RSSI Issues

[fokat]

Hi there,

I have a Taranis Plus to which I performed the SMA antenna mod and replaced the speaker more than a year ago. After the modification the radio operated flawlessly for a long time.

Since a few months ago I started having RSSI issues that have been getting progressively worse. I've had a few failsafes well under 100 meters away. I've tested multiple receivers (brand new XSR receivers with standard antennas and later with the "29mm mod", D4RII stock as well as D4RII with my "tinification" mod). In all cases, the poor range persists.

I'm flying carbon fiber miniquads. In all cases, the antennas are mounted at 90º angle. The frames are all different and the antenna locations are also different. Transmitter or receiver antenna orientation does not seem to be the issue. I've had failsafes at multiple altitudes, from ~3m up to 50m while flying in clear line of sight, at separate locations.

Most of the time SWR is between 0 and 1 with 2dB or 5dB antennas. SWR goes momentarily up to 30 while I touch the antenna to change orientation, and it usually gets back to 0-1 after contact ceases. Using either antenna does not change the poor range.

I removed the hot glue dab covering the solder using isopropyl alcohol and took the following pictures for reference. There's continuity between the center pin in the SMA connector and the signal trace in the RF module as well as between the outer wall of the SMA connector and the radio's ground. There's no continuity between the center pin and the outside of the SMA connector, so the connection is sound.

My specific question: Is it possible for the transmitter module in the Taranis to somehow be degraded / damaged, so that it only outputs a fraction of the required power? If so, is there any way to diagnose this on my end?

Is it possible to replace only the RF assembly (the X9DP_BK_RF / 150618) part rather than the whole back board?

Thanks in advance for any help / suggestions.

 

[Wayne]

Yes, all of those things are possible.

Solder joints on the antenna lead look to be cold. If they are this could be your entire issue.

More than likely your probably had the RF circuit powered up with no antenna at some point. This will damage the RF chip and kill your range. We see this sort of thing a lot.

You can swap out the RF chip, but looking at your solder joint for the antenna, I don't think that is a wise idea at all. It needs specialty tools and some practice to replace that chip. We typically replace the entire board as the labor costs are too high to replace the individual component and retest.

Sometimes the RF connector you screw your antenna into is the issue. They can wear down with use. Another thing we have seen is damage from garbage antennas from Ebay and Amazon suppliers. Some of those cheap antennas are total radio wreckers.

Hope this helps.. Probably not the news you had hoped to hear.

-Wayne

 

[fokat]

Hi Wayne, thank you for looking through this.

Solder joints on the antenna lead look to be cold. If they are this could be your entire issue.

I'll redo the solder. They look dull because I cleaned the solder with a fiberglass cleaning pen prior to taking the picture, however this is a pretty easy thing to check.

More than likely your probably had the RF circuit powered up with no antenna at some point. This will damage the RF chip and kill your range. We see this sort of thing a lot.

This has indeed been the case. I was under the impression that when the radio complained that there was an antenna problem it would cut power to the RF circuit. If this is not the case, then I believe this is the most likely cause of the issue.

You can swap out the RF chip, but looking at your solder joint for the antenna, I don't think that is a wise idea at all. It needs specialty tools and some practice to replace that chip. We typically replace the entire board as the labor costs are too high to replace the individual component and retest.

I'm not equipped for SMD soldering (or very small soldering for that matter), so yes, replacing the board is the cheapest option for me in this case.

Is there a replacement for the small RF board (internal XJT module) or do I have to order the full Backboard + internal XJT module?

Again, thank you very much!

 

[Wayne]

Full board:
https://alofthobbies.com/frsky-taranis-plus-backboard-internal-xjt-module.html

I used to think the radio turned off the RF if powered up with no antenna, but recently found out I was wrong on that. I knew it would not power down once powered up.. Well, it turns out it will always power up the RF unless it has been set to OFF.