HamSCI Telecon this Week

[Dr. Nathaniel A. Frissell Ph.D.]

Hi everyone,

Please join us this Thursday, July 23nd at 1900z / 3 PM Eastern for our bi-weekly HamSCI telecon. This week we have two speakers:

 

1. Ward Silver N0AX will be giving us an update on the new RBN receivers funded by the Yasme foundation.
2. Zach Leffke KJ4QLP (Virginia Tech) will present on his crossed dipole active antenna design for HF (based on the LWA active balun design). He is hoping that his presentation of his RF measurements might help provide a strawman for the defining requirements for the PSWS project. Zach is also looking for ideas and constructive criticism.

 

Have a good week and see you Thursday!

 

73 de Nathaniel W2NAF

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-----------------------------------------------

Dr. Nathaniel A. Frissell, Ph.D., W2NAF

HamSCI Lead
Assistant Professor
Department of Physics and Electrical Engineering
University of Scranton
(973) 787-4506

 

[pa5bw.ben]

I'm very interested in both items, will be there!

(But maybe only the first hour)

Ben PE5B

[Dr. Nathaniel A. Frissell Ph.D.]

Thanks, Ben! We look forward to seeing you!

 

And this also serves as the friendly reminder to everyone that we are meeting today 1900z / 3 PM Eastern. Here is the zoom link: https://zoom.us/j/286316405

 

73 de Nathaniel

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[Dr. Nathaniel A. Frissell Ph.D.]

Hi all,

 

Great talks today from Ward N0AX and Zach KJ4QLP!

 

Here is the Zoom recording: https://scranton.zoom.us/rec/share/z-FXc7X60DtOAaeSuW6HaoUdMcPaeaa8hHAX_qYEnh1Bgo3oMRuC9jPT-zsV_m3a

73 de Nathaniel W2NAF

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[Gerry Creager - NOAA Affiliate]

Listening to the meeting  now. Kristina, let's talk maps. I've a fair bit of experience with Mapserver. We should be able to make this work with that or GeoServer. 

gerry

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/MN2PR03MB51662345DCDF036E0F1A08A3F2760%40MN2PR03MB5166.namprd03.prod.outlook.com.

--

Gerry Creager

NSSL/CIMMS

(C) 979.229.5301 <--- NOTE THAT MY OFFICE NUMBER HAS CHANGED

++++++++++++++++++++++

The way to get started is to quit talking and begin doing.

   Walt Disney

[Ward Silver]

Hi folks,

Turns out my understanding of the KA9Q-assisted floating platform was backwards - it's a WSPR transmitter, not a receiver.  (See http://www.arrl.org/news/high-school-marine-buoy-transmitter-now-active-on-20-meter-wspr)  Phil and I talked about a floating receiver in passing and I got the two projects mixed up. At any rate, the WSPR buoy is a good thing.  Maybe a floating receiver is not so far-fetched.

73, Ward N0AX

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/MN2PR03MB51662345DCDF036E0F1A08A3F2760%40MN2PR03MB5166.namprd03.prod.outlook.com.

[Leffke, Zachary]

I really like this idea (and the WSPR TX one that is underway).  One area of interest to me is the ‘data exfil’ problem if running a receiver.  Of course there is Iridium and their SMS services, used a lot for things like larger high altitude balloons, the MIST magnetometers at the south pole (and elsewhere) and tons of other Machine to Machine (M2M) applications…but the nerdy Ham in me wants an Amateur Radio solution.

 

My knee jerk desire/thought is a ham radio smallsat (cubesat) for store and forward services.  Might be able to get higher data rates than the Iridium service, but obviously lose the coverage they offer, so net ‘throughput’ and delays/time lag would be an issue (waiting for the orbit to line up, first with the buoy for uplink, then with the command GS for downlink).  Also, getting such a system built and launched is no small task (probably obvious).  I mention all this as it might make for a fun mission analysis style project for interested AOE/ECE students (the O means ocean hihi, and the Aerospace students could work the orbits, with the ECEs working the comm analysis)……and as far as getting it built and launched, its not impossible for educational cubesats to get funding / CSLI slots (particularly if the store and forward payload is in addition to other science objectives/payloads).

 

I wonder if QO-100 might be able to provide some type of capability on this front (Amateur GEO bird, roughly covering ITU Region 1, maybe a little of region 3).  Not sure of the footprint….its over the equator obviously, but not sure what the antenna pattern coverage is and if its focused more on land masses and how much ocean it covers (particularly in the southern hemisphere).  But it might cover a decent amount of the Indian Ocean and Eastern/Southern Atlantic.  Imagine a relay from ocean buoy to QO-100 to a station with the right equipment in ITU Region 1, to forward the collected data on to the ground network.  Building a 2.4 GHz transmitter for the uplink that works reliably in the ‘high seas’ sounds like a pretty tough challenge…..then there’s the regulator aspect for remote control of the TX per part 97 rules…..also, I’m probably not the first to think of this…especially if Phil, KA9Q is involved…..…but it might be feasible and a fun project (yet another reason to get a GEO bird over Region 2….and Region 3….). 

