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AE9RB • View topic - Help understanding TX stage

Help understanding TX stage

General discussion and support for the Peaberry SDR V2.

Help understanding TX stage

Postby mosheen » Mon Apr 20, 2015 1:31 pm

I'm troubleshooting my TX stage (zero output) right now and would like to understand it better.

-Q9: Is this a 1:1 buffer? B and C have the same output on my scope.
-Is Q9 the carrier buffer, or is it the I/Q buffer?

-Q4: Is this the buffer for signal modulation?
-Q10 and Q6: Preamp? Is this a push pull setup? How does Q5 play into this and how does the feedback through the transformer play into the amp stage?
-Q7 and 8: Final power amplification correct?

Sorry if this is a bunch of complicated questions, or if I'm way out in left field. I'm just trying to understand the radio better. I'm just going point to point until I see were the fault is. Thanks for looking.
mosheen
 
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Joined: Sun Mar 29, 2015 10:02 pm

Re: Help understanding TX stage

Postby W4MMP » Mon Apr 20, 2015 2:38 pm

73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Help understanding TX stage

Postby mosheen » Mon Apr 20, 2015 4:28 pm

Thanks. That helps a lot. I had it stuck in my head that everything was signal in that area.

So the output of Q9 going into T4 on leg 1 is the complete signal going out to the Amp / antenna. I assume everything below T4 from leg 2 around to C43 is biasing, and the TX switch?

I guess I should check Q4 as well seeing how I have 0.00v across 50 ohm dummy load. Seems like I would have something there even with a fault. I've already pulled T4 and rewound it. It is curious that Q9 has 1:1 output, but I need to get T4 back in.

I'll keep plowing through it one solder joint at a time.
mosheen
 
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Joined: Sun Mar 29, 2015 10:02 pm

Re: Help understanding TX stage

Postby W4MMP » Mon Apr 20, 2015 7:35 pm

73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Help understanding TX stage

Postby mosheen » Mon Apr 20, 2015 9:21 pm

RIP Q10. I don't have any voltage on the drain during TX and if I jump it the amp lights up. A huge thank you for the help!

EDIT: never mind. Rewetted everything in that area and BAM! I'm talking.
mosheen
 
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Re: Help understanding TX stage

Postby W4MMP » Mon Apr 20, 2015 10:48 pm

Great that you have it working ! Good show :)
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Help understanding TX stage

Postby mosheen » Fri Apr 24, 2015 5:54 pm

Just to follow up, I made a 5700 mile QSQ to Russia last night on JT65! I'm loving this little radio. I was using a 20 meter (poorly tuned) wire dipole strung inside my apartment. It runs through 3 rooms to hooks on the walls. It's crazy but it works! :D
mosheen
 
Posts: 10
Joined: Sun Mar 29, 2015 10:02 pm

Re: Help understanding TX stage

Postby Sanath » Mon Apr 27, 2015 2:37 pm

One novice question on the same topic! should we expect a modulated carrier @ C44 ?

I completed the build for the TX driver and Mixer and am having issues testing it .

I hear (heard on an AM radio after i touched C44 with finger) a carrier at the Tune frequency, however did not hear my voice when i tried to modulate it (have a mic connected to my sound card). I do see my voice spectrum HDSDR scope though but it is not heard on the radio. The manual (p23) says expect a carrier on c44 which is seen in my build but i dont see a modulated carrier there.

I have not played with any HDSDR settings as of yet , anything i may be missing ?
Cheers
Sanath
AD0BK
Sanath
 
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Re: Help understanding TX stage

Postby W4MMP » Mon Apr 27, 2015 2:56 pm

73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: Help understanding TX stage

Postby Sanath » Mon Apr 27, 2015 4:29 pm

Thanks Ron you nailed it.
The TX I/Q swap was not set. I could now hear myself Oh boy what a joy !.PS I am running winxp and dont have any volume sliders for peaberry Radio sound device.
Thanks and hope to meet you all in the air soon !
Cheers
Sanath
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Sanath
 
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