TeleGPS antenna length

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watermelonman

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Has anyone out there got a TeleGPS unit handy today? I would love to get an exact measurement of the antenna length.

I am at a multi day launch, and I ripped mine off mid flight. Thankfully I have a battery soldering iron and the proper wire, but need to know the length. Thanks!
 

mpitfield

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6.5", that is measured from the edge of the PCB to the end of the wire.
 

ksaves2

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Post how the flight goes. I'd be interested if you're using a Dongle, Tele-BT or the APRS side only. Running Altus-Droid with cached maps?

The Altus Metrum products are the only ones that concurrently send coded information digitally to their receivers AND an APRS packet so one who simply wants
to track, can do so with an APRS ground station only. I can fire up a Kenwood D-72A I have interfaced to a Garmin 60Cs(X) and use this same ground station with Beeline GPS trackers. The Tele-GPS is the smallest rocketry purposed based GPS tracker out there so if a Ham flier needs something smaller than a Beeline, it can be used with their same receiver hardware and they wouldn't have to buy anything else. Kurt
 

keithp

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Has anyone out there got a TeleGPS unit handy today? I would love to get an exact measurement of the antenna length.
Sorry, lost internets over the weekend due to a storm! It's a 1/4 wave whip using the PCB as the 'ground plane'. With that, the speed of light, frequency and velocity factor of a solid copper conductor, you can compute the length on your own:

Frequency: 435MHz
Speed of light: 3 * 10⁸m/s
Velocity factor: 0.95
Antenna design: 1/4 wave

speed of light
----------------- * velocity factor * 1/4 = 0.164m or 16.4cm or 6.5 inches
frequency
 

mrwalsh85

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Hi @keithp - is there a material that is preferred for the antenna? I also have some 0.020" brass rod, would this material be sufficient?
 

plugger

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I asked this question to the mailing list in 2019. Below is Bdale's reply.

I use 22 awg solid with PVC insulation, 17cm long with about 5mm stripped at one end, in our production process. Note that "optimal" wire length is a function of both operating frequency and installation environment, this size has proven to work well in a variety of airframes...
And here's what I bought. Remington hook up wire
 
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billdz

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It's a 1/4 wave whip using the PCB as the 'ground plane'.
Hi folks, I'm glad to have found this thread. I have a similar issue, the wire antenna broke off. I prepared a 6.5" wire to replace it but discovered that the old antenna had pulled off the soldering pad. Any suggestions for how to mount the new wire? Guess I could solder to the end of that tiny component that apparently attaches to the pad, but hopefully there is a better, more secure way.
Thanks,
Bill
telegps.jpg
 
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billdz

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Anybody have any ideas?

The only thing I can think to do is glue the wire to the board and then try to solder the end of the wire to the tiny component. But that looks difficult and does not seem like a strong configuration. Any better ideas?

Thanks much,
Bill

PS - I believe that the two pads on the side of the missing antenna pad are the ground connections for an SMA connector that a previous owner of this tracker must have put on. It has only had the wire antenna since I have owned it.
telegps blow up of missing pad.jpg
 

Johnly

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Yes, the upper pad looks like there is a portion of a SMA connector on it.
Clean the two solder pads next to the antenna lead(ground plane) and install a PCB mount Male SMA connector on the PCB and solder the ground legs to the outer pad set.
The use a solder bridge or a short piece of wire to connect the center lead of the SMA connector to the butt end of the SMT component to drive the antenna element.
 

OverTheTop

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Yes, the upper pad looks like there is a portion of a SMA connector on it.
Clean the two solder pads next to the antenna lead(ground plane) and install a PCB mount Male SMA connector on the PCB and solder the ground legs to the outer pad set.
The use a solder bridge or a short piece of wire to connect the center lead of the SMA connector to the butt end of the SMT component to drive the antenna element.
Sounds like a good method of repair mostly, except do not just use a solder bridge to connect the center lead of the SMA connector to the SMT component. Solder is crystalline and brittle and will crack, resulting in an unreliable connection. You need to put some fine wires in the joint between the two components. Some strands from a multistrand hookup wire work well.

This method should also be used for repairing PCB tracks or jumpering between pads. Do not just rely on the solder bridge as it will crack. I have seen this many times over the past decades. Just don't, or you will likely regret it!
 

billdz

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Sounds like a good method of repair mostly, except do not just use a solder bridge to connect the center lead of the SMA connector to the SMT component. Solder is crystalline and brittle and will crack, resulting in an unreliable connection. You need to put some fine wires in the joint between the two components. Some strands from a multistrand hookup wire work well.
You can buy an SMA connector from Bdale’s store at https://shop.gag.com/parts/sma-connector-pcb-edge.html and could solder that to your board.
Thanks for the replies! Think I'd prefer to stick with the wire antenna instead of an SMA. The original wire was solid. Perhaps I should use stranded wire and solder the end directly to the tiny component, and then put glue where the pad was to hold the wire steady and relieve stress on the solder joint?
 

Voyager1

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Thanks for the replies! Think I'd prefer to stick with the wire antenna instead of an SMA. The original wire was solid. Perhaps I should use stranded wire and solder the end directly to the tiny component, and then put glue where the pad was to hold the wire steady and relieve stress on the solder joint?
I’d be more inclined to follow Wills’ suggestions and reinstall a new SMA connector after removing the original grounding connections. You can still use a wire antenna. I think the one he suggested is a wire one attached to a mating SMA connector.

The center conductor the SMA connector would almost get to the SM coupling capacitor. You could bridge the remaining gap as suggested by OTT.

I wouldn’t recommend a stranded antenna because it won’t remain straight without support. If your antenna is too flexible and doesn’t remain straight, then you risk messing with its characteristic impedance and radiation pattern if it flops around. If you do use a stranded antenna, then you might have to adjust the resonant length a little because stranded wire might behave a little differently to solid wire at RF frequencies.
 

billdz

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I’d be more inclined to follow Wills’ suggestions and reinstall a new SMA connector after removing the original grounding connections. You can still use a wire antenna. I think the one he suggested is a wire one attached to a mating SMA connector.
Bdale also recommended an SMA connector. I ended up sending the unit to him for repair, because the mini-USB also broke off. He's way behind and has not started working on it yet.
 

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