Radio Beacon on the Amateur Radio bands for RDF, foxhunting, and (of course) tracking rockets

mbeels

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I haven't got any proper rocket builds going on at the moment, but this electronics project could have some relevance for rocketry. Although GPS based systems (I'm a fan of the Eggtimer stuff) are usually the preferred tracking solution, there may be cases where a GPS module doesn't fit, a backup to the GPS is desired, or perhaps regular RDF is preferred for some other reason. My goals for this are:
  • Small version with +10 dBm output to fit within a 24mm body tube
  • Larger +20 dBm version with LED display and beeper
  • USB interface (specifics TBD) to set call sign ID, power level, etc...
  • Shared layout between 2m, 70cm and possibly 33cm version
  • CW output
It is based on the Silicon Labs Si4060 or Si4063 transmitter IC which handles most of the difficult RF stuff. It's more sophisticated than necessary for a simple beacon, but the cost reasonable, the package is small, and it could potentially be used to transmit telemetry. The schematic is basically done, this will be a larger prototype version for writing the firmware and working out the RF matching networks and filters.

TX-1_A.png
 

mbeels

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This will probably be a very slow "build" thread, with many time consuming steps and not much to show for it. Maybe it will get more interesting once real hardware is involved. Anyway, with the schematic basically done and required footprints drawn, it is time for the layout. It starts with a literal "rats nest".

1669767229294.png
 

cerving

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I quit using the Eagle autorouter, it does strange and inefficient things, like making all of the traces 90-degree bends. I basically put things that connect together nearby as much as possible, and use the connect button to draw the lines between the pads. Ratsnest is good for showing you what you missed, though.
 

mbeels

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I quit using the Eagle autorouter, it does strange and inefficient things, like making all of the traces 90-degree bends. I basically put things that connect together nearby as much as possible, and use the connect button to draw the lines between the pads. Ratsnest is good for showing you what you missed, though.

I haven't used Eagle, my experience is limited to gEDA Schematic editor and PCB layout software, but I haven't had good results with auto routing either. I pretty much just draw the traces with lines, it's kinda repetitive but fun, like the "sanding" process of electronics. (I'm one of those weirdos who likes sanding)
 

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Interesting project.
Are you going the RDF (Radio Direction Find) to locate the Rocket?
What RX and antenna will you use?

I built some small 2m RF beacons and use an HT to RDF. Output power is very low with a range of under 100 feet but works well to find my rocket in the corn since I have a general idea of where it is and can get close enough to pick up the beacon.

As to PCB layout, I use a number of PCB layout software at work and home and never use the auto-routers. I have tried them the they never do a good enough job.
 

mbeels

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Interesting project.
Are you going the RDF (Radio Direction Find) to locate the Rocket?

I'll probably stick to the Eggfinder GPS for my 38mm+ diameter rockets, but I'd like to have a small and light RF beacon for 24mm rockets. Actually, I think with a tight layout and a 1/2AA 3.6 V battery, this could conceivably fit in an 18mm tube. (for a MD 18mm rocket and Aerotech 18/20 case)

What RX and antenna will you use?

I have in mind a small (and hopefully simple) direct conversion receiver (that'll be the next project). For RDF, sensitivity and selectivity won't be as important as being able to attenuate strong signals. For an antenna I'm not sure, I'll probably try a few, but I'm intrigued by the TDOA design. I'd like to try it.

I built some small 2m RF beacons and use an HT to RDF. Output power is very low with a range of under 100 feet but works well to find my rocket in the corn since I have a general idea of where it is and can get close enough to pick up the beacon.

Interesting, how did you generate the 2m signal? I've done a VCO + PLL for 2m and that was quite challenging (but it did work).
 

waltr

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49.152MHz XTAL with circuit tuned to 3rd harmonic at 147.46MHz (2m Ham band, simplex channel).
This does produce a lot of harmonics due to not having a good low pass filer on output. But power is very low and the 3rd harmonic output falls in the 70cm ham band (442.38MHz) and is also useful when close (attenuated).

Here is the design I used:

The NTE108 transistor is important to get enough FM deviation. It uses the Miller effect to pull the XTAL frequency.

Also use a rubber duck antenna and my body to get a heading like in the article under Body Fade:
This does fit into a 24mm BT and has worked very well to find rocket in the corn.
 

mbeels

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49.152MHz XTAL with circuit tuned to 3rd harmonic at 147.46MHz (2m Ham band, simplex channel).
This does produce a lot of harmonics due to not having a good low pass filer on output. But power is very low and the 3rd harmonic output falls in the 70cm ham band (442.38MHz) and is also useful when close (attenuated).

