Question about IF Signal

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SoxxZ
 

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Joined: 13 Jul 2022, 13:32

Question about IF Signal

Post by SoxxZ »

Can i get an IF signal from anywhere in the board, so i could use an RTL-SDR dongle as a panadapter for the (tr)usdx?
Thanks
wa2t
 

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

Re: Question about IF Signal

Post by wa2t »

There is no IF, this is a direct conversion (to baseband IQ) receiver.
SoxxZ
 

Posts: 5
Joined: 13 Jul 2022, 13:32

Re: Question about IF Signal

Post by SoxxZ »

so i could get the iq outputs from the opamps and feed it into an ADC then?
dl6sez
 

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

Re: Question about IF Signal

Post by dl6sez »

Yes if your RTL SDR Dongle receives from DC to a few kHz (maybe 100kHz) and you take two of them one for I and one for Q..... :mrgreen:

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
dl6sez
 

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

Re: Question about IF Signal

Post by dl6sez »

Have you heard about a very magic thing which can propably record analog signals in two channels?

Just think about what you could use for such a purpose....

My 2 Cents

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
AC9YY
 

Posts: 133
Joined: 21 Mar 2022, 00:04
Location: Illinois, USA

Re: Question about IF Signal

Post by AC9YY »

dl6sez wrote: 13 Jul 2022, 17:14 Have you heard about a very magic thing which can propably record analog signals in two channels?

Just think about what you could use for such a purpose....

My 2 Cents

73 de Chris
You mean like a stereo audio card? :D
dl6sez
 

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

Re: Question about IF Signal

Post by dl6sez »

Oh my god, you got the secret answer.... :D
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
SoxxZ
 

Posts: 5
Joined: 13 Jul 2022, 13:32

Re: Question about IF Signal

Post by SoxxZ »

that's why i said an ADC, i'll use my soundcard. Anyway, thanks, 73!
N1CJ
 

Posts: 31
Joined: 07 Jul 2022, 15:54

Re: Question about IF Signal

Post by N1CJ »

so, for those of us that aren't familiar with this modification, how exactly do we get the IQ signal from the opamps?
73 - N1CJ
dl6sez
 

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

Re: Question about IF Signal

Post by dl6sez »

Take the outputs and you made it ;)

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
N1CJ
 

Posts: 31
Joined: 07 Jul 2022, 15:54

Re: Question about IF Signal

Post by N1CJ »

oh...so you're gonna make me read the schematics...ok.

Google tells me that u9 (LT6231) is an op-amp chip. So I just take a cut 3.5mm audio cable and solder tip and ring to pins 7 & 1 of the op-amp and ground the sleeve? Is that it?

Or is there more to it?
73 - N1CJ
dl6sez
 

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

Re: Question about IF Signal

Post by dl6sez »

Yes, simplest way but please after the series Capacitor (DC blocking)....
but i would use a double OpAmp as buffer additionally.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
N1CJ
 

Posts: 31
Joined: 07 Jul 2022, 15:54

Re: Question about IF Signal

Post by N1CJ »

Great! Now we're getting somewhere!

So if I'm looking at this right, I should connect to the points I circled (sort of) here:
tr-usdx iq tap points.png
tr-usdx iq tap points.png (53.35 KiB) Viewed 1823 times
That is going to be interesting to solder to. Now, I'm not familiar with this double OpAmp buffer that you mentioned. Google tells me I would wire the C22/C29 tap points to the positive (+) side of a new opamp, and wire the output of the opamp back to minus (-). So basically I would connect another LT6231 like that and take the outputs of that chip to my 3.5mm cable? Am I looking at this right?

And just for clarification, what is the purpose of creating an opamp buffer after the DC blocking capacitors?

Trying to learn here, so any additional information is helpful.
73 - N1CJ
N6YWU
 

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Location: CM87SO
Contact:

Re: Question about IF Signal

Post by N6YWU »

One of the purposes of adding an op amp buffer after and near the first op amp would be to isolate that first op amp from the capacitive loading, inductive crosstalk, and noise pickup of the audio cable from the (tr)uSDX to the stereo sound card. 73, Ron, n6ywu
N1CJ
 

Posts: 31
Joined: 07 Jul 2022, 15:54

Re: Question about IF Signal

Post by N1CJ »

Thanks for the insight on the opamp buffer, Ron. Much appreciated. I will make sure to use that whenever I get to make this mod.

Otherwise, is my description of this mod correct?
73 - N1CJ
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