LO NOISE STUDY - LEO BODNAR GPSDO

[David Eckhardt]

Many of us use this convenient "box" in our systems.  Therefore, after looking at it's noise output, I had to assess its noise contribution to my direct receiver system which I use for Dopplergrams of HF signals.  Therefore, please see the attachment for my contribution to these groups for the day.  I believe I did things pretty rigorously.  

For those using that unit, it should be an eye-opener.  Now I must ask myself what the noise contribution is for the RX-888 MKII and other SDR receivers.  Again, have an eye-opening read of the attachments.  I'll also include my noise assessment of the unit by itself in the attachments.

Dave - WØLEV

[David Bengtson]

This is interesting. What Receiver are you using for this, and what are the LO and Receiver frequencies? I've got some thoughts about potential solutions. 

Dave

--
Please follow the HamSCI Community Participation Guidelines at http://hamsci.org/hamsci-community-participation-guidelines.
---
You received this message because you are subscribed to the Google Groups "HamSCI" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hamsci+un...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/hamsci/CAODdWWH67X7C1fpmVFkFWBJteWVA_Y0pis%2BXtA7Q1UsYQMQeKA%40mail.gmail.com.

[Phil Erickson]

Hi Dave,

  There is no color bar on the spectrum plot showing the range from blue (low) to red (high).  What is it?

  Also, did the results change without the opamp leading to the oscilloscope?  Probably not, but did you check?

73

Phil W1PJE

On Mon, Apr 6, 2026 at 4:28 PM David Eckhardt <davea...@gmail.com> wrote:

--
Please follow the HamSCI Community Participation Guidelines at http://hamsci.org/hamsci-community-participation-guidelines.
---
You received this message because you are subscribed to the Google Groups "HamSCI" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hamsci+un...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/hamsci/CAODdWWH67X7C1fpmVFkFWBJteWVA_Y0pis%2BXtA7Q1UsYQMQeKA%40mail.gmail.com.

--

----
Phil Erickson
phil.e...@gmail.com

[David Eckhardt]

I diagrammed the receiver chain at the beginning of the write-up.  It's all homebrew.  That's why I did a responsible job of documenting it at the very beginning of the documentation.

No change with or without the audio op amp.  I don't care for relating quantitatively to colors as everyone perceives color differently.  This is why I still much prefer with RadioJove to use the older method of display which can be quite well calibrated.  The spread of no color and no trace on the waterfall or trace at all to that using the Bodnar as the LO is 30 dB:  -90 to -60 dB which is set in Spectrum Lab.  

Dave - WØLEV

--

Dave - WØLEV

[Frank Howell]

Hi Dave,

Have you sent your study to Leo Bodnar for his reaction and comments? I've found him very open to analysis of his products.

73,

Frank

K4FMH

To view this discussion visit https://groups.google.com/d/msgid/hamsci/CAODdWWHceC8H_cr%3DsPkn-LUqDCX%2BZaQ2ecowxgEii44LA%3DFNYA%40mail.gmail.com.

[David Eckhardt]

No, I have not forwarded either write-up to Leo.  Yes, he is very amiable to work with.  I've also done some work on another of his products addressing RFI.  He was very good about fixing the problem I found.  

Excellent suggestion, but my intention was certainly not to single out his product(s).  I just wanted to evaluate the noise contribution motivated by a deep technical conversation Dr. Terrance Bullett and I had regarding the subject about a week ago over lunch.  That was the real motivation for the latest set of tests.  Besides, once I found the output of the unit was "rather" noisy, I wanted to determine the effect(s) of that on my DC receiver I use for HF Doppler.  I was not pleased!  

Dave - WØLEV

To view this discussion visit https://groups.google.com/d/msgid/hamsci/CAFz2rFg5iu64W%2BgONpjv4EYo32CAVFM%2BauP9dfD6ZKPJep-zZw%40mail.gmail.com.

--

Dave - WØLEV

[Tom McDermott]

HI Dave,   direct conversion receivers can be sensitive to some local oscillator artifacts at very low frequencies:

1. 2nd order distortion. This causes signals that appear near DC.

2. Zero-frequency DC offset caused by coupling or reflections at the input to the mixer.

3. Low frequency noise, such as from ground loops, power supply noise or loops, etc. that will appear at baseband.

4. Power supply noise from the frequency source.

Is your local oscillator transformer coupled to the DC mixer?

Can you isolate the grounds between the OSC and the Mixer?

Is the power supply on the Bodnar clean?

-- Tom, N5EG

To view this discussion visit https://groups.google.com/d/msgid/hamsci/CAODdWWFD3-J5Ua3XeTbZOXjmNOzeHJH-Qi75kX4Oc-4M19WiEA%40mail.gmail.com.