Fix for bad sideband suppression on 30 and 20m Band

wa2t
 

Posts: 180
Joined: 01 Jan 2022, 16:30

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by wa2t »

Hi Group,

Last night, I tried WebSDR with my (tr)uSDX and SSB really did not sound any better to me. But, as I was tuning around, I found W9IMS (Indianapolis Motor Speedway special event station) on 7.240MHz and called him with about 655W (using my RF2K+ LDMOS power amp and the (tr)uSDX). I was using my modified Baofeng speaker mic. He responded with a 59 and said I was very strong. I did not ask specifically how my audio was (I should have) but obviously I was intelligible enough for him to complete the exchange. So, this has changed my feeling a bit on SSB with the (tr)uSDX - for the better. It will never be as good as a more traditional SSB XCVR, but it does work. Your mileage may vary...

73,

Robert, WA2T
N6YWU
 

Posts: 27
Joined: 24 May 2022, 16:09
Location: CM87SO
Contact:

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by N6YWU »

Magnus wrote: 27 May 2022, 22:40 I just got my assembled (tr) usdx, om 20 m there is a small carrier wave transmitted even though the unit is om recieve.
If you put two receivers next to each other on the same table, it's not uncommon for each to hear the other's LO, due to PCB to PCB or case to case parasitics. (Except for direct sampling rigs, where the LO might only exists virtually in software). 73, Ron
km4ezk
 

Posts: 6
Joined: 07 Oct 2022, 00:46

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by km4ezk »

I seem to be having this issue. I opened up my radio kit I had purchased from Amazon
https://www.amazon.com/dp/B09YH2V2ZP and assembled, and I do seem to have the preferred OpAmp. I'm still seeing quite bad splatter similar to what KB9RLW sees in his radio shown in this youtube video. https://youtu.be/UWcDLq0WM1o?t=237

I'm curious if maybe there is some tuning in software that I could maybe try. I've tried testing with an external mic as well and see the same results, so I don't think its that the mic has a short causing weirdness.

Image

EDIT: Some clarification. I've been testing by transmitting about 0.5w into a dummy load and receiving the signal on a very close proximity SDR ~1 meter away from the tr usdx.
DL2MAN
 

Posts: 483
Joined: 30 Dec 2021, 19:18
Contact:

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by DL2MAN »

In the Titel mentioned Sideband suppression is an rx issue.
What Kevin and you are seeing, is a nearfield Effect of tx. Add at least 60dB attenuation between (tr)uSDX and Control rx.

Here is a Text that disappeared from the YouTube comments (Not caused by Kevin):

Guido and me were joking today about a start up message, that says never test (tr)uSDX Audio in near field.

On a near-field receiver, the SSB signal is so strong that the small artefacts of the digitally processed signal in the (tr)uSDX becomes audible. In a normal QSO setting there is so much path-loss involved that these artefacts are well attenuated below the noise floor and hence not observable.

Note that every signal that is digitally processed has this limitation, it is called quantisation noise and these are noise signals in the background of the main signal. It is only when you start amplifying the signal that this noise becomes apparently observable.

To test the SSB/AM signals on a near-field receiver, the recommendation would be to use an attenuator of 60dB or more in-front of the receiver. Watch for proper shielding along the whole path, so RF does not escape your dummy load. Best is still to access a remote receiver and check your audio. You will see the difference immediately.

73 Manuel DL2MAN
km4ezk
 

Posts: 6
Joined: 07 Oct 2022, 00:46

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by km4ezk »

Just wanted to follow up on my previous query. After watching your video https://youtu.be/dHttnDdADqo I flashed my bootloader and firmware fresh to test this. I've only been able to test on 40m into a WebSDR about 450km from me and to my very local personal SDR. The splatter locally appears to be much less and splatter and readability into the WebSDR is *much much* better. Just wanted to give you another data point.

I'm confused how the bootloader could affect splatter, but in any case I'm more comfortable using this radio now and not worrying about interfering with my spectrum neighbours. Thanks DL2MAN!
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

Dear colleagues, I immediately apologize for my indiscretion, but it makes no sense to override the operational amplifiers, you just need to connect 1uF capacitors in series with 100 ohm resistors to the inverting inputs on pins 2 and 6 and the mirror channel disappears on all ranges including 10m
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

who can please let me know
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

Dear colleagues, despite the fact that my messages are deleted due to the fact that I am from Russia, I will once again tell you how to modify the usdx receiver so that the non-working sideband is suppressed, I have already done this and everything works from 80m-10m. just add two 1uf capacitors in series with 100ohm resistors connected to 2.6 pins of the op amp
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

please listen to me and get rid of the problem of suppressing the non-working side
DL2MAN
 

Posts: 483
Joined: 30 Dec 2021, 19:18
Contact:

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by DL2MAN »

Ra9oau wrote: 30 Nov 2022, 07:49 Dear colleagues, despite the fact that my messages are deleted due to the fact that I am from Russia,
Are you a little paranoid ? Noone here has deleted anything. There are 4 postings in a row from you. Visible for anyone. I know you´re having a hard time with borders, but please be careful with such accusations.....
Ra9oau wrote: 30 Nov 2022, 07:49 I will once again tell you how to modify the usdx receiver so that the non-working sideband is suppressed, I have already done this and everything works from 80m-10m. just add two 1uf capacitors in series with 100ohm resistors connected to 2.6 pins of the op amp
Thanks ! We will try that.

73 Manuel, DL2MAN
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

I deeply apologize for what I wrote, but there is no paranoia, I just didn’t understand the chat and didn’t find my messages, but since the political situation in Russia and border states is very complicated, I thought that my messages were deleted. once again I apologize
Ra9oau
 

Posts: 6
Joined: 29 May 2022, 03:55

Re: Fix for bad sideband suppression on 30 and 20m Band

Post by Ra9oau »

https://youtube.com/shorts/9L0xI-mmDig?feature=share there are still improvements to the transmitter, a demonstration on the video, and somewhere in the comments there is a google disk 0 link to other improvements
Post Reply