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70cm quadrifilar helix tuned for 434.55 - 435.45 range

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mpitfield

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Can you tune a quadrifilar helix antenna for a frequency range vs. a specific frequency?

There are a lot of documents as well as calculators for designing and tuning these home made antennas to a specific frequency. However as you know, sometimes we have to change frequencies on the field. Obviously making multiple antennas tuned to all of the potential frequencies is not practical so I would prefer to tune one to a range. Being home made antennas its not a stretch to imagine that the tolerances of these "tuned" antennas can vary, but they still seem to work, at least on YouTube. This leads me to believe that there is some forgiveness with the design.

My application is with the Altus Metrum TeleGPS trackers. I use the TeleBT tethered to my Android and my unidirectional Yagi when out recovering and if I am not at my setup table for launch. However I also have the TeleDongle, which allows me to use my Mac while sitting at my setup table. I would prefer this to be a stationary setup even though I realize that I am giving up some range for the convenience.

So I have been kicking around the idea of fixing an extension pole mounted omnidirectional antenna to one of the legs on my tent, specifically a 70cm quadrifilar helix tuned for 434.55 - 435.45 full range of the TeleGPS units.

Do any of you hams know if this is possible?
 

ksaves2

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I be no expert but I suspect that perhaps an efficient antenna on 400Mhz would be too large to launch. Perhaps someone else could comment? I did have a Ublox Neo6M chipset with an amplified quadrifiler antenna that would get
a reasonable GPS lock while in my basement! I dropped it and that was the end of it. The chips have been surpassed and more imporatantly the antennas went out of production.
The CSG shop still has the chips listed on pages 6 and 7: https://www.csgshop.com/category.php?id_category=16&p=6 Kurt
 

mpitfield

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I be no expert but I suspect that perhaps an efficient antenna on 400Mhz would be too large to launch. Perhaps someone else could comment? I did have a Ublox Neo6M chipset with an amplified quadrifiler antenna that would get
a reasonable GPS lock while in my basement! I dropped it and that was the end of it. The chips have been surpassed and more imporatantly the antennas went out of production.
The CSG shop still has the chips listed on pages 6 and 7: https://www.csgshop.com/category.php?id_category=16&p=6 Kurt
Hi Kurt, I was hoping you would notice this one and reply. At the end of the day I am hoping for a passive solution and not another bit of electronics to deal with.

Found this. Might help answer your questions:

http://jcoppens.com/ant/qfh/calc.en.php
Thanks sooner, that is one of the sites that I was thinking of when I posted this. I hit that site last week and ran the numbers for my frequency range just to see the difference is measurements and it is minimal.
 

Adrian A

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Hi Kurt, I was hoping you would notice this one and reply. At the end of the day I am hoping for a passive solution and not another bit of electronics to deal with.



Thanks sooner, that is one of the sites that I was thinking of when I posted this. I hit that site last week and ran the numbers for my frequency range just to see the difference is measurements and it is minimal.
Not sure if this also applies to quadrifilar antennas, but on a 1/4 wave whip antenna, small errors in length produce insignificant effects on antenna performance, so optimizing for the middle of the band works just fine.
 

ksaves2

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Not sure if this also applies to quadrifilar antennas, but on a 1/4 wave whip antenna, small errors in length produce insignificant effects on antenna performance, so optimizing for the middle of the band works just fine.
Yeah, A long nosecone with a nosecone mounted 70cm or even a 2meter GPS tracker is a nice position to be in. Can even add a counterpoise or "tigertail" to turn the vertical antenna
into a vertical dipole. For sport fliers don't bother but if going to be flying in an extreme regime might give one a little edge. For instance another element on the 70cm
Beeline GPS might improve the situation a bit. Here's a representative site that explains it: https://w3atb.com/tiger-tail-antenna/

Again, If one's rockets aren't expected to go more than 2 miles I wouldn't bother with this with any tracker.

This link is about Quadrifiler antennas on 70cm: http://uuki.kapsi.fi/qha.html There might be an advantage on the receiving end with being able to decode positions from
a tumbling rocket but I don't think you would be able to fit it inside of a rocket on the tracker end unless it was a large project. Kurt
 

RocketDestroyer

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Every antenna has a bandwidth that they will work over. At 435Mhz a quadrafiler antenna should work over several MHz just fine.

I'm using a Crossed Moxon Array on 435 MHz for tracking rockets. I've had success with flights to 20,000 feet. It should work higher that is just the highest flight I have tested it with. Mine sits on a PVC stand about 6 feet tall and I don't have to touch it during a flight. I use a 1/4 wave vertical in the nosecone for the rocket end of things.

http://www.oocities.org/w9bci/VHFUHFSatelite.pdf
 

mpitfield

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Not sure if this also applies to quadrifilar antennas, but on a 1/4 wave whip antenna, small errors in length produce insignificant effects on antenna performance, so optimizing for the middle of the band works just fine.
That is what my intuition was telling me so it's comforting hearing it from someone else with more knowledge on this subject than myself, which is not hard. Still having a firm answer is what I am hoping to get. BTW one of the flights I am hoping to have this rig up and running on will have a Raven 3 and your new Mag switch on board.

