 MHz). For beginners, it's probably useful to find a digital Elmer to help you test out your hardware and software before getting on the net (some possible Elmers: K2YG, K2GLS, K2MUN, KB2FCV, K2EZR, and WB2EDO.)
Most digital modes can be run with "sound card" software (below) which requires an interface (3 cables) to connect your radio to your computer's sound card. Interfaces can be homebrewed, made from a kit, or purchased. See club member Ralph
NM5RM's (formerly KC2RLM) web site for information about these options:
NM5RM's site describes an interface suitable for 2 meter packet and the AGWPE packet program, the interfaces described will work for all digital sound card modes.
One advantage of pre-built interfaces or kits is that they will usually be designed to work for the radio you specify and you won't need to worry about "pin-outs", the connection points (MIC jack, data port) on your radio for received and transmitted audio and PTT control. If you homebrew an interface, you will need to determine the pin-outs. Your radio's user manual should provide this or it may be on the internet. Club members can also help you sort it out.
A few modes, such as RTTY and packet, can be run with a special radio modem (a hardware device) that is designed for that mode. Some net participants may be using these hardware devices, instead of using a sound card program.
Software for Digital Modes
Net participants should have RTTY and PSK31 software, since these two modes are the most popular net modes. You should be able to find a club member willing to help you test out the software before you get on the net. There is a chart below which has information about download sites for these and other digital mode software programs.
If the net experiments with other modes they will probably be modes designed specifically for keyboard-to-keyboard/ "live" conversations (rather than transmissions of previously composed copy or files). These 'conversation' modes (such as RTTY, PSK31, MFSK16 and Hellschreiber) work well for 'round table' nets since everyone can 'listen in' to the transmitting station, and transmission rates are not slowed by protocols that check to make sure each station received perfect copy. In fact, it is a given that when using conversation modes, you will not receive perfect copy. Even if the transmitting station typed perfectly (rare!), other factors such as noise can produce errors. So please understand that what you receive is not necessarily exactly what was sent. Still, you can usually make out the meaning of the sender's message.
Other modes such as packet, PACTOR, and AMTOR were designed primarily for error-free transmissions. These 'error checking' modes are generally used in one-to-one situations where it is important to verify that the receiving station has received all data perfectly from the sending station. These modes are generally not used in 'roundtable' nets, since error-checking protocols are difficult to use where there are many receiving stations. (Note: Packet does have a special 'roundtable' mode called 'unconnected' or 'UI' mode).
Most sound card modes were developed for use on HF frequencies. The wide variety of modes stems from the objective of achieving the ideal mode for various situations. Each of the modes has advantages and disadvantages in the areas of bandwidth, speed, accuracy, and resistance to the noise, fading and distortion that is common on HF frequencies.
1 Mode: In the chart above, "Mode" refers to the basic modulation scheme. Some modes have more than one variation. The primary variation is listed in parentheses beneath the mode and it will be the first variation used in the first net of the month. Other variations may be explored during the month.
2 Software: Generally, all of the digital modes above can be run with free Windows software that uses the computer's sound card to transmit and receive the mode's modulation scheme. Net participants are encouraged to download the suggested software well in advance of the first net that will use that mode. This will give them time to configure and learn to operate the software before the net. A few modes, such as RTTY and packet, can be run without a sound card if you have the special radio modem (a hardware device) that is required for that mode. Thus, some net participants may be using these hardware devices, instead of using a sound card program.
For some popular modes, such as PSK31, there are several programs that can be used. The first software listed is the program that most club members seem to use. For beginners, this means it is the program for which you are mostly likely to find help from other club members. Still, net participants are encouraged to experiment with different programs, since you may find a program better suited for you and maybe even for the group! Not listed above are "multi-mode" programs -- programs that can handle several digital modes. Hamscope is a free multimode program. Another is MultiPSK. Still another is MixW, but it is NOT free; there is a $50 fee for this program after a 15 day test period. Finally (?), Digital Master 780 (DM780) is a modern multi-mode program which uses Ham Radio Deluxe (4.0 and higher), a radio control program .
Software for Apple/Mac computers:
- Cocoamodem 2.0 - http://homepage.mac.com/chen/w7ay/cocoaModem/index.html
Modes: RTTY, PSK, MFSK, Hellschreiber, CW, Sitor-B, Hf Fax reception & Synchronous AM reception
- Multimode for Macintosh - http://www.blackcatsystems.com/software/multimode.html . CW, RTTY, FAX, SSTV, PACKET, ACARS, PSK31, ALE, and many other modes, but this program is NOT free.
- Other web sites with ham software for MacIntoshes:
LINUX users: Try N9NU's page for some possibilities. Then do a web search to UNIX information pages for the mode in which you are interested.