Becoming a Digital Relay Station (DRS)
Getting Started in the Digital Traffic Network (DTN)
What is called "Digital Relay Stations" (DRS)
by Dave WB2FTX Originally printed in December 2012 issue of QNI- The NTS Newsletter
Updated September 2015/ Updated April 2017 by W5KAV
In a past issue of QNI, stations learned a little about the structure and operations of DTN Digital (DTN). To refresh, the DTN network consists of a series of automated bulletin-board-type stations operating 24/7, 365 on HF using high speed PACTOR 2, and 3, transferring messages between major digital stations. These stations are known as either Hubs or MBOs. The Hub/MBO operations roughly correspond to the old TCC network, along with Area and Region Nets in the traditional RRI system.
The goal in DTN is to get the traffic to the closest point to for delivery via digital means, before it is removed from DTN and taken to either a Region, Section net, or local net.
That function of removing the traffic is the role of the Digital Relay Station (DRS) or what can be called a Target station.
Since the DRS is probably the first step in becoming part of DTN, we will focus on that role in this article.
What exactly is a DRS? DRS is a DTN Area appointment made by or either reporting to a Regional Hub/Sysop Manager (RSM) in some but not in all Area's (Central and Western) or the DTN Area Digital Manager(ADM)in the Eastern Area.
These Appointments are similar to the Official Relay Station (ORS) appointment, which are made within the RRI at the Region level, In this case a DTN appointment is made by the Region Manager/Sysop in conjunction with the RRI Net Manager makes these appointments accept in the Eastern Area were the ADM in conjunction with the RRI Net Manager makes appointments.
DRS requirements include RRI membership, a monthly activity report to the appropriate either Region Digital Manager in the Central and Western Areas or the ADM in the Eastern Area, and continued service as a DRS Station.
DRSs are usually made for stations below the Region level but is some cases if there is no Regional Hub/MBO at the Region level then a DRS appointment is made. Again mostly in some Area a DRS is at the state, or Section level, although it could also be a local level assignment.
The function of the DRS is to check into (connect to) their “assigned” hub/MBO, download traffic for their areas, and take it to the Region, Section or local nets for further relay and ultimate delivery. Since the Hub/MBOs operate 24/7, the connection can be done at any time, at the convenience of the DRS, although it makes the most sense to do it shortly before the scheduled nets.
When the DRS connects to their Hub/MBO, traffic routed (by zip code) for their area of responsibility is automatically downloaded to their station. Likewise, any outgoing traffic they may have can be automatically uploaded to the Hub/MBO in the same session. Depending on the traffic load, this could take up to several minutes to complete. While the Hub/MBOs use the higher speed PACTOR 2 and PACTOR 3 protocols to communicate among themselves, such speed is not necessary for a DRS, since they are only in contact with the Hub/MBO for a short time. The older PACTOR 1 speed is suitable for a DRS. Fortunately, PACTOR 1 is very easy and inexpensive to operate. Modems (TNCs) like the AEA PK-232 MBX and the Kantronics KAM and KAM Plus can be obtained used for about $50. In addition, DTN operates an Equipment Bank that can loan one of these modems to a new DTN recruit for a flat shipping charge of $15. The modem is theirs to use until such time as they leave DTN, buy one of their own, or upgrade. Then they are obligated to return the loaned modem for use by another newcomer. The Equipment Bank is always looking for donations of equipment and/or cash to further this program.
What else does a new DRS need? Although some of the Hubs/ MBOs also have VHF packet capability, most of their activity is on HF, usually on 80 and 40 meters. That means you need a HF rig and antenna for 80 and 40 meters.
The rig doesn't have to be the latest and the greatest, but it should have a quick transmit/receive turnaround time (most modern rigs do) and preferably a digital frequency readout. Rig control by computer is handy, although not absolutely required. The primary requirement is frequency stability. An older rig that meets the rest of the above requirements, but takes time for the frequency drift to settle down, may still be used provided you turn it on and let it warm up before making your connection.
Controlling the Transceiver
You need a cable to go from your modem to your rig. There are two ways of doing this. The preferred way is to use the accessory connection on your radio. The second method involves the use of the microphone and external speaker connections. The accessory route is preferred, because usually the audio levels on these ports are fixed. Also, such a connection avoids having to plug and unplug connections when you want to use your rig for other modes, such as SSB or CW.
There is very little standardization between modem and accessory port connections. Thus you must specify a particular cable by the modem/rig combination. In my capacity as manager of the DTN Equipment Bank, I have or can get copies of the operations manuals for most common rigs and tell you what type of connector is needed. Because my eyesight and soldering skills are not what they used to be, I prefer to buy these cables already made. Assembly is especially difficult with the 13 pin DIN and 6 pin mini-DIN connectors found on most current radios. Ready made cables are available from W7TUT and Buxcomm, both of which sell a vast selection of cables for different modem/rig combinations for about $22 plus shipping, or from MFJ, which does not have the same large selection. I can give you a link to the proper cable for your modem/rig setup, and you can buy it online.
