Apologies if I have not put this in the right category!
I need to gin up a beacon transmitter for 144.424MHz with a power output of 20 watts. It needs to have GPS training for the frequency standard. It needs to be programmable to transmit the assigned callsign and the grid square where it is located in Morse (CW) and then send a 30sec dead carrier before repeating, continuously.
There is a beacon transmitter on eBay which does most of what I need but doesn’t have a freq standard input. It only has 500mW power output but I think that’ll be sufficient to drive a 50W VHF amplifier we have on hand to 20W.
The fact that HackRF has a clk input is a big plus.
However, there are concerns with the HackRF module regarding the low power output (ca. 30mW at 144MHz) and spectral purity. It’s a good signal generator but I don’t think I could put one on the air. My legal constraint is spurious emissions must be -60dB from carrier power above 30MHz. With filtering and a couple of amplification stages, I might be able to get it there.
It needs to be programmable to transmit the assigned callsign and the grid square where it is located in Morse (CW) and then send a 30sec dead carrier before repeating, continuously.
There are two aspects to the beacon, setting aside the non-trivial antenna & propagation discussion.
The primary is the controller that is generating the CW tones & keeping track of time. These are frequently used for repeater IDs and beacons, one common term is memory keyer or just, as seen, beacon controller. A neat enhancement would also allow some remote control functions by listening on another freq. At a minimum, I’d want to be able to disable to transmitter in case something goes wrong. The controller component is strictly audio and related control signal for keying the tx; you can design and troubleshoot (or program a ready-made) the controller with just a speaker and perhaps an indicator lamp.
A well designed controller makes the radio component effortless. A 50 Watt 2 meter amateur mobile or base transceiver would probably do fine for your 20 W at something like 30% duty cycle (Unless you really mean dead carrier when no CW which doesn’t sound like what’s intended/legal?). The ham rigs are built to take ‘normal’ audio levels and use RS232 handshaking (CTS/RTS) or similar for keying controls (as contrasted with commercial or public safety gear).
The beacon controller linked upthread has both incorporated but does look a bit, er, entry-level for the cost.
Tell us what you have in mind for the GPS synch transmit frequency. There’s generally very little to be gained by what I’ll call better transmitters. There’s always more power to be had and spurious RF & regulatory hurdles to recognize but being RIGHT ON freq is seldom needed outside the lab, at least for straight up dx performance. There are all sorts of neat radio-timing projects to undertake (audible redshift on sat beacons, for example) but I don’t know what a coarse grid square on a VERY accurate TX freq gets you and I hope it’s not wasted effort.
Beacons are used to monitor propagation and reveal transient effects like tropospheric ducting (aka tropo) and sporadic E-layer skip (Es). In example, signals on the 2m band normally only propagate as far as the radio horizon (typ 80-100km depending on antenna height) before travelling off into space.
Tropo will cause signals to travel a couple thousand km eg eastern Australia to NZ. Tropo from VK2 into NZ only happens a couple of time a year, usually in peak summer. From my location west of Sydney, I might listen for the ZL2WHO beacon in Wharite (North Island NZ) on 144.271MHz to see when the band is open.
It’s impractical to listen for ordinary stations calling intermittently on a certain frequency to determine if tropo or Es propagation is happening, but a continuously transmitting beacon station reveals the existence of the effect. If I can hear the ZL2WHO 144.271 beacon, I might call CQ on 144.200 calling frequency and hope to contact Bob ZL2IU near Wellington. I usually hear from Bob right around xmas day each year. Conversely, if I put up a beacon on a tall tower at Mt Tomah NSW (1100m elev), Bob might hear it and call for contacts in NSW.
The pattern most beacon stations transmit is [CALLSIGN] [GRID SQUARE] [DEAD CARRIER 30 sec (keydown continuously)], repeats. The rather crude transmitter I linked on eBay will do the signalling I want, but it is a battery powered unit intended for Foxhunting (aka radiosport) competitions where hams with portable direction finding equipment try to find a hidden transmitter (the fox). Quickest to find it wins.