Here is the design I used:

The NTE108 transistor is important to get enough FM deviation. It uses the Miller effect to pull the XTAL frequency.

Also use a rubber duck antenna and my body to get a heading like in the article under Body Fade:
This does fit into a 24mm BT and has worked very well to find rocket in the corn.

Really neat design, that is the epitome of functional simplicity.
 

mbeels

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Alright, layout is pretty much done. I'm going to give it a rest and then check everything over once again. Without fail, I always have at least one error in my first layout revision. Either a foot print is wrong, pin number, or something.... So we'll see what it is this time.

This is a large (3.25" x 1.75") prototype for development purposes, with extra test points, parts, connectors, trimmer caps, and such. I think the essential components could be fit on a 2" x 5/8" PCB, so fitting in an 18mm tube should just be possible.

1670120043292.png
 

waltr

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Looks good for a prototype. Yes, prototypes need options for testing and trouble shooting.

What Ham band/Frequency are you going to use?
What are you going to use for the TX antenna?
 

techrat

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Are you planning to produce a run of these once past the prototype stage? Color me interested, as I'm looking for a simple RF tracker for my MPR's. I've done plenty of fox-hunting, so I am familiar with the process, and have my own equipment (Yaesu handeld, attenuator, tape-measure Yagi).
 

mbeels

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What Ham band/Frequency are you going to use?
What are you going to use for the TX antenna?

I'm planning on doing the first one for 2m, then second 70cm as it is probably a more useful band for RDF (smaller antennas and all that). For a TX antenna, that probably depends on how it will be used. According to the data sheet, at +10 dBm, this IC is pretty forgiving, meaning the final output components of the IC are unlikely to exceed their maximum voltage or current rating even with a mismatched antenna. At +20 dBm, it requires a bit more care. Also a 1/4 wave radiator is more practical at 70cm than 2m, especially in the confines of a rocket.

Are you planning to produce a run of these once past the prototype stage? Color me interested, as I'm looking for a simple RF tracker for my MPR's. I've done plenty of fox-hunting, so I am familiar with the process, and have my own equipment (Yaesu handeld, attenuator, tape-measure Yagi).

Sure, I don't expect to do any high volume production or anything like that, but when making PCBs you always get some minimum quantity. I'd be happy to send you one. Just realize that you'd be something like a beta tester, so don't necessarily expect a polished commercial product. But especially since you've got fox-hunting experience, your user input would be good to hear. MPR is what I've got in mind as well, something lighter, smaller, and cheaper than GPS.
 

cls

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Kinda wish you would put it in the CW beacon part of the band, instead of 147.46MHz in the FM part.

Same with 70cm, aim for 433 MHz.

Why not use a synthesizer chip, Analog Devices has quite a few.

Last, instead of a 1/4l monopole, I'm noodling about drawing a slot antenna for 70cm, made with strips of aluminum tape, that would wrap the outside of the ebay section... Advantage is hpol in the air and vpol on the ground.
 

waltr

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Kinda wish you would put it in the CW beacon part of the band, instead of 147.46MHz in the FM part.
It is the Beacon I built that is on 147.46MHz which is FM Simplex. This beacon is FM so it is on a good and proper frequency.

The OP of this thread has not listed exact frequency nor the modulation.
 

cls

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Yeah, modulation is important, too. But it's a compromise...

FM beacons like Big Red Bee are difficult to DF by sound. My eyes are busy looking for the rocket, duh.

AM beacons like Walston are easier by ear because I can hear the signal quality and strength, without looking at the S meter. My FT60 has an AM RX mode but many HTs do not.

MCW might be a good mode, dunno...
 

techrat

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Going FM is the way to go, because then you don't need an expensive handheld for tracking, hell, you can use a $20 Baofeng (I've done it). Mind you, not the best radio for that purpose, but it works.
 

John Kemker

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Going FM is the way to go, because then you don't need an expensive handheld for tracking, hell, you can use a $20 Baofeng (I've done it). Mind you, not the best radio for that purpose, but it works.
I've used an FM handheld for tracking CW. You hear a pulse of noise for each "dit" or "dah" transmitted, not a pure tone. It works. Not great, but it works.
 

mbeels

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Why not use a synthesizer chip, Analog Devices has quite a few.

