Backyard Ballistics (tm)

Rocket Recovery Electronics
Content Copright 2001, 2002, 2003, 2004 by Private Data, LLC

Recovery Electronics
I'm very surprised at 1) how long it takes folks to find their rockets, and 2) how often folks don't find stuff - particularly the really high dollar Level 2 & Level 3 stuff. And, after coming close to not finding Periwinkle's Pride after my L1 Cert flight, I decided my desire for recovery aids was now a need for recovery aids.

I'm just starting this page, and it'll be in a disarray for a while. There is a lot of stuff on recovery aids, particularly beacons / beepers. I'll be pasting in my references as I find them and slowly organizing them.

To start, I ordered a Transolve Trans Beep. It packs with your chute and I can move it to different rockets. I am strongly considering their PK6 kit as it's $60 and about 2/3 the cost of a commercial product. It is bigger, but if I can leave one in a rocket then flying multiple rockets is easier as well as rocket design (if batteries are all that one needs then be concerned with). I will see if this is lound enough. If not, I'll build one of the louder sonic beacons. I really DO want my rockets back!

Given how far Periwinkle's Pride drifted on that windy day (about a mile), and given the fact that I lost track of her partway down, I'm strongly considering radio location. Look at where Warren found his L1 Cert rocket - buried in the Tobacco. A beacon would have helped him! There are a number of alternatives here. From Pete's compact unit, to another I saw that hacked up the cheap 2 for $30 FRS  radios. I'll likely have an entires section on this topic.

I must say, Pete's got a bunch of good projects going on his site. And Rocketry Online forums has a "classroom" altimeter project.

Right now for Dual Deploy I have a MissleWorks RRC2. I have a my variant of PETE's RDF for locating, and I have a Gaejis MAD that isn't installed yet.
There is a lot to say here. I'll start by saying I'm interested in the Transolve P6K Altimeter Kit. The main interest is cost - the kit is $58 - 2/3 the cost of commercially assembled units - and I can solder.

Pete's got a project page on Altimeters. Of course. I'm not sure if I've got the time unless I could crank 'em out for substantial savings over the other options. I do want dual deployment on anything that is going very high. It seems pointless to not do that - esp w/o radio tracking options.

I sent an e-mail "Dubious Distraction" to and got back many responses. I found no negative responses, but a big cluster around the MissleWorks RRC2. Second favorite seemed to be the Olsen. The GWhiz is nice; also PerfectFlight's micro-alt is popular with the tiny rocket crowd. But on the darboard, there was a huge cluster around the MissleWorks RRC2.

I've ordered the Missle Works RRC2. Geez. what a dated page, I have 2 RRC2, 1 RRC2X, and a PerfectFlite MAWD.


The acelerometer models sence the rockets aceleration. They're immune to mach effects. Some used to be sensitive to the effects of Hybrids - so check that a model has adequate programming to be fine with hybrid motors. Some models, like the GWhiz  use a barometric sensor for main deployment (well, all would need to) but it's not armed until the main (acelerometer) fires. Some don't trust acelerometers as they don't know much about "UP" and seemingly can be fooled by some motors / motor-rocket combinations.

Barometric Pressure

The barometric pressure models fire based only on barometric pressure. This is thought in general to be more deterministic than acelerometers. The main issues seem to be proper venting and mach effects

Proper venting requires the proper number & placement of holes to give the barometer the air pressure (i.e. altutude) without inducing errors. Errors can be caused by air flow over the sensor (venturi type effects lower the read pressure). Also, rocket parts can cause airflow disturbances larger than perceived so holes need to be placed so they're not downline from screws, fore-fins, etc.

Venting can also be an issue with hybrids. I've read some reports of hybrid fill venting issues causing early (even on the pad) faux apogee detects & recovery system initiation. This is appearently caused by NO2 venting into the barometer chamber. The lighter NO2 fools the altimiter into thinking it's reached apogee and is now falling. And the barometer fires. This should be programitically avoidable but proper venting for hybrids should take into account the location of the motor fill vents and the location of the barometer vents.

