im usually tied to my computer by a cable when using my headphones, so i wanted to change that. For that i ordered a cheap chinese bluetooth receiver. I went for the Blitzwolf BW-BR1 as i've seen the name in several placed, and hoped it would be at least a bit higher quality than any noname receiver. Today it came in the mail, and of course i tested it shortly after. *insert fail sound here* Its reception was miserable constantly losing connection when you held the device in your hand and complete signal loss when holding it close to your body (trouser pockets). Now i intended to at least grab this thing when getting up to close the window or otherwise move short distances from my computer, but in the current state it was basically useless for me.
So i wanted to know what kind of antenna it had. I consulted the internet if it had anything on a teardown with that device. Answer: nope. I decided to take matters into my own hands and open it to have a look myself. here it is before opening it
And here after i pried of the back with a screwdriver
You can see the nice chew marks there. Luckily they are mostly covered by the back cover. The cover was held in place by 6 pretty strong plastic pins. I pushed the case itself outside instead of pulling on the pins, so none of the pins broke of. We see the battery that is taped on the pcb with double sided tape. There are just testpoints under it, so no pic of that. On the left the phone jack and the + and - buttons. And on the right lower side of the PCB, we see the antenna, or at least one part of it. Lets open up the other side. The pins of the other side are reachable from here, so i didnt had to chew on the front cover.
Here we can see all the nice components and of course the other side of the antenna.
But wait a minute... i remember, that all the other bluetooth modules i looked at, only had the antenna on one side of the pcb, and the other side completely free of components and copper. Is this the reason why its reception is so bad? I dont know. lets solder on a longer antenna :D
scratched of the soldermask from the end of the antenna and placed copper wire conveniently next to it
soldered it on. Please refrain from comments on my soldering skills. I know they suck. Also i have a suspicion the leaded solder i bought does not contain any lead. Oh well, it makes a connection, and thats all we need (im pretty sure that botched piece of solder sprays radio waves all over the place, but meh).
back in the casing. I drilled a hole in there by hand using a 1mm hss drill.
Tadahhhh *fanfare*. Now i can at least hold it in my hand without loosing signal. But when moving behind a wall the same problem arises. Except in a tiny spot downstairs where i get wonderful reception when i just hold it right :D
Im using the bluetooth device that is built into my motherboard, so maybe that also contributes to a bad signal, as its encased in a metal cage. But i dont want to solder around on that. Mostly because im too lazy to get it out of my pc. Maybe i'll get a bluetooth dongle and solder an antenna on that in the future.
Nice! I have been looking for this!
ReplyDeleteBluetooth is 2.4GHz right? Have you calculated the antena's lengh for optimal reception? Or is that just a random little wire? :) Could actually be worse than the built-in despite interferences.
Here a little link for you: http://www.antune.net/demo/bluetooth/
When using a dongle, you could also use a USB extension to move it further away from the computer ;)
:O someone actually read my post!!
Deleteyep bluetooth is 2.4GHz. i couldve calculated the optimal length, but i didnt find much information as to WHY 1/4th of the wavelength is the optimal length. my suspicion is that this is also depending on the way you use the frequency. for FM you would get a "blurry" signal if its radiated of from a rather long conductor (might be a future post).
the antenna already increased reception for my computer but it was still bad. so i recently tested it with a phones bluetooth. i can now listen to my phone in the basement while its still in my room on the first floor XD. so it was just that the onboard bluetooth has bad reception.
i actually ordered a dongle, which will also get the antenna treatment when its here (if i can manage to get inside without breaking it). but shipping from china this time of year is really bad =/ takes ages
Quarter wave length antenna is half of a 0.5 wavelength which is the shortest length that you can make radiate with good efficiency. For a quarter length antenna, is half of the antenna mirrored in ground-plane of PCB so it is actuallae 0.5 wavlength long.
ReplyDeleteA random length will radiate less effective. By coincident do a such as above 0.5 wavelength antenna have an impedance that makes impedance mismatch relative low, for most transmitters which also adds to total efficiency.
It is much same situation as if a rope is tied to a wall and you tries to make it oscillate by rotating other end of the rope by hand. Shortest length you can do this is for is when rope is shaped as a half wavelength. Next possible length is a full wave length. Anything in between in length will be hard hand-oscillate or to tune for high efficiency for transmitter and antenna. Antenna efficency will affect length of coverage both for transmitter and receiver.