Blog Post 4 – FLDIGI – Radio Teletype (RTTY) the WRAP Utility and RS-ID Wednesday July 1, 2009
This is Curt Black, WR5J with the Educational Radio Net – Please stand by for a PSK-31 Digital QST
(As before please set up your FLDIGI software for Menu OP MODE, then select PSK then slide over to select BPSK-31 – for binary phase shift keying – 31baud. Just a reminder from last week - don’t have your volume very loud – place your microphone fairly close to your speaker so you don’t confuse the modem with echoes of the audio..
If none of this sounds familiar, go to the blog and look at post #2. OK off we go.
That was a little chunk of field day to remind you what fun that was. There were more digital signals than ever before on the bands. How did folks do on the copy?
We have about 10 weeks to go till September 2, so I think I’ll change the format just a bit skip the check-in process so as to recover that 10 minutes I took last week. Although I appreciated the chance to get some feedback from folks on how their installations have gone, maybe we can make it less formal and just grab questions as they come up.
I’m beginning to have faith that there are people out there in radio land. Just a reminder, there are now 20 people signed up on the YAHOO! WA-DIGITAL list – that is turning into a good resource for the software and instructions and background documents for this series. Please signup if you haven’t yet. Just this week I put up background documents on PSK-31, RTTY, WSPR and a proposed schedule for the rest of the summer. As always, please feel free to break in with any questions at any time during the net. Also, don’t hesitate to send an email during the week at firstname.lastname@example.org.
This week I’d like to go over a few more features of FLDIGI. I’d like to get setup for automatic switching to the proper mode using the Reed-Solomon Identifier or RS-ID feature. I’d also like to get us to the point where we can send each other error free messages using the WRAP utility included in the NBEMS suite.
Review from Last Week
Several useful features are included in FLDIGI for changing quickly “on the fly”. For example, you can right-click on the macro buttons to edit their content or to cut or paste information. Remember, there are 4 sets accessable from by clicking on the right end of the menu bar. As we discussed on the net, you can left-click on the mode name in the far lower left corner of the screen to switch to other variants of the mode currently selected. A right click of the same button brings up the configuration pane for the mode currently in use.
There are just a few features that are not configurable, “on the fly”. During the net I was asked how to customize the height of the waterfall. I had trouble finding it which seemed odd because I’ve rooted around quite a bit in the program. After the net I found it under the Configure Menu / UI (User Interface) choice / then click on the “Restart” tab. This is a strange name and I would say it is why I couldn’t find it during the net, but it is called that because changes made here don’t occur until the next restart of the program.
Under the Restart tab you can set how high the waterfall is in pixels and how wide the waterfall is in Hertz. I usually use the max height of 160 and 3500 for the width. You can always zoom in with the X1, X2 or X4 in the bar under the waterfall, using the left facing arrow next to that magnification control to slew the waterfall to the left and the right facing control to move it to the right. The double bar that looks like a pause button is for centering the currently selected location where the modem is focused in the waterfall (all these only work when you are zoomed in enough to need them).
We talked about the 2 minute buffer that is constantly saving the audio and how you can change modems in the OP MODE menu, and then click over an interesting signal with the right mouse button and then left click to decode the last 2 minutes with that new modem.
Last time we talked a little about the makeup of a PSK-31 signal and how sensitive the mode is during transmission to avoid over driving and splattering. We looked at the information in the bottom line of the screen next to the mode identifier. While decoding PSK-31, those boxes contain information on the Signal to Noise ratio and Inter-Modulation Distortion (IMD). Remember to make those measurements on an idling PSK-31 station and that we are working to keep the value below minus 24 dB (for example minus 34 dB would b a great signal – a minus 11 dB would be a nasty signal that would be attracting lots of attention on the band). These values are only for received signals – so you need the help of your fellow hams to find the quality of your own transmitted signal. There are at least two devices to help you monitor your own signal as it is being transmitted – the IMD Meter by KK7UQ, Clint Hurd and the PSK Meter by George Rothbart, KF6VSG. A comparison of the two products is on the bottom of the page found at http://kk7uq.com/html/imdmeter.html
The Wrap Utility
The WRAP utility program checksum feature lets sending stations transmit a plain text message, an image or a binary file with embedded coding that includes a checksum calculation. Multiple receiving stations can then verify 100% copy on received text. I thought we would try that now. I’m running version 3.11.5 but all versions in the 3.11 series work for this.
Before we get to wrapping, I want to say, “YOU SHOULD NEVER WRAP any of the MICROSOFT OFFICE APPLICATION FILES WITHOUT CONVERTING THEM” You should convert a word document to text, an excel spreadsheet to a Comma Separated Value (CSV) format text file, etc. A Word Document with 1 character in it is 13.8 kilobytes, when zipped it drops to 1.8K, but it is still a ratio of nearly 2 thousand to 1. The WRAPing process expands the file to half again its original size during the ASCII Base64 encoding so that 1 character word file is still nearly 3 k. Send text whenever possible. This is a training issue, we are communicators trying to help transmit information – not a specific file, but the information in that file. Think about efficiency before you hit the TX button.
To set up for automated receipt of a “WRAPPED” message, please go to the CONFIGURE menu and slide down to the MISC item. On the window that opens click on the TEXT CAPTURE tab. Click the check box next to, “Enable Detection and Extraction”.
