Date: Tue, 27 Jun 2017 15:20:52 -0400
From: Markus Vester <markusvester@aol.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Octo-soundcard for the Raspi, EMC
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Hi Stefan,

interesting! I suspect that the microwave noise may be due to the digital d=
ata on the unshielded multipin connector. At high frequencies, those pins w=
ith the PCB on top might form an array of little top-loaded monopole antenn=
as. As soon as I receive my board, I'll try to hook it up and look with a s=
pectrum analyser.

Best 73,
Markus


-----Urspr=C3=BCngliche Mitteilung-----=20
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 27. Jun 2017 17:21
Betreff: Re: LF: Octo-soundcard for the Raspi, EMC


The octo-soundcard seems to cause QRM in the GHZ range during operation:
I had successful GPS reception after booting the Raspi. As soon as i=20
initialized the soundcard, the blue PPS LED remained dark!

Tried to identify the mechanism:
I monitored the supply voltage, found nothing suspicious.
Added common mode chokes on the coax leading the PPS signal, even=20
disconnected that cable to break any eventual ground loops, but still no=20
GPS reception.
In a next step i removed the DC/DC converter which was mounted quite=20
close to the GPS antenna on my plate. Still lost GPS reception during an=20
active soundcard.
Added 470 uH in series and 1 uF in parallel to the supply voltage. Still=20
the same problem.
Applied a grounded shield (against E fields) between Raspi+soundcard,=20
still the same problem.
Disconnected the RXD TXD cables of the serial interface, still the same.
Used a separate supply voltage (9V block + 78L05) to power the GPS=20
module. So there was conducting connection any more between the GPS=20
module/antenna which is located in 6 cm distance to the Raspi (it has=20
never been a problem in the past). =3D> Still the GPS reception was lost=20
when activating the soundcard!
Even WLAN access is lost when running the soundcard. First i thought it=20
is due to the real time priority of vlfrx tools. But now i have some=20
doubts...
When placing the GPS module about 6 cm more distant to the soundcard,=20
GPS reception is restored!
So now i have to apply a better shield against E and H fields coming=20
from the board.

73, Stefan
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<div style=3D"font-size:10pt;font-family:arial,helvetica,sans-serif;color:b=
lack;"><div style=3D"color: black; font-family: arial,helvetica,sans-serif;=
 font-size: 10pt;">Hi Stefan,<br><br>interesting! I suspect that the microw=
ave noise may be due to the digital data on the unshielded multipin connect=
or. At high frequencies, those&nbsp;pins with the&nbsp;PCB&nbsp;on top migh=
t form an array of little top-loaded monopole antennas.&nbsp;As soon as I r=
eceive my board, I'll try to hook it up and look&nbsp;with a spectrum analy=
ser.<br><br>Best 73,<br>Markus<br><br><br>-----Urspr=C3=BCngliche Mitteilun=
g----- <br>Von: DK7FC &lt;selberdenken@posteo.de&gt;<br>An: rsgb_lf_group &=
lt;rsgb_lf_group@blacksheep.org&gt;<br>Verschickt: Di, 27. Jun 2017 17:21<b=
r>Betreff: Re: LF: Octo-soundcard for the Raspi, EMC<br><br></div>The octo-=
soundcard seems to cause QRM in the GHZ range during operation:<br>I had su=
ccessful GPS reception after booting the Raspi. As soon as i <br>initialize=
d the soundcard, the blue PPS LED remained dark!<br><br>Tried to identify t=
he mechanism:<br>I monitored the supply voltage, found nothing suspicious.<=
br>Added common mode chokes on the coax leading the PPS signal, even <br>di=
sconnected that cable to break any eventual ground loops, but still no <br>=
GPS reception.<br>In a next step i removed the DC/DC converter which was mo=
unted quite <br>close to the GPS antenna on my plate. Still lost GPS recept=
ion during an <br>active soundcard.<br>Added 470 uH in series and 1 uF in p=
arallel to the supply voltage. Still <br>the same problem.<br>Applied a gro=
unded shield (against E fields) between Raspi+soundcard, <br>still the same=
 problem.<br>Disconnected the RXD TXD cables of the serial interface, still=
 the same.<br>Used a separate supply voltage (9V block + 78L05) to power th=
e GPS <br>module. So there was conducting connection any more between the G=
PS <br>module/antenna which is located in 6 cm distance to the Raspi (it ha=
s <br>never been a problem in the past). =3D&gt; Still the GPS reception wa=
s lost <br>when activating the soundcard!<br>Even WLAN access is lost when =
running the soundcard. First i thought it <br>is due to the real time prior=
ity of vlfrx tools. But now i have some <br>doubts...<br>When placing the G=
PS module about 6 cm more distant to the soundcard, <br>GPS reception is re=
stored!<br>So now i have to apply a better shield against E and H fields co=
ming <br>from the board.<br><br>73, Stefan<br><br><br><br><br></div>
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