Re: QUESTIONS re. YOUR GPSDO's

[David Eckhardt]

I will gladly accept the DC blocks!  I made my own but it's a git clugie!  With or without the DC block seen not to make any difference with the LO noise when connected to the receiver.  If I disconnect the antenna input, the LO cleans up.  Puzzled at that.  I also tried DC blocking the cneter conductor of the antenna input to the BCB SBF with no change in LO noise behavior.  Next, I need to power the BB 70-dB gain block off another supply.  Haven't tried that , yet.  But I doubt that will change anything as when I'm using the HP sig. gen. of the LO, things remain clean.  

Progress.......  Removed the BCB SBF and installed the 15 MHz BPF.  Also shifted the antenna connected to the filter, gain block, and DC receiver.  LO noise is gone.  Go figure.......

Dave - WØLEV - 

On Wed, Apr 8, 2026 at 9:25 PM Terry Bullett <te...@4thstatecommunications.com> wrote:

Dave,

I believe the Leo GPSDO has a square wave 0 to +V, which of course has a net DC value.  I have always used my Bodnar units with a DC blocking capacitor, and often a low pass filter.  I do not think I provided a blocking capacitor on the Direct Conversion Receiver LO  (or RF) input.  I only ever tested it with a sine wave input, not a raised square wave.  

One thing I do know about mini-circuits is that their transformer cores, being so small, are very intolerant to even a few 10's of mA DC current.   The cores they use saturate. 

This may be the origin of your phase noise.

I have a couple of extra SMA format DC blocks from MCL that look just like their attenuators.  You are welcome to have these.
And you can test the DC offset theory with your Siglent AWG, which nicely gives you square waves and DC offsets as well as plenty of phase noise to work with :P 

IN THEORY the mixer should work better with a zero-mean square wave than a sine wave as the switchover time of the diode bridge is shorter, but you have to consider that the odd harmonics of the square wave LO will mix with the RF and you may mix higher frequency noise power in both inputs to the IF output.
Normally at HF we are worried about IP3 inter modulation response and not noise floor.

73,
Terry
W0ASP. 
  
<snip>

All the image capture parameters are given on the images.

LESSONS LEARNED:

1)  A big apology to Leo Bodnar for misrepresenting his very useful and affordable offerings!!!  Again and again, thank you, Leo ! ! 

2)  A big thanks to everyone who contributed and ultimately motivated me to find my problem.

2)  Inspect every even small portion of a system BY ITSELF!   The Icom 8600, 7300, and 7610 are far too complicated for this ! ! !  

3)  Be aware and very careful what you connect the GPSDO's to.  Measure everything - INDIVIDUALLY!!

Now I've got to determine what I'm going to do to eliminate pollution of the DC receiver by connecting the Bodnar unit, DC blocked, to the LO input of the DC receiver.....

Dave - WØLEV  

   

On Wed, Apr 8, 2026 at 5:19 PM Support <sup...@leobodnar.com> wrote:

Hello David,

Your pdf file SL diagram does not have any axes markings and no colour map so I can’t figure out what is it illustrating.

I have measured the phase noise of the Precision GPS clock you have at two frequencies and also LBE-1420 model for comparison.

I don’t have HP8640B to measure its performance at 15MHz.

Many thanks,
Leo Bodnar

On 7 Apr 2026, at 20:09, David Eckhardt <davea...@gmail.com> wrote:

--

Dave - WØLEV

--

Dave - WØLEV

[J. Gordon Beattie, Jr.]

Hi Folks!

Way back, we had a misstep when an IT guy had used an MCL Type N DC Block without noticing that it was a 75 Ohm device.  

He kept using 50 Ohm male connectors which trashed the female center pin.  

This happened twice with four of these blocks being trashed each time because the 50 Ohm center pin is so much larger.  I spotted his issue immediately once asked to investigate the problem.  

As the installation was for GPS, high power wasn't an issue so the issue was solved with SMA adapters and the MCL SMA DC blocks.  Once installed, all was well and years later, still is.  You'll get good sevice from them.  

The lesson here is to be careful about the impedance of the connectors you use!

73,

Gordon Beattie, W2TTT 

201.314.6964 

W2...@ATT.NET

Gordon.B...@VIAVISolutions.us

Get On The Air!

---

From: ham...@googlegroups.com <ham...@googlegroups.com> on behalf of David Eckhardt <davea...@gmail.com>
Sent: Wednesday, April 8, 2026 6:19:57 PM
To: Terry Bullett <te...@4thstatecommunications.com>
Cc: Support <sup...@leobodnar.com>; ham...@googlegroups.com <ham...@googlegroups.com>; Doppl...@groups.io <Doppl...@groups.io>; Bascombe J. Wilson <jay.w...@vodec.net>; Kenneth Wyatt <wyatt...@mac.com>
Subject: [HamSCI] Re: QUESTIONS re. YOUR GPSDO's

 

--
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/CAODdWWFy56PRo7A8K%2BRNRj%3D8TwmghmOfuPhC1OSxVbq-7jW-mw%40mail.gmail.com.