Radio Teletype (RTTY)

By Bob Wexelbaum, W2ILP

 

December 2005                      VOL.  78, NO. 12                                                   CIR 120

 
Some time ago your editor gave a series of lectures at GARC Club Meetings on Ham Radio digital modes, which may now be operated by interfacing an HF SSB transceiver to a home computer.  The first of these lectures covered RTTY.  I am again tackling that subject here for those who may have missed my lecture, for our out of town members,  or for those who would like a refresher.

 

After CW, the first popular digital mode used by Hams has been Radio Teletype, RTTY, affectionately known as “Ritty”.  Like Morse code, Teletype, TTY was first used for wired communication and later commercially and by the military as a radio communication mode.   Up until the 1960s Western Union continued to use TTY for telegrams. TTY, like CW is now obsolete for commercial purposes.  Obviously it has been replaced by FAX and E-mail.  RTTY remains a very practical digital keyboard mode for hams, and is now the most popular digital ham mode after CW and PSK-31. 

There are specific timing standards that have been used for RTTY.  The Ham Radio RTTY standard is similar to the military standard, but differs somewhat from the Western Union standard in its start and stop timing.  Early RTTY operation required an elaborate electro-mechanical keyboard, which looked like a typewriter, but could only print capital letters (no small case).  This RTTY teleprinter was affectionately called a “mill”.  Such units were too expensive for most hams to purchase new, thus most old RTTY ops bought, repaired or modified old mills and adjusted them to the Ham timing standard when necessary.   Now that many Hams own PCs, setting up for RTTY operation is very inexpensive.  The PCs keyboard, display and printer can easily perform all of the functions of the old RTTY teleprinters.

RTTY uses Baudot Code, which is a 5 bit code.  PC keyboards and displays use ASCII code which is an 8 bit code.   RTTY is limited to 2^5 = 32 possibilities.  This enables 26 letters (capital letters only), carriage return (like PC <Enter>), and two possibilities that are used to shift to numbers and figures. When shifted to numbers/figures there are another 32 possibilities that are used for 10 numerals, punctuations, and shifting back to the letter possibilities.  There are some differences in RTTY characters when RTTY is to be used for languages other than English.   Early land-line RTTY did not have the shift capability.  Numerals had to be spelled out with letters in Western Union telegrams.  Since there was no period punctuation, the word “STOP” was used to denote a period. 

Compared to the RTTY code, the ASCII computer code is much more versatile.  ASCII’s 8 bit code, where 2^8 offers 256 possibilities, provides for both capital and lower case letters,  as well as everything on a standard QWERTY typewriter keyboard, plus “F” keys and other keys for PC control features.

RTTY is actually a frequency shift mode.  It can be compared to narrow band FM modulation.  It is not a pulse mode.  Like FM, the RF carrier is always on, but unlike FM the carrier frequency is only shifted to one of two possible RF frequencies at any one time.  Thus the duty cycle is 100% just like analog AM and FM, and unlike CW, Pulse modes or Hellschreiber  where the RF carrier is actually turned off during “key up” conditions.  When the shifted RF is heterodyned by a BFO it produces two possible audio tones.  “1” is represented by a 2125 Hz tone called a “mark”.  “0” is represented by a 2295 Hz tone and is called “space”.  The difference is a frequency shift of 170 Hz, which permits RTTY to take up not much more spectrum space than high speed CW.  There are start and stop timing pauses between characters.  The standard commonly used by Hams sends and receives at 45.45 baud or about 60 wpm.  Other shift differences and speeds have been experimented with and the software allows for varying both the receiver and transmitter parameters. If we type slower than 60 wpm there are going to be some pauses in transmitting during real time communication.  If we type faster, there is less of a problem as the typed information gets stored in the PC buffer until ready to transmit.  There are many ways to store the usual types of Ham information, such as calling CQ and giving signal reports, in the PC, and transmitting them automatically by clicking on only one display button.   Early Ham RTTY users actually shifted the RF frequency of the transmitter but this is not necessary when we use a modern HF SSB transceiver, using the tone method.  To use the tone method the transceiver must be operated in the LSB SSB mode.  This is the same for all Ham bands, including 20, 15 and 10 Meters where USB is more commonly used.  The tone method depends on precise audio filtering that is now available from modern PC sound cards.

If you own an HF transceiver and a PC, you can connect them together and work RTTY.  For best results you can build a very simple interface or you can buy the lowest cost RigBlaster interface.

