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Need help understanding how to make the best antenna choice.

Discussion in 'Radio and Communications' started by Jack.Straw, Jan 3, 2018.

  1. Jack.Straw

    Jack.Straw Member

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    Ron, I'll probably take your advice and just keep it in its currently location. The pucks are a bit too big and expensive, but the little nipple ones like the picture in post #12 might still be an option. Currently i could get away with a 10"-11" coax cable comfortably, and with the pending redisign of the internals I could potentially reduce that to 7"-8". Would that be ok?

    So i've spent a lot of my morning searching for bluetooth modules. I've only seen 1 so far that had an actual antenna connector on it. Almost all of them have an on-board antenna, but say that you can solder an external antenna if needed. I've narrowed it down to 4 contenders at this point. I'm leaning heavily toward this one:

    https://www.ebay.com/itm/CSR64215-M...r-Board-For-Audio-Lossless-APT-X/142637218060

    Does that look ok to you? It doesn't have a specific spot for an antenna connection. I'm assuming i'll solder the coax to where the on-board antenna exists. Hopefully you'll be willing to explain the proper way of doing that.

    The other 3 top options that had all my requirements (except the antenna jack):

    https://www.ebay.com/itm/NEW-12V-24...ard-Wireless-Stereo-Sound-Module/253107596025
    https://www.ebay.com/itm/Audio-Rece...reo-MP3-For-PC-New-Car-Phone-T2L/263366081302
    https://www.ebay.com/itm/CSR8635-Module-Bluetooth-4-0-Audio-Receiver-Board-AUX-/282577443321?

    That last one is probably getting scratched. It looks very much like the one i am replacing, and is showing 5v-12v power requirement. When i'm running on batteries my pack will provide anywhere between 10v-14v (ish), and i don't really want to deal with a voltage regulator just for the bluetooth module.

    Thanks Ron!
     
  2. RadioRon

    RadioRon Well-Known Member

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    The one you are leaning heavily toward looks ok, but the attachment of the antenna coax will be about as tricky as the module you own now and will follow the same procedure of cutting a trace, and clearing some ground plane to solder the coax braid to.

    Of the other three, the item 253107596025 appears to have a balanced antenna on board which implies that they didn't bother including a balun circuit to allow for coax connection, so I don't like this one. Item 263366081302 is very similar to your favorite, and same procedure will be needed to attach a coax. I would not use the pcb hole marked ANT for this purpose. Item 282577443321, same as your favorite as far as antenna attachment is concerned.

    These ads all suffer from tortured English translation, eh? I also noticed that the specification on one of these shows frequency range from 80 Hz and up. That doesn't seem very low for good bass response, does it? Might be ok, I guess.

    Keep you coax as short as practical, but you don't have to go crazy with this. The difference in loss between a 8inch piece and a 12 inch piece isn't enough to get excited about. It is much more important to do a good job connecting it to the pcb and as I mentioned before, it would be extremely helpful if the plastic in the coax doesn't melt while soldering. Plus, the coax needs to be very thin for a good fit (1.3 to 1.8mm ?) and have the right connector (SMA ?) for your application already attached. RG178 coax isn't bad, its a bit on the thick side, but all PTFE so it won't melt.
     
  3. Jack.Straw

    Jack.Straw Member

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    Yes, the translations are pretty painful to read. I searched the web for bluetooth modules, not just ebay, but didn't come up with much in the way of complete boards like these. I'd be willing to spend a bit more and get something local, but haven't really found much out there. So, it looks like your recommended surgery needs to happen. Unless you happen to now another source i should check, i'll go ahead and pull the trigger on my first choice linked above. I just read through your post twice more to wrap my head around what needs to be done. I may practice on the board i have now before attempting it on the new module.

    Good to hear on the coax length. I'll purchase a nice and thin coax with a pre-attached connector at one end, and long enough to cover both antenna options we discussed. I'll look for PTFE so the casing doesn't melt when i'm soldering.

    Thanks!
     
  4. dave

    Dave New Member

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  5. RadioRon

    RadioRon Well-Known Member

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    I use one of these things for streaming audio to my hi-fi. I'm pretty happy with it.
    https://www.logitech.com/en-us/product/bluetooth-audio-adapter

    How would that look mounted on your keg? Don't know if it is kind to batteries or not.
     
  6. Jack.Straw

    Jack.Straw Member

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    In the past i have used the little receiver dongles like the one below, as well as a similar external option to the one you linked as well. The problem i've had with those options is battery life. It's fine for a few hours of use, but not so much for a long camping trip. Also, having another external thing to bring along is a (very minor) inconvenience. I decided i really want to do an internal module this time even though the steel container is far from ideal for that. I've been using the amp with my current module and no antenna for a couple weeks now and i love it. The lithium-ion pack has been awesome, and the class D amp sounds so much better than the sillly little 9v amps i played with in the past. I can't wait to have a proper antenna hooked up so i can get a bit more distance!



    [​IMG]
     
  7. JimB

    JimB Super Moderator Most Helpful Member

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    As an extra discussion point, I would like to introduce the concept of a "Slot Antenna".
    Look here for a basic idea:
    http://electriciantraining.tpub.com...-Antenna-And-Its-Complementary-Dipole-163.htm

    This would probably be an ideal solution to the problem of adding a discrete antenna to a metal barrel, you just have to cut a slot in the metal and attach the coax to opposite sides of the slot.
    I realise that this would not be a good solution at the moment, hacking (precisely dimensioned) holes in your nicely decorated barrel. But for a future project, it may be worth considering.

    Unfortunately, I cannot offer any practical advice on constructing a slot antenna, as I have never done it.
    Maybe one day I should try it, along with all the numerous other things which are waiting for "round tuits".

