Help understanding TX stage

General discussion and support for the Peaberry SDR V2.

Re: Help understanding TX stage

Postby W4MMP » Wed May 20, 2015 1:20 am

But you didn't say what you are seeing on Q9.

(I think I was seeing about 4V P-P on U8 but I will double check in a bit.)

Also, what are you seeing on the input of U8 (6/13 3/10 5/12 4/11)? You should see a solid 10KHz signal on each input IF your LO is 10KHz down from the TUNE freq. I will double check again what the levels are, but they are very close to identical on each of the four inputs. It is easiest to check on the "top" side of C33,C43,C35 and C36.

EDIT:
OK, I just checked the output of U8 (pin 7 or 9) and the level is 2V P-P. The input to U8 is about 3V P-P. The QSE_Q (14) and QSE_I(2) is about 6V P-P at the LO frequency.
73
Ron / W4MMP
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Re: Help understanding TX stage

Postby mrwizardly » Wed May 20, 2015 8:20 pm

I get 1v p-p on input of U8 (6/13 3/10 5/12 4/11) and is solid 10KHz with LO -10KHz.
QSE_Q (14) & QSE_I(2) = 8v p-p at LO Freq
U8 (pin 7 or 9) = 0.5v p-p
I removed L9 and injected a 1KHz modulated 14.076Mhz AM carrier on the L9 side of C44 and was able to increase the PA output to the 20v p-p signal across my 50ohm dummy load with 1V p-p drive signal.
So, I know the PA is working well.

It appears there is something amiss between U8 and/or T3.
Knowing what happened it looks like U8 might be the culprit given the output is so low compared to your measurements.
Mark
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Re: Help understanding TX stage

Postby mrwizardly » Wed May 20, 2015 10:09 pm

From the gazillion types there are, (U8) even from Texas Instruments, trying to match the spec is going to take some time.
http://www.mouser.com/Search/Refine.asp ... N74CBT3253
Is there some place that these were supplied from originally that I can be sure to get the same specs?
Dave?
Mark
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Re: Help understanding TX stage

Postby W4MMP » Wed May 20, 2015 11:43 pm

mrwizardly wrote:I get 1v p-p on input of U8 (6/13 3/10 5/12 4/11) and is solid 10KHz with LO -10KHz.
QSE_Q (14) & QSE_I(2) = 8v p-p at LO Freq
U8 (pin 7 or 9) = 0.5v p-p
I removed L9 and injected a 1KHz modulated 14.076Mhz AM carrier on the L9 side of C44 and was able to increase the PA output to the 20v p-p signal across my 50ohm dummy load with 1V p-p drive signal.
So, I know the PA is working well.

It appears there is something amiss between U8 and/or T3.
Knowing what happened it looks like U8 might be the culprit given the output is so low compared to your measurements.
Mark


Hi Mark,
That is good news that the PA is working. At least that is one piece of the puzzle out of the way.
Just a couple of more things about U8. First are you sure you have full audio drive from HDSDR to the Peaberry? I say this since I see your audio input to U8 is about a third of what I see. Yours is 1V P-P , nine is 3V P-P, a 33% difference. If you take that figure and factor it when comparing the output of U8 of yours versus mine: My output is 2V x 33% = .66 which is just about where your output is (.5v P-P). While the RF values of the Peaberry may vary depending on band model and overall build, the AF values should be damn near identical. For all practical purposes the ONLY thing that controls the power output of the Peaberry is the audio drive level supplied to U8. Please double check the HDSDR audio levels. (Make sure the volume sliders are set to maximum for the Peaberry Audio devices).

Also, does the voltage on pins 15/1 toggle between 5V and near 0V? Those pins are held low when in transmit mode (0v).

As for the replacement, this is what I think you want:

http://www.digikey.com/product-detail/e ... ND/3478347
73
Ron / W4MMP
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Re: Help understanding TX stage

Postby mrwizardly » Thu May 21, 2015 4:33 am

I had to remember that every time you start HDSDR you have to turn up the power output.
Once I got that figured out again I took some measurements at full power.
Ron, you can view the scan of page 2/5 of my PA section at this dropbox site: https://www.dropbox.com/s/m3evwh8ux7ggy ... y.jpg?dl=0
I didn't know how well a large scan would end up here. That's why I dropbox'd it.
Let me know if there are more measurements you need.
The most peculiar measurement I see is the unbalanced sides of T3 and the mis-matched outputs from U7: (1,14) VOUTL+/-
Now it's getting where I'd definitely need a theory of operation to go much further now.

Thanks for all your help, Ron.
Mark
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Re: Help understanding TX stage

Postby W4MMP » Thu May 21, 2015 1:21 pm

Hi Mark,
Great mark up diagram. I will study the measurements. But at first glance , there is some real weirdness going on.

EDIT: As for a theory of ops, the most information I found is when I build a Softrock RXTX: http://www.wb5rvz.org/ensemble_rxtx/index?projectId=14. The instructions are relevant for only certain sections of the Peaberry such as the PA and mixer(s) (U6/U8). For other sections, I studied the component spec sheets. As for the theory of I/Q, I took a pass on that as the math is way over my head (I only got as far as Calculus I way back in 1972).

To address the sections we are examining, it really is pretty straight forward. HDSDR (or any I/Q based host application for that matter) generates an I/Q digital audio signal at the LO/Tune offset frequency. This is applied to the USB port of the Peaberry. This signal is routed thru the PSoC via the DIN pin to the PCM3060 (DAC section) which generates a true analog audio signal and output on the VOUT(L/R)(+/-) pins. These four signals are 90° phase shifted (don't ask me how that happens, I don't have a clue). The signals are applied to the U7 op amp and then to the U8 mixer. It is essentially a balanced mixer with I/Q magic mixed in. The audio is beat (to use an old radio term) against the LO frequency (QSE_Q, QSE_I) and out comes the product of LO + Audio. From there it is nothing more than plain old amplifier theory.

I also monitor the Softrock40 Yahoo group. But Peaberry owners are more or less persona non grata there.
David appears to be missing in action as I have not seen him on this board for quite a while and there are no Peaberry kits available.
73
Ron / W4MMP
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Re: Help understanding TX stage

Postby W4MMP » Thu May 21, 2015 2:22 pm

Mark,

I need to ask (again) are you using a modulated signal? If so, please don't. Using a modulated signal make trouble shooting very difficult. Use only CW or FM (with no modulation).
73
Ron / W4MMP
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Joined: Fri Jan 03, 2014 3:31 pm
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Re: Help understanding TX stage

Postby mrwizardly » Fri May 22, 2015 3:06 am

I'll start a new thread when I get back with a solution to the TX problem.
I'm shelving it for a while- got to do some studying up on the parts and figure out some of the imbalances of signals.
73's
Mark
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