You can get free software for RTTY called MMTTY from:-

http://mmhamsoft.ham-radio.ch

This is the site of Makoto (Mako) Mori, JE3HHT, the developer of MMTTY.  On its home page, scroll down to MMTTY and click on it.  Then download MMTTY V1.65D.  This is the latest version (Jan. 25, 2005).

                                                                                                   Page 2

 

 

 

                                                                                                                                                  

                                         RADIO TELETYPE (continued)

 

Connecting an HF SSB transceiver to a computer is basically simple.  The audio output of the transceiver must get connected to the computer sound line input.  The audio output of sound card must be connected to the transceiver audio line input, or if it lacks a line input, to the microphone audio input. These two connections work best when 1:1 audio transformers are used so that RF is blocked from going to and from the transceiver.  We only want audio. The next connection is required to automatically transmit when commanded to do so by the computer.   It takes the output signal from an unused serial COM PORT of the computer and using a transistor or an optoisolator device, it keys the Transceiver’s PTT.   As I said a commercial unit to do this can be bought from RigBlaster, but the circuits involved are so simple that many hams build their own.  An article in “QST” April 2005.  shows how to build either a simple interface or a deluxe one that derives the PTT signal from the computer audio and also includes a transmit audio level meter.   Once one had the interface connected for RTTY it can also be used for PSK-31, MFSK, Hellschreiber and SSTV.  Each of the modes requires different free software that I will describe in future articles.   When using the interface, you must disconnect your microphone from your transceiver.  Begin by tuning to the proper frequencies where RTTY is most frequently used and looking for received signal printouts.

Here is where you may find most RTTY Activity:  All frequencies are kHz.

80 Meters: 3580 - 3650 (3520 – 3525 in Japan)

40 Meters: 7080 – 7100 (see also below)

30 Meters: 10110 to top of band

20 Meters: 14080 – 14099 (avoid the beacons on 14100)

15 Meters: 21080 – 21100

10 Meters: 28080 – 28100

RTTY allocations vary greatly on 40 Meters all over the world.  In the U.S. RTTY has traditionally been permitted between 7000 – 7150, although most activity is now between 7080 – 7100.  DX activity is often found between 7020 - 7040. According to FCC regulations, data modes such as RTTY are permitted in all CW bands.  Watch for new sub band regulations which may classify modes according to bandwidths, rather than type.  Be advised that although RTTY signals are narrow, some CW operators complain that they interfere with their transmissions, especially during contests.  It is best to stay within the above frequencies.

When receiving RTTY by the audio method your transceiver must be in the SSB LSB mode, as this is the convention used by most operators.  Most phone SSB on 20, 15, 10 Meters use USB so remember to change to LSB on those bands.  Your transceiver should not be in the RTTY or FSK mode when you use the audio method.  It must be in the SSB mode.   Once the software is successfully downloaded you will have an MMTTY icon on your desktop display.  When you click on it you will see the RTTY operating display.  You can then set up your options and learn how to tune to signals.  A traditional “crossed bananas” type display is available.  It features two ellipses

 at right angles to each other.  When an RTTY signal is tuned to both ellipses will appear clearly.  This method of tuning is not the best way now that we are able to use the spectrum analysis display method.  We can see all the activity in the 2.5 kHz bandwidth of SSB.  There are two yellow vertical lines on the spectrum display.  We can tune by aligning those lines to the two peaks of an RTTY signal or the two tracks in the waterfall display below it.  Once you receive signals you will be ready to try to transmit.  The audio level going to modulate your transceiver is critical.  You may control it with a potentiometer in the line or with software control.  If you have an ammeter on your transceiver power supply, you can increase the audio modulation level until the transmitter current peaks, but no more than that.  Operating instructions are available  at MMTTY web site.  If you need help you can also contact w2ilp@optonline.net                Page 3

 

 

 

 

                                                                                                  

PRESIDENT’S PAGE

BY

KE2LJ

 

           

