Eggfinders & Yaggi antennae: Part 2
The Thrifty Rocketeer continues...
One critical feature is to have a Yaggi antenna that you can attach to your hand-held receiver, so you can walk about and receive the signal. By pivoting and sweeping with the antenna held out at arms length, you can narrow down the direction of the strongest (loudest) signal, and know which way to walk toward it.
If you hold the antenna and receiver close to your body, you can block reception and the pick-up pattern becomes more carotid shaped, or a heart shape in front of you. The instructions suggest that with a little practice, you can become skilled at sweeping an area and walk pretty much to the transmitter (your rocket).
But, there are a couple of downsides to this concept.
First, it assumes that your batteries are still fresh and operating. Second, that the batteries haven't been knocked out of the contacts from a rough landing. Third, that your rocket is on land or in a tree... NOT in water. Fourth, that you have permission to walk the fields. Fifth, that you coated your transmitter with some sealant to protect it and the components from the ejection charge gasses in the rocket. Sixth, that the payload or nosecone where the transmitter is located, is still attached to the rocket. Seventh, that it comes down close enough to you that you can hear the signal, and that you start off in the right direction. and Eighth, that there aren't a lot of structures in the search area which might reflect the signal and give you a false reading... or send you off into the next field past the landing location of the rocket. (echo confusion)
My Ham radio friend and I tried my unit out one dry winter afternoon. We taped it to the outside of my sliding glass door with painters tape, with the two branches of the antenna running vertical. We walked down the hill and around the neighborhood with his receiver and brand new collapsible Yaggi antenna, and found considerable reflection and confusion on the direction of the signal...allegedly from dozens of houses and garages in our immediate vicinity. This despite the fact that I knew exactly where my house was in relation to us.
Not wanting to invest anything more than I needed for this simple tracker system, I searched the Ham web-pages for a cheap Yaggi antenna kit. You will best recognize this as the old 1960s style TV antenna that are wedge shaped, due to shorter and shorter elements tuned to different channel frequencies. Yaggi antennae are still in use for reception, however my design comes straight from home brew.
There are two basic elements of construction. First is the 1/2" PVC water pipe t-shape and backbone that supports the structure. It requires a T-joint and two X-joints, but under 2 feet of pipe. The second element is an old, worn out or broken retractable tape measure. You'll also need six small 1" hose clamps, about 3 feet of coax cable, an inch or two of hook-up wire, and a single BNC connector (preferably already connected to the end of the coax).
I happened upon a used measuring tape with an almost one inch wide tape, but the lip on the end was broken off. Oh, you could keep the tape extended, but once retracted, the tape would never come out of the housing again. As a result, the prior owner had bent the tape, making it pretty useless.
But perfect as material for our antenna radials.
The paint on the tape had to be scrapped off only where the electrical connections were going to be made. And the length of the aerials are critical, which is where your tape measure reading and math skills come in. The three aerials run between 35, 35 and 41 inches. And the leads of the antenna are attached (soldered) in the middle of the split middle aerial. About two to three feet of coax cable run back to a BNC bayonet connector for quick connect in place of your HT antenna.
The point is that as constructed, the aerials are not only SHARP AS HELL (wrap the ends with tape for safety) but also flexible to allow for storage in the back seat of your car without poking someone's eye out or ripping the seat. In theory, you could take this out only when you need to use the device, and keep it stored. (No, your spouse will not understand why you made it, have to store it, or can't fold the aerials up. So prepare for a lot of haggling if you go this route.)
I've tried this antenna with my transmitter at one club launch... leaving the XFM1 transmitter powered up at our launch table, and walking out into the field and sweeping the antenna around, listening for an increase in the sound of the signal. Although I thought I could detect the increase in signal when I was pointed in the right direction (back to the launch table), I may have been kidding myself. It almost seemed more practical to me that I could eyeball where the rocket fell and walk to it.
I removed the two batteries from their contact harness and stored the unit in my tackle box, where it has stayed for almost four years now, unused. The antenna has been underfoot in the basement ever since. But it was a fun project.
Which returns me to my initial problem. A Red Nova rocket that descended into a small pond and is presumed to have sunk. No tracker, no return address, no phone number. I'm afraid it is gone, and dissolved into mush... but I still wonder if I should be writing my phone number on the nosecones.... just in case.
Anyway, that was my foray into tracker and egg-finders a couple of years ago. Now, I understand there are other styles and companies that sell these types of complete kits and devices for a price. But this was just about the cheapest I could come up with and was a lot of fun to play around with it.
And yes, I not only could hear my call sign on 147.455 Mhz once every 30 seconds, but recognized it as well. So I felt my 15 bucks was well invested. The Yaggi antenna probably cost me under seven bucks to assemble, the major expenses being the PVC connectors, 2 ft of pipe, the 6 hose clamps and the BNC connector. The rest was scrap laying around.
