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Old Mar 20, 2010, 10:44 AM
RC Wannabe!
areis81's Avatar
vercelli, ITALY
Joined Dec 2009
529 Posts
Help!
need help with trimersion headset!

hi guys, i create a new thread since the trimersion thread is dedicated to other issues...

i just modded trimersion headset with mehlik mod, but i have a problem: with or without antenna plugged in the SMA plug the reception is the same, so something must be wrong.

i'm not very good with soldering so i post some pics but i checked with a tester and there are no undesired bridges where i soldered.

everything works fine and actually reception and transmitting distance with the original base is kinda good (i would say 20 meters in line of sight). so i stepped away until (without any antenna plugged) i saw a disturbed image and then i plugged the antenna (11dbi, circular patch, kinda like the flytron one but bought on ebay because of RP SMA). nothing changes, i see no improving when aiming at the transmitter nor when aiming away from it.

now:
1) the sma plug and antenna plug do a good contact (checked with tester)
2) i see no undesired bridge

what should i check? what can i do?

thanks guys for your time and help!
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Old Mar 20, 2010, 12:06 PM
RC Wannabe!
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vercelli, ITALY
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maybe this pic will help, i did my best to make it clear... do you see any contact that is not supposed to be there? because here is the part i had most difficulties.... someone?
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Old Mar 20, 2010, 04:51 PM
electronics gremlins hate me..
middlesbrough, uk
Joined May 2007
155 Posts
Hi, looking at your third pic, it is possible you have a short where the middle pin crosses the ground plane to get to the place it is supossed to connect. The green varnish stuff is not intended to insulate against wires being soldered over it. I can't tell from your pictures, how close is the middle pin to the pcb at the place where it is not soldered? It is pretty much inevitable that you are getting some stray capacitance between the signal and ground. I have to be honest and say I'm not sure what effect that would have, but I know things can start acting pretty weird at ghz frequencys.

It looks ok from the pics you posted, but here are a few suggestions.
1- Look over all the traces on the pcb that connect between the sma and the rx module, preferably with a magnifying glass, look for minute bridges or cracks. It might not be a mistake you made, the manufacturing standards arent high on these things....
2- my suspision is that there is a short where you wired across the green stuff, like I said above. If no one has a better idea, try resoldering the sma connector the way it is supossed to go, with its legs in the five holes. If this improve things you will likely have to buy a straight antenna instead of the round one to fit the casing, but thats the way these things go sometimes.
3- check the antenna in the base station. In one of my headsets this had one of its wires snapped. Strangely it seems to make no difference.
4- Do a chicken dance and offer it a beer. It can't do any harm!!!
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Old Mar 20, 2010, 05:00 PM
RC Wannabe!
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vercelli, ITALY
Joined Dec 2009
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Quote:
Hi, looking at your third pic, it is possible you have a short where the middle pin crosses the ground plane to get to the place it is supossed to connect. The green varnish stuff is not intended to insulate against wires being soldered over it
hi thanks for your help! i checked and, with the signal wire desoldered from the module there is no continuity between positive and ground in the SMA plug, so that soldering must be ok.

my concern is that the problem is where the original antenna was soldered. do you see any difference or any bridge that should not be there from my pics to what you remember of your module? because i see a trace from the middle pin (signal) that goes from the soldering point to under the case of the module... is that ok or maybe i scratched the pcb? (it's the pic of the second post)
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Old Mar 20, 2010, 05:23 PM
The Fixer
Canada, ON, Mississauga
Joined Jan 2009
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Aresi81
What antenna are you using? As 2.4 ghz antenna's have there inside pin reversed just for that reason. A normal SMA antenna won't work. You may need a reverse SMA connector.
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Old Mar 20, 2010, 05:50 PM
electronics gremlins hate me..
middlesbrough, uk
Joined May 2007
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It looks ok in the pic you posted, but without having the board here with me I can't be certain. There is one part thats looks like it could be a bridge, or it could just look that way in the photo. Your eyes looking at the board in your hand are always going to be better than some internet guys eyes looking at a picture. You really need to check for yourself. I have higlighted it in this photo...

If nothing else works try what I said in step 2 in my last post. Things get weird at high frequencys.
"The width of those traces on PCBs are relevant because they are "transporting" some very high frequency signals. Note that the distance between them is also deliberately designed."
This link explains better than I could
http://letsmakerobots.com/node/15084#comment-39365

edit-- for some reason it wont let me upload the pic, but what I was trying to show is that there might be a bridge on the top left of the five sma pins in the pic in your second post.
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Last edited by bob_v5; Mar 20, 2010 at 05:56 PM.
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Old Mar 20, 2010, 06:10 PM
RC Wannabe!
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vercelli, ITALY
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martin, i'm using an RP sma plug with an RP 2.4ghz circular polarized patch.

bob, i just checked. no bridge there. with a bridge somewhere would i receive the signal from the original base so far? i read somewhere here that it worked 2 meters away, today i walked for 25+ meters without antenna plugged and still receiving signal. would it be that way even with an unwanted bridge?
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Old Mar 20, 2010, 06:33 PM
electronics gremlins hate me..
middlesbrough, uk
Joined May 2007
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I don't know. I expect not. If your received picture is clean, then you are already getting better performance than I do with the standard antennas.
(edit, I use my headset indoors in my computer room, outside in a fields will have much less electronic noise)

If you are getting signal at 25m I don't understand why you want to improve it anyway. If you are planning on transmitting from your model directly to your headset, do a range check, if it works, don't worry about why. Use the antenna just in case.
(edit 2-- I assume the transmitters mounted in models are far more powerful than the ones in the trimersion base units, I have no intrest in fpv, I am hacking my headset to make it better at its intended purpose)

Perhaps your problem is actually interference rather than lack of range.
I have no other ideas, I'm better at this stuff than many, but I'm no expert.

Maybe try asking on a ham radio forum instead, people here are more into models than electronics.
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Old Mar 21, 2010, 06:29 AM
RC Wannabe!
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vercelli, ITALY
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anybody has removed a RF module from the headset (receiver) because is using rca jacks and is willing to sell it?

mine works but i would like to try with a new one since doesn't change quality with or without antenna plugged in...
thanks!
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Old Apr 19, 2010, 04:33 PM
Registered User
Australia
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I'm with bob regarding the possible capacitive effect of the sma plug you are using. You could try removing the copper from the PCB below the signal line.and see if that helps.
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Old Apr 19, 2010, 04:54 PM
RC Wannabe!
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vercelli, ITALY
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thanks... i gave the module to a friend of mine, electronic engineer, he unsoldered and resoldered everything but i have been so stupid to try it in the air! meanwhile a very kind RCG user has sent me for free a spare module, i will try it if this will not work...

meanwhile i crashed everything due to my uncautiouness... electronic is still alive, as soon as i will have the time i will try it on the grounf and let you guys know... thanks!
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