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.