HowTo: TDA7492/CSR8635 – External antenna mod to improve reception

After the Bluetooth retro speakers After using it for a few days, I noticed relatively quickly that the integrated antenna had a somewhat modest radio range.
Most of the time it was over after about 2m as the crow flies. A connection through one or even two walls was out of the question. So simply disappearing into the toilet with your cell phone while the music is playing wasn't possible either.

After a few more days, I decided to get to the bottom of the problem. Ultimately I blamed the poor reception quality on the tiny PCB antenna on the CSR8635 Bluetooth module. So the only solution was to connect a new antenna with better amplification.

How you can do this is described in this article.

Safety instructions

I know the following notes are always kind of annoying and seem unnecessary. Unfortunately, many people who knew "better" have lost eyes, fingers or other things due to carelessness or injured themselves. Data loss is almost negligible in comparison, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Because even the coolest project is not worth injury or other trouble.

Affiliate links/advertising links

The links to online shops listed here are so-called affiliate links. If you click on such an affiliate link and make a purchase via this link, will receive a commission from the relevant online shop or provider. The price does not change for you. If you make your purchases via these links, you support in being able to offer other useful projects in the future. 🙂 


Helpful articles:
Before you start with this article, you should have dealt with the basics of soldering. You can find information about this in the following article.
Electronics - My friend the soldering iron

Required material:

In the following list you will find all the parts you need to implement this article.

Required tool:

In the following list you will find all the tools you need to implement this article.

Overview – What’s where?

The following photos explain the problem and the solution somewhat.

After opening the back of the case, the amplifier board should be easily accessible.
This is what your unprocessed amplifier board should look like. The integrated PCB antenna can be clearly seen on the blue Bluetooth module.
In this photo you can see the conductor track between the Bluetooth module and the PCB antenna. This will be removed later to no longer use the integrated PCB antenna.
The aim of this mod is to replace the integrated (bad) PCB antenna with an external Bluetooth antenna. This could also be an old WiFi antenna. Since Bluetooth and WiFi work in the same frequency range, both antennas can be swapped with each other.
The external antenna can then also be attached outside the housing with a screw thread.
For this conversion you will need a connection cable for the antenna. Make sure that both fit together. Special RP-SMA plugs/sockets were introduced for the WiFi antennas. This means that they do not mechanically fit the normal SMA connectors.
So make sure that the socket of your antenna...
...matches the plug of your antenna cable.

Disconnecting the old PCB antenna from the Bluetooth module

Before you can connect the new antenna, the old antenna must of course first be removed. To do this, the connection between the Bluetooth module and the PCB antenna must be separated at the appropriate point.

To separate the old PCB antenna from the Bluetooth module, the small conductor track between the Bluetooth module and the PCB antenna is interrupted with a sharp knife. If the knife is sharp enough, you can easily separate the conductor track and bend it up a bit. This way you can clearly see that the conductor track is interrupted. To be on the safe side, you can also use a multimeter/continuity tester to check whether the conductor track is actually interrupted.
Here you can see a close-up of the conductor track between the Bluetooth module and the PCB antenna. The area circled in red is the part you should interrupt.
Close-up of disconnected connection between Bluetooth module and PCB antenna. You can clearly see the bent up conductor track.
In a highly enlarged image you can…
...see that the conductor track is clearly broken.

ATTENTION: In this state - i.e. without an antenna connected - you must under no circumstances switch on the Bluetooth module. This can damage the module.

Soldering the antenna cable to the Bluetooth module

Now it's time to solder the new antenna cable to the Bluetooth module.

To do this, you must – if available – remove the plug at one end of the antenna cable.
Unfortunately, this plug is very small but only crimped on and is therefore relatively easy to separate from the antenna cable.
Rear view of the IPX connector used - especially in devices with little space.
To remove the plug from the antenna cable you must first... shown, bend the holding arms crimped onto the cable outwards. These are responsible for the mechanical fit on the cable.
The holding arms located closer to the plug also provide electrical contact for shielding the antenna cable. This… can now bend it outwards.
Now the plug should move carefully towards the antenna cable...
...let it be deducted from this.
This will reveal the two lines in the antenna cable. The inner and outer conductors or shielding must now be separated from each other and prepared for soldering.
To do this, carefully remove approx. 1.5cm of the insulation.
The outer conductor is placed around the antenna cable in the form of a wire mesh and can be removed with a needle or tweezers...
…slightly “unravel” and separate from the inner conductor.
So that the two conductors can be soldered more easily later, it is recommended to tin both the inner and outer conductors with a little solder.
Now you have to connect the prepared cable to the antenna contacts of the Bluetooth module. The inner conductor of the antenna cable must be connected to the contact marked green and the shielding of the antenna cable (the outer conductor) to the contact marked red on the Bluetooth module.
The whole thing should look like this when soldered on.
After soldering, check again that the solder has not caused any short circuits. To do this, you should check both the soldering point of the first…
…and check the second contact.
Close-up of the soldered antenna cable.
After you have tested the newly attached antenna and everything works, you should secure the place where you soldered the antenna cable with some hot glue. This protects the delicate soldering point from mechanical stress.

Installation of the antenna connection in the rear wall of the housing

So that the external antenna can later be connected outside the housing, the screw connection must now be attached.

You can find the right drill by measuring the thread thickness of the antenna connection. In this case you will need a 6mm drill for the later through hole and...
...a (rounded up) 10mm drill for the blind hole. The blind hole is necessary because the thread is shorter than the thickness of the speaker back wall. If you don't know what a blind hole is yet: don't worry, it's explained in the following steps.
However, before any large holes are drilled, first find a place where your external Bluetooth antenna will later be attached and pre-drill a hole there with a diameter of 3mm.
Now the small, pre-drilled hole is first drilled out to the larger diameter with the 10mm drill (the one for the blind hole). Danger! Don't pierce. First drill only about 5mm deep. This hole is only intended to make room for the overly wide “collar” of the antenna thread.
Once the hole has been drilled to 10mm you can now...
...drill through with the 6mm drill.
The antenna plug should be able to be inserted into the resulting hole.
Unfortunately, the blind hole (the 10mm diameter hole) was not deep enough after the first drilling. If, as in this photo, the thread does not protrude far enough from the back of the housing, you will have to drill out the hole a little more with the 10mm drill. The following applies: Always drill deeper in small steps and check whether the plug now fits. This will prevent you from accidentally piercing it all the way through.
Once you have found the right depth for your blind hole, you can...
…secure the antenna plug with a union nut.
From the inside the whole thing looks like this.
And from the outside – with the antenna attached – like this. Please note that you should never switch on the Bluetooth module without an antenna. This could damage the Bluetooth module.

Once you have completed these steps, the rear panel of the housing can be closed again. Be careful not to pinch the very sensitive antenna cable.

Before commissioning, you should now follow the tips from the article Eektronik - Commissioning of a new circuit note.

And then enjoy the increased radio range of your self-made Bluetooth box. 🙂

Have fun with the project

I hope everything worked as described for you. If not or you have questions or suggestions please let me know in the comments. I will then add this to the article if necessary.
Ideas for new projects are always welcome. 🙂

PS Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you think it's cool that I share the information with you, I would be happy about a small donation to the coffee fund. 🙂

Buy Me a Coffee at       

Kommentar hinterlassen

Your email address will not be published. Erforderliche Felder sind mit * markiert

This site uses Akismet to reduce spam. Learn how your comment data is processed.