I can mod this foxhunting unit to run on a mains powered power sply and drive an amplifier for continuous service. Beacon transmitters usually incorporate a GPS trained 10MHz frequency standard input so they can also be used as a high accuracy frequency source to aid in troubleshooting one’s own equipment. If I am hearing a high accuracy beacon on a frequency I don’t expect, I can then adjust my radio so it displays the true frequency of the beacon.
I know what beacons are but am questioning the the need for what seems to be the bottleneck of the project: the GPS frequency synch. Some beacon networks (and two-way digital modes) need a coordinated scheduling clock but even that doesn’t need to be sub-second accurate.
I’m still not sure about the 100% transmit on your beacon. I’m an experienced ham but haven’t run a beacon and rules/bandplans vary, anyhow, so I defer but my understanding is that most have periods of inactivity so as to share the freq. It also occurred to me that the beacon is probably going to be sideband (?) which I hadn’t thought of yesterday so a lot of the surplus FM commercial rigs I had in mind wouldn’t work. They’re very stable freq-drift-wise, durable, and pennies on the dollar surplus, the 180° opposite of ham radios!
Beacons need to run 100% duty cycle (that’s the whole point of them) and transmit in CW. Beacons operate on assigned licence frequencies (at very least in VK). That’s how you know where they are. The high accuracy freq standard is necessary for aforementioned reasons.
Not much in amateur radio is inexpensive. The radio club has budgeted about $1500 for the beacon project. This is in concert with a new repeater project which will cost about $8000. It’s all public service stuff! When the cellular networks go down in cyclones, floods or bushfires, we’re still around.
Assigned to a particular licensee (like a broadcast lic) or assigned for exclusive beacon use?
The latter is typical. A listening station can tune around the beacon portion of the band of interest and log reports from received stations. But without coordination or pauses, other beacons on the same frequency may go unnoticed.
I cheerfully reiterate my disclosure that haven’t built or run a beacon and most of what I do know about operating one was learned researching my replies yesterday and today. However, I DO have quite a lot of experience with amateur Automatic Link Establishment (ALE) on HF which incorporates many of the concepts we’re discussing. There, the computer (embedded FW/SDR/PC/etc) automates the reporting of received stations to predict a reliable TX band at a given time of day. The beacon component is called sounding in the ALE environment and it’s on staggered schedules, in part to accommodate weaker stations. The band selection headaches on HF that ALE really helps solve won’t factor into 2m so much but ALE can be used for those bands that open and close for other reasons like ships or other vehicles moving or after major earth movement and other disasters.
In the end, even with all the technology and know-how from doing this for decades, I wind up just kerchunking the repeaters.
Beacons are assigned a frequency with their apparatus licence. Frequencies are sole assignments on the continent. There are no other beacons on the same frequency.
If you hear a beacon on 144.420, it will ID as VK2RSY in Morse (CW) and you’ll know it’s located at Dural NSW.
If you’re more than 80km from Dural and hear the VK2RSY beacon, you can surmise there’s unusual propagation conditions in effect (tropo or Es)- or the signal is bouncing off an aircraft. Aircraft scatter is a common communications mode for very short contacts over about 200-500km.
I’m building the beacon for the proposed Blue Mountains assignment. Beacons and repeaters have a suffix beginning with ‘R’ and use the remaining two letters to ID the station, in this instance MT = Mt Tomah so VK2RMT. The Blue Mountains Amateur Radio Club has VK2RBM (BM=Blue Mountains) for our repeaters.
Kerchunking is a practice we Repeater Managers discourage. It’s hard on the repeater, can be a nuisance to others and is usually an unidentified transmission. We’d prefer stations ID and say ‘testing’ if you don’t want to establish a contact.
Thanks for that. Amateur radio (aka ham radio, no caps, it’s not an initialism or acronym like CB, we’re weird about this) is about 72 hobbies in one with something for everyone.
Got mic fright? No problem. You can work CW (Morse) or digital modes like FT8.