I first would like to congratulate W2ILP for the excellent job he is doing with the GARC Newsletter. In fact, it gets better every month. I guess it’s true in this case that practice makes perfect. I really enjoy reading his articles, and personal observations. And it takes the pressure off me to make this paper interesting to read. I can get way with writing some lame verbiage, like the stuff you are reading right now.  At our November meeting we had Club elections.  normally, there are no surprises, and the usual victims are continually reelected. This may be good or bad, it depends on your point of view. Our one-year Board members were recycled, and will serve another two-year term. The two-year Board members now become one-year Board members. That’s how we do it every year. But, we did have a surprise. Pete, N2PYV, was looking for some relief from the grueling Secretary job. He’s done it reliably for a long time, and wanted some time off. We were lucky that our new member Karen KC2OPX, volunteered to assume the responsibilities. So we now have a new Club Secretary, and I’m sure she’ll do a good job. Karen has also been checking into the Thursday night nets regularly. Hear that guys? She got a 2 meter radio, and is making the nets. Our net attendance hasn’t been too bad lately, but we should be hearing from many of you. TV can’t be that good, can it?

 There’s not much doing in radio here, and I have been pursuing other interests. As you know, I have an IC706 in my Blazer, and that’s the best radio I ever owned. I get a ton of use from it, both on 2 meters, and HF. Lots of fun. Last year, Icom announced a new radio with similar characteristics, but with new features, and some improvements. This model is called the IC7000, and it lists at $1500. You can read all about it at aesham.com. I am seriously thinking of selling my 706 and getting the new radio, but I will wait awhile. I don’t like buying new models as they roll off the assembly line. The 706 had problems when it first came out, and it took Icom a few tries to get the firmware all corrected. When we get to Dayton in May, I’ll check it all out. Why would I change to a more expensive radio? This one has lots of new features, and I readily admit I won’t be using most of them. But, it does have some that I find interesting. The front panel is now a high resolution color screen. In fact, you can supposedly watch TV on it. There’s a video output jack to use if you want to see the screen on your PC monitor. The radio has 2 DSP chips, so you never have to buy and install separate filters for any mode. You can dial in the pass bandwidth and the shape factor as well. All kinds of noise filters, blankers, etc. Very flexible. All I have to do is figure out a way to pay for it. When I sell my house for a million dollars, there should be some money left over for a new radio.

   Be sure to attend the Holiday party at the Country Buffet in Levittown. Bob mentions it elsewhere in this newsletter, and there’s some info on our web site. Hope to see you all there.

CQ DE WA2LQO DECEMBER 2005

GRUMMAN AMATEUR RADIO CLUB

MINUTES OF GENERAL MEETING -11/16/2005

Pete N2PYV

The meeting was called to order by Pat at 5:45 PM.

 

TREASURERS REPORT – Ed, WB2EAV          REPEATERS – Gordon, KB2UB

 Finances continue to be in good shape.                    Nothing new to report.

                                                                                                                                                                                                                                 

VE REPORT – Bob, W2ILP                                  NET REPORT- Zack, WB2PUE

No VE session in November because                        The Sunday morning 40-Meter was good.

scheduled date fell on election day.                           I was able to hear all of the guys.  The Thursday                                                                                                                                                                               evening 2-Meter net was pretty good. .

NEW BUSINESS

Election of Officers and Trustee for 2006

The meeting was turned over to Marty, NN2C, our Election Chairman, who nominated candidates for                    officers and trustee of our club. The following slate was nominated and duly elected by the members             present.

President – Pat Masterson, KE2LJ                           Vice President – Gordon Sammis, KB2UB

Secretary – Karen Cefalo, KC2OPX                        Treasurer – Ed Gellender, WB2EAV

1 yr Board Member – Bob Cristen, W2FPF             1 yr Board Member – Dave Ledo, AB2EF

1 yr Board Member – Zack Zilavy, WB2PUE         2 yr Board Member – Jack Cottrell, WA2PYK

2 yr Board Member – Bob Wexelbaum, W2ILP      Trustee, WA2LQO – Ray Shubnel, W2DKM

 

IMPORTANT: - It was announced that the December Meeting/ Holiday Party will be held at the

Old Country Buffet, 3023 Hempstead Turnpike, Levittown, NY.  On Dec. 21, starting at 5:30 PM..

Please bring cash for restaurant cost (approximately $10.).  Club dues for 2006 will also be collected at the meeting.  Those who are unable to attend may mail dues to Ed Gelender.

 

PROGRAM

Pat showed a video produced by the ARRL.  It was narrated by Walter Cronkite, and showed the ARRL  interfacing with Washington, D.C. to explain the Radio Amateur’s position on rules and legislation  affecting the hobby.

The meeting was adjoined at 6:30 PM.

