Antenna

Tipp:
The further away you are from the received radio station the higher the selected frequency should be. If, for example, you are in the German area of the Baltic Sea, you will receive „Meteo Offenbach“ very well on 147,3kHz or 4553kH. If you are cruising in the Mediterranean you need to tune your receiver to 13885kHz or 14467kHz.

The first test should always start with a clear reception. If you don’t receive any usable signals you need to improve the antenna. You can also wait for the reception to improve. If you ignore this rule and try with a very weak signal, it will be difficult to interpret the tuning elements and their function properly. This is not to say that it won’t work at all. A knowledgeable individual can still use a signal that seems unintelligible.
How am I supposed to adjust something that I can’t see or hear?
Once you have tuned a signal under good receiving conditions it can still be decoded in less favourable circumstances. Since tuning and parameters are saved in the frequency list, it can be reloaded in exactly the same way later on. It is therefore not necessary to do the tuning procedure again. This is where the decoder shows off its real capabilities. It still decodes the signal because it does not “hear” the interferences the same way you do with your ears. The electronic components are able to filter through the unwanted parts of the signal and pick out the essential ones. The loudspeaker on the other hand simply reports what is being received. You will hear all kinds of things which make it impossible for the human ear to ascertain whether there still is a usable signal or not.

Backstay

Tuning a signal – What is a usable signal?

In order to tune a signal it is useful to be able to distinguish the tone signals of the various operation modes.
There is a demo version on your CD. Open the demo, bring up the frequency list and double-click on a frequency. The reception window will open, as it will in the full version. You can now hear the signal and also observe how MeteoCom processes the different tones, in a weather fax map for example.

A signal is composed of tones with varying pitch, which are decoded differently. The spacing between the first tone and the last is called band width. All decodable signals have one thing in common: If you have doubts that the signal is usable, it usually isn’t. Intelligible signals are always discernable and stand out of the general noise and other indefinable signals. Now we need to find out whether the signal is Morse code, RTTY or FAX. The MeteoCom demo CD will help you with that.

Distinguishing the various RTTY signals, however, is a little bit more complicated. „BordTerminal“ only analyzes Navtex and RTTY. There are other forms of RTTY that are not picked up by the software even though they are received by the radio. That’s why not every intelligible signal is a usable signal in the context of maritime use. There are also signals that are decoded properly but don’t make any sense. This could be the case when you pick up a station from an Arab country that uses different letters.
In order for the receiving program to work properly, you will need assistance for correct tuning. The tuning assistant shows you where the signal is and how much interference there is in its neighbourhood. There are two different tuning assistants for RTTY: the frequency spectrum and the X/Y tuning assistant. For Fax you only have the frequency spectrum.

If you control your radio using the software, all frequencies and parameters are set perfectly. If the radio is stable there should be no deviations and the program should be starting to decode right away. In this case the tuning assistants are used merely to monitor the signal.
 

Receiving Weather data
Receiving Radio Teletype (RTTY, Navtex, and Synop)

This is the RTTY surface. The text window displays the received message. Usually you will see the lowest row, meaning the one being received at that moment. If you want to read text that has scrolled off the screen and is no longer visible, click on the screen once. To reverse the process click onto the title bar above the text screen.

The MeteoCom 6 Demo version can be very helpful www.bonito.net/software/MC6DWebInstall.exe

Tuning RTTY
Usually, the tuning displays process the tones received by the radio in such way that you can observe the way the radio tunes the signal. These displays should help you understand how the tuning process works. As a first test it may be useful to just turn the main tuning knob of your radio to acquaint yourself with it. If, later on, you want to tune more precisely, you need to use the „Receiver-Control“ because your radio doesn’t report to MeteoCom when you tune your radio manually.

Frequency-Spectrum
This is a display showing all tone frequencies up to 2500 Hz from left to right. The height corresponds with the volume (amplitude). The amplitude is dependent upon the tone’s frequency. You should always try to find the tone frequency yielding the strongest amplitude. There are precise technical standards which specify at which tone a signal is tuned properly. In real life, however, all this depends on the filters used in your radio. The filter curves are not always the way they should be. This means that the frequency list is always a theoretical tool and not adapted to your specific radio.

Make sure that both amplitudes are lined up exactly with the red lines. The spacing between the red lines corresponds with the band width (shift). The position on the scale is the tone’s frequency or pitch. The height shows the volume. This picture shows an RTTY signal with two different tones. One for “mark” and one for “space”. Both tones should be lined up with the vertical red lines. In case of a Fax signal, the bandwidth is usually greater, meaning that the two vertical lines are further apart and there is almost always only one bar at the red line on the right. The tuning process is explained in detail later on.

X/Y-Tuning Display (Tuning Cross)

The previous page showed an example for a RTTY-signal. The exact tuning possibilities are indicated here on the X/Y display. This tuning tool is used only for RTTY. Before using the tuning cross you should tune the signal with the frequency spectrum in such way that it lines up with the red vertical markers. Only after that should you try to use the tuning display and establish a cross shape. If this should not work initially, try playing with the bandwidth (page 25). If the bandwidth is correct the tuning display will show a cross. Now make sure that the lines forming the cross shape are straight, meaning aligned with the X-axis and Y-axis respectively.

