Something on the center frequency

General discussion and support for the Peaberry SDR V2.

Something on the center frequency

Postby mrwizardly » Tue Feb 03, 2015 10:25 pm

I had finally reached the test part on page 20 of the assembly instructions.
I have a signal generator and 100MHz scope so I could do some signal tracing. I had a faulty T2 transformer- but rewinding it a bit more carefully cured everything plus a few re-flow of some critical parts.
I connected the generator and got my +40 S-unit signal at the expected frequency.
Removed the generator and turned it off and there is some sort of phantom signal on the zero beat frequency. See attached.
Is this some artifact of the tuning calibration that I'm going to get into later on?
Mark
W7EAZ
Screenshot 2015-02-03 14.11.01.png
Phantom signals?
Screenshot 2015-02-03 14.11.01.png (238.23 KiB) Viewed 4187 times

Screenshot 2015-02-03 14.43.28.jpg
Phantom Signal Wide
Screenshot 2015-02-03 14.43.28.jpg (218.28 KiB) Viewed 4181 times
Last edited by mrwizardly on Tue Feb 03, 2015 10:48 pm, edited 1 time in total.
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Re: Something on the center frequency

Postby AE9RB » Tue Feb 03, 2015 10:30 pm

What is your power supply voltage?
73 David AE9RB
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Re: Something on the center frequency

Postby mrwizardly » Tue Feb 03, 2015 10:50 pm

Running a little on the hot side: 14.5V
Mark
W7EAZ
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Re: Something on the center frequency

Postby mrwizardly » Tue Feb 03, 2015 10:53 pm

Appears that I have about 1V p-p ripple.
It's a wall wart.
I'll knock that down with some better supply voltage and see if that is part of the problem.
Mark
W7EAZ
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Re: Something on the center frequency

Postby mrwizardly » Thu Feb 05, 2015 4:53 am

The phantom signal only shows up when the LO = TUNE and the bandwidth is open wide enough to overlap where this signal originates.
I have a power supply that has less than 1mV ripple at 13.8VDC.
The PCB appears to be micro phonic as well. I would expect it to some degree in view that the LO is running very fast and any small change (due to vibration) would induce a micro phonic result. Sort of mechanical modulation.
Other than this, it appears the receiver side is in good shape.
Mark
W7EAZ
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Re: Something on the center frequency

Postby WB8ENE » Thu Feb 05, 2015 1:04 pm

Mark,

Don't have LO and TUNE at the same frequency. If you are using HDSDR, type a C. It will automatically set the LO frequency 10kHz below the TUNE frequency.

73,
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Re: Something on the center frequency

Postby KD31 » Wed Feb 25, 2015 8:42 am

I have a very similar problem hopefully I can get some help with. This is my first experience with SDR radios and I just began building my Peaberry for the 10,12,15 & 17 meter bands and I am at the receive testing stage. I have the same noise image on the center freq with or without the antenna connected. In fact, without the antenna the image is a bit worse. The radio also has very low RX sensitivity. If I transmit from another radio within my shack I can see it's image but that's it. Would a bad winding cause these symptoms? I have tested this using a 12volt wall wart and also 13.8 volts from a power supply with the same results. I have attached a screenshot. Thanks in advance for any help that anyone can give me. 73's
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Screenshot (12).jpg
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Re: Something on the center frequency

Postby KD31 » Thu Feb 26, 2015 4:59 am

I rewound T1 & T2 and finally got receive. Reflowed the IC and that cleaned up the noise a bit. The filter took out the DC spike.
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