(tr)uSDX Forum

Hi All
I just received my new wired transceiver but all I hear is squeaks and howls. It does appear to transmit (over 5 watts carrier)) but it receives nothing. Anybody have any ideas? Yes...it has 12 volts on it and yes the antenna is connected.
thanks, radioguy

Hi OM,

i don't realy believe this. If you hear the birdies of the trUSDX (normal, there are quite a view , than you should be able to receive something because it is sending through the same way.
Check with a local transceiver and a dummyload connected to it sending maybe 5W into Dummyload and add an antenna to the trUSDX. That's my way i check, quick and easy.
If you hear nothing check all solder connections with magnifier exspecially on these ICs:
It could probably be a deaf receiver because of bad chinese copys of SN74CBT3253 chip or the LT6231.

73 de Chris DL6SEZ

Hi OM
BELIEVE IT........having been a ham operator for over 60 years, I know the difference between random birdies and a circuit that has gone into oscillation. The unit was hooked up to two antennas, a beam and a dipole, with the same results. The transmitter does appear to work, although I have not tried it with a microphone....approx. 5-7 watts out and it sounds relatively clean. On receive, however, having an antenna connected makes NO difference at all. I hear nothing but howling and squeaking no matter where it is tuned or how it is adjusted.

I ordered the unit assembled and wired to AVOID exactly what it is your suggesting. You would think that each unit would be tested before shipment but apparently that is not the case. As far as "bad copies" of a chip.....again.......testing the unit before shipment would help eliminate problems like this. I waited 6 weeks to receive the little radio and have to admit that I was extremely disappointed. As you mentioned, I will take a look at it for any obvious issues, but if I don't find any I will simply return it and just consider it a lesson learned. I have watched several YouTube videos of this radio in operation and they simply add to my disappointment. It appears to do a great job for what it is......WHEN it is working. I realize, of course, that this is not a commercially made device but if it is being sold as a wired and assembled unit it is not unreasonable for the purchaser to expect it to work. 73's

Which vendor did you get this from? I know one vendor actually logins here once in a while.

Hi
I purchased it thru Hison-818. FWIW......I just removed the four covers and inspected the boards and I see nothing "out of place" or anything that looks like it could be a problem. In fact, the torroid's look very professionally done. Still not working (receiving) VERY DISAPPOINTING. (

radioguy

I bought mine fully assembled from the uellyqh store on eBay and have had no problems at all except operator error, not sure about the success rate of others.

Joel
N6ALT

Check with contact Sunny below: Hello, dear friend, I'm Sunny, Up Tech, could you please contact me in the AliExpress message about this issue ？(because I don't know which order number you are from, so I can't take the initiative to contact you on AliExpress ) or you can send email to me：yangqiu8866@163.com

Hello Radioguy,

from what i think now it could be, because you are saying it is birding everytime, or did i understand wrong?
The Output to the speaker has no extra Amplifier. It is directly fed out of the Atmega328. There is than a audio feedback.... This was also at the USDX much harder and was improved by a larger power supply capacitor after the 5V regulator C4.
If you crank up the volume up to 13 at mine i can, depending on supply voltage, get it to howl everywhere!
Have you tried with headphone and volumes 10 to 11?
And sorry i want to help YOU and not to blame you.
I could also let it be.

73 de Chris DL6SEZ and happy eastern

Hi Chris
Thanks for the suggestion but I've already tried that (along with almost everything else...lol)....even at lower volume levels the effect is the same.

Have a good Easter radioguy

Hello radioguy,

I had feedback issues on mine, self-oscillating on volume settings larger than +11, even on headphones. Apparently, the issue is in qsd mlcc capacitors c25-c28, changed them to some tht 100nF polyester ones, and the feedback is mostly gone. C22 and C29 could also cause some issues, but no confirmation on that yet. Check my findings in my video
https://www.youtube.com/watch?v=jImurYa7SOg
There are some details in the description and comments sections. I'll open a new topic later on for this issue.

Happy Easter & 73.

Hi maybe this is the problem with this CU2531BK?
The diagram is Texas Instruments SN74CBT3253.

Krzysztof

Hi Krzysztof

Regarding markings, CU253 is a proper top side marking for TI's SN74CBT3253 on ssop, tssop, and vqfn package types as shown on the 5th page of the pdf datasheet:
https://www.ti.com/lit/ds/symlink/sn74cbt3253.pdf
The rest of the markings belong to a Lot Trace Code.

msax wrote: ↑19 Apr 2022, 01:40
Regarding markings, CU253 is a proper top side marking for TI's SN74CBT3253 on ssop, tssop, and vqfn package types as shown on the 5th page of the pdf datasheet:
https://www.ti.com/lit/ds/symlink/sn74cbt3253.pdf
The rest of the markings belong to a Lot Trace Code.

It says in the data sheet:
"NOTE 4: All unused control inputs of the device must be held at VCC or GND to ensure proper device operation. Refer to the TI application report,
Implications of Slow or Floating CMOS Inputs, literature number SCBA004."

"With increased speed, logic devices have become more sensitive to slow input edge rates. A slow input edge
rate, coupled with the noise generated on the power rails when the output switches, can cause excessive output
errors or oscillations. Similar situations can occur if an unused input is left floating or is not actively held at a valid
logic level."

It appears that 1A and 1B1-4 are open.
But I'm not an expert. Is someone here who can process or discard my idea?

That's true for control inputs (!OE, S), and that was an issue some time ago with the QCX-SSB project where OE2 was left floating causing degraded receiver performance. The analog part shouldn't create such issues if left floating.

msax wrote: ↑19 Apr 2022, 09:14 That's true for control inputs (!OE, S), and that was an issue some time ago with the QCX-SSB project where OE2 was left floating causing degraded receiver performance. The analog part shouldn't create such issues if left floating.

OK, I had considered 1A to be an "input" too.
Thank you.