85Hz bandwidth 425 Hz bandwidth

Tuning

If you can make out the two signals clearly, then you can also read the bandwidth. Using the „Receiver-Control“ tune the radio in such way that both of the green colored signal amplitudes line up with the red markers or the lines of the tuning cross are exactly perpendicular. Also refer to page 17 (X/Y tuning display (tuning cross) or frequency analyzer.

Operation Modes

Baudot:
This operation mode usually concerns common teletype text and is an asynchronous mode. It is often used by press and weather services. SYNOP messages are also broadcast in this mode.

Asynchronous means that the characters are marked with a start- and stop bit, because they are transferred in an irregular way.

Sync. Baudot:
Baudot is an asynchronous mode. But it can be assumed that today’s broadcasters use automatic machines for their transmissions. If the reception of the signal is distorted the program presumes that the start and stop bits are transmitted at a certain expectable position. It is therefore likely that there really are start and stop bits at those positions, even though they are not received properly. This logic contributes to a low amount of reading errors. Should a message be transmitted by a manually operated typewriter, this mode of operation should not be selected.

Sitor-B:
This is a synchronous mode which is different from Baudot. But it does use the same logic. This mode is much less affected by distortion. Sitor is used for Navtex and is then always at 100 Baud.
 

Adjusting the Baud rate

The speed of the individual bits in teletype is called Baud rate. Baud rate is derived from BAUDot. The most frequently used Baud rates for normal Baudot are usually 50 Baud, sometimes 75 Baud (Meteo Bracknel). On rare occasions you may encounter 100 Baud (Meteo Grengel). Navtex always uses 100 Baud, in mode Sitor-B, however.

Shift + Marker frequency
The spacing of the two chirpy warbling sounds is the shift. The sounds indicate the bit status of a RTTY bit. The shift is represented by two red markers in the frequency analyzer. The marker frequency governs the position of the markers. Meteo Offenbach 147.3 for example transmits at an 85 Hz shift. Navtex uses a 170 Hz shift. Above 3 MHz Radio Offenbach uses 425 Hz. Meteo Moscow and Meteo Roma both use 850 Hz.

Polarity
If reception is clear but the received characters don’t appear to make sense, try switching the polarity to improve readability. Navtex for example always transmits with an inverted polarity. But there may be other reasons for an unreadable signal. It is possible that the message text includes a character which causes the decoder to only read digits and other data.

In this case you should try using the LE-mode to improve readability. Activate FI only in a contrary situation when Synop 5-digit groups are turned into groups of letters.

Stopbits
Baudot normally uses 1.5 stop bits. But it is possible to come across a station using 2 stop bits. That is why there is an adjustment possibility. Adjustment is not necessary in Sitor mode, since this mode does not use stop bits.
 

Weatherfax

Weather maps are broadcast using „WeatherFax“. WeatherFax is the most frequently used way of broadcasting processed weather data.
Normally there is no need for adjustments because all parameters are set automatically when double clicking the frequency. If, however, you still wish to make adjustments, you may use the following procedures:

IOC
There are several different image formats that can be used to receive Fax. They are called modules. In our case module 576 is used most often, sometimes module 288.

Drum Speed RPM
The drum rotation speed of a fax is denominated in revolutions per minute (rpm). A normal weather fax uses 120 rpm. Weather maps from Russia and Japan may come at varying speeds such as 60, 90 or 120 rpm.

Shift & Center frequency Fax Decoder
It is important to shift the tuning from high frequency tones to lower frequency tones in order to avoid interference. This means you are shifting the red markers in the frequency spectrum along the horizontal scale.

Fax PreFilter
„Width“ is the spacing between the lowest and highest tone frequency of a signal. That is the spacing between the two red markers in the spectrum display. The filter should be the same width. Filter adjustments that are narrower or wider may also improve the reception.


Start/Stop Frequencies
Start- and Stop frequencies are sounds played at the beginning and end of an image. Normally there would be a 450 Hz tone for start and a 300 Hz tone for stop. After the start tone MeteoCom starts recording the fax and saves it to the hard drive after the stop tone.

Spectrum- Analyzer
This is the display for tuning the tone frequency. In most cases a fax signal USB shows more activity on the right side that degrades towards the left end of the bandwidth (red marker).

In order to receive good, clear images, the main signal activity bar should always be just in front of the red marker. In case of distortion you can shift the IF to the left or right, narrow the bandwidth or manipulate the filter.
Slant Correction

Navtex

Sie können weltweit die NAVTEX-Meldungen der Küstenfunkstellen auf den Frequenzen 490 kHz und 518 kHz in Küstennähe empfangen. Die Navtex Nachrichten finden Sie unter "Texte"  "Navtex"

WICHTIG ! NICHT ZU VERWECHSELN!

NAVTEX Meldungen beinhalten z.B. Nautische Warnungen, Seenotmeldungen, Wetterberichte für 24 oder 48 Std., Sturmwarnungen.

Die Navtex Nachrichten werden mit dem Fehler korrigierenden Funkfernschreibverfahren SITOR-B auf der Frequenz 518 kHz in englischer Sprache, und in einigen Ländern auch auf den Frequenzen 490 kHz sowie 4209,5 kHz in Landessprache verbreitet. Japanische Sender übertragen Navtex-Meldungen in japanischer Sprache auch auf der Frequenz 424 kHz.