[RTTY] IARU and 14100 Beacon QRM from Digital Signals

[Bill Coleman]

On Sep 25, 2006, at 9:22 PM, Andrew O'Brien wrote:

> FROM IARU Website.
>
> Beacon Interference
> The major interference problem for beacon listeners occurs on the
> twenty meter frequency of 14100 kiloHertz. The IARU/NCDXF beacons have
> been on this frequency since 1979. The frequency was established
> before the tremendous advances in the popularity of the digital modes
> occurred and today the frequencies on both sides of 14100 kiloHertz
> are full of digital signals.
>
> On the ham bands, no station has a legal right to exclusive use of any
> particular frequency. However, as the digital-mode signals began
> encroaching on the beacons, both the IARU and the ARRL incorporated
> into their official band plans the idea that the frequencies between
> 14099.5 and 14100.5 should be kept clear to protect the beacons at
> 14100.0. Although these band plans do not have the full force of law,
> there is general agreement that a properly operated amateur radio
> station should normally operate within such band plans and the vast
> majority of digital operators do so.

The ARRL also has this to say:

"5) Interacting with non-contesters
...
c) Band plans
...
Band plans are just that - plans. They are designed for normal  
circumstances when band loading is much lighter than during a  
contest. During major contests, the bands will be very crowded,  
resulting in conditions that the band plan is not intended to  
address. Avoid willful interference and be as courteous as possible  
to non-contest QSOs within the limits of the contest rules and  
licensing regulations."

 From the HF Contest FAQ:
http://www.arrl.org/contests/hf-faq.html

> If one listens for the beacons with a receiver whose bandwidth is
> designed for voice reception, the 2.8 kiloHertz bandwidth typical of
> such receivers will inevitably receive adjacent digital signals as
> well as the beacons. When this happens, the resulting interference
> should not be blamed on digital operators so long as their signals are
> more than 500 Hertz from the beacon frequency.
>
> It is recommended that when you listen to the beacons you use a
> receiver with a CW IF filter of 500 Hertz or less. Such a narrow IF
> filter is primarily needed to reduce interference from digital signals
> on 14100 kiloHertz, but will help you to hear the beacons better on
> all bands by reducing atmospheric and other noise.

This is a very important tip.

> Unfortunately, not all digital operators are familiar with fact that
> the official band plan for twenty meters calls for keeping the
> frequencies around the beacons clear. Furthermore, some digital
> operators do not realize that their transmitted RF energy occupies
> frequencies which are different from the frequency which shows on
> their dial.

This is also important. It shows that the conflict here arises from  
ignorance, not from malice. A RTTY operator tunes to what he thinks  
is a clear frequency, and perhaps checks his frequency dial. If he's  
running AFSK LSB, and the dial says 14.002, he may think he's clear  
of the beacon frequency (assuming he's even aware of it). Instead,  
he's within that 500 Hz passband with both tones. (This assumes he is  
running the high tones of 2125 and 2295 Hz - I myself use 1415 and 1585)

> If you notice a station which is not abiding by the band plan and is
> transmitting RF energy too close to 14100 kiloHertz, you may, in a
> nice way, call that station's attention to the interference he is
> causing.

This may be hard to do in a contest. "In a nice way" is hard to get  
across sometimes, especially when people are in a hurry.

Many contest operators are courteous, and will move their operations  
if politely requested for good reason. There's a few stubborn ones  
who won't.

> You are welcome to send interference reports to the Beacon  
> Committee/a>.
> In the typical case of a digital-mode interfering signal, the most
> useful reports are from stations which can actually receive the
> digital transmission and which include the time, the date, the
> callsign of the transmitting station, the mode being used, and the
> dial frequency used to monitor the transmission. It is also useful if
> you include the IF bandwidth you use for listening to the beacons.

Good stuff.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901