To HAM or not to HAM

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Sleestak

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Can someone explain how much better (or not) a HAM band GPS tracker is over the 900 MHz band units? Is it a more powerful signal for any distance (line of sight and through terrain changes like hills, trees, valleys)?

Typically how much range is expected from both?

And yes I know about getting a HAM license, and that some scally wags choose not to.

Thanks!
 
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The 435MHz signals are less line-of-sight (thus more forgiving) compared to the 920MHz signals, and in many cases are allowed to use higher transmit power because a HAM license is needed for their use. Having a license opens up many more possibilities.

Depending on what you are flying this may or may not make a difference.

Of course the disadvantage is that the Tx antenna needs to be bigger.

I don't have any comparative range figures so I won't discuss them.

Note that once the rocket is on the ground the range is reduced considerably, and that goes for either frequency band.

I held off getting a license for years but now I have it (Advanced license) I wish I had gotten in earlier.
 
Although I’m a ham, I really haven’t seen any real advantages of using ham trackers. I see really good results from the 900 MHz units.
Same here. Have my ham license but use 900MHz GPS units. Now I am on the East coast where the fields are smaller compared to out West so don't need 10km range.
If you fly out west and go very high then a Ham radio 70cm tracker may be highly desired.

Now I do use 2m/70cm low power beacon TX's to RDF rockets that go into the corn fields. I build these and they send my call sign to be legal.
 
I 900MHz for my GPS transmitter and 433 MHz for the altimeter telemetry. We also use the ham radios to communicate with each other when looking for rockets that don't have GPS.
 
I already had my Ham license so I got the 435 MHz trackers. As several have mentioned the 435 MHz signals will travel farther for the same power level. In the air you won't see to much difference and on the ground neither one has much range. I like the ham license because I can chat on the repeater on the way home and when I get home I can talk to the world on HF. If none of that appeals to you stick with the 900 MHz units.
 
Same here. Have my ham license but use 900MHz GPS units. Now I am on the East coast where the fields are smaller compared to out West so don't need 10km range.
If you fly out west and go very high then a Ham radio 70cm tracker may be highly desired.

Now I do use 2m/70cm low power beacon TX's to RDF rockets that go into the corn fields. I build these and they send my call sign to be legal.
I guess I should point out I'm in the mid-west and fly my big rockets with KLOUDBusters in Argonia, KS. I want to go by bigger and higher, but the excessive wind drift is killing me. I'm working on dual deploy now. I already have a 900 MHz Eggtimer...looking to add another...
 
70cm/435MHz will have better propagation on the ground when compared to 900MHz. When combined with a directional antenna like a yagi this means you'll get your final 'on the ground' packet sooner with 433MHz when compared to 900MHz. That's the value add for lower frequencies from what I've seen.

From a distance perspective it's kind irrelevant imho as Featherweight advertises their 900MHz LoRa backed GPS as good up to 300,000' and the ISS operates a downlink on 70cm, which are both well beyond the limits of GPS chipsets we currently use from an altitude perspective.
 
The non-ham receivers don’t seem to have an audio output or any other indication of a partial packet. So I think it will be tough to use a directional finding antenna unless it’s enough to get you clean packets again. If your system remembers the last packet it received that will probably be good enough to get you close to where it landed and hopefully the signal strength will go back up again and you can get packets and get to the final landing spot.

I personally like ham systems because it gives me a sense of satisfaction to have the Ability to mix and match components and have a better sense of what’s going on in the guts. And there are lots of other uses for the ham gear.
 
I guess I should point out I'm in the mid-west and fly my big rockets with KLOUDBusters in Argonia, KS. I want to go by bigger and higher, but the excessive wind drift is killing me. I'm working on dual deploy now. I already have a 900 MHz Eggtimer...looking to add another...
How has the Eggfinder been working in Kansas?
Do you have a signal once rocket is on the ground or do you need to walk a ways to pick it up?
If no signal from ground then is the last know coordinates good enough to get close and pick up the signal?
 
One upside to 70cm trackers compared to 900Mhz is that they 70cm's don't hop.
Hopping makes it near impossible to use RDF to get the final bead on a rocket on the ground.
We fly in somewhat hilly terrain.
If your rocket goes over the hill your last GPS packet is from a rocket that's still ~1000ft in the air.
This can leave a lot of room to drift.
Finding the rocket is often hard to impossible without RDF'ing from the last reported position.
You can't really pull out a Yagi and sniff out a hopping radio.