That'd be much more work for a less functional solution, not to mention much more expensive. This IC has several FSK modes available (thinking telemetry down the road), adjustable power output via internal registers, and shares a common internal platform with full transceiver ICs. So if I can work out all the details for this transmitter, I'm that much closer to a working transceiver (if I ever wanted that for something, much of the motivation here is just to learn).

The OP of this thread has not listed exact frequency nor the modulation.

My intent is for the exact frequency to be user settable, via the USB interface (TBD). This will be straight, plain vanilla CW. My other reason for building this is to setup a CW beacon on 2m from my QTH (on the beacon sub-band). I think it would be fun to eventually have a beacon on as many VHF+ bands as I can figure out how to build.

FM beacons like Big Red Bee are difficult to DF by sound. My eyes are busy looking for the rocket, duh.

That's my experience as well, FM "works", but I think it is less than ideal.

Going FM is the way to go, because then you don't need an expensive handheld for tracking, hell, you can use a $20 Baofeng (I've done it). Mind you, not the best radio for that purpose, but it works.

Yes, it certainly works. After this project, my intent is build a simple DC receiver to go with it. Lack of image rejection isn't an issue for RDF, and other design criteria that make those other receivers expensive (low noise figure, selectivity, sensitivity) don't matter either.

I've used an FM handheld for tracking CW. You hear a pulse of noise for each "dit" or "dah" transmitted, not a pure tone. It works. Not great, but it works.

Yup, I've done that as well. And if the radio has a decent RSSI, you can watch that and determine where the strongest signal is coming from.
 

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Altus Metrum seems to have solved this with similar criteria and both the hardware and software are open source. I'm not sure whether that's interesting or not but I thought you should be aware of existing work.
 

mbeels

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Altus Metrum seems to have solved this with similar criteria and both the hardware and software are open source. I'm not sure whether that's interesting or not but I thought you should be aware of existing work.

Wow, that is interesting, the TeleMini is a fully functional DD altimeter plus telemetry transmitter in a 1.7" x 0.5" board. That's impressive. Thanks for the info. So this won't be anything new, but it'll still be a fun project to learn something in the process.

PCBs are ordered, and now I'm ordering parts which requires determining the component values for the output match and filter network. Fortunately Silicon Labs has a lot of extensive application notes. Without going into all the details, there are several types of output topologies described in their notes. For 2m, I'm going with their Class E with square wave harmonic trap basic design.

The output filter was designed as chebyshev low pass:

1670521554099.png
 

mbeels

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Parts are here and the development circuit boards arrived today. Hopefully I can get them assembled this week and start working on firmware soon.

PC190231.JPG
 

ksaves2

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49.152MHz XTAL with circuit tuned to 3rd harmonic at 147.46MHz (2m Ham band, simplex channel).
This does produce a lot of harmonics due to not having a good low pass filer on output. But power is very low and the 3rd harmonic output falls in the 70cm ham band (442.38MHz) and is also useful when close (attenuated).

Here is the design I used:

The NTE108 transistor is important to get enough FM deviation. It uses the Miller effect to pull the XTAL frequency.

Also use a rubber duck antenna and my body to get a heading like in the article under Body Fade:
This does fit into a 24mm BT and has worked very well to find rocket in the corn.
I built an XFM-1 aloooong time ago. Kits and boards were available from the designer so I bought several. I used full length antennas with a counterpoise trailing the very long-necked rockets I was flying. I use a 2 meter H/T, homemade 3 element Yagi and homemade attenuator. Very directional and good for modest high flying rockets that go out of sight for "not too long" to avoid drifting long distances. Commercial stuff and GPS trackers of modest power are better for long distance tracking. I believe few fliers really need high power Rf as launch sites are more restricted in the Midwest.
One has to be careful when flying homemade Rf devices with commercial altimeters as Rf can dork deployment devices. Had two lawndarts before I figured out the Rf whacked the altimeters after launch.
Kurt Savegnago TRA 10384 NAR 11583 (KC9LDH) too
 

waltr

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How close was the XFM-1 to the Altimeter in the rocket?

I have not had any issues. This may be due to better altimeter boards or that I attach the XFM-1 to the shock cord below the Ebay. Also, the antenna is stuffed into the BT so not extended until after deployment.
I get a range of less than 100 feet once rocket is on the ground with an HT and rubber duck. A Yagi would increase range but I use this when the corn is up and rocket flight is in sight so I have an idea where it landed. then can get close enough to pick up the signal and get a bearing into the corn to find the rocket.
 
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