<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr"></div><div dir="ltr">Phil,</div><div dir="ltr"><br></div><div dir="ltr">This design (Integrated VLF antenna/preamp in PVC pipe with Raspberry Pi box) was used for an MIT study and the author of vlfrx-tools built a bunch of these antennas and boxes for those conducting the study. This was in 2018. Since this might have fallen under your umbrella, did you hear of it or know who the PI might be? The DC-DC converter has an operating frequency of 100-600 kHz, so it doesn’t really affect anything below that. Paul really liked the performance of his design. He even wrote a guide on how to set up the Radpberry Pi as a VLF SDR using his vlfrx-tools software. </div><div dir="ltr"><br></div><div dir="ltr">Jules,</div><div dir="ltr"><br></div><div dir="ltr">I really appreciate the supplied schematic. Should I use the Schottky diode where you drew the regular diode, in parallel like you said? I could also probably solder the MLCC across the leads of the electrolytic and install it. Also, that TVS is bidirectional. Should a unidirectional TVS be used so it clips any negative spikes closer to 0V? </div><div dir="ltr"><br></div><div dir="ltr">David, </div><div dir="ltr"><br></div><div dir="ltr">Tom mentioned the same. I’ll be working on trying to fit an electrolytic and a ceramic capacitor. </div><div dir="ltr"><br></div><div dir="ltr">Khan,</div><div dir="ltr"><br></div><div dir="ltr">This is good news. Email me if you have issues. </div><div dir="ltr"><br></div><div dir="ltr">Jonathan</div><div dir="ltr">KC3EEY</div><div dir="ltr"><br></div><div dir="ltr"><br></div><div dir="ltr"><br>On Jul 28, 2021, at 2:27 PM, Julius Madey <<a href="mailto:hillfox@fairpoint.net">hillfox@fairpoint.net</a>> wrote:<br><br></div><blockquote type="cite"><div dir="ltr">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Jonathan,<br>
I still think you need to get rid of the series polarity protection
diode and suggest the following schematic (with 22uf 50 volt
Aluminum electrolytic)<br>
<br>
<br>
<eaeficdplljflikc.png><br>
<br>
The PTC poly fuse will open either on overload, sustained voltage
above TVS rating or reverse polarity. This will also snub
transients on the line the series diode may have permitted. There
might be some virtue in adding an MLCC cap of ~ 0.47uf in parallel
with the electrolytic for lower overall ESR.<br>
<br>
Regards,<br>
Jules-K2KGJ<br>
<br>
<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 7/28/2021 12:41 PM, Jonathan wrote:<br>
</div>
<blockquote type="cite" cite="mid:59FAEE9C-11F5-4CDF-B960-2E583E42E89C@gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Hi Tom,</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">That makes a lot of sense. I’ll try fit a 0.1uF and
a 22-47uF electrolytic on the feedline loop. </div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Thanks again! </div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Jonathan</div>
<div dir="ltr">KC3EEY</div>
<div dir="ltr"><br>
On Jul 28, 2021, at 10:55 AM, Tom McDermott <<a href="mailto:tom.n5eg@gmail.com" moz-do-not-send="true">tom.n5eg@gmail.com</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">
<div>Hi Jonathan - a concern is that the DC-DC converter
input stage would become unstable and oscillate</div>
<div>with the cable inductance. If that happens then there
could be high frequency AC voltages present at the</div>
<div>input of the converter. Would those over-voltage the
input? Possibly. Would it radiate RFI from the cable?
Likely.</div>
<div><br>
</div>
<div>Good design dictates sufficiently low source impedance
to the DC-DC converter. Almost all linear regulators</div>
<div>require it. An electrolytic and ceramic bypass pair
right at the DC-DC input would be considered good design
by many.</div>
<div><br>
</div>
<div>-- Tom, N5EG</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Jul 28, 2021 at
7:30 AM Jonathan <<a href="mailto:emuman100@gmail.com" moz-do-not-send="true">emuman100@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">John, </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">Thanks
for the suggestion! I think I’ll start with the
overvoltage age spike of 50V for 100ms or less based
on the datasheet spec of the DC-DC converter. I was
thinking of some sort of fusable circuit protection
now that I’ll be using a TVS diode to mitigate
stress from the follow current. </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)"><span></span><br>
</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">Tom,</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">The
datasheet wasn’t clear on the need for input
filtering. On the output of both the IP2415S, I have
0.1uF ceramic capacitors. In the datasheet, it only
mentions a spec of “Input Reflected Rated Current”
with a series inductor and shunt capacitor. I don’t
really understand exactly what this is, but it lists
“20mAp-p through a 12uH inductor and 47uF
capacitor”. Nothing else is mentioned about input
protection or filtering.</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">In both
situations that the DC-DC failed, the cable length
was only 4’ of cat 5. This circuit that was proved
and tested by Paul, including the receiver and
schematic I attached, did not have such an issue,
but the only difference is that the voltage was
lower than 30V. That’s why I was thinking it was a
turn-on/off spike. I think that in a lot of typical
applications, the input voltage isn’t that high, so
spikes don’t normally present a problem. The DC-DC
that feeds the receiver DC-DC has never failed and
it was always fed with 18V or less. </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)"><span></span><br>
</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">Jules,</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">You
recommend the Schottky diode in parallel with the
TVS, then a series PTC, so during a spike, the TVS
will conduct and the PTC would fuse, and during a
reverse polarity condition, the Schottky diode will
conduct with limited current due to the PTC fusing?
