Just Noise on Receive

General discussion and support for the Peaberry SDR V2.

Just Noise on Receive

Postby gtilford » Sun May 31, 2015 11:33 pm

I just finished the build on the receive section and when I listen through HDSDR there is nothing but across-the-band noise. It is a strong buzzing sound. At first I thought I was picking up noise through the antenna, so I connected a dummy load. Same result. Then I went to battery power on both my laptop and the receiver...same noise (see snapshot below). Suggestions on the the source?

73, Greg, KM5GT
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HDSDR Noise.PNG
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Re: Just Noise on Receive

Postby W4MMP » Mon Jun 01, 2015 1:35 am

HI Greg,

Well, I guess I spoke too soon. Sorry to hear you are experiencing troubles with the receive portion. The only thing I have to offer is to triple check your soldering job with at least a 10X magnifier. Check for shorts. For opens, one method I have used (although some may disagree) is use a wooden tooth pick and using the schematic, following the RF receive path, press on the solder connections. 99% of the time the issue will be related to a soldering issue.


EDIT: Please take a look at this post: viewtopic.php?f=4&t=243&p=1020&hilit=buzz#p1020
73
Ron / W4MMP
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Re: Just Noise on Receive

Postby gtilford » Mon Jun 01, 2015 2:26 am

Great suggestion Ron, and thanks for the link. I like the toothpick idea as I have already done the visual inspections. I also poked around with the scope, but since I don't have a reference, I don't know what normal looks like.

BTW, I tried searching on "Noise" in the forum but that was too generic. I guess "buzz" is the magic word!

73, Greg, KM5GT
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Re: Just Noise on Receive

Postby mrwizardly » Mon Jun 01, 2015 2:41 am

I had the same trouble.
Then, to my chagrin, found that the sound card mode I had set for receive was incorrect.
This looks very similar to the feedback issue I had when I first fired up my peaberry.
I was too embarrassed to admit the problem...ha ha ha

Just something to check...just in case.
BTW- I can repeat what you are seeing by setting things incorrectly and getting all kinds of feedback.
To get this menu, click Sound card [F5]
See below for a 'typical' sort of setup.
Mark
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SoundCardPeaberry.JPG
Sound card setting on my setup
SoundCardPeaberry.JPG (28.78 KiB) Viewed 8049 times
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Re: Just Noise on Receive

Postby W4MMP » Mon Jun 01, 2015 3:04 am

Hi Greg,

This is what you should see. Nice clean noise at about -125db :D
No problem on the search. I just happened to remember I had a similar issue with my first Peaberry build. The rub is that just about anything that is wrong in the receive path can cause this observed issue. Or as Mark has mentioned the HDSDR configuration is incorrect. Please double check your HDSDR configuration.
Attachments
Screenshot 2015-05-31 22.59.20_cr-a.jpg
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Re: Just Noise on Receive

Postby gtilford » Mon Jun 01, 2015 8:54 pm

Hi Mark. It is a good suggestion. I made the same mistake on a SoftRock some time ago, so when I had the "buzz" I thought, "I know what this is..." Alas, it isn't that simple. The Peaberry is selected correctly in HDSDR.

Ron - Thanks for the shot of the "working" screen. I expected a quiet display, but not that quiet! Something to look forward to.

It will be a few days before I can get back to troubleshooting the build. I'll let you know how my efforts go.

73, Greg, KM5GT
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Re: Just Noise on Receive

Postby gtilford » Mon Jun 08, 2015 12:38 am

Well, I started troubleshooting again. I had the (not so) bright idea of removing U6 and grounding pins 3,4,5 and 6, thinking that if I presented the next op amp stage with no difference signal it that I would be able to determine if the problem was before or after this stage. After doing this, and seeing absolutely no change I realized that no difference signal may be at the root of this problem. I've poked, prodded, and re soldered everything in sight. I just don't know enough about the nature of this problem to get much further. I need some way to narrow it down a bit. Any and all suggestions are welcome.

Thanks in advance,
73, Greg, KM5GT
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Re: Just Noise on Receive

Postby W4MMP » Mon Jun 08, 2015 4:16 pm

Hi Greg,

I'm not clear on whether U6 has been re-installed. If not, "put the chip back" :D

I would like to be of more assistance, but unless the chip was installed upside down (which I highly doubt) or the chip is defective, this comes down to tracing out the receive circuit and checking every component connection. As I have mentioned, it appears there can be multiple causes for the "buzz" issue. In my circumstance it was R6 that was not soldered properly.
However, just for FYI, U6 and U8 are balanced mixers. In the case of U6 if either side of the balance is missing (Pins 7/9, Pins 2/14) it appears buzz can occur. Again in my case it was due to bias not being present on T2 (and therefore missing on Pins 7/9).

Again, as has been pointed out, even misconfigured software may cause the buzz.

Have all the checks and tests listed in the build document passed (up to but not including the receive section)? These checks and tests primarily test the USB interface, PSoC and Si570. All this must be working correctly before moving on to the receive build portion.
73
Ron / W4MMP
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Re: Just Noise on Receive

Postby gtilford » Wed Jun 10, 2015 2:22 am

Update: The receiver is working! David T. let me know that a signal of a few hundred mvV would not cause a world ending event for the receiver front end so I used my humble MFJ-207 antenna analyzer as a signal source (I reduced the signal from 2 Vpp down to around 200 mVpp) and started tracing.With power off I could see a clean signal up to Q1. While probing around I found a suspicious looking solder joint that I somehow missed in previous inspections on C27. In my weak defense it only looked bad from one angle... :oops: . I touched this up and I applied power and had a slightly dirty, but still a signal up to pins 7 and 9 on U6. I reinstalled U6 and viola, I now have receive! Per Ron's screenshot, my noise floor is down at about -125db as it should be with a dummy load. Just to celebrate the victory I have attached a screenshot of the receive. I want to thank everyone for your help. Now on to the tx side.

73, Greg, KM5GT
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HDSDR Receive.PNG
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Re: Just Noise on Receive

Postby W4MMP » Wed Jun 10, 2015 2:46 am

Hi Greg,
Excellent ! Good job.

Please, take your time as you build the remained of the rig. Double check every solder connection made. As has been said so many time, the vast major of issues with the Peaberry build are related to soldering issue. Second to that is misconfigure software.
73
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