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Old Nov 08, 2012, 03:56 AM
iskess is offline
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Help!

Adding a directional antenna to a Walkie-Talkie for tracking UHF beacons


Can someone help me figure out how to solder an SMA connector to this Motorola walkie talkie PCB?Name: ImageUploadedByTapatalk1352364717.676241.jpg
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I want to add an SMA connector so I can add a Yagi antenna to help track a UHF beacon.
The problem I see it that there is only one wire for the stock antenna, and I need to know where to attach the ground. The ground should be on the RF Module, not just the battery ground. Can anyone identify it for me?
Thank you for your help.
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Old Nov 12, 2012, 08:45 AM
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If noone has a better idea, I would use the ground one can see in the last image, with the many vias in it.
Old Nov 12, 2012, 06:31 PM
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Thank you do much for your reply. No one else has chimed in yet. Can you try to describe the location you are talking about in the photo?
Old Feb 03, 2013, 01:51 AM
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Bump.
Maybe this will catch someone else's eye who can help me.
Old Feb 03, 2013, 11:02 PM
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The RF ground is where the antenna wire departs away from the groundplane. Scrape off some solder mask right next to the RX out and solder there.
You can't take any ground other than a couple mm from the RX out or it becomes part of the antenna.
Old Feb 04, 2013, 04:18 AM
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Quote:
Originally Posted by jakestew View Post
The RF ground is where the antenna wire departs away from the groundplane. Scrape off some solder mask right next to the RX out and solder there.
You can't take any ground other than a couple mm from the RX out or it becomes part of the antenna.
Thank you so much for the reply. So just to clarify, you are saying to just pick any point right next to the existing antenna solder blob and scrape off the green?
Old Feb 04, 2013, 02:19 PM
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Yes. It's hard to see on what's going on with your board, so make sure you tap into the ground.
The antenna starts wherever the TX path departs from the ground. Right on one side or the other will be your best point to attach the connector.

If you want to put on a connector you need to ground the outside of it, otherwise the connector will be part of the antenna. Same if you use some sort of coax cable to connect to the antenna. If you just want to try a straight wire as an antenna then you don't have to worry as you'll just solder directly on the TX output.
Old Feb 04, 2013, 04:33 PM
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Quote:
Originally Posted by jakestew View Post
Yes. It's hard to see on what's going on with your board, so make sure you tap into the ground.
The antenna starts wherever the TX path departs from the ground. Right on one side or the other will be your best point to attach the connector.

If you want to put on a connector you need to ground the outside of it, otherwise the connector will be part of the antenna. Same if you use some sort of coax cable to connect to the antenna. If you just want to try a straight wire as an antenna then you don't have to worry as you'll just solder directly on the TX output.
Ground the outside of the SMA connector? Isn't that what I am doing when I scratck off the green and solder the conector there? Or do you mean ground it again to the battery ground?
Old Feb 05, 2013, 11:44 AM
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> Ground the outside of the SMA connector? Isn't that what I am doing when I scratck off the green and solder the conector there?

Yep, that's right. The SMA connector is grounded right next to the old antenna. Don't ground it anywhere else or you could cause some ground loop problems.


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