I can see the benefit that the series PTC in normal
a normal circuit condition would drop much less
voltage that the Schottky diode. </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)"><span></span><br>
</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">All in
all, I agree with adding some capacitance to filter
voltage spikes and reduce or eliminate them. I’ll
need to be sure not to exceed the DC-DC max load
capacitance, which is 47uF in this case. </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">But, to
me, the most plausible cause for the failures are
turn on/off voltage spikes, even with a short length
of cable. Adding electrolytics is a bit difficult
due to the tight space constraint as seen in my
previous email, so I’ll try out the TVS and a PTC.
Other than voltage spikes, does anything else come
to mind? </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)"><span></span><br>
</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">Thanks
guys. </span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">Jonathan</span></p>
<p style="font-family:UICTFontTextStyleBody;font-size:17px"><span style="background-color:rgba(255,255,255,0)">KC3EEY</span></p>
</div>
<div><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Jul 27, 2021
at 9:34 AM Jonathan <<a href="mailto:emuman100@gmail.com" target="_blank" moz-do-not-send="true">emuman100@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div dir="auto">
<div dir="ltr">
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">Hi
Everyone,</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">Before
the meeting ended last night, I wanted to
discuss the issues I’ve experienced with my
VLF active antenna. As I mentioned, the
DC-DC converter (XP Power IP2415S) failed
after I applied power. I turned the volume
up because I wasn’t hearing sferics, and
shortly after, I heard the squeal of the
DC-DC converter. When I pulled out the
smaller foam core partially, I heard a
squeal coming from the DC-DC converter
itself. </span></div>
<div dir="ltr"><image3.jpeg><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">I
had a failure of the DC-DC converter when I
first built the VLF preamp. It was being
powered by the Raspberry Pi box (same power
circuit as my text box). I had a power
failure and when the power was restored, the
DC-DC converter failed. In both situations,
it was being supplied with 30VDC, with the
limit is 36V. The reason for using 30V is to
overcome the voltage drop from long cable
lengths.</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">After
both failures, there was a low impedance
across the input of the DC-DC converter
causing the supply to be pulled down.
Because the input and output are isolated, I
figured the fault had to have been caused by
a voltage spike on the input due to power
being turned on and off. The datasheet
mentions that it can withstand 50V spikes at
100ms, but I can’t think of anything else
that could cause the DC-DC to fail,
especially that 30V is used to power it and
any voltage spike would ride on top of that
30V. I contacted XP Power about the issue. </span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">Here
is the schematic of the power path. The
blocks are the IP2415S DC-DC converter.</span></div>
<div dir="ltr"><image1.jpeg><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)">I’m
powering the DC-DC converter with 30V from
another DC-DC converter in the test box and
Raspberry Pi box (Raspberry Pi box not
shown, but same circuit). </span>Keep in
mind, the length is still relatively short in
my testing, so cable inductance isn’t the
primary reason for the spike. Plus, at long
lengths, the voltage would be much lower due
to voltage drop across the length, and I think
this was why Paul might not have seen this
issue when he originally tried and built this
design. </div>
<div dir="ltr"><br>
</div>
<div dir="ltr">To mitigate this problem with the
supply voltage at 30V, I decided to use a TVS
diode across the input of the DC-DC converter.
