[TangerineSDR] TangerineSDR Digest, Vol 28, Issue 31
Julius Madey
hillfox at fairpoint.net
Wed Jul 28 23:34:00 EDT 2021
And, if you're going to 'play' with chokes, etc, a good, relatively
inexpensive VNA like the DG8SAQ VNWA3, which, with careful setup and
calibration can accurately measure high impedances to 10Kohms at 30MHz.
I have been able to duplicate K9YC's measurements with my VNWA3.
Kurt Poulsen OZ7OU has an excellent application note on high impedance
measurement with the VNWA3. The nanoVNA, at under $100, has reasonable
accuracy to about 1K ohm (which I believe is limited by the return loss
S/N ratio) but requires careful calibration with setting of the
"measurement plane" for the device under test .... and, probably,
shielding of the test fixture.
I have not been able to find the original article "how to measure very
high impedances" by Poulsen in a Google search, in which he discusses
K9YC's measurements but I will forward a copy (9.2MB) to anyone who
would like to have it.
73,
Jules-K2KGJ
On 7/28/2021 10:09 PM, tangerinesdr-request at lists.tapr.org wrote:
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> 1. Re: [HamSCI] RE: Notes from PSWS / TangerineSDR call of
> 07-26-2021 (Ward Silver)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 28 Jul 2021 21:08:41 -0500
> From: Ward Silver <hwardsil at gmail.com>
> To: TAPR TangerineSDR Modular Software Defined Radio
> <tangerinesdr at lists.tapr.org>
> Subject: Re: [TangerineSDR] [HamSCI] RE: Notes from PSWS /
> TangerineSDR call of 07-26-2021
> Message-ID:
> <CAFr7d=qkP1Dh6nBnqfQDOu5LaZGbS7No7uERsdUrzptxXo+Sjw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Recent editions of the Handbook offer several polarity protection circuits
> in the Power Sources chapter (Chapter 7). Some of them use P-channel
> MOSFETS that have much lower forward voltage drops than standard diodes,
> even Schottky barrier diodes.
>
> Regarding common-mode chokes, I think it is better to determine the need
> first - what frequency range and amplitude, for example - and then select a
> type of choke to do the job. For example, blocking RF common-mode at VLF,
> HF, and VHF/UHF requires different ferrite mixes and the number of turns
> also makes a difference in the choke's peak rejection range. (See Chapter 5
> - RF Techniques - of recent Handbook editions. Much of this was written by
> K9YC and comes from his tutorials.)
>
> I realize the original post was about power supply failures and not RFI but
> nothing like a good digression :-) Analog Devices also just published a
> couple of articles about protecting inputs for low-power interfaces in the
> Analog Dialogue - a little Googling will find the recent issues which are
> free and public. All good stuff.
>
> 73, Ward N0AX
>
> On Wed, Jul 28, 2021 at 7:54 PM <tangerinesdr-request at lists.tapr.org> wrote:
>
>> Jonathan,
>> You can use a standard silicon diode like the 1N4000 series (1A rating)
>> for the polarity protection diode unless you want to clamp the reverse
>> voltage at less than 0.7-0.8 volts, in which case a Schottky will
>> provide a lower clamping voltage.? Since the reverse protection diode
>> will clamp reverse transients, you don't need a bidirectional TVS.
>> Jules
>>
>>
>> On 7/28/2021 3:16 PM, Jonathan wrote:
>>> Phil,
>>>
>>> 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.
>>>
>>> Jules,
>>>
>>> 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?
>>>
>>> David,
>>>
>>> Tom mentioned the same. I?ll be working on trying to fit an
>>> electrolytic and a ceramic capacitor.
>>>
>>> Khan,
>>>
>>> This is good news. Email me if you have issues.
>>>
>>> Jonathan
>>> KC3EEY
>>>
>>>
>>>
>>> On Jul 28, 2021, at 2:27 PM, Julius Madey <hillfox at fairpoint.net
>>> <mailto:hillfox at fairpoint.net>> wrote:
>>>
>>>> Jonathan,
>>>> 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)
>>>>
>>>>
>>>> <eaeficdplljflikc.png>
>>>>
>>>> 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.
>>>>
>>>> Regards,
>>>> Jules-K2KGJ
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On 7/28/2021 12:41 PM, Jonathan wrote:
>>>>> Hi Tom,
>>>>>
>>>>> That makes a lot of sense. I?ll try fit a 0.1uF and a 22-47uF
>>>>> electrolytic on the feedline loop.
>>>>>
>>>>> Thanks again!
>>>>>
>>>>> Jonathan
>>>>> KC3EEY
>>>>>
>>>>> On Jul 28, 2021, at 10:55 AM, Tom McDermott <tom.n5eg at gmail.com
>>>>> <mailto:tom.n5eg at gmail.com>> wrote:
>>>>>
>>>>>> Hi Jonathan - a concern is that the DC-DC converter input stage
>>>>>> would become unstable and oscillate
>>>>>> with the cable inductance.? If that happens then there could be
>>>>>> high frequency AC voltages present at the
>>>>>> input of the converter.? Would those over-voltage the input??
>>>>>> Possibly.?? Would it radiate RFI from the cable?? Likely.
