[600MRG] XXM and XSV note

[Edward R Cole]

Just to add to the 60/120 Hz RFI topic, I encountered a situation 
where my 1296-MHz transverter was transmitting 120-Hz sideband 
noise.  Immediately suspecting power supply as source I changed to 
another supply but it remained.  I checked the ripple level on both 
12v PS and they were almost not detectable on my scope -wow!  So 
where was it coming from?

My transverter uses a PLL LO locked to an external 10-MHz 
high-stability reference osc. (OCXO).  I found the 120-Hz riding on 
the reference signal and traced the source to a 1.5 amp wall cube 
that I use(d) for charging a large capacity 12v battery to supply the 
OCXO.  There was 1.5v 120-Hz ripple on the 13v dc output of the wall 
cube (no filtering inside apparently).  I had assumed the battery 
would provide some capacitive filtering but not enough.

I switched battery charging source to the station's 50A PS and 120-Hz 
disappeared from the 10-MHz and my 1296 MHz output.  Too many dc 
power sources are "dirty"!  Of course 60/120-Hz can show up in audio 
ground loops, too!  Computers in general are too often RFI 
sources.  I found the best computers were laptops with metal cases 
(IBM Thinkpads).  Totally RF quiet (especially when run on battery-only).

73, Ed - KL7UW

At 05:50 AM 10/28/2014, Frank Lotito wrote:
>Or - another possibility for a signal containing 60*n Hz side bands 
>instead of power supply hum - The circuits being used to generate 
>the digitally coded audio tones and the 630 meter exciter signal may 
>be the cause of the 60 Hz hum?  I'm sure we all remember the early 
>days of computer generated digital modulated methods where the TX 
>and RX audio lines going to and from the sound card a 1:1 isolation 
>transformer was used to "break the ground loop."  (I believe that is 
>still the case today.) Could the ground loop at the transmitting 
>station be the culprit for some "transmitting" stations?  Can the 
>"monitoring" station be part of the problem? -
>One more point - 60*n Hz hum or 120 *n Hz hum?  Would a full wave 
>rectified DC power supply be characterized by 120*n Hz hum?  If so, 
>that may be a clue -
>
>73 Frank Lotito K3DZ - pending WH2XHA
>
> > From: dick.bingham at gmail.com
> > Date: Mon, 27 Oct 2014 18:49:56 -0700
> > To: ku4xrradio at gmail.com
> > CC: 600MRG at w7ekb.com
> > Subject: Re: [600MRG] XXM and XSV note
> >
> > Greeting everyone
> >
> > I, too, get the +\- n*60Hz decodes on some signals but only when 
> the 'main' signal is in the plus dB range and the sideband levels 
> are around SNR = -30 dB.
> >
> > What this indicates to me is folks probably need to clean-up 
> their power supplies to minimize the residual AC-ripple in their 
> power supplies.
> >
> > Dick/w7wkr and xsh-26 CN98pi
> >
> > 
> --------------------------------------------------------------------------------------------- 
>
> >
> >
> >
> > > On Oct 27, 2014, at 5:54 PM, KU4XR <ku4xrradio at gmail.com> wrote:
> > >
> > > Hi all:
> > >
> > > Band is exceptionally quiet tonite, and signal are already quite strong..
> > > Ken - XXM started out in positive numbers.. 2 stations I have 
> yet to decode,
> > > is XPQ, and XSV in Neils new QTH.. I have a problem that really nothing
> > > can be done about.. I get the 60 Hz Up and Down decodes on XXM all the
> > > time.. This starts in the early evening, and lasts until the wee hours of
> > > the morning, and then disappears.. I have also seen multiple decodes
> > > on XIQ several times, and even at 120 Hz from his mean frequency..
> > > XJM has also shown the extra 60 Hz decode on occassions..
> > > The thing that makes XXM's decodes " my problem " is that 60 Hz UP
> > > from his mean frequency of 475.706, puts the extra decode at 475.766 KHz
> > > which is right on top of where Neils signal is.. There is 
> nothing that can
> > > be done about the " WSPR Anomaly " which has happened to probably
> > > about every receiver at some point.. Just wait it out, because it_Does_
> > > go away..
> > > An added observation here.. My cleaning of the ground connections
> > > recently, has also quieted 630 meters noticably.. The biggest problem
> > > as far as noise is concerned that I will now have to contend with, will
> > > be the noisy powerlines as the WX starts getting colder.. Buzz, 
> Buzz, Buzz
> > >
> > > 73 all:
> > >
> > > Andy - KU4XR
> > >
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> >
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73, Ed - KL7UW
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