Telemetrum SMA antenna installation help

Greetings all.


I have a Telemetrum V1.2 with the stock wire antenna. I would like to use a SMA antenna for my application. When removing the wire antenna for those who have done this there are 3 pads on the PCB. It looks like with my old eyes that the wire is only soldered to the center pad, is this correct. If that is the case then I can just desolder that pad and install and edge mount SMA connector correct? Any other hints. tips, or suggestions?


Thank you

Chris

The center conductor of the SMA connector attaches to the one that the current antenna wire is on. The pads on the side of this one and on the back are for the outer connector / body of the SMA connector.

Best of luck,
Doug

Thanks Doug

So no part of the wire currently on the pcb connects to the outer pins?

Thank you

73

de vk2icj ..

Chris

No, those are connected to the groundplane that you can see in the image at https://altusmetrum.org/TeleMetrum/v2.0/telemetrum-v2.0-smt.jpg. You can also see where the wire should be connecting. As you unsolder, be careful of the SMT parts near the antenna; it's easy to knock one out of place if you're not careful.

Are you planning on using an external antenna for a CF bird or some other nefarious purpose?

Doug

Hi Doug

Well that might be another question in and of itself. This telemetrum is going into a Hawk Mountain Transonic 2. 54mm MD (all fiberglass) I was wanting to move the antenna to the rear of the bulkhead of the Ebay so that it is out of the BT when the drogue is deployed. I'm concerned about the ability of the wire antenna to transmit effectively from 10000 + feet. I understand that the fiberglass is RF invisible however my concern was more with the wire antenna vs a rubber duck.

Any experience?

Chris

Actually, the wire antenna is probably *better* than any dual-band rubber duck you'd be able to get. Those will have extra components inside to tweak them to work at both 2m and 70cm.

The footprint on TeleMetrum is indeed designed to work perfectly with a standard edge-launched SMA connector; just solder the center pin to the pad where the wire was attached and the four ground pins (two on each side) to the pads that land underneath them. If you've got a TeleDongle or TeleBT, you'll see exactly the same footprint used for this purpose.

I have flown a TeleGPS (which I believe has lower transmitting power; Keith you can correct me if needed) than the TeleMetrum/Mega and I have received packets from a weather balloon over 80,000 feet in the air. Granted, this was with the antenna exposed, but I don't think you will have any issues with a signal. This was off of a simple wire antenna. Packets were sparse, but there was a LOT of turbulence that day as evidenced by the onboard video; the wild gyrations made it difficult to get a good/full packet with the yagi. Get a 7-element from Arrow with the break-apart boom and use half of it for lower flights and you can crank it up to 7 for the high flights.

Adding rocket experiences:

I've flown to 12,000 feet AGL in fiberglass airframes; the only issue ever was an apprentice (my son) that wasn't carefully pointing the yagi during flight. That rocket is either in a Kansas field still or (hopefully) has been recovered; time will tell. Moral of that story is, practice tracking, and use a bigger battery than you think you should. (It hit the ground and was not recovered / located before the expected shutoff.

Doug

Yup, TeleMega and TeleMetrum v2 put out 33mW, TeleGPS 14mW and TeleMetrum v1.0 10mW, and we've had several people fly TeleMetrum v1.0 boards to 30k'+ with reasonable tracking. Nice to hear that you've flow TeleGPS to 80k'; I think that's the highest I've heard of!

Note that the current TeleDongle/TeleBT designs use a receiver which isn't as sensitive as most commercial amateur transceivers, so if you've got one of those with built-in APRS decoding, you'll get even longer range using that instead of the regular telemetry. We're working on a new receiver design that has better specs on paper; we'll see how that works in practice.

Thanks for the info Keith

Can I ask.. Isn't the V1.X board all proprietary with the data exchange? IE not APRS? My Telemetrum is V1.2 I have the Teledongle from the same time period as well as mine were bought as a kit.


Chris

I don't have the first flight data on this computer (106,000+ feet) but the second flight reached 92998.7 feet as reported from another device onboard; it looks like the highest read from the ground was about 75,000 feet. (Mental note to download data from the TeleGPS soon.) We were too busy trying to get to the predicted landing site to get any fixes until a bit later in the flight. I may need to play with an antenna that is a bit more omnidirectional and sensitive for the chase vehicle.



So as to not entirely hijack this thread; the earlier versions did not output APRS but I can tell you that the encoding and software is all open source. The packets are sent at a much higher rate than APRS could be and conserve battery life.

As for SMA connectors; Keith and I had a similar discussion at AirFest 2014 on antennas. I switched my TeleMega to a simple wire antenna and have noticed no issues compared to SMA/wire or SMA/70cm ducky. I do foresee the day when I use a remote antenna in a carbon fiber rocket; but I'll cross that bridge when the time comes. :wink:

Doug

V2rocketeer said:

Thanks for the info Keith

Can I ask.. Isn't the V1.X board all proprietary with the data exchange? IE not APRS? My Telemetrum is V1.2 I have the Teledongle from the same time period as well as mine were bought as a kit.


Chris

Click to expand...

All of our boards use TI radio devices designed to send digital packet data, and that's the "normal" data mode that we use. You can hack them to send audio data by a careful selection of modulation parameters and digital data. The TeleMetrum v1.x boards used a part that had a small upper bound on the packet length, so while we could get them to emit a short RDF beacon, there wasn't any way to send a long APRS packet. TeleMega and TeleMetrum v2.0 use a different radio part that can send arbitrary packet lengths, so we just cook up a huge "packet" that happens to sound like APRS.

I use a short section fiberglass tubing to house the wire antenna and a magnetic switch (lower left of sled).

I'd love to see the magnetic switch further from the RF source; that's about the best place you could put it if you want to maximize the chance of RF energy interfering with the flight computer operation..

Hi Keith


I assume the power switch term 1 and 2 are not a momentary switch? Shorted it is on and open the unit is off? I was confused about that part in the instructions.



Shown here is my Ebay. I will need to run my antenna out the top bulkhead as well.

I intend on running a sled along the centre bolt and attaching the Telemetrum to the sled

Chris