Why Altimiters Fail

There's a good article on why altimiters fail on Info-Central. It's good reading and through it you'll learn many of the common mistakes folks make that cause the electronics to fail or not work properly or not work at the correct time.
Locating Beacons
Transolve Trans Beep is going in Periwinkle's Pride; It is easily movable - intended to attach to the nosecone hardpoint. I'll report as to how loud it is and how much it helped.
Magnetic Apogee
The Magnetic Apogee dectors are just too cool. At $30 for one of the kits, and it's a just do it addition to any rocket. Magnetic Apogee Detection was pioneered by Robert Galejs. His page is here. His kits are sold by Aerocon. And they have a nice article here. Transolve has entered the fray with their Flux Capacitor. It's nice in that it adds a timer for backup deployment of the main parachute.

I've purchased a kit from Aerocon but haven't built it yet.

Radio Tracking / Rocket Fox Hunting / RDF

Tracking in Practice

There is a good article on the Colonial Virginia HPR website titled Radio Rocket Location using Walston Transmitters and Receivers by Sue McMurray; I've also cached it here.

Do be sure to "check your backside" especially when driving into a search field without using the beam. In a previous launch I drove into the search field and stopped to drop off another rocketeer who's rocket was visible. As it turns out, I'd passed my rocket, thinking it was farther along. I then got out of the truck and took a bearing. well, I was *past it*, but relatively close,  so I got a good signal, but I didn't realise the signal was off the backside, so I ventured further on for about 30 minutes. I even thought my battery had gone out as the signal dissapeared. As it turns out, I had been just 50 yards past it. So do be sure to check your backside from time to time, esp if you just pulled up and hadn't been tracking while driving.

Circuitry and Projects

Pete's Alternative Beacon Circuit - is a 70cm tracking transmitter based off of his RDF Page. I built this using a 12C508A and a RadioMetrix TX-2. I also built Pete's receiver circuit and the yagi. I bought all the parts from DigiKey. I bought the programmer kit from Dontronics and highly recommend the Kit96 (splurge and buy it assembled). I plan on using it all for the first time Sat, July 26, 2003 at the Whitakers launch. This will be particularly timely as the club's Walston receiver will be at LDRS and may not make it back in time for this launch. The RadioMetrix radios are available in the US from Lemos International.

I've also seen a page (looking for it again) where somebody hacked up the cheap 2 for $30 FRS radios.

Charles ( has a nice battery time curve too, showing a 9V should last a week on this setup, and also confirming my theory that the tiny 12V batteries are barely good for a day.

I built RDF TX & RX circuits based on Pete's designs but need to work up a page detailing that work. I tested them at the July Whitakers launch in my PML Bullpuppy 2.1. Then folks left cleared out when a small shower rolled in so after that cleared I tossed the TX into various places, like a corn field, then one end of the pasture, etc, and determined my working ranges through corn (1/2 mile max), pasture (3/4 mile), and open ground (about 1 mile).

Continuing on this (fodder for a real page) I'll detail the flight report for that BullPuppy. I flew it on an AT F20-7 for an estimated 1000 ft flight (maybe a little more). Straight up and nearly straight down. I then "forgot" where the rocket was and used the RDF to find her (only 100 yards away max). As I got close, the RX was overloaded and I started losing directionality on the yagi. Using body shileding, I still got a reading straight ahead. But wait! Over to the right was, what?,  my rocket! With no RDF TX. But the RDF RX Ant was pointing ahead. I had to clear and wait for another relay of rockets and then found the TX, by itself, with the end cap popped off, merrily beeping away.

Looking further I saw that the kevelar thread (about like carpet thread) was cut. Looking on the rocket I saw a nick in the top of the ejection piston. The kevlar thread had been cut, at apogee, and the TX had come in by itself, ballistic, from apogee and survived! That is rugged! I did replace the kevlar with heavier cord (Pratt "small"), longer, and with looping to prevent losing the end cap and to keep it together. I also tape the battery in again.

Now, I drop that TX in almost any flight at all. For the close ones, I'll leave the RX in the truck in case I really need it, and for the high ones I'll go ahead and bring it to the pads to get a bearing on it as the rocket descends.