    JimB
     
  8. Jack.Straw

    Jack.Straw Member

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    So this little guy came in the mail today. I hooked it up to the existing antenna jack... the one i wired into the two holes on the bluetooth module. I have to say that i'm impressed with how well it works as-is. I'm currently in my basement typing this with my phone in my pocket that is playing music on the kegamp, which is upstairs in the kitchen. I haven't done any kind of distance test yet (it's too cold!), but it's already working better than what i thought my best case scenario would be. I'm basing that on other people's bluetooth speakers that i've used over the years. I'm really curious what you think the expected range would be if i had done things properly in the way you described, and with an antenna with a higher dBi.

    The antenna:
    https://www.digikey.com/product-detail/en/taoglas-limited/GW.26.0112/931-1119-ND/2690255

    [​IMG]
     
  9. RadioRon

    RadioRon Well-Known Member

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    OK, well, that's a nice little antenna, but why did you buy a right-angle style? My intention, when I suggested it before, was that it stick out the side of the keg in line with the connector, not at right angles to it. This was for electrical and cosmetic reasons. The electrical reason is a bit complicated, and there are two main factors. One is that, since this is a monopole antenna, it needs a ground plane to work optimally and the ground plane must be at right angles to the whip (ie. across its bottom). Also, as we are working at a very high frequency, the distance from the base of the black part to the ground plane should be minimized. These things affect both the impedance matching (discussed below) and the radiation pattern.

    Polarization is also a factor, where the sending antenna should be the same orientation as the receiving antenna. At 2.4GHz indoors this is not critical because we expect a considerable amount of polarization scattering due to multipath reflections. Also, the access point antennas are usually very flexible on how they are oriented which compensates for the lack of flexibility in the client device (ie, your speaker). The right angle antenna is actually polarized ok.

    However, this antenna is presenting an unknown impedance due to the very close proximity of the reflecting metal keg, which appears to be about a quarter wavelength away, and also due to the long distance between the base of the antenna (the black part) and the ground plane (the keg). We antenna folks fuss about impedance a lot because it is one of the key things that contributes to how effective an antenna is. We seek "maximum power transfer" in both receiving and transmitting directions. Matching impedances from source (the transceiver), through transmission line (the coax) to load (the antenna) ensures that power is not wasted, it gives us maximum power transfer and minimum loss of power. Impedance matching is important because mis-matching costs you power, and power directly leads to range, and we all like a lot of range.

    The coax cable you use has a characteristic impedance of 50 ohms, and you need your antenna to also have an impedance of 50 ohms, which is what I mean by impedance matching. In order for your monopole antenna to have an impedance close to 50 ohms, you have to provide it with a ground plane that is in the correct position and orientation. In this case you have not. As a result, you may be wasting anywhere from 0 to 10 dB. Its hard to say exactly how much.

    Now, you could say that I'm obsessing over details and that the way you have it now should work adequately well, even if it is not optimal. That's true. But from a looks point of view, I think this is only a partial improvement over what you had before. You can stick with this if it looks ok to you, but it could be better. Its hard for me to argue for changes if you are happy with it.

    I also want to mention that, if you are satisfied with the range, perhaps doing the change to how the coax connects to the module is not necessary. While doing the mod would optimize the connection (and possibly buy us an additional 1 to 10 dB of additional range), it also has some risk that we may break something that becomes hard to repair. Is the risk worth it? Then again, I think you mentioned that you were thinking of changing out to a new module anyways.
     
    Last edited: Jan 13, 2018
  10. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Generally speaking a larger antenna is better. This antenna looks small. I have antennas for this frequency that are 2x and 4x and some much longer.

    This antenna has a right angle. In this direction the antenna is probably too close to the "ground plane". Any large piece of metal. If the antenna stuck out to the right the ground plane would help, not hinder.

    upload_2018-1-12_21-55-53.png
     
  11. Jack.Straw

    Jack.Straw Member

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    Well shoot, it sounds like i screwed up my choice. I chose the right angle one in an attempt to minimize how far it sticks out. I actually planned on putting another nut and washer on the connector inside of the keg to bring the antenna in another 1/8" or so. It sounds like that would be counterproductive though. Aesthetically i like the right angle better actually (except the polished brass part).

    So, if after some outdoor testing i'll decide if it's worth it to me to spend more on another antenna & shipping. If i do (i'm guessing i will), which of these do you think would be best?

    1. https://www.digikey.com/product-detail/en/taoglas-limited/GW.26.0111/931-1113-ND/2690286
    2. https://www.digikey.com/product-det...-SMAM-S-S-17/DELTA8A-X-SMAM-S-S-17-ND/6096316
    3. https://www.digikey.com/product-detail/en/taoglas-limited/GW.26.0111.HT/931-1317-ND/4849883
    4. https://www.digikey.com/product-detail/en/rf-solutions/ANT-24G-S21-SMA/ANT-24G-S21-SMA-ND/5845752
    5. https://www.digikey.com/product-detail/en/silicon-labs/ACA-1SSRPP-2400/1586-1015-ND/5269919

    When my new bluetooth module arrives i may go ahead and attempt your board modification. It may not be strictly necessary, but it's experience and learning. If i screw it up i'll have a backup.


    Thanks guys!
     
  12. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    upload_2018-1-13_10-6-49.jpeg
    This antenna has 8db more output than what you are using.
    upload_2018-1-13_10-8-34.jpeg
    This one has a gain of 14db. It needs to be pointed at the right direction. It will not care what it is mounted on.
    upload_2018-1-13_10-11-53.jpeg
    This is the pattern(s) for whip antenna(s). The short antenna you have is like the "ARC" pattern. As you can see, a 13db antenna needs to be pointed in the right direction.

    A directional (high gain) antenna is like a flashlight. The energy is mostly pointed where you want it to go.
     

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