Extend bluetooth antena

[SentinelAeon]

Hello, you can see on the images a simple bluetooth speaker. The bluetooth is working fine, but occasionaly, expecialy when there is someone between mobile phone and the speaker, it will cut off. As you can see from the images, on the left image (the way it was now), the tweeter is right on top of the speaker and also some wires. That means interference. I was wondering if there was a way to extend this little antena on the PCB, so it could be larger and i could put it on top of the speaker where there is no metal parts to interfere. How would i improve bluetooth performance ?

 

[rjenkinsgb]

Bluetooth operates in the 2.4 GHz band, the same as common WiFi.

The wavelength is roughly 125mm, so a 1/4 wave ground plane antenna just about 30mm.

A WiFi antenna from a laptop may work (they are cheap on ebay) but due to the frequency the connections must be very! short and the antenna cable would need connecting in place of the PCB antenna loop or zigzag track.

eg. The cable inner to the feed point or coupling capacitor, and cable screen to the ground plane, with ideally no more that 2 - 3mm separated wire from the coax.

Note that you do not want any kind of "high gain" antenna as they rely on being directional, a bit like adding a reflector or lens on a lamp. The ideal antenna for bluetooth is omnidirectional, so moving around has minimal effect.

The downside of a laptop antenna is that they likely are slightly more directional; they are normally used in pairs (or more) in different orientations, with the wifi module selecting whichever antennas are working best at any instant (diversity), or even using multiple ones simultaneously or for beamforming on some recent types.

With only a single antenna point as on basic bluetooth modules, there will always be some nulls; it has to rely on signal reflections and frequency hopping, which can move the nulls to some extent.

Post a picture of the antenna on the bluetooth module you are using?

 

[SentinelAeon]

This is the amplifier with bluetooth module

 

[rjenkinsgb]

I got the antenna in the screengrab I did, as well.

To connect an external antenna, you would need to cut the existing antenna feed track at the red line, then connect the coax inner to the blue spot and coax outer/screen to the green spot. Remember lengths are critical, keep things short and neat.

(The short loop of track between blue and green is the impedance match "transformer" to the rest of the antenna zigzag track, so you can see how tiny things are at that frequency).

You could try it without cutting the track, but the effect are likely to be rather random, depending on relative distances and orientations of the two antennas to the device at the other end of the BT link.

 

[SentinelAeon]

I have plenty of bluetooth and wifi antenas from laptops at home, if i could somehow use that. Now the real question is, should i do that or first just leave it as it is and just move the amplifier.


On the left picture u can see where amplifier was positioned till now. Its in the middle of the backside of speaker (on picture thats the bottom part but obviously when i use it, its so that woofer and tweeter are directed towards me). In this position u can clearly see that depending on where i am positioned with my mobile phone, either tweeter or woofer is blocking the path between me and bluetooth, also there are some wires.


On the right picture you can see where i could position the amplifier with bluetooth. That was i could almost completely avoid tweeter and mostly the woofer also.


Do you think i should try that and see how it goes ? Or should i just go for the antena right away ? Btw bluetooth is working ok as far as distance goes, i can go very far, to the point where i can just barely see the speaker. But then sometimes even when i am like 2 steps away from the speaker, it will stop the music for a split second, this expecialy happens when there is another person between me and the speaker (and they have a mobile phone in their pocket obviously. )

 

[rjenkinsgb]

If the speakers will be facing towards you, so the open top of the box is actually the front - will it fit upright in the top left corner (as the box is in the photo), so the antenna is as near to the front panel as possible & some distance from the tweeter?

You could well get better results with separate amp and bluetooth audio modules, so the BT is not near the power switching class D amp.

 

[SentinelAeon]

I could make wires longer (it wont add to much resistance i suppose ..) to fit it in the left corner. But the woofer is there, its a lot bigger than tweeter. I was thinking i would fit it in the top right corner, on top of the port, so the tweeter wont be directly in its way. Or is the problem that tweeter is playing more frequencies that will interfere with bluetooth than the woofer ? They are both playing a lot of 2400Hz if thats important.

 

[rjenkinsgb]

Sorry, top RIGHT corner - I was looking at a copy of the photo rotated trying to get a better close up of the board & used the wrong one..

The heatsink on the bluetooth IC is a bit odd, that should not get warm.
Unless it's due to overloading because of no mixing resistors, which could damage the IC anyway..

Having that heatsink so close to the antenna may be affect it to some extent.

 

[SentinelAeon]

I will try that ! Yea, the heatsinks, i installed them. At the time i didnt even know what chips are those, im just used to overclocking and therefor slapping heatsinks to everything i can. I will try to heat up the heatsink on bluetooth module, i just hope i will not kill it. This epoxy should get a bit softer around 80C i read. I will report back and if it wont be good enough i can still try to do the antena. Thank you

 

[SentinelAeon]

If i put it in the top right corner, should the amp be facing me or facing the top ? I dont know if this antena is directional or 360. Should i point it as its in this picture ? I usualy position speaker so that i am looking at the woofer and tweeter.

 

[rjenkinsgb]

The least sensitive direction is probably looking across the board, eg. across the aux socket at the volume control or vice-versa.

 

[SentinelAeon]

Should i leave it in how its in the picture or should i turn some other direction ?

 

[rjenkinsgb]

Try it either as it is, but as near the front as it can be, or with the volume control spindle facing the front.