Help with diagnosing signal loss from 868mhz wireless device

Thread Starter

wc1lad

Joined Sep 3, 2019
6
Just looking for help or thoughts what to look for on this transmitter circuit inside my RC boat. To explain, I have inside my boat a modified fish finder system in that I have the transducer fitted in the hull connected to a transmitter which than sends the data via 868mhz to handheld unit I have on shore. This display gives me the depth, temp, etc. I guess the same principle as drones that send video feeds but instead this is the classic display you would see on fish finder hard wired but it’s wireless

The signal keeps dropping out at around 80 yards and I have no clue what has been causing it. The normal max range is 500+. I have had the multi meter connected and it’s consistently 12.06 volts being sent into this circuit via the dc -dc power regulator (This is the requirement for the transducer to run. Seriously doing my head in now as I have virtually covered everything, and it still doesn’t want work. I have checked everything including antenna cable, changing antennas as well.

I have gathered that the fault does not exist in the hand-held unit I have on shore as it works perfectly with another boat that a friend has. It appears the transmitter in my boat is the issue

Any thoughts what I should looking for on this circuit would be greatly appreciated! Also, my wife is hoping I fix this because she is sick of hearing about this!

David



RT4 Circuit.JPG
 

MisterBill2

Joined Jan 23, 2018
7,020
The antenna connection, in the lower right corner of the picture, does not look right. If that red wire is the antenna connection then it is connected to the ground side of the output instead of the center connection of the SMA connector, and I am amazed that it works at all. Can you provide a picture that shows the antenna connection better? That is probably where the problem lies.
 

Thread Starter

wc1lad

Joined Sep 3, 2019
6
I hope this helps, I can always get a better picture tonight when I get home. The sma has RG316 coax cable screwed into as the antenna attachment. Btw thank you so much for the reply!


Antenna connect.PNG
 

MisterBill2

Joined Jan 23, 2018
7,020
OK, I see that there is an SMA connector mated to the board. The first thing that I would check is the antenna, because it is important and probably the only part of the system that can be repaired or fixed. If the connector pin is not entering the socket right then the range will be much less.
 

Thread Starter

wc1lad

Joined Sep 3, 2019
6
I don't recall the pin being bent or anything on the antenna. I guess it might be worth checking the female to see if anything is lodged inside it.
 

MisterBill2

Joined Jan 23, 2018
7,020
I don't recall the pin being bent or anything on the antenna. I guess it might be worth checking the female to see if anything is lodged inside it.
I am also thinking about possibly a cracked solder joint, so I am suggesting a resistance check between the in and the antenna. Those very small connections are sometimes fragile, and since there is a problem, it must be someplace. the effort will be finding it. And if you have another antenna, trying that one may reveal something.
 

Thread Starter

wc1lad

Joined Sep 3, 2019
6
Just an update on this one, so I am just waiting on a new RF Sma bulkhead to arrive to replace the one on the circuit. I have decided to change it after getting unusual ohms showing when using the multimeter. This could potentially be the cause.

Just another another question, I am embarrassed to admit this.. but i never realized I had a button on the circuit! Any idea what this would be for? The module I have is the LoRa RF 96.
IMG_2193.PNG
 

MisterBill2

Joined Jan 23, 2018
7,020
Since I see two ICs with lots of pins, I am guessing that there is a processor and probably a synthesizer to set the frequency, and the button may have something to do with the setup mode of them. And it may even be that the frequency has been changes a small amount and that might even relate to your problem. So now I am suggesting a detailed study of the instructions for that transmitter board. It may have even been switched to a lower power mode, if that is one of the options.
 

MrSoftware

Joined Oct 29, 2013
1,912
Antenna is super important for anything wireless. What kind of antenna is it, and has it been modified or altered (shortened) in any way? In the RC car market simple dipole antennas are common, and if the tip gets knocked off (also common) the dipole becomes a monopole and the range becomes extremely short. The wires are so small that most people don't realize the tip is the dipole part. If your antenna had a tip that has fallen off, this may be the case.

Did this problem just begin suddenly, or has it been an issue from the start? If it just started, did anything change or happen just prior to the problem beginning?
 

Thread Starter

wc1lad

Joined Sep 3, 2019
6
Thank you both for the replies and my apologies for the delayed response. The Antenna was a dipole rated to 7db and it has not been modified anyway, still very much stock. The problem literally came out of nowhere and over time the drops outs become more frequent until this point now. The problems really started in the first week of June here in Australia when the weather started cool down.
In the TX module chip we have discovered a tiny hole under magnification straight through it. On comparison to another with exact same specification and make no hole existed. The old one has now been replaced with a new module and hopefully i can take it for a test to see. I wonder if this is the problem after all this time!
 

MisterBill2

Joined Jan 23, 2018
7,020
Thank you both for the replies and my apologies for the delayed response. The Antenna was a dipole rated to 7db and it has not been modified anyway, still very much stock. The problem literally came out of nowhere and over time the drops outs become more frequent until this point now. The problems really started in the first week of June here in Australia when the weather started cool down.
In the TX module chip we have discovered a tiny hole under magnification straight through it. On comparison to another with exact same specification and make no hole existed. The old one has now been replaced with a new module and hopefully i can take it for a test to see. I wonder if this is the problem after all this time!
It will certainly be interesting to see if such hole was the cause. Usually any hole in an IC that allows smoke to escape indicates the end of operation. So I look forward eagerly towards the report. Please let us know.
 

Thread Starter

wc1lad

Joined Sep 3, 2019
6
Well I took it for a test last night and a marginal improvement occurred, however, still signal loss at some time. I have now had the board checked by a second party who confirmed that all is okay with it and no dry joints, bad capacitors, etc. The only other thing now for me to is too look at the the transducer fitted in the hull. I am even considering the possibility of electrical interference and will try placing several ferrite chokes along the cable to see if that makes a difference. This will be test 836 tonight haha!
 
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