>>>>>>
>>>>>> Good design dictates sufficiently low source impedance to the DC-DC
>>>>>> converter.? Almost all linear regulators
>>>>>> require it.? An electrolytic and ceramic bypass pair right at the
>>>>>> DC-DC input would be considered good design by many.
>>>>>>
>>>>>> -- Tom, N5EG
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Jul 28, 2021 at 7:30 AM Jonathan <emuman100 at gmail.com
>>>>>> <mailto:emuman100 at gmail.com>> wrote:
>>>>>>
>>>>>> John,
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>>
>>>>>> Tom,
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>>
>>>>>> Jules,
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> 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?
>>>>>>
>>>>>>
>>>>>> Thanks guys.
>>>>>>
>>>>>> Jonathan
>>>>>>
>>>>>> KC3EEY
>>>>>>
>>>>>>
>>>>>> On Tue, Jul 27, 2021 at 9:34 AM Jonathan <emuman100 at gmail.com
>>>>>> <mailto:emuman100 at gmail.com>> wrote:
>>>>>>
>>>>>> Hi Everyone,
>>>>>>
>>>>>> 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.
>>>>>> <image3.jpeg>
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> Here is the schematic of the power path. The blocks are the
>>>>>> IP2415S DC-DC converter.
>>>>>> <image1.jpeg>
>>>>>> 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). 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.
>>>>>>
>>>>>> 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)
>>>>>> <image2.jpeg>
>>>>>> 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.
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> 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.
>>>>>>
>>>>>> Jonathan
>>>>>> KC3EEY
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Jul 27, 2021, at 7:21 AM, Dr. Nathaniel A. Frissell
>>>>>> Ph.D. <nathaniel.frissell at scranton.edu
>>>>>> <mailto:nathaniel.frissell at scranton.edu>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Thank you, Tom.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> The recording will be available later today at
>>>>>>>
>>>>>>> https://youtu.be/AammohuygMw
>>>>>>> <https://youtu.be/AammohuygMw> and hamsci.org/telecons
>>>>>>> <http://hamsci.org/telecons>.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 73 de Nathaniel W2NAF
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> *From:* TangerineSDR <tangerinesdr-bounces at lists.tapr.org
>>>>>>> <mailto:tangerinesdr-bounces at lists.tapr.org>>
>>>>>>>
>>>>>>> *On Behalf Of *Tom McDermott via TangerineSDR
>>>>>>>
>>>>>>>
>>>>>>> *Sent:* Monday, July 26, 2021 10:02 PM
>>>>>>>
>>>>>>>
>>>>>>> *To:* TAPR TangerineSDR Modular Software Defined Radio
>>>>>>> <tangerinesdr at lists.tapr.org
>>>>>>> <mailto:tangerinesdr at lists.tapr.org>>
>>>>>>>
>>>>>>>
>>>>>>> *Cc:* Tom McDermott <tom.n5eg at gmail.com
>>>>>>> <mailto:tom.n5eg at gmail.com>>
>>>>>>>
>>>>>>>
>>>>>>> *Subject:* [TangerineSDR] Notes from PSWS / TangerineSDR
>>>>>>> call of 07-26-2021
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Notes from PSWS / TangerineSDR call of 07-26-2021
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 1. Bill is using chart.js for magnetometer charting. He is
>>>>>>> setting up a database using Django web and database
>>>>>>> framework for Python.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 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
>>>>>>>
>>>>>>> while awaiting FPGA component availability. The 10 GX
>>>>>>> development boards are pretty expensive.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> -- Tom, N5EG
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>>
>>>>>>> Please follow the HamSCI Community Participation
>>>>>>> Guidelines at
>>>>>>> http://hamsci.org/hamsci-community-participation-guidelines
>>>>>>> <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+unsubscribe at googlegroups.com
>>>>>>> <mailto:hamsci+unsubscribe at googlegroups.com>.
>>>>>>>
>>>>>>>
>>>>>>> To view this discussion on the web visit
>>>>>>>
>> https://groups.google.com/d/msgid/hamsci/SA0PR03MB5547CBF733EFEB4D829E659FF2E99%40SA0PR03MB5547.namprd03.prod.outlook.com
>>>>>>> <
>> https://groups.google.com/d/msgid/hamsci/SA0PR03MB5547CBF733EFEB4D829E659FF2E99%40SA0PR03MB5547.namprd03.prod.outlook.com?utm_medium=email&utm_source=footer
>>> .
>>>>>>>
>>>>> --
>>>>> Please follow the HamSCI Community Participation Guidelines at
>>>>> http://hamsci.org/hamsci-community-participation-guidelines
>>>>> <http://hamsci.org/hamsci-community-participation-guidelines>.
>>>>> ---
>>>>> You received this message because you are subscribed to the Google
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>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>> send an email to hamsci+unsubscribe at googlegroups.com
>>>>> <mailto:hamsci+unsubscribe at googlegroups.com>.
>>>>> To view this discussion on the web visit
>>>>>
>> https://groups.google.com/d/msgid/hamsci/59FAEE9C-11F5-4CDF-B960-2E583E42E89C%40gmail.com
>>>>> <
>> https://groups.google.com/d/msgid/hamsci/59FAEE9C-11F5-4CDF-B960-2E583E42E89C%40gmail.com?utm_medium=email&utm_source=footer
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