RX main board only noise

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erossi
 

Posts: 6
Joined: 22 Oct 2022, 10:04

RX main board only noise

Post by erossi »

Hi,

I'm trying to debug my main board without much luck. The RX part does not work, I cannot hear anything. I have check the RF board and the incoming signal reach the RF pin on the main board without problems, so I'm concentrating on the main board.
I set the trusdx in CW at 3560Khz, ignite a signal with the signal generator and I start hearing some clicking noise at Vpep > 4mV, and it became a tone only with Vpep > 20mV.
The signal, as soon as I connect it to the board, became very noisy, difficult to follow with the oscilloscope.
Some random checks:
Si5351 U3 which generates the two 3560Khz signal phased shifted - OK.
Power from USB 5V - OK.
Following the RX path I have attached these scope images:

- The RF in.
RF in
RF in
RF_in.png (5.53 KiB) Viewed 1085 times
- The LT6231 U9 pin 1 and pin 7
U9 pin1 pin7
U9 pin1 pin7
u9_p1_p7.png (5.47 KiB) Viewed 1085 times
- The MCU pin 24 and pin 23
MCU analog IN
MCU analog IN
MCU_p24_p23.png (3.88 KiB) Viewed 1085 times
If someone can help.
Any help is very much appreciated.
Thanks
E.
73 de IU4JRU Enrico
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: RX main board only noise

Post by dl6sez »

Hello OM,

i don't understand why your injected rf signal is so high in amplitude and why you are not using a good sinewave rf signal with a let's say 600Hz higher or lower than your tuned frequency on the (tr)uSDX?
Don't know if (tr)uSDX switches at frequencies lower 10MHz to CWL and above to CWU but you can only get a good audio sine signal with an unmodulated good sine wave carrier at delta f from your receiving frequency....
As you know you will hear at the speaker the difference of the frequencies eg. 600Hz in the example above.
The amplitude should be in the uV region, let's say 10uV you used factor 1000 to high !!!
Your injected murder high amplitude frequency is 11kHz above your tuned frequency....if the oscilloscope tracked info is right.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
erossi
 

Posts: 6
Joined: 22 Oct 2022, 10:04

Re: RX main board only noise

Post by erossi »

Hello Chris,

Thanks for answering me, I have increased the level of the signal until I have heard/see something.
Ok the signal freq. is offset, no beat zero. It is a signal generator sine wave and in the range of uV I cannot see anything, consider also that my oscilloscope (Rigol Ds1000e) is not capable to probe in the uV range.
Also the freq. reported in the scope image cannot be trusted so much, It is actually unable to fix a frequency with such details.
Clearly something is broken in the RX path but I am not able to understand what.
Any idea/suggestion?

Thanks
Cheers,
Enrico
73 de IU4JRU Enrico
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: RX main board only noise

Post by dl6sez »

Hello Enrico,

okay but the input level is veryvery high when you start hearing a tone it is when your amplitude s9+40dB to 50dB i can't believe this...
Maybe AGC is already clipping all of, so please test with an antenna, maybe a small wire 1m plugged into your signal generator and place your (tr)uSDX main board directly in the near without connecting it directly to signal generator only 1cm of the cable!
I tested here a -7dBm signal at my 20cm telescopic whip from tinySA in about 1cm distance of my (tr)uSDX sma socket with nothing inputted and i can hear it quite good (not load). My (tr)uSDX is also showing S4 without any signal. This is maybe a not very good sn74cbt3253 (series from 1/2021) but it works good enough although at the antennas.
Your measured signals seem to be okay you have very high amplitudes...

Can you measure at LT6231 pin1 and pin7 in the above supposed experiment and take a photo again pleace? I would like to see what happens with a nearly standard receiver signal in comparison.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
erossi
 

Posts: 6
Joined: 22 Oct 2022, 10:04

Re: RX main board only noise

Post by erossi »

Hello Chris,

I've done as you asked, generating a signal on a wire and tuning it with an ft-991a nearby with a signal S5 more or less. On the trusdx I can hear a faint-noise like an engine-car.

LT6231 pin1
p1.png
p1.png (3.65 KiB) Viewed 1001 times
LT6231 pin7
p7.png
p7.png (3.79 KiB) Viewed 1001 times
and the pin23 of the micro
p23.png
p23.png (2.91 KiB) Viewed 1001 times

any idea?
Thank you for your time and help.

Enrico
73 de IU4JRU Enrico
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: RX main board only noise

Post by dl6sez »

Hello Enrico,

i think there is probably a bad solder joint at the Si5351 (ms5351) DDS IC.
Can you resolder them? It was sometimes on other boards the cause for a motorboating sound.
Did you use battery or USB powersupply? USB power supplys are often very bad due to ripples on the 5V.
You could also resolder the very easy to solder pins of the LT6231, the leadfree solder paste used is sometimes not everywhere good soldered.
I think the chance that this is the reason of the malfunction is very high :)

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
erossi
 

Posts: 6
Joined: 22 Oct 2022, 10:04

Re: RX main board only noise

Post by erossi »

Hello Chris,

fortunately I've found the problem using a working trusdx to analyze the signal path. The LT6231 was broken. Changed and now everything seems ok.

73 de IU4JRU
E.
73 de IU4JRU Enrico
Dirkus
 

Posts: 20
Joined: 07 May 2023, 12:14
Location: Elizabeth City, NC, USA

Re: RX main board only noise

Post by Dirkus »

dl6sez wrote: 01 Mar 2023, 20:07 ... i think there is probably a bad solder joint...
...Can you resolder them? It was sometimes on other boards the cause for a motorboating sound...
...You could also resolder the very easy to solder pins of the LT6231, the leadfree solder paste used is sometimes not everywhere good soldered...
I SAY OLD MAN YOU'VE FIXED MY RADIO!

I thought for sure that my radio had a fault that must have turned several ICs into SERs "Smoke Emitting Resistors". While I'm good with through-hole component soldering, my surface mount soldering skills with components this small are on par with those of a slightly drunken gorilla. However, thinking I had nothing to lose, I reheated ALL the pins on ALL the ICs with the finest tip soldering iron I had, and now it seems to be working! I've yet to make a QSO with it, but tomorrow is another day.

I do still have the constant weak carrier transmission that someone else has mentioned, but it seems like it has improved from what it was. I'm also having better luck with getting flrig to connect via CAT. Perhaps a floating leg on some component was causing noise all across the radio. RF is still dark magic to me.

Thank you, Chris. If you ever find yourself in the northeastern corner of North Carolina, USA, let me know and I'll buy you a beer!

73 Dirk
-=-=-=-=-=-=-=-=-=-=-=-
DE KO4PCX
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: RX main board only noise

Post by dl6sez »

Hello Dirk,

good to hear it works now :)

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
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