|PSK31 Audio Beacon|
App #1: Tone Gen
The Warbler's Guide to Considerate Beaconing
by Joe Everhart, N2CX
Operating a beacon can truly be fun. One can determine antenna performance, propagation characteristics, effects of different power levels, etc. However itís not something done every day and many will never use a beacon on the air. But if you do couple your PSK31 Audio Beacon with an SSB transmitter, here are some guidelines for considerate beacon usage.
Any use of a transmitter to radiate a signal should be done with courtesy in mind. The electromagnetic spectrum is like real estate Ė itís a limited resource that we share with others. And the radio amateur bands are like limited access parkland to which we are granted access so long as we use them properly. Other licensed hams want to enjoy them too and we must keep that in mind so that we donít lessen their pleasure by our use of the bands. After all, you wouldnít play baseball in the middle of a picnic ground and picnickers are unlikely to spread their lunch out on a ball field!
As mentioned, beacons are not an everyday tool. When they are put on the air itís for a specific purpose ó often to gauge signal propagation. This means that we do want them to be heard by someone.
Beacons may simply be an unwelcome intruder to others. Only shorts periods of operation should be limited to only that short period of time when it will do some good without being and annoyance. Similarly, it is extremely impolite to just plop it on the air willy-nilly and let it transmit for extended periods when band activity is high. Its use to judge propagation is questionable when a band is highly populated; simply "reading the mail" on existing signals gives much the same information.
Then, too, at least on the HF bands, running a long duration beacon is not a legal activity. Only on VHF and higher (in the US) can one run a full-time beacon and then only under certain conditions. To remain legal one has to constantly monitor the operating frequency to ensure that no interference is caused by the beacon and operation must cease if such interference is likely to occur. This means that there must be a full-time operator monitoring the frequency for the duration of beacon operation. Continuous or unattended operation is clearly illegal and will likely gain the FCCís attention in addition to arousing ire on the part of other band occupants.
To ensure legality the beacon must use a valid callsign for operation and any transmissions must take place on an appropriate frequency for the class of the operatorís license. Abuse of this will be very evident to any government monitoring station or ARRL Official Observer.
Another important consideration in coupling this PSK31 Audio Beacon with an SSB transmitter is the audio drive level feeding the transmitter. The design of this project accommodated a high level audio power amp in order to drive a speaker, however this speaker drive level is far in excess of the proper drive level for a transmitter. You should at least use the direct output of the R-2R DAC as the input to the transmitter, and your will likely even need to pad it further with a potentiometer. The "splash" caused by overdriving an SSB transmitter with these audio tones causes severe side channel energy and interference to others near your frequency. Either use an oscilloscope (looking at the RF signal) to determine if you are over modulating the transmitter, or get on-the-air reports from others while backing off the drive level until an acceptable signal is being transmitted.
While you want your beacon to be receivable, you really should not interfere with normal operations on a given frequency. It is in extremely band form (as some CW beacon operators have found) to run a beacon exactly on a frequency commonly in use for other purposes. This means that beacons should not operate on calling frequencies, net frequencies or those used regularly for code practice. For example on 80 meters, most PSK-31 operation takes place near 3580 to 3581 kHz. But a number of CW folks are rockbound just below at 3579 kHz, and W1AW runs CW bulletins and code practice on 3581.5 kHz. So any beacon operation in that region should be preceded by careful monitoring to ensure that the beacon will not clobber anyone else. Besides, if your beacons causes interference the other station will probably cause you not to be received either.And finally, in the best amateur tradition the beacon should use the minimum power necessary.
Page last modified:
November 28, 2001