Date
1 - 13 of 13
RFzero aggregated comments #rfzero
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Hi all
Erwin, PE3ES/F4VTQ, was so kind as to send me a tread from the group where the use of RFzero was mentioned. Subsequently, I have joined the group and also seen a few more messages along the same line. So here are some aggregated comments. RF performance https://rfzero.net/documentation/rf/ Power More than 13 dBm/20 mW. Perhaps a dB more can be achieved by fiddling with the coupling capacitors. Stability It “must” be good enough for FST4W on 630 m. The RFzero can be used for WSPR on 23 cm, i.e. the frequency wobble is reduced more than 300 times. Empiric data shows that the short term stability on 27 MHz is less than 13 mHz with a foam covered crystal. This should give max less than 228 uHz at 474 kHz. If you don't think the RFzero is stable enough you could always resort to the Next Generation Beacons platform: https://rudius.net/oz2m/ngnb/ It is 20 dB better but also 10 dB more expensive. It is the Rolls Royce of beacon platforms. The exciter, 1 GHz clock and distribution is used scientifically for time keeping purposes in Hydrogen Masers and Optical Clocks. Use Besides Steve, KD2OM, also Pino, ZP4KFX, is using an RFzero for 630 m among other things. There may be more since I don’t hear from everyone. I could make OZ0RF transmit on 630 m, but my antenna is really bad for the purpose. Already on 160 m it under performs. Availability Indeed this is the sad part of the story. Of the unique components I am only short of the MCU. Bo www.rudius.net/oz2m :: www.rfzero.net |
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Rob Robinett
Hi Bo, Thanks for joining our group and your interest in this topic. We seek to use the spectral width of FST4W transmissions on the HF bands (primarily 20M at first) to study the motion of the ionosphere and its other interactions with solar weather. With a recent SW upgrade, the standard GPS-aided KiwiSDR used by most WD stations has generated 20M spot reports with about .015Hz spectral spreading, which is well below the .100Hz or greater spreading introduced by most ionosphere motion. So there are now hundreds of KiwiSDR Wsprdaemon receive sites which are capable of making these ionospheric motion measurements. However there are only a few FST4W beacons and among them only a handful with the needed spectral spreading. Among those tx sites is Steve KD2OM who has been running a RFZero on 20M and locally monitoring it with his KiwiSDR, so there is no ionospheric spreading in the measurment. The chart below taken from https://mail.google.com/mail/u/0/?tab=cm&zx=6vakowi65f9y#inbox/FMfcgzGqQvwbhfdpQbGqvqPhgWqdwksr shows that for most of Steve's transmissions during the lat 24 hours the end-to-end spreading is an 20-30 mHz (.020-.030 Hz). This is an excellent result which shows that both the oscillator and the implementation of FST4W modulation on the RFZero can meet the needs of this application at a price which would make it affordable for an upgrade to existing WSPR beacon sites. As you can see, there are some samples which show greater than 100 mHz spreading and those would need to be investigated, but I expect that could be addressed. I am contributing to a project of the HamSCI group to study the ionosphere during the upcoming Oct 2023 and and April 2024 eclipses (https://hamsci.org/article/solar-eclipse-qso-party-20232024-planning-kickoff). I have proposed that they deploy many FST4W beacons in order to obtain a more detailed measurement of the ionosphere during those events than can be gained from a single tx site like WWV. HamSCI has a budget for this project and the RFZero is the first device which could meet their needs. There is almost a year of lead time, so perhaps the parts availability problem could be addressed. Is this of interest to you, and if so could the availability problem be addressed? 73, Rob  On Thu, Oct 13, 2022 at 5:56 AM Bo, OZ2M <groups.io@...> wrote: Hi all --
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Rolf Ekstrand
Morning Bo,
If it was available I would have bought a rfzero way back, but like a lot of other things these days there are things in products that are simply not available in a timely and cost effective way. I know you are working like crazy to get what you need, and it is probably very frustrating and time consuming. Rolf K9DZT |
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Jim Lill
Bo,
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Is the MCU you mention the Atmel D21G ? On 10/13/22 03:15, Bo, OZ2M wrote:
Hi all |
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Hi list
OK about 20 m. Don't know where I got the 630 m from. Anyway, I doubt it will be a problem. The path spreading is indeed something worth taking into account. It was one of the reasons I designed PI4 for VUSHF beacon purposes: https://rudius.net/oz2m/ngnb/pi4.htm It can be decoded even if subject to aurora distortion which can be 400 Hz on 2 m. Chris, G4IFX, is doing a path study for his PhD thesis but with the focus on 50 MHz. Perhaps he can be consulted for the HamSCI project? RFzeros for 2023/2024 should not be a problem - knock on wood. Yes, the MCU is the Atmel, now Microchip, ATSAMD21G18A-AU or -AUT since the RFzero is largely an Arduino Zero, hence its name. The other parts I currently miss are generic, and can be sourced from multiple distributors. So I have already incurred a lot of cost, that can only be converted by having some finished units. The RFzero are assembled by a professional Danish EMS for reliability reasons. So far I have been very satisfied with the outcome. I do the final mounting of the connectors and functional testing too. After posting here I received an email from a component distributor. A coincidence? Probably not. Bo www.rudius.net/oz2m :: www.rfzero.net |
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Glenn Elmore
Bo
Have you measured the spectral spreading of the RFZero on FST4W on 20m? Is the