RX CW/LSB on 20m-band with 12V/5V

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dl2gde
 

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Joined: 04 Aug 2022, 09:58

RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Hello,
after assambling and testing my (tr)uSDX- specimen I noticed a strange behaviour only in the 20m band:

With a power supply of 12V (even at 9V) the reception of CW and LSB does not work. Sending works, but only on USB you have reception. If the device is powered via USB with 5 V, everything seems to work normally – of course with correspondingly lower transmit power. Even if you connect both power sources (12V and 5V), the reception in the 20m band for CW and LSB only works after removing the 12V.
With my device I achieve with 12V a transmit power of approx. 5 W in the 80m band, on the other bands approx. 3. 5-3 W.
Thank you for any help to fix the 20m problem!

73 de DL2GDE - Egon -
DL2MAN
 

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Re: RX CW/LSB on 20m-band with 12V/5V

Post by DL2MAN »

That´s a strange one....
In both cases (5V via USB or 12V via Main Power Supply) the related components (Mixer and OpAmp) are fed with 5V. Either via 7805 or directly via D4.
The only thing that comes to my mind is L1: Does it create too much Voltage drop ?
Please measure Voltage on any VCC Pin while connected to 12V Main Power Supply and while on 5V USB.

73 Manuel; DL2MAN
dl2gde
 

Posts: 6
Joined: 04 Aug 2022, 09:58

Re: RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Hello Manuel,

thank you very much for the fast replying to my post!
So I will do. I will measure the voltage on the related pins and will report later.

tnx agn es vy 73
DL2GDE - Egon -
dl2gde
 

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Joined: 04 Aug 2022, 09:58

Re: RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Good morning to you!

Unfortunately, due to time constraints, I was able to carry out the measurements only yesterday.
At the main power input I could measure 12. 25 V. After the L78L05 it was still 4. 91 V. On the VCC pins of the ICs I measured 4. 75 V. With the power supply via the USB socket, the VCC pins still reached 4. 57 V. However, my digital multimeter is not calibrated.
When switching in the 20m band, from CW to LSB or USB, nothing changes the supply voltage of the ICs, but neither does it change on the other bands. However, the mute of CW and LSB in receiving mode only happens in the 20m band, when the power is supplied via the main input with 12 V. All other bands are not affected.

73 and have a nice weekend!
DL2GDE – Egon -
DL2MAN
 

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Re: RX CW/LSB on 20m-band with 12V/5V

Post by DL2MAN »

I´d check for
- cold solder joints and misplacements around the OpAmp in that section:
QSD.JPG
QSD.JPG (40.96 KiB) Viewed 1400 times
This sounds to me like there´s an IQ inbalance, suggesting higher than usual component tolerances.
The parts with equal nominal value should be as equal as possible. (especially the 470nF/1nF caps and the 82k resistors)

From what source did you get your rig ?

73 Manuel; DL2MAN
dl2gde
 

Posts: 6
Joined: 04 Aug 2022, 09:58

Re: RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Hello Manuel,

thank's for the Informations and suggestions! I will try to do my best in finding the "intolerant" piece. ;)

The source where from I got my rig is Stephan, DC8LZ.

Have a nice weekend!
73 de DL2GDE - Egon -
DL2MAN
 

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Re: RX CW/LSB on 20m-band with 12V/5V

Post by DL2MAN »

Ah OK, Do you know which group buy ? So I´d ask Stephan for the JLC PCB Parts list, that were used.
And do you have the LT6231 OpAMp ? Or something else ?
You might want to have a look at this:
viewtopic.php?t=145

73 Manuel; DL2MAN
dl2gde
 

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Joined: 04 Aug 2022, 09:58

Re: RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Hello Manuel,

"Trusdx-gp2"- is may be the asked group buy...? I found this expression in an e-mail of Stephan at the beginning of march 2022, where he announces us, that he got the LT6231 OpAmp. In the package of my (tr)uSDX there was originally the LMH6622 OpAmp, but I have wait with the assembling of the rig untill I got from Stephan the LT6231. So, in my rig is placed the "right" one.
May be I should try also an uodate of the firmware to "beta"-version... Who knows...?

Best regards
Egon
dl2gde
 

Posts: 6
Joined: 04 Aug 2022, 09:58

Re: RX CW/LSB on 20m-band with 12V/5V

Post by dl2gde »

Hello everyone,

I can tell you with great satisfaction, that I was able to solve the problem!
You were right Manuel, that I should check the device for cold soldering points. I have resoldered the LT6231 and its surroundings. Now normal operation is ensured on all the 5 bands.
Thanks again for the good tip!

73 of DL2GDE – Egon -
DL2MAN
 

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Re: RX CW/LSB on 20m-band with 12V/5V

Post by DL2MAN »

Thanks for the feedback Egon and glad I could help !

Enjoy your rig and hpe to cu on bands !

73 Manuel; DL2MAN
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