I am very happy with this project. And while not having the same range as the popular Walston RDF it is very workable. Sheesh. You know, I really think I have a hacked up page on this somewhere ... but until then, here are a couple of pictures:

RDF TX, RX, Ready to use
This is the completed TX, RX, ready to use. I do now have a neck strap on the RX box.

RDF TX, RX, Internal view
This is an internal view of the TX and RX. Note the TX is deadbug on the back of a N battery holder. The antenna is RG-174 coax and it's strain relief'd by being gobbed on with E6000 glue.

TX Deadbug Closeup
Deadbug construction closeup. Note the PIC (in the middle) is hot glued onto the Radiometrix TX. The 3V 90ma regulator is to the right. The Radiomextrix nearly perfectly matches the size of the N battery holder. With the regulator I can run anything from a 3V to a 12 V battery in the N holder. The 12V and 6V camera batteries are the best candidates with 6V the best.

Voltage Regulators

I prefer low quiescent current / low dropout voltage regulators. The low quiescent current may not be a factor since I'm don't think the PIC idles at low enough current to let the regulator go quiescent - but these regulators also seem to be more efficient in their internal current needs and I like that. This class of regulator is specifically designed for battery operated devices. Every mah saved is more time to find a rocket. The low dropout also helps as it provides both stable power to the output down to a much lower supply voltage. The voltage delta also seems to be much lower. Getting a decent regulator with these characteristics, such as a LP2950 costs about 0.80 whereas a generic LM78L05 is about 0.26. Myself, I'll drop the 0.50 extra. These are the 100ma parts.

As an example, a generic LM78L05 may require as much as 7.7V input to reliably provide 5V output, whereas a low dropout may require as low as 6V to reliably provide 6V output. That can make a difference if your rocket is lost and you're on day 3 of searching. It also provides longer overall service life of a battery if you're not losing your rockets for long.

Note that these regulators, particularly the 100ma and smaller, really do need input bypassing and output bypassing is also suggested.  A 100nf ceramic on the input is usually recommended, and a 1uF to 10uF on the output is also nice. A larger output value helps some too if your regulator shutsdown and motorboats and might help keep this from happening. For bypassing, when building ugly bug, I usually use the ground pin of the PIC as the solder anchor for both the input and output capacitors for the voltage regulator (and the Vcc pin of the PIC as the other output cap pin). This is just a deadbug mechanical arrangement. Note the above picture doesn't have the bypassing. It seems to work fine, but I now use the bypassing.

I've used both the 100ma parts and also the even lower power parts - some as low as 40ma. The 40ma parts will power the PIC and a TX with no room to spare but will perform that reliably.  The 90-100ma parts aren't required unless you're also going to be powering a piezo or other circuitry - and then usually only if the piezo will be powered at the same time as the tx (hint, modify the pic code to use a separate pin for piezo and to direct every third beep to the piezo instead of the transmitter and remain at the lower power budget).

When purchasing, also be aware of the packaging. I didn't once, and ended up with ultra tiny SOT-23 packages which make wire wrap wire look like a high current bus bar. They are almost an inhalation hazard and carpets are very hungry for these! The SOT-223 are a bit more workable - you can at least hot glue them easily onto your TX and then solder the fine wires. The above pictrure shows SOT-223 packaging - and a SOT-23 will entirely fit inside the black area of the SOT-223. I prefer the TO-92 packages as they're even easier to work with. But note the 100ma devices are probably the lowest current you'll get in TO-92 packages (and you can get 90-100ma in SOT-223).

Battery Choices

The above uses a miniature 12v battery in an N cell holder. It's compact and works fine - but has it's issues. The battery doesn't last long for one, and it's inefficient due to the high delta voltage to our PIC/TX needs. They're good for about a day's (or launch weekend's) use.

Next prefereable would be one of the 6V camera batteries in a 1/2 AA or similar size (there is a slightly larger size I don't know what it is). These are excellent for power capacity and life. They are more expensive as a downside. Another advantage is if you use a silicon diode in series instead of a regulator, you'll have 6V - 0.7dv == 5.3V which the PIC is happy with - eliminating a voltage regulator. If you use a regulator (esp with the 3.3V Radiometrix parts)  you may want to ensure you use a low dropout regulator to have a tighter voltage.