Just want to see where your signals go? Try WSPR. Keep reducing power if you want to see how far you can go on how little power. I have worked Canary Is (my antipode from Sydney) on 20m band with 1 watt when the conditions were right.
Want to keep up with local ham radio happenings? Join or just listen to nets (on-air roundtable meetings, daily or weekly).
You can talk to ham astronauts on the International Space Station or use the repeater onboard ISS to talk to other hams on the surface. There’s heaps of amateur radio satellites and have been since 1961.
Bored with artificial satellites? Bounce your signal off the moon (EME aka earth-moon-earth) to contact hams distant from you on the ground using VHF & UHF.
Join your local ham radio club. They will usually offer classes to get your licence. There’s no longer a requirement to learn Morse but you can if you want. Want a second-hand radio? Someone in the club will probably have one and no self-respecting club member will rip you off or sell you junk.
That covers about 10% of it.
Go have fun!
73 de Brian VK2AAF/WD9GYO
(yes, I have Australian and US licences because I’m a recovering American, in Australia for about 30 years)
My first call in 1978 was WN8NWU, soon after changed to WD8NWU when FCC eliminated Novice callsigns. I’m in the Winter 1978 Radio Amateur Callbook. Lived in Dover, Ohio at the time. Still miss driving to Holmes Cty for Amish trail bologna & brick cheese.
Think I got my ticket around 92, I was an hour east of Columbus at the time and not far from the Amish. They had a restaurant in town that served really good food at a good price. Wasn’t uncommon to see horse’s and buggys at the grocery store there.
I obviously didn’t realize the beacons were so channelized and coordinated. No surprise, there’s a 1001 aspects of the hobby I’m barely familiar with (wow, 2m aircraft scatter!) and probably 100x more that I’ve never even heard of yet.
I’ve been licensed since the late 90s, it’s a wonderful pastime that stays relevant.
The exam is a piece of cake and entry level equipment has never been so cheap or capable.
I usually tell semi-technical people that they’d probably already know a third of the exam answers via common sense & safety (True or false: Power lines are dangerous near antennas), correctly figure or guess another third (Ohm’s law-level math), and only need to study numeric things like band edges and power limits (which I myself would need to review). Seek a local hamfest. Even today, I find them inspirational and my variable interest in ham radio swings right back.
Instead of getting chores done this weekend, I was thinking about beacons. A thought occurred and you’re the highest level expert I know: Since the objective is to be heard and you have exclusive use of the frequency, wouldn’t a shrill whistle or at least a tone be better for getting out there? Similarly, WWV has the drone & ticks to listen for between vox segments.
An unmodulated ‘dead’ carrier is the most efficient radio signal owing to its narrow bandwidth. A CW signal only occupies about 150Hz of spectrum. No modulation is required. Information is conveyed by switching the transmitter on & off (Morse code).
It’s hard to hear a transmitter simply being turned on & off, so a BFO (beat frequency oscillator) is used in the receiver, usually in the IF (intermediate frequency) stage. Google ‘superheterodyne receiver’ for details. This produces a tone that is easy to hear in the receiver speaker.
An unmodulated carrier is the narrowest bandwidth and thus most power efficient way to send a radio signal. The amplitude power is consistent thus easy to measure and to identify the character of propagation on a given signal path.
A beacon needs only to demonstrate signal propagation. Modulation is unnecessary. CW is sufficient to send an ID of the transmitter. The 30 sec dead (unmodulated) carrier gives receiving stations an opportunity to aim directional antennas for maximum signal and identify the general location of the beacon.
WWV is amplitude modulated, even the time ticks. When you amplitude modulate (AM) a carrier, 2/3 of the signal is unnecessary. One sideband contains all the intelligibility information.
Just filter out the carrier and one sideband before amplifying and transmitting it. The carrier can be re-inserted in the receiver with a BFO. The result is known as SSB (single sideband).
However, SSB is trickier for non-technically oriented people to receive. First the frequency must be found, then the BFO must be adjusted to produce an intelligible signal.