Plus - as mentioned above - you can talk over the recovery channel with the team searching.
 
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How has the Eggfinder been working in Kansas?
Do you have a signal once rocket is on the ground or do you need to walk a ways to pick it up?
If no signal from ground then is the last know coordinates good enough to get close and pick up the signal?
I have only used it a few times and in most cases I didn't need it as it was a low flight and I saw where it went.

However, I do find it very high on the fiddly scale. I am not sure what the issue is. It does appear that I have some fraying wires where the battery attaches to the PCB, potentially causing intermittent power failures. For that, I got some new silicon wire and will incorporate some strain and flexing relief. So I will address that and re-test. When doing hide and seek yard testing with my kids, there are no issues.

There was one time that it did fail me. And as crazy at it seems, I think it might be because there was another guy with the same frequency as me. My ground station was losing signal and then telling me the rocket was way far away from where I saw it land, and then flipping back to where I saw it land...but I didn't see the rocket in the milo fields at last year's AirFest. Eventually the other guy found my rocket and let me know. I turned off my Tx and I believe he was able to locate his rocket in a galaxy far far away.

The other part is the Rocket Locator app on my Andriod. It is hard for me to tell when it is receiving data or when the last package was received, so I never know if I am dealing with stale data. I was so frustrated with this app, that I even started writing my own (but that stalled out since building rockets is more fun lol). The Rocket Locator app does remember the last packet sent, so in theory it should get you close enough until you get a fresh signal.
 
We recommend turning on your receiver first and waiting a few minutes in case somebody else is on the same frequency/ID. That doesn't happen very often unless you leave it on the default 915/0... which I've seen. A lot.

Yes, the RX/Bluetooth with Rocket Locator is fiddly. That's why I recommend getting the LCD receiver... it's way easier, especially with the GPS module. Let it tell you where to go instead of fiddling with your phone.

You can expect a 70cm transmitter with the same power output to go about twice as far as 900 MHz. Now, if you're flying in a field with a pretty typical < 20,000' AGL ceiling, it probably won't matter, but if you're thinking of a 98mm MD full-M or decent N then 70cm might not be a bad idea.

Getting a Ham license is a good thing to do if you're going to be working with anything having to do with radios, if you're not familiar with radio propagation and things of that nature you'll learn a lot. You'll also learn how different antennas can affect things, which is another good thing to learn.
 
One upside to 70cm trackers compared to 900Mhz is that they 70cm's don't hop.
Hopping makes it near impossible to use RDF to get the final bead on a rocket on the ground.
We fly in somewhat hilly terrain.
If your rocket goes over the hill your last GPS packet is from a rocket that's still ~1000ft in the air.
This can leave a lot of room to drift.
Finding the rocket is often hard to impossible without RDF'ing from the last reported position.
You can't really pull out a Yagi and sniff out a hopping radio.

Plus - as mentioned above - you can talk over the recovery channel with the team searching.
900MHz doesn't necessarily imply FHSS. The Featherweight GPS operates in the 900MHz band and sits on a single channel.
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We recommend turning on your receiver first and waiting a few minutes in case somebody else is on the same frequency/ID. That doesn't happen very often unless you leave it on the default 915/0... which I've seen. A lot.

Yes, the RX/Bluetooth with Rocket Locator is fiddly. That's why I recommend getting the LCD receiver... it's way easier, especially with the GPS module. Let it tell you where to go instead of fiddling with your phone.

You can expect a 70cm transmitter with the same power output to go about twice as far as 900 MHz. Now, if you're flying in a field with a pretty typical < 20,000' AGL ceiling, it probably won't matter, but if you're thinking of a 98mm MD full-M or decent N then 70cm might not be a bad idea.

Getting a Ham license is a good thing to do if you're going to be working with anything having to do with radios, if you're not familiar with radio propagation and things of that nature you'll learn a lot. You'll also learn how different antennas can affect things, which is another good thing to learn.

Thanks for the input Cris. I had forgotten about the LCD receiver. I am looking to add another GPS and will go with the LCD-GPS option when the time comes...which will hopefully free me from the shackles of the Rocket Locator app (and from having to write my own app). As I understand it the LCD unit will allow me to change the frequency of the Tx...