Since I fly mostly high power, and room is not an issue, I've switched almost exclusively to 9V radio batteries. The're commodity items so cost is relatively cheap and they can be had in high capacity version if desired. Charles Barnett found useful life up to a week (though with reduced output) in his RDF applications.

Battery Holders

Always use a very secure battery holder with good end bracing. And always secure the battery - you don't want it popping out!

PIC Code Modifications

I'm considering modifying the timing of the PIC to have
Pete's baseline code that I started with for the 12C508 is beacon2; and I've linked my KM4UL version here. It's just got the callsign changed, and is linked more for my reference.

TX/RX/RDF Resources

Charles Barnett's RDF work he's got a line on, in particular new RX that may be better and may also be making some PCBs. check it out.  The Rocketry Online Electronics forum is also a good forum for information, questions, and answers. Dave Muesing started a good RDF / Radiometrix thread on that forum.

The TX2 / RX2 Data Sheet
Programming & Customizing PICmicro Microcontrollers is a great book.
Build Your Own Low-Power Transmitters : Projects for the Electronics Experimenter looks interesting
Here's Joe, WB2HOL's good RDF Project page (tape measure, PL-259 attenuator, TDOA).

Attenuation / Attenuators

The yagi antenna described gives me about a mile of range, yet when within even 50 yards, it's nearly omnidirectional. Techniques such as antanna tilting, off axis rotation, etc, can help, but an attenuator is desired to just "flip in" some or a range of attenuation to allow the antenna to be used to a much closer range. At some point, it's still down to no antenna and body shielding (say, when in the corn).

I haven't built one yet, but googling ham radio RDF links come up with some nice inexpensive solutions.

A bnc / PL-259 based attenuator. Simple.
A rotary switch variant of a resistive attenuator
A pi network resistive attenuator (as the arrow antennas kit is baed)
A relatively inexpensive kit Dave Muesing dug up.
A potentiometer simple attenuator

On attenuation, I had another thought of folding back the active elements, say if you had 6 directors, you would fold 3 back on themselves.i.e. the boom folded back. I don't know if the reduction would be significant or not. I suppose one could also have folding elements Similar to the Walston, and just fold back the elements or arms so they were effectively out of circuit (though I'd worry about side signal confusion).

Gain / Pre-amps / Antenna mods.

I find that the Radiometrix TX / RX pair has acceptable performance, but I would really like more gain. The Walston has such further range and the TX is much lower power. That tells me that I need more RX performance. RX performance is antenna and receiver.
I think the Radiometrix RX is likely not tuned to high sensitivity figures. I should look them up and compare them to an HT and /or scanners. But I am thinking a pre-amp would help a lot.

Here is one inexpensive 440 mhz kit: Perhaps one could build that into this kit replacing one of the attenuation stages (for compactness)
The Pete's Yagi seems roughly comparable to the Walston. I haven't done the math, but if anything the Pete's has more gain. So from that perspective I guess I'm not thinking of adding more elements. Though it's compact enough I could probably add 2 or 3 more and still have a reasonable sized antenna.

I am also investigating a loop antenna, much as to build. The null is very sharp, but it's an intermediate solution - it doesn't have the gain of a yagi - but may still require attenuation at some point. But the sharp null is very attractive. Perhaps using the yagi to get close and then finishing the job with attenuation and loop? something to ponder.

Tape measure spring steel for elements - advantages are durable in the woods and the box. Might not be rigid enough for poking out the truck window while driving. The dimensions aren't for this 432 mhz, but I like the idea and was thinking I'd use the tiny tape measures for narrow spring steel (3/16" or so)

High Gain Quagi

Loop Antenna Resources (one hit) look for addl links at the bottom. The loops seems nice due to the sharp null, but I am finding essentially no untuned  loop projects; all seem tuned. I am thinking that Arrow Antennas may perhaps be resistively swamping their loop to de-tune it. If that's the case then that'd be easy. That would fit with some reviews liking the antenna but stating that it is rather "deaf". I suppose I could also take a shot at resonating one, but that is so sensitive (due to small size) that it may (?) be better to swamp it resistively. Esp since I don't have a grid dip meter or other equipment to resonate one.
A TDOA may be as inexpensive as a loop, and the gain wouldn't be as down as the loop. Not sure about the sharpness of the NULL.