 

And while typing this, and letting my mind wander……now I have visions of buoy to cubesat to QO-100 to expand the coverage, both in ‘real time’ and as store and forward system…..that might actually be ‘easier’ in the sense that the buoy antenna wouldn’t need to be as stable if the link can be closed with omnis (perhaps at a different band than 2.4 GHz…..like a UHF or L-Band uplink to the cubesat and then the cubesat to AO-100 at 2.4 GHz, then QO-100 to Region 1 GS at 10 GHz.  All that assumes that the cubesat has good attitude control for pointing at QO-100….

 

I’m probably thinking up solutions to problems that don’t exist……but hey experimenting is fun, and its after 6pm……(and its good fodder for student projects).

 

-Zach, KJ4QLP

 

P.S. Nathaniel, I’m about to send you the link to access the PDF for my talk for the HamSCI page (with typos/errors corrected).  Thanks again to all for the time/attention!

 

--

Research Associate

Aerospace & Ocean Systems Lab

Ted & Karyn Hume Center for National Security & Technology

Virginia Polytechnic Institute & State University

Work Phone: 540-231-4174

Cell Phone: 540-808-6305

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/CAFr7d%3DrnMceQQj3bG5C4VYSQLn3aCdx%2BT9iwWDmuNhxmC-zuQw%40mail.gmail.com.

[McGwier, Bob]

Great talk.

 

I disagree on NOT wanted a sky noise limited system, especially with the small antenna.  This will allow regular hams to put up < 10w EIRP systems that emit in the ham bands and see the ionospheric returns.  We know this because the fantastic work done by Dr. Greg Earle’s and my students around the eclipse led to a PhD and three Masters degrees.  Along with the Tangerine SDR,  and possibly other SDR instruments, this will lead to inexpensive major advance in deploying ionospheric mapping tools.

 

You and I need to do some propagation work between McGwier Antenna Farm near Auburn and the stuff to be deployed at Kentland and your home or even the ham station or satellite station.

 

Great talk Zach and this work might be submitted to TAPR for kitting and distribution.

 

So glad you are working on your doctorate. I am very proud of you.

 

Bob

N4HY

1.      Ward Silver N0AX will be giving us an update on the new RBN receivers funded by the Yasme foundation.

2.      Zach Leffke KJ4QLP (Virginia Tech) will present on his crossed dipole active antenna design for HF (based on the LWA active balun design). He is hoping that his presentation of his RF measurements might help provide a strawman for the defining requirements for the PSWS project. Zach is also looking for ideas and constructive criticism.

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/MN2PR05MB7037605649A44196A26416DCDF760%40MN2PR05MB7037.namprd05.prod.outlook.com.

[McGwier, Bob]

Sorry, I forgot this.  The trick I was taught early on by Tom Clark, K3IO and now used in Kerberos SDR is the introduction of wideband noise at a low level into the front end.  This noise allows one to maintain some level of phase synchrony and certain more than enough, IMO, for HF measurements.    In fact, Tom convinced me that in many cases you can allow the noise to ride along with the signal and it makes very little difference to the measurements of the signal.

 

Tom introduced a pulse train which produced a comb of coherent tones.  But a noise generator based on some simple circuit like that sold by Elecraft and spread by a “corporate feed in reverse” to near the connectors on your multiple channel radio.

 

Bob

[McGwier, Bob]

And the single MCO is cool but the noise injected hear the front end makes this software and probably sufficient for HF.

[Phil Erickson]

Hi Bob,

  As Tom K3IO knows, of course, this technique is a staple of radio astronomy applications for decades now.  For a while, it was driven by the fact that ADCs (Sigma/Delta, whatever architecture) were not that linear at low bit counts but were much better at high bit counts.  So you traded a bit less bandwidth (that occupied by the out-of-information-band tone) for much better quantization / Van Vleck noise.  It could be useful as you say here.

73

Phil W1PJE

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Phil Erickson
phil.e...@gmail.com

[McGwier, Bob]

Thanks Phil:

 

I hate to tell you when Tom taught me this trick.  I cringe when I think it was half a century ago.

 

We used it again in a USG application that oooops, I shouldn’t mention. HA HA HA.

 

Bob

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[Leffke, Zachary]

Thanks Bob!  I’m excited to startup the PhD work (and a bit nervous….but good nervous!).

 

Concerning the noise limited thing, I completely agree, and think I maybe misspoke a bit in my haste to get through my notoriously long slide deck (I think I said something like ‘its not a driver, or not a design goal’ which is inaccurate).  I think striving for a sky noise limited system should be a design goal (desirement?...requirement?).  When the discussion was going on a while back on the list around this topic, there was a lot of good feedback on the various design parameters/goals (as well as design architectures).  Linearity was brought up as another major concern, especially given the potential deployment in high QRM environments (as opposed to generally radio quiet observatories).  Ward brought up some good points/ideas about low end performance as another example.  It should also be mentioned though that the active antenna isn’t the only factor in achieving this goal, the backend SDR systems and overall dynamic range will also be a factor for the complete system design.

