Harmonics around zero

General discussion and support for the Peaberry SDR V2.

Harmonics around zero

Postby smull » Thu Mar 12, 2015 2:25 pm

I have the RX end of the peaberry v2 built and working. But am getting harmonics around the LO freq center at 120Hz intervals. It is very visible on 20 meter, even more so on 30 Meters, and hardly seen on 40 meters. See attached Pics. I have adjusted the phase and amplitude in HDSDR to eliminate imaging. I also have it set to Auto to eliminate the DC spike. That only works so-so and the harmonics remain in all settings: (on, off, and auto).

I am using a 12.5 - 12.9 volt SLA battery. I have read in other posts that the peaberry needs 13.8 to work and that using 12v can cause harmonics. However, the receive circuits are powered from the regulators and the 12v only plays in the PA.

I have reflowed the board with a hot air tool and everything seems kosher physically. I even tested the torids on an inductance meter before I soldered them. They were all within 5%-10% of the listed value on the schematic.

Otherwise the radio receive is good, even with a thrown up wire antenna. But, I would like to eliminate these harmonics before I precede with the TX section.

Anyone else seen this and fixed it?

20 Meters
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30 Meters
screen2.JPG
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40 Meters
screen3.JPG
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smull
 
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Re: Harmonics around zero

Postby kb3cuf » Thu Mar 12, 2015 5:04 pm

Having a resonant 50 ohm antenna makes a world of difference with small rigs derived from the Softrock genre. I thought a random wire was enough too- but it's not. Get out the tuner and tune for maximum band noise- that will get you close- and I bet the harmonics go away.

I use a Butternut HF6V with an additional EleCraft T1 tuner, and I have no harmonics or soundcard related trash.

73
Larry
KB3CUF
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Re: Harmonics around zero

Postby W4MMP » Fri Mar 13, 2015 5:03 pm

What happens if you short the antenna input? My display is absolutely clean with a noise floor of about -120db on both my Peaberrys. If is not clean then there is a chance of a ground loop or something along that line.
73
Ron / W4MMP
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Re: Harmonics around zero

Postby smull » Fri Mar 13, 2015 5:34 pm

I'll try that next!

I did try a tuner on the peaberry (t-network 2-caps 1-grounded inductor). That did help with the harmonics and raised the noise floor up. I could hear WWVH (Hawaii) easily on top of WWV on the East Coast of the USA. I could pickup some RTTY that I could not hear on my Kaito KA1103, which is all I have for comparison.

Interestingly, instead of a peak of DC I have a null. It remains even if I tune out the harmonics. A spectral plot in quisk shows it even more pronounced in every band. The other SDR's I used had a peak. I think this is indicative of a problem.

I have a 50ohm dummy load I can use to and I can short it out at well. I do appreciate all the support I am getting on the forum. Hopefully documenting my experience with the peaberry v2 here will help another poor soul in their struggles!
smull
 
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Re: Harmonics around zero

Postby smull » Sun Mar 15, 2015 12:04 am

I shorted the antenna to the ground and got these screenshots for 20, 30 and 40. Notice the harmonics around DC on the wide plot and the dip at DC on the 1500Hz plot. The noise is right at -125.

The question is does this look right for the PB?

20m.JPG
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30m.JPG
30m.JPG (144.04 KiB) Viewed 5187 times


40m.JPG
40m.JPG (143.21 KiB) Viewed 5187 times
smull
 
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Re: Harmonics around zero

Postby W4MMP » Sun Mar 15, 2015 1:32 am

Hi,
I would say you are looking good. Here is my rig with HDSDR configured the same as your configuration.
Screenshot 2015-03-14 21.19.31_cr-a.jpg
Screenshot 2015-03-14 21.19.31_cr-a.jpg (245.28 KiB) Viewed 5185 times


I even have some hash coming from somewhere. Could be my switching PS. I think it is safe for you to continue on with the build :)
Truth be told I have never noticed this before as I always run with LO 10KHz below Tune frequency and seldom run displaying this much bandwidth.
73
Ron / W4MMP
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Re: Harmonics around zero

Postby smull » Sun Mar 15, 2015 1:41 am

Thanks for the assurance! Your screenshot makes me feel much better.

I have been working on getting fldigi and quisk talking under linux. I have rig control working great but audio... That is another story. Can't want to get the TX assembled and on the air.

Thank again for all the help!
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