Quoting: from one nice page for a $10 TDOA unit: "

The TDOA works by detecting the difference in the phase of the RF signal received by each dipole. If both dipoles are exactly the same distance from the RF source (the "fox"), the phase of the RF signal will be the same at each antenna. If you rotate the array, or the RF source moves to the left or right, then one dipole will be closer to the source than the other one, causing a small phase difference between the signals received. Your FM receiver will then detect an abrupt change in the phase of the RF signal it receives as the antenna switching unit switches rapidly back and forth between the two dipoles. To the receiver, the signal looks like square-wave- modulated FM ! Your receiver's speaker will emit an audio tone at the antenna-switching frequency. As the phase difference increases, the tone becomes louder. When both dipoles are equidistant from the source, the tone almost completely disappears.

One disadvantage of the TDOA is that when you have found the "null" or antenna position where the tone disappears, you cannot tell if the source is directly in front of you or directly behind you. Fortunately, there are other ways to determine this. A quick way, if you are using a handheld, is to use the "body shield" method - disconnect the antenna, hold the handheld close to your chest so that you can see the signal strength indicator, and turn your body. When the indicated signal strength is minimum, the source is somewhere behind you. Another technique involves converting the TDOA antenna to one which has a cardioid or heart-shaped radiation pattern - the null (which corresponds to the "notch" in the heart-shape) can be used to point a rough bearing to the source."

Joe Leggio WB2HOL, has a couple nice TDOA units on his RDF Page.

Radio Tracking On The Cheap

Off of Charles Barnett's RDF work he's linked to some inexpensive AM transmitters, and there is a corresponding AM reciever. These aren't the hottest thing around but they are tiny and one could build out an entire setup for probably $25 (!)

Transmitter: and I think the data sheet is this  for the TX/RX(or similar model by now).

GPS & Radios

The Byonics Pocket Tracker looks to be a pretty sweet radio / GPS integration package.

Dual Deploy Recovery

The new alimeter bays. The upper for the Periwinkle's Pride Bash rebuild. It's the upper bay; the lower is the new bay I built at the same time for the Bullpuppy.

Altimeter bays

Top shot; Periwnkle with RRC2 and MAD for backup; Bullpuppy with PerfectFlite Mini-Alt altimeter

Altimeter bays

Bottom shot;

Pete's got some timer circuits. There are many available from a Google Search. Note that Perfect Flight has some very tiny timers - some smaller than a quarter. I'd highly recommend you check them out (I haven't but plan to - just so nice a compact package and for a good cost).

I'll also note that the GWhiz has a built in staging / cluster timer. It's not a true timing circuit, but if all you want to do is some basic staging / clustering it looks nice, and is built in to all of the GWhiz Altimiter models.

Data Sheets

PIC12F508/509/16F505 Data Sheet. This is the flash part not the OTP part.
PIC12C5XX Data Sheet. This is the OTP part.
PIC & AVR Microcontroller links

This should be in a different section, but I'll capture some of my favorite links here.
I have the PIC16Pro kit (kit96) from DonTronics. I've used it to program 12C508A's for the Pete's Morse Code ID'er.

I don't intend to make this list all inclusive as there's too much out there. But I highly recommend Van Ooijen's site for starters.

Van Ooijen's site - as a good starter for PICs and AVRs;
DonTronics - a classic for programmers, links, resources;
PicAll for the programmer complementing the Pic16Pro kit
Microchip - manufacturer of PICs
Microchip MPLAB - ASM IDE link - free - you want this

Recovery Electronics Links

Programmin' by Pete's Project Pages - Pete's got a lot going in the recovery electronics pages.
Transolve - Altimeters, beacons, ...
Aerocon - lots of good stuff
Lemos International. - The TX2 and RX2 radio modules for my RDF.
Charles Barnett's RDF work
Rocketry Online Electronics forum