Enjoy, and let me know what you come up with.
One critical feature is to have a Yaggi antenna that you can attach to your hand-held receiver, so you can walk about and receive the signal. By pivoting and sweeping with the antenna held out at arms length, you can narrow down the direction of the strongest (loudest) signal, and know which way to walk toward it.
If you hold the antenna and receiver close to your body, you can block reception and the pick-up pattern becomes more carotid shaped, or a heart shape in front of you. The instructions suggest that with a little practice, you can become skilled at sweeping an area and walk pretty much to the transmitter (your rocket).
But, there are a couple of downsides to this concept.
First, it assumes that your batteries are still fresh and operating. Second, that the batteries haven't been knocked out of the contacts from a rough landing. Third, that your rocket is on land or in a tree... NOT in water. Fourth, that you have permission to walk the fields. Fifth, that you coated your transmitter with some sealant to protect it and the components from the ejection charge gasses in the rocket. Sixth, that the payload or nosecone where the transmitter is located, is still attached to the rocket. Seventh, that it comes down close enough to you that you can hear the signal, and that you start off in the right direction. and Eighth, that there aren't a lot of structures in the search area which might reflect the signal and give you a false reading... or send you off into the next field past the landing location of the rocket. (echo confusion)
My Ham radio friend and I tried my unit out one dry winter afternoon. We taped it to the outside of my sliding glass door with painters tape, with the two branches of the antenna running vertical. We walked down the hill and around the neighborhood with his receiver and brand new collapsible Yaggi antenna, and found considerable reflection and confusion on the direction of the signal...allegedly from dozens of houses and garages in our immediate vicinity. This despite the fact that I knew exactly where my house was in relation to us.
Not wanting to invest anything more than I needed for this simple tracker system, I searched the Ham web-pages for a cheap Yaggi antenna kit. You will best recognize this as the old 1960s style TV antenna that are wedge shaped, due to shorter and shorter elements tuned to different channel frequencies. Yaggi antennae are still in use for reception, however my design comes straight from home brew.
There are two basic elements of construction. First is the 1/2" PVC water pipe t-shape and backbone that supports the structure. It requires a T-joint and two X-joints, but under 2 feet of pipe. The second element is an old, worn out or broken retractable tape measure. You'll also need six small 1" hose clamps, about 3 feet of coax cable, an inch or two of hook-up wire, and a single BNC connector (preferably already connected to the end of the coax).
I happened upon a used measuring tape with an almost one inch wide tape, but the lip on the end was broken off. Oh, you could keep the tape extended, but once retracted, the tape would never come out of the housing again. As a result, the prior owner had bent the tape, making it pretty useless.
But perfect as material for our antenna radials.
The paint on the tape had to be scrapped off only where the electrical connections were going to be made. And the length of the aerials are critical, which is where your tape measure reading and math skills come in. The three aerials run between 35, 35 and 41 inches. And the leads of the antenna are attached (soldered) in the middle of the split middle aerial. About two to three feet of coax cable run back to a BNC bayonet connector for quick connect in place of your HT antenna.
The point is that as constructed, the aerials are not only SHARP AS HELL (wrap the ends with tape for safety) but also flexible to allow for storage in the back seat of your car without poking someone's eye out or ripping the seat. In theory, you could take this out only when you need to use the device, and keep it stored. (No, your spouse will not understand why you made it, have to store it, or can't fold the aerials up. So prepare for a lot of haggling if you go this route.)
I've tried this antenna with my transmitter at one club launch... leaving the XFM1 transmitter powered up at our launch table, and walking out into the field and sweeping the antenna around, listening for an increase in the sound of the signal. Although I thought I could detect the increase in signal when I was pointed in the right direction (back to the launch table), I may have been kidding myself. It almost seemed more practical to me that I could eyeball where the rocket fell and walk to it.
I removed the two batteries from their contact harness and stored the unit in my tackle box, where it has stayed for almost four years now, unused. The antenna has been underfoot in the basement ever since. But it was a fun project.
Which returns me to my initial problem. A Red Nova rocket that descended into a small pond and is presumed to have sunk. No tracker, no return address, no phone number. I'm afraid it is gone, and dissolved into mush... but I still wonder if I should be writing my phone number on the nosecones.... just in case.
Anyway, that was my foray into tracker and egg-finders a couple of years ago. Now, I understand there are other styles and companies that sell these types of complete kits and devices for a price. But this was just about the cheapest I could come up with and was a lot of fun to play around with it.
And yes, I not only could hear my call sign on 147.455 Mhz once every 30 seconds, but recognized it as well. So I felt my 15 bucks was well invested. The Yaggi antenna probably cost me under seven bucks to assemble, the major expenses being the PVC connectors, 2 ft of pipe, the 6 hose clamps and the BNC connector. The rest was scrap laying around.
Enjoy, and let me know what you come up with.
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