Yeah, A long nosecone with a nosecone mounted 70cm or even a 2meter GPS tracker is a nice position to be in. Can even add a counterpoise or "tigertail" to turn the vertical antenna
into a vertical dipole. For sport fliers don't bother but if going to be flying in an extreme regime might give one a little edge. For instance another element on the 70cm
Beeline GPS might improve the situation a bit. Here's a representative site that explains it: https://w3atb.com/tiger-tail-antenna/

Again, If one's rockets aren't expected to go more than 2 miles I wouldn't bother with this with any tracker.

This link is about Quadrifiler antennas on 70cm: http://uuki.kapsi.fi/qha.html There might be an advantage on the receiving end with being able to decode positions from
a tumbling rocket but I don't think you would be able to fit it inside of a rocket on the tracker end unless it was a large project. Kurt
Good article on the how to make a Quadrifilar Helical Antenna (QHA or QFH), the tiger tail is not something I had considered so I will have to dig a bit deeper. Did you notice the author of the article used one of these antennas in an amateur rocket http://haisunaata.avaruuteen.fi/. It's not uncommon for me to fly in the 3+ mile range, although I am also hoping that this antenna might perform well enough for some higher alt flights I have planned in the 40-60K range. We will see. As I state I will have my yagi going as well so this is more a backup.

Every antenna has a bandwidth that they will work over. At 435Mhz a quadrafiler antenna should work over several MHz just fine.

I'm using a Crossed Moxon Array on 435 MHz for tracking rockets. I've had success with flights to 20,000 feet. It should work higher that is just the highest flight I have tested it with. Mine sits on a PVC stand about 6 feet tall and I don't have to touch it during a flight. I use a 1/4 wave vertical in the nosecone for the rocket end of things.

http://www.oocities.org/w9bci/VHFUHFSatelite.pdf
Good to hear another opinion on the range or accuracy of antennas. The trackers I will be using this with are the TeleGPS units, which have a 1/4 wave whip vertical antenna on them.
 

ksaves2

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Every antenna has a bandwidth that they will work over. At 435Mhz a quadrafiler antenna should work over several MHz just fine.

I'm using a Crossed Moxon Array on 435 MHz for tracking rockets. I've had success with flights to 20,000 feet. It should work higher that is just the highest flight I have tested it with. Mine sits on a PVC stand about 6 feet tall and I don't have to touch it during a flight. I use a 1/4 wave vertical in the nosecone for the rocket end of things.

http://www.oocities.org/w9bci/VHFUHFSatelite.pdf
Nice Terry, That looks easier to build than a Quadrifiler. Do you recover most of the positions on descent? I've noticed with simple antennas like a stock wire on a 70cm BeelineGPS and an aftermarket duck antenna, there are missed positions via Rf with the long fall under drogue from high up 8k or more. These losses which vary from flight to flight are occurring well before loss of signal. I suspect (especially with the 16mW BLGPS) that changes in polarity with the tracker flopping around under drogue were responsible for the position losses.

Worst case I've seen was loss of two positions that would be over a 15 second span and then positions resume. I've heard one missed position too. Easy to observe with the once every 5 second APRS transmission. Sometimes makes me sweat
but breathe a sigh when reception returns. Another reason why I like to blow the main out as high as practicable because with the slower descent and a more or less vertical position of the tracker antenna, packet reception is much more reliable.
That's what really counts to have a successful recovery. Get as many positions as possible down low before Loss of Signal (LOS)

I just might look into making one of these Moxon arrays for the fun of it. Seems simplier than a Quadrifiler ground station. Learned something today. Oh also learned that if one is going with a Quadrifiler ground station, since the transmitter is using a vertical polarized antenna it doesn't matter if the receiver Quadrifiler is Right Hand Circularly Polarized or Left Hand Circularly Polarized.

Only way to improve receiving is use the best antennas for the job on both ends, more power output on the tracker and a good quality of receiver. Thanks again for posting. Kurt KC9LDH
https://aprs.fi/#!mt=roadmap&z=11&call=a/QCRS&timerange=3600&tail=3600
 

ksaves2

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That is what my intuition was telling me so it's comforting hearing it from someone else with more knowledge on this subject than myself, which is not hard. Still having a firm answer is what I am hoping to get. BTW one of the flights I am hoping to have this rig up and running on will have a Raven 3 and your new Mag switch on board.



Good article on the how to make a Quadrifilar Helical Antenna (QHA or QFH), the tiger tail is not something I had considered so I will have to dig a bit deeper. Did you notice the author of the article used one of these antennas in an amateur rocket http://haisunaata.avaruuteen.fi/. It's not uncommon for me to fly in the 3+ mile range, although I am also hoping that this antenna might perform well enough for some higher alt flights I have planned in the 40-60K range. We will see. As I state I will have my yagi going as well so this is more a backup.