The modem requires power, and fortunately that connection is one of the few that is standardized. The power connection is the DC coaxial type with a 5.5 mm OD, and a 2.1 mm ID, the center pin being positive (be careful about that, because the penalty for reversing the polarity is the destruction of the modem!). The nominal voltage is 13.8 V DC at about 750 ma, either from the supply in your shack (not recommended, since this might cause ground loop problems) or via a separate supply. “Wall wart” transformer supplies are ideal; just make sure you get one with the right voltage and sufficient current capacity. I recommend one with at least 1 amp capacity. And please check the output voltage. I have spent several weeks and multiple modems getting a DRS online, only to find that his power supply was only supplying 4 V DC. The modem was not happy with that.
Any antennas that works for you on 80 and 40 meters is fine, although an NVIS configuration can be advantageous. As a DRS, you do not need an elaborate automatic antenna tuner, since you will be operating on one frequency at a time.
Lastly, you need a computer, which also doesn't have to be the latest and greatest. The used software used by a DRS is Airmail 2000, which will run on any Windows computer from Windows 95 through Windows 8. The version suggested for use is version 3.4.062, which can be downloaded from http:// siriuscyber.net/ham/
There are some unique issues with this version that we will go over as part of the walk/talk through.
You will also need the correct Airmail SystemNTSD.ini file that you will get from your either your ADM, Alternate ADM in some Areas or Regional Digital manager is some but not all Areas this program will help you to determine the best frequency to connect to the Hub/MBO at a given time of day.
The PACTOR 1 modems are older designs with a physical serial port (female DB-25 pin serial connector). If your computer has an older serial ports with a male DB-9 connector, all you need is a cable to go from the modem to the serial port, male DB-25 on one end and female DB-9 on the other. But life is not always easy. Computers with serial ports are becoming harder to find. If all you have is a USB (Universal Serial Bus) port, you have two options. The best option, in my opinion if you are using a desktop computer, is to buy an add-on serial port board that fits into one of the PCI expansion slots. They come in single, dual, and multiple serial port varieties starting at about $15 to $25. Get at least a dual port card (you will see why later).
If you don't have available expansion slots or are using a laptop, you may only have a USB port available. In that case you need a USB-to-serial converter. They also come in single and multiple port configurations. Unfortunately, not all USB-to-serial converters are created equal. Some are up to the task at hand and some are not; usually the cheaper ones are not. Rather than guess, I suggest you get the DTN-proven Keyspan HS-19. I have never had one not work. They install themselves with a simple executable program, so you don't have to search for the correct drivers. Amazon (and others) sells them. Here is the link to the Amazon site:
Why the dual serial port card? The Airmail software can also control your radio, if the radio is so equipped. For this you most likely will need the second serial port, unless your radio can be controlled directly via a USB connection. Airmail has computer support for most of the recent rigs in the past 20 years. The advantage is that you will no longer have to manually set either the frequency or operating mode on the radio; Airmail will do it for you. For those of you without computer controlled radios, Airmail will tell you which “dial” frequency and what mode (LSB/USB) to set manually on your radio.
Once you have everything together, I or one of the other ADCs will walk/talk you through the hookup, installation and setup, either by telephone or via Skype. Skype is a free VOIP protocol that allows free Skype-to-Skype member calls. We use it quite a bit within DTN for multi-station discussions and conferences. You can get it here: http://www.skype.com/ intl/en-us/home If you sign up with Skype, send a connect request to whomever is going to do the walk/talk, so you are on their connection list. I have also found that it is very helpful to use the Teamviewer remote control software to take control of your computer at the same time we do the conversation via Skype. This allows either Region or Area managers along with amateur with vast knowledge to help you with a problem an to exactly show you how to use and operate the software. Both Skype and Teamviewer are free for private use and you can download Teamviewer here:
If you are concerned about computer security you can remove this software once we are finished.
All of this will culminate in your first connection to your “assigned” Hub/MBO and instructions and practice on how to down load and upload traffic. After that, you will be part of the expanding DTN network. Have fun!
If you want additional details or help, please contact one of the three Area Digital Coordinators (ADC):
Eastern Area Manager: Dave Struebel WB2FTX firstname.lastname@example.org or email@example.com
Central Area Manager: Don Moore KM0R firstname.lastname@example.org or email@example.com
Pacific Area Manager: Chuck Verdon W5KAV firstname.lastname@example.org or email@example.com