 

So, what I should have said is ‘noise performance isn’t the ONLY design goal or isn’t the ONLY major driver’.  Other performance parameters, such as linearity, also deserve serious consideration and shouldn’t be sacrificed just to achieve a sky noise limited system.  Practically speaking, its likely going to be about balance, where we maybe accept some degraded performance in one area, for increased performance in another area for a given implementation.  Also, as Nathaniel mentioned, there could be a range of options for antennas on this front, maybe some with better features in one area and some with better features in another area, giving Hams different options for their given local conditions.

 

For my version of the design specifically, the PGA-103 recommendation from Dr. Ellingson is fantastic, as it should improve both linearity (P1dB and IIP3/OIP3) while simultaneously dropping the noise figure significantly.  The datasheet values for Gain/P1dB/IP3 are only slightly better (around 1 dB or so), but the noise figure numbers are significantly better, with the PGA-103 being roughly 2 dB or so better (PGA-103 is listed as 0.5 dB NF at 50 MHz).  Those numbers are very rough (quick look at datasheet), and there is plenty of room for experimentation with the bias voltages to optimize IP3 and NF.  So in that case, we won’t have to sacrifice performance in one area in favor of another area, which is why I’m excited to try it.  It’s also a relatively quick and easy thing to test as the footprint matches the GALI-74 footprint and I happen to have a few of the PGA-103s in the garage (I might start that testing with my third PCB this weekend).  They’re also a bit cheaper than the GALI-74 (every little bit helps!).  Finally, Dr. Ellingson sent me a paper where they explore different combinations of PGA-103 architectures to further improve linearity, which might get baked into future versions/revisions as well once I’ve had time ingest the paper.

 

Thanks for pointing this out!  This is exactly the sort of detail / constructive criticism I’m looking for to stimulate conversation on the topic.  Other than getting the opportunity to talk about fun stuff that folks might actually care about (thank you HamSCI!), I was hoping my presentation might serve as a bit of a strawman design for folks to throw darts at and poke holes in.  Hopefully that sort of effort (done constructively) will lead to better understanding of overall set of design criteria to aim for if you want to get in on prototyping antennas for the PSWS or other projects (not necessarily rigidly defined requirements….defined to 6 decimal places on the logscale….with ‘thous shalt’ language) more like an better idea of the targets to aim for, and what parameters to pay attention to and why, ultimately leading to a better overall suite of antenna options for folks.

 

 

Thanks again to all!  I’ll send out updates as things progress!

 

-Zach, KJ4QLP

 

--

Research Associate

Aerospace & Ocean Systems Lab

Ted & Karyn Hume Center for National Security & Technology

Virginia Polytechnic Institute & State University

Work Phone: 540-231-4174

Cell Phone: 540-808-6305

 

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/DB700C3D-07C4-4FD5-8561-91841F59E1DE%40vt.edu.

[David G. McGaw]

The addition of low-level, usually broad-band, noise to the input of an ADC to reduce quantization noise is called dithering.  It has for instance been done in digital audio since the introduction of CDs to alleviate the crunchiness of early 16-bit recordings.  Some ADC architectures, such as Sigma-Delta, can be self-dithering and often using noise-shaping to move the dithering signal out of the passband.

David N1HAC

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[David Kazdan]

It showed up on the decoding side of CD players, too.  There was one early, high-end player that detected runs of the playback that were soft enough to be down to single-bit modulation and added dither noise.  It was a problem in early classical music CDs that very soft passages would get down to one bit.  Even two-bit (so to speak) parts weren't objectionable, but the single-bit ones were buzzy.  The realization was that people preferred noise to distortion and the dithering was added.  It was a niche issue and I don't think the solution was carried down in any other make/model CD players.

Argh!  Which CD player was that...a Carver unit? Anybody on the mailing list who was into classical music and stereo equipment c. 1985?

          David

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[Gerry Creager]

reminds me of an application to "unjam" GPS L2 signals once upon a time. My idea for it was never accepted or classified...

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/BE9490C6-6E1E-4A68-9561-0138CEF257D0%40vt.edu.

--

Gerry Creager N5JXS

It's kind of fun to do the impossible. -- Walt Disney

[David G. McGaw]

They all do it now, recording and playback.  As I say, Sigma-Delta converters which are ubiquitous, whether they are single-bit or multi-bit, have it in their design.  There have been very active discussions within the Audio Engineering Society as to what the best dithering schemes would be, and I have heard some great demonstrations.  I will have to see if I can find a recording (read You-tube ;-) ) of a demo.  Proper dithering made it possible to put classical music on CDs and it is still used, and necessary, at the 24-bit level.  This all relates directly of course to the design of a VLF front-end for the PSWS.

David

To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/415221182.6762240.1595616015454%40mail.yahoo.com.