This will cause any text that begins with the string, or series of characters between, “[WRAP:beg] and [WRAP:end] to be pulled out and saved in your WRAP folder inside your FLDIGI.FILES folder under your login name in DOCUMENTS and SETTINGS. This is very WINDOWS centric, but there are similar settings for Linux and Apple OS users. If you navigate to that folder, I would suggest putting a shortcut to it on your start menu. Then you can quickly open it and look for files saved there. I would also put a copy of NOTEPAD and the WRAP.exe file in there – then everything is in one place and you have a shortcut to it on your start menu.
You should now be ready to receive a wrapped file – so lets try that now – Questions?
To send a WRAP file, just create a text file by saving from your favorite word processor or pasting text into NOTEPAD. Then save the file into the WRAP folder as a text file. Take that text file and drag it over the icon for the WRAP.EXE utility and a new file will be created in the same directory with the same name except with a.WRAP extension. To send this file, drag the new file to the bottom of the screen over the FLDIGI task and wait for that window to open, then continue dragging until you are anyplace in the send window, most of the bottom half of the screen. Release the mouse button and the wrapped text will appear in the window to be sent. You may want to put some explanatory text in the window before the file, but when you are ready, just press the TX button on the macro line and off it will go.
The powerful thing about this is that it allows transfer of files from one station to many in a format that allows all stations to know they have received the file error free. Previously we would have to use an ARQ (Automatic Repeat reQuest) linking protocol one station at a time. This has great potential for digital nets like this one or those that follow. The NBEMS suite has an application called FLARQ.exe. It allows two stations in QSO to form a linked condition and send error free data back and forth – however it is only one station at a time. Since we can’t demo it through a repeater, and it only works on one station at a time, just check out the documentation on the PA-SITREP website or the author’s website at http://www.w1hkj.com/FlarqHelpFiles/flarq.html
Since that was pretty dense and a radio net is clearly not the best format for such a hands-on lesson, the blog post and Yahoo group file for Post #4 has links to two files on UTIPU which show exactly the steps I’ve described here, but much more graphically.
http://www.utipu.com/app/tip/id/10407/ Receiving and unwraping example with Olivia 8/500 and very bad powerline noise
The "RS" ("RS" for "Reed-Solomon") identifier allows automatic identification any digital transmission done in one of the RX/TX modes handled by FLDIGI. If the sending station is using the feature (currently available in MULTIPSK, FLDIGI and by this August, HRD/DM780 – probably someday in MixW). It detects the mode used and the center frequency with a precision of +/- 2.7 Hz.
As soon as this identifier is received, FLDIGI switches to the proper mode and frequency and immediately decodes the QSO in progress or the call (CQ). This identifier is transmitted in 1.4 sec and has a bandwidth of 172 Hz. It is usually detected down to a Signal to Noise ratio of -18 dB (or perfectly at about -16 dB), so it has a sensitivity equal or better than the majority of the digital modes (RTTY, PSK31...).
This identifier can be transmitted before each CQ call or prior to each answer in a QSO. Turn on this feature by going to the CONFIGURE menu and selecting the ID item. On the window that opens, check both the, “TRANSMIT MODE RSID” box and the “Detector Searches Entire Passband” check box. The actual searching is somewhat processor intensive, so to turn on the function in receive mode, there is a control in the upper right corner of the screen next to the TUNE button labeled, “RSID”. Go ahead and make those settings. Questions ?.
Now that you are set up, keep your mode setting on BPSK-31 and we will give it a little test. I’ll pick a new mode and a new frequency. Make sure your RSID button is pressed in the upper right corner of the FLDIGI screen. We’ll see if everyone switches over and starts to decode it.
RTTY (Radio Teletype)
The second most popular digital mode. Somewhat more complex to set up and much less spectrally efficient than PSK-31. I think the designer of PSK-31 was hoping his new mode would replace RTTY, but for better or worse, it is wildly popular all around the world and, while somewhat brute-force, is a lot of fun to use. It can be hard to know what frequency to spot either yourself or others. Unlike almost all the other digital modes we will use, this one can be found in Lower Side Band. That is from tradition – and gets more confusing as we try to figure out how to spot our own frequency. We need to pay attention to which sideband we transmit on in SSB. So once we get back to HF and away from these demonstrations in FM, the sideband and frequency will rear their ugly heads as issues. On RTTY, the inverted signal matters in contrast to PSK-31 or the other PSK flavors.
Rather than get too bogged down at this stage of our hour together, please look to the following websites for guidance:
Getting Started in RTTY with MMTTY at
A RTTY Tutorial For Beginners at
Next Week one of Joe Taylor’s modes, K1JT, called WSPR, “Whisper” – the Weak Signal Propagation Reporter”. An amazing mode that takes about 300hz of HF bandwidth and lets people all over the world share it to test RF propagation. Your individual transmission will only be about 3 Hz wide. It has been tremendously enhanced by the presence of the website, http://wsprnet.org/ where after you easily create a free account, you can look at worldwide activity and a database with 7 million spots and growing at about 1000 spots an hour, 24 hours a day. I’ve already put the software on the Yahoo group and the blog post with more info should be up early this weekend.