Here is the schematic: (my apologies for the
TVS diode being backwards)</div>
<div dir="ltr"><image2.jpeg><br>
</div>
<div dir="ltr">I chose a unidirectional TVS so
there is also protection if the voltage spikes
have any negative components. I picked a TVS
with a working voltage of 33V, a Littel Fuse
P4KE39A. According to the datasheet, it looks
like this would be adequate. TVS diodes have a
PN junction that is more rugged, with a larger
surface area for greater current density. One
thing I overlooked with this type of circuit
protection is that once the TVS conducts,
current from the power supply will be shunted
too, known as the follow current, and in some
situations, this may cause issues requiring a
fuse. In this case, since the spikes are
probably short duration, and since the DC-DC
converter in the text/Pi box has short circuit
protection, this should not be an issue. </div>
<div dir="ltr"><br>
</div>
<div dir="ltr">So the questions I have are: do
you also think it could be voltage spikes that
caused the failures, and if so, was my choice
of TVS diode adequate. Also, one important
question, if I connect the anode of the TVS
diode to the receiver side ground, will I lose
isolation? I know that during spike current
conduction, I will. I’m sure I can still get
adequate protection with the TVS diode anode
connected to the negative of the isolated
power loop too, but I just wanted to be sure. </div>
<div dir="ltr"><br>
</div>
<div dir="ltr">Lastly, since the magnetometer
board will undergo another revision, I feel it
may be worth it to add some sort or adjustable
regulator or use of an external power source
(not connected to the 5V pin of the Pi header)
because even with paralleling wires or pairs,
some installations will require very long
lengths (especially since interference-free
locations are often far away from the shack)
and the voltage may drop to where the LDO cant
regulate. Using a higher voltage at the Pi end
(like I do with the VLF preamp) may be
required for some installations. I think this
should be considered if it already wasn’t
addressed. </div>
</div>
</div>
<div dir="auto">
<div dir="ltr">
<div dir="ltr"><br>
</div>
<div dir="ltr">Jonathan</div>
<div dir="ltr">KC3EEY</div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
<div dir="ltr"><span style="background-color:rgba(255,255,255,0)"><br>
</span></div>
</div>
<div dir="ltr"><br>
On Jul 27, 2021, at 7:21 AM, Dr. Nathaniel A.
Frissell Ph.D. <<a href="mailto:nathaniel.frissell@scranton.edu" target="_blank" moz-do-not-send="true">nathaniel.frissell@scranton.edu</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div dir="ltr"><br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal">Thank you, Tom.</p>
<br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
<p class="MsoNormal">The recording will be
available later today at <a href="https://youtu.be/AammohuygMw" target="_blank" moz-do-not-send="true"><br>
<br>
https://youtu.be/AammohuygMw</a> and <a href="http://hamsci.org/telecons" target="_blank" moz-do-not-send="true">hamsci.org/telecons</a>.</p>
<br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
<p class="MsoNormal">73 de Nathaniel W2NAF</p>
<br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
<div style="border-color:rgb(225,225,225)
currentcolor
currentcolor;border-style:solid none
none;border-width:1pt medium
medium;padding:3pt 0in 0in"><br>
<br>
<p class="MsoNormal"><b>From:</b>
TangerineSDR <<a href="mailto:tangerinesdr-bounces@lists.tapr.org" target="_blank" moz-do-not-send="true">tangerinesdr-bounces@lists.tapr.org</a>><br>
<br>
<b>On Behalf Of </b>Tom McDermott via
TangerineSDR<br>
<br>
<br>
<b>Sent:</b> Monday, July 26, 2021 10:02
PM<br>
<br>
<br>
<b>To:</b> TAPR TangerineSDR Modular
Software Defined Radio <<a href="mailto:tangerinesdr@lists.tapr.org" target="_blank" moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>><br>
<br>
<br>
<b>Cc:</b> Tom McDermott <<a href="mailto:tom.n5eg@gmail.com" target="_blank" moz-do-not-send="true">tom.n5eg@gmail.com</a>><br>
<br>
<br>
<b>Subject:</b> [TangerineSDR] Notes
from PSWS / TangerineSDR call of
07-26-2021</p>
<br>
<br>
</div>
<br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
<div><br>
<br>
<div><br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal">Notes from PSWS /
TangerineSDR call of 07-26-2021</p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal">1. Bill is using
chart.js for magnetometer charting.
He is setting up a database using
Django web and database framework
for Python.</p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal">2. Scotty is
looking at the Intel (Altera) Arria
10 GX FPGA 10GX270 for the version 2
Data Engine (supporting 10GE). These
FPGAs appear to be more available
than the MAX10 FPGAs. The intention
is to develop DE Ver 1 and DE Ver 2
in parallel<br>
<br>
while awaiting FPGA component
availability. The 10 GX development
boards are pretty expensive. </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal">-- Tom, N5EG</p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
<div><br>
<br>
<p class="MsoNormal"> </p>
<br>
<br>
</div>
<br>
<br>
</div>
<br>
<br>
</div>
<br>
<br>
</div>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
-- <br>
<br>
<br>
Please follow the HamSCI Community
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</blockquote>
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