Tricky FM antenna question for the experts

Raynald

Addicted Member
I have a remote equipped TPA3116 amp board with Bluetooth, USB and SD inputs (plays FLAC!) that sounds great and even has FM capability. One AK member who has one has soldered an antenna directly onto the board but I would like to have a way of connecting and disconnecting the antenna.

It would be nice to be able to just strip the ends off of one of the many 75/300 Ohm transformers I have lying around and solder that to the bottom. Then I could just hood up whatever antenna I want with the right connector/transformer. The question is, what sort of antenna is likely best for these little guys? 75, 300 Ohm, or something else? Should I consider soldering something else to it?View attachment 947447 View attachment 947448 View attachment 947447 View attachment 947448

Then the question is, where? If you look at the close up picture you can see what is presumably the FM input in the middle. The other user claimed good results by soldering the other end to the point just to the right which is connected to traces on the PCB. There is also another point just above it that does not seem connected to anything. Would that be a better choice? Or do these "tuners" work with only the single FM point attached?

I am only guessing, but maybe the technology here is closer to what you find in cellphones than our conventional FM tuners which is why I suspect the conventional rules may not apply.

Any guidance would be appreciated. Thanks!
 

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Pics are too blurry for me... Which board are you using? Lots of them out there.
The one thought about antennas would concern overloading (since phones, for
instance, use pretty small ones).
 
Ah, seeing the FM terminal now... SDR USB dongle antennas run small
coax, solder the connector you need on the board.
 
The "2nd antenna connection" likely goes to the ground plane, which is what your "another point just above it that does not seem connected to anything" is connected to. But there is a (probably) better spot to connect to the ground plane, right next to the "FM" input ON THE BACK (at least if the backside of your board is like the one pictured in the ebay link). I agree with RxDx that there might be a connector that fits in that position but I think that buying it might cost you more than the whole rest of the board, if you can find it. As a first step, I would try just soldering a single length of insulated wire to the FM input and see how well that works.
 
The "2nd antenna connection" likely goes to the ground plane, which is what your "another point just above it that does not seem connected to anything" is connected to. But there is a (probably) better spot to connect to the ground plane, right next to the "FM" input ON THE BACK (at least if the backside of your board is like the one pictured in the ebay link). I agree with RxDx that there might be a connector that fits in that position but I think that buying it might cost you more than the whole rest of the board, if you can find it. As a first step, I would try just soldering a single length of insulated wire to the FM input and see how well that works.


I think you might be on the right track as I have just found what could be a relevant clue by looking at another board I found that has FM and seems to have the antenna installed. Sure enough, a single short length of insulated wire:

http://www.ebay.ca/itm/311665334342?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

If you zoom the image you can see the wire attached at the lower right hand side. I have to assume that is the FM antenna. Of course at these prices nothing says they are using the ultimate antenna solution but that is probably a good place to start.

I might just pick up one of those boards. TPA3118 chip amp, relatively recent CSR8635 BT chip, FM with antenna, AUX input, headphone socket, remote control, speaker terminals and DC input already soldered to the board. They even throw in a power cable I can use with my Pyramid PS! Not bad for $25 Canadian.
 
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