                    

GARC NETS:

40 Meters: 7.289 MHz at 7:30 AM EST Sundays.

20 Meters: 14.275 MHz at 12 Noon EST Wednesdays.

2 Meters (via repeaters): 146.745 MHz  (-.600)at 8:30 PM EST Thursdays.

                                           145.330 MHz (- .600) at 9:00 PM EST Thursdays.

[Tone for both repeaters is 136.5 Hz]         (ARES/RACES) Mondays

                                                                                                                Page 5

 

 

 

                                                                                                                   

 

                                                                                   

MEETINGS

General Meetings of the GARC are held on the third Wednesday of each month, starting at 5:30 PM.   The meetings are usually held at the Underwriters Lab, 1285 Walt Whitman Road,  Melville, NY.  Driving directions and maps can be obtained from http://www.mapquest.com   It is suggested that the GARC Web Site be checked to be certain of meeting location, which may change after this newsletter is distributed. Board meetings are held eight days before the General Meeting and GARC members are invited. to attend, but please call Pat Masterson, KE2LJ, at 516-346-7125 to confirm place and time of meeting.

                                                          

GARC WEB SITE

The web site of the GARC can be found at http://www.qsl.net/wa2lqo/     Webmaster is Pat Masterson KE2LJ.  Pictures of GARC activities, archives of newsletters, roster of members, and other information about the GARC may be found there.

                                                                                                                                                                                                                                                                                                                                                                                                                    

Internet Link of the Month for Internerds

 

The following Internet link was suggested by Tom Provost, AG2A: –

   It is http://www.ac6v.com

Tom said that this was a very useful URL for “everything Ham Radio”.  He said that he had gotten lost for hours reading about subjects that he didn’t think he had any interest in.  This URL is certainly a great resource.

After looking at it, your editor certainly agrees.  It is well indexed, so that you may click on any subject and get to pages of good material, including useful operating aides for every type of radio operating.    I spent some time checking out this site but I must admit that I couldn’t find time to take advantage of all of its features.  Yep…It seems to be a very extensive site for Hams and probably contains more technical information than the ARRL.org site.

 

                                  

PUZZLE

Here is another cryptogram:-

 

H  OIGGHJI KHZ  EI  GIZA  HWLYZP  ARI  ULWCP  QZ  LZI – BQBAR  LB  H  GIKLZP,  FIA  QA  OHF

 

AHSI   FIHWG  BLW  QA  AL  JIA  BWLO  ARI  LYAGQPI  LB  GLOILZI’G  RIHP  AL  ARI  QZGQPI.

 

Solution to November’s cryptogram:   CHRISTMAS IS A TIME WHEN KIDS TELL SANTA WHAT THEY WANT AND ADULTS PAY FOR IT.  DEFICITS ARE WHEN ADULTS TELL THE GOVERNMENT WHAT THEY WANT -- AND THEIR KIDS PAY FOR IT.     –RICHARD LAMM—

 

                                                                                                                                                         Page 6

 


GARC VE SESSIONS

 

We are continuing to proctor exams for all classes of ham licenses on the second Tuesday of each month, starting at 5:00 PM.

 

The present exams are: Element 1: 5 WPM CW, Element 2: Technician,

Element 3: General and Element 4: Amateur Extra Class. The fee for 2005 is $14 for all exams taken in one sitting.

 

Applicants for upgrading should bring a photocopy of their present license and their FRN number.

 

New, first time, applicants should be aware that their Social Security

number will be required on their application form. All applicants should bring drivers license or other picture ID. The exams are given at the Underwriters Lab in Melville,

unless otherwise noted.   This is the same building where GARC meetings are presently held.

 

For any further information e-mail: -

w2ilp@optonline.net or phone: - (631) 499-2214

 

Study material information is available at the http://www.arrl.org or the http://www.w5yi.org web site.

 

All VECs use the same Q & A pools.

 

Since the beginning of the VE program the GARC has provided opportunities to take ham exams monthly, during all twelve months of every year.

 

 

 

Bob Wexelbaum, W2ILP

and the Grumman VE team.

 

 

                                   Page 7

 

CQ de WA2LQO

Decemberr 2005

 VOL.  78,  NO.  12

 

EDITOR

Bob Wexelbaum  W2ILP

(631) 499-2214

w2ilp@optonline.net

 

CONTRIBUTING WRITERS

PAT MASTERSON, KE2LJ

PETE RAPELJE, N2PYV

And all the members of GARC (we hope!)