Good to hear another opinion on the range or accuracy of antennas. The trackers I will e using with this antenna are the TeleGPS units, which have a 1/4 wave whip vertical antenna on them.
Mike, 40 to 60k range I've never been there but if I was going there, I don't know if I'd use a Tele-GPS as the primary or only tracker. If required due to rocket geometry I'd make sure I'd have the best receiving antenna to
make the most out of the 10mW Tele-GPS. I've heard of 15mW 2 meter band RDF trackers being heard 125 miles out (with a Yagi no doubt on the receiving end) from a high altitude balloon but transmitting with optimum
antenna position in a sedate HAB is a piece o' cake. A tumbling rocket on the way down after apogee is another thing I'd be worried about using just a 10mW tracker. Just say'in. Kurt
 

mpitfield

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Nice Terry, That looks easier to build than a Quadrifiler. Do you recover most of the positions on descent? I've noticed with simple antennas like a stock wire on a 70cm BeelineGPS and an aftermarket duck antenna, there are missed positions via Rf with the long fall under drogue from high up 8k or more. These losses which vary from flight to flight are occurring well before loss of signal. I suspect (especially with the 16mW BLGPS) that changes in polarity with the tracker flopping around under drogue were responsible for the position losses.

Worst case I've seen was loss of two positions that would be over a 15 second span and then positions resume. I've heard one missed position too. Easy to observe with the once every 5 second APRS transmission. Sometimes makes me sweat
but breathe a sigh when reception returns. Another reason why I like to blow the main out as high as practicable because with the slower descent and a more or less vertical position of the tracker antenna, packet reception is much more reliable.
That's what really counts to have a successful recovery. Get as many positions as possible down low before Loss of Signal (LOS)

I just might look into making one of these Moxon arrays for the fun of it. Seems simplier than a Quadrifiler ground station. Learned something today. Oh also learned that if one is going with a Quadrifiler ground station, since the transmitter is using a vertical polarized antenna it doesn't matter if the receiver Quadrifiler is Right Hand Circularly Polarized or Left Hand Circularly Polarized.

Only way to improve receiving is use the best antennas for the job on both ends, more power output on the tracker and a good quality of receiver. Thanks again for posting. Kurt KC9LDH
https://aprs.fi/#!mt=roadmap&z=11&call=a/QCRS&timerange=3600&tail=3600
Along with the Crossed Moxon Array that Terry recommended, others recommended a Texas Potato Masher as well as the Eggbeater, as possible options for this application.
 

ksaves2

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I misunderstood your question Michael. I initially thought you meant to put this on the tracker:(. Stupidhead me. Looks like it could be something to use on the receive end to optimize a Tele-GPS tracker.
I got one and it's a nice little tracker. Me suggests when you settle on an antenna, loft some Tele-GPS trackers up higher and higher to see what you get and perhaps use a "tracker dog" rocket (ie. something
that's akin to an automobile "beater") for testing with another tracker backup so you can get your hardware back in case the Tele-GPS has reached it's limits. Best of luck for a good flight. Kurt
 

mpitfield

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Mike, 40 to 60k range I've never been there but if I was going there, I don't know if I'd use a Tele-GPS as the primary or only tracker. If required due to rocket geometry I'd make sure I'd have the best receiving antenna to
make the most out of the 10mW Tele-GPS. I've heard of 15mW 2 meter band RDF trackers being heard 125 miles out (with a Yagi no doubt on the receiving end) from a high altitude balloon but transmitting with optimum
antenna position in a sedate HAB is a piece o' cake. A tumbling rocket on the way down after apogee is another thing I'd be worried about using just a 10mW tracker. Just say'in. Kurt
Hi Kurt,

I picked up Kate for the flight to 60K, which may hit 65K but that might be optimistic. If I have the space, my hope is that I will have the TeleGPS along for the ride, assuming they place nicely together, which will be more of a test. However this antenna is really meant for my local club so up to 18K flights...regardless it will be fun to experiment.

The 40K flight sim, different rocket, I am not confident on, due to the design being a bit difficult to sim properly with the tools I have. The current sim indicates just over 45K and my sense is that it will be closer to 40K, but I am only confident claiming 35K. From discussions with others I am confident using a Yagi for my TeleGPS for 35K but 45K might be a stretch. FWIW I typically have the Comspec AT-2B on board with my TeleGPS, just for an RDF backup. They play nicely together but I will have to do a bit more research for these flights.

I normally use the Arrow (440-3) 3 element 70cm portable yagi, however I also own the 5 element Arrow (440-5) and 7 element Arrow (440-7). Both of which I have yet to use becasue the 3 element is so forgiving in direction, but they should provide more gain at the cost of a narrowing beam. With the 3 element the highest I have successfully tracked is just over 23,000' AGL vertically and 3.46 miles horizontally, different flights. If I recall the RSSI was floating between -90 and -95 at apogee and -30 on the pad. I would have to find the files, load them into AltosUI and replay them to confirm.
 
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