That actually brings me to some other questions...
  • I bought my current setup back in late 2020 and it was shipped with a freq of 923/6 (not 915/0)...did the default freq change at some point?
  • Will the LCD unit allow me to change the freq on my current RF-BT ground station, or does it only change the Tx (and the corresponding Rx on the LCD unit itself)?
 
Thanks for the input Cris. I had forgotten about the LCD receiver. I am looking to add another GPS and will go with the LCD-GPS option when the time comes...which will hopefully free me from the shackles of the Rocket Locator app (and from having to write my own app). As I understand it the LCD unit will allow me to change the frequency of the Tx...

That actually brings me to some other questions...
  • I bought my current setup back in late 2020 and it was shipped with a freq of 923/6 (not 915/0)...did the default freq change at some point?
  • Will the LCD unit allow me to change the freq on my current RF-BT ground station, or does it only change the Tx (and the corresponding Rx on the LCD unit itself)?
If you got a TX/RX combo, they come pre-set to a non-default frequency/ID, i.e. NOT on 915/0. If you buy a TX/LCD combo, they're on the default 915/0, since you can (and SHOULD) change them. There is no way to change the frequency/ID on a TX (or Mini) without the LCD receiver. You can also use the LCD receiver to change the frequency/ID on the RX receiver, too.
 
If you got a TX/RX combo, they come pre-set to a non-default frequency/ID, i.e. NOT on 915/0. If you buy a TX/LCD combo, they're on the default 915/0, since you can (and SHOULD) change them. There is no way to change the frequency/ID on a TX (or Mini) without the LCD receiver. You can also use the LCD receiver to change the frequency/ID on the RX receiver, too.
Thanks for the speedy clarification Cris! I just sent you an email for my next order...fingers crossed I won't be a victim of COVID supply chain backorder problems!
 
If you got a TX/RX combo, they come pre-set to a non-default frequency/ID, i.e. NOT on 915/0. If you buy a TX/LCD combo, they're on the default 915/0, since you can (and SHOULD) change them. There is no way to change the frequency/ID on a TX (or Mini) without the LCD receiver. You can also use the LCD receiver to change the frequency/ID on the RX receiver, too.

I bought a second hand Egg Finder system and tried it out last weekend at home. If I would have built it all myself, I would have a better understanding of how it works, most likely, but I started figuring out things a bit slower than someone who touched each piece, most likely. Having said that, the units I have on hand and assembled right now are:

Rx LCD version 1.09d
Tx 915 Rev B4d

By reading the current user manual, I believe I am going to be at 915Hz and ID 0 no matter what, due to the Tx generation. If that's correct, is it a good idea to try and coordinate with others who are flying with an Eggtimer product to ensure that we aren't messing with each other - kind of like old school RC racing was, where you had to get the 'official' crystals from race control to prevent you taking over control of someone else's car? My main concern isn't losing my own stuff, but I really don't want to screw with other people by accident. . . I have some newer Tx's, but don't have the time to confidently build and test prior to NSL this weekend.

Sandy.
 
I only needed a ham license to buy a telemetry device. Got talked into taking all 3 tests the same day, got the Extra class license, then didn't shoot off another rocket for 10 years. :( You're talking a lot of money to buy a HT unit with built-in GPS.
 
I only needed a ham license to buy a telemetry device. Got talked into taking all 3 tests the same day, got the Extra class license, then didn't shoot off another rocket for 10 years. :( You're talking a lot of money to buy a HT unit with built-in GPS.
True, but it's probably the simplest and most effective way to track. A Yaesu with GPS and APRS TNC will tell you the distance and bearing of your transmitter in real time. Combined with a yagi and compass it's really hard to mess up. Everything else is more complex and convoluted in comparison, at least imho.
 
What is the rule on 900MHz? Is FHSS required or not? I looked but couldn’t find the right reference. I’m u sure of what’s required to technically be legal.

900MHz is an ISM band, so technically unlicensed, all emissions from straight CW to FHSS with cryptography and compression are allowed.

What's required, you asked? Don't exceed power limits, don't splatter outside the band, don't cause interference with other users, the usual.

Amateur privileges allow more power. But you don't need that for rocket tracking.
 
FHSS is not an absolute requirement in Australia. See.post #19.
What about the US? I ran over some documentation about a requirement of FHSS on the US ISM band. It was something like a 400ms transmit time limit on any given channel during a 20s period. There was a specified minimum number of channels required too IIRC. However, I could not find any common references to these requirements, so that's why I ask.
 
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