 

CQ de WA2LQO is published monthly by the Grumman Amateur Radio Club for its members and friends. Send articles and amateur equipment advertisements to:

KE2LJ or W2ILP

 

ELECTRONIC SUBMISSIONS

If you want to submit articles or amateur equipment ads via e-mail do the following:

1. For submission direct to editor call him at above number to set up a transfer.

2. For e-mail transfer:

Internet Address

bat@grumman.com

 

 
EDITORIAL

 

On behalf of all of the members of the GARC, and myself, I want to wish all readers of this newsletter: -

********************************

        HAPPY HOLIDAYS and                      

        HAPPY NEW YEAR 2006.

*******************************

2005 was a rough year for many of us Earthlings.  Let us hope that 2006 will be a better year - Let our winter be warmed by the global warming cyclic effect and our summer be cooled by the melting of the polar cap.  Let our DX be improved by the most appropriate ionization of the ionosphere’s layers and our ecology be improved by the decreased pollution of our atmosphere’s layers. Let family values increase and oil barrel values decrease.

Let acid rain be sweetened by no sugar substitutes.   Let the continental shelves drift where they can’t cause perilous earthquakes.   Let the hurricanes go out to sea and not cause any devastation.  Let the tires hold air and the levees hold water.

Let the tornado’s whirls be unwound.

Let BPL be outlawed and RF radiation levels controlled.   Let Hams mount their antennas anywhere that a ground plane exists.

Let there be peace on Earth and good will to all humans..

 

73,

W2ILP (I Like Peace)

 

GRUMMAN AMATEUR RADIO CLUB OFFICERS FOR 2005

 

President                Pat Masterson              KE2LJ            V01-01    516-346-7125

Vice President       Gordon Sammis            KB2UB          Retiree     631-666-7463

Secretary               Karen Cefalo                KC2OPX      
Treasurer               Ed Gellender                  WB2EAV        X02-14   516-575-0013

2Yr Board Member    Zack Zilavy            WB2PUE        Retiree     631-667-4628
2YrBoard Member     Dave Ledo             AB2EF

2Yr Board Member   Bob Christen         W2FPF             

1Yr Board Member   Bob Wexelbaum    W2ILP             Retiree     631-499-2214

1Yr Board Member    Jack Cotterell        WA2PYK         Retiree     516-249-0979

Trustee WA2LQO        Ray Schubnel        W2DKM          Retiree

 

STANDING COMMITTEE CHAIRMEN

 

Meeting Programs       Contact a Board Member

FCC Exam Coord.      Bob Wexelbaum     W2ILP                          631-499-2214

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 


GRUMMAN AMATEUR RADIO CLUB

Sixty Years 1944 -2004

P.O. Box 0644

Bethpage, NY 11714-0644

 

 

 

                                                                                                        FIRST CLASS

                                                                           DO  NOT DELAY

                               TECHNICAL BITS                

 

Last month I started to talk about radio receiver selectivity.  Because the I.F. amplifiers remain tuned to the same center frequency throughout the frequency range of most receivers, the I.F. amplifier usually serves as the best place to introduce filtering that will determine the receiver’s band pass.  Even when crystal or mechanical filters are to be used it is best to design I.F. transformers that will also l filter out unwanted noise and nearby signals.  

The response of the I.F. amplifiers depends on the design of the I.F. transformers.  Either the primary or the secondary or both may be tuned to the I.F. center frequency.  The amount of either capacitive or inductive coupling, or both, between the primary and secondary is also important.  The most important parameter is the Q (figure of merit) of the transformer tuned circuits. .  In order to obtain a Q that will provide the proper band pass, physically large transformers were formerly required.  When vacuum tubes were replaced by transistors it became important to miniaturize the size of the IF transformers, while maintaining the same Qs.  This led to research in developing powdered iron or ferrite transformer cores that could provide large Qs in tiny transformers.  There are equations that include the loaded Q, and the coupling factors of the transformers and then predict the response of the transformers.  In the simplest case, where we get a single peaked response, Butterworth equations are used, but in most cases we need to use

Chebishev filter equations, which relate to poly-peaked responses. The results of solving  the equations can accurately graphically predict the final response of the IF amplifier.  The next important specification for radio receivers is called Dynamic Range.  This is the ability to maintain the specified sensitivity and also to be sure that very strong signals will not saturate the receiver.  This requires Automatic Gain control (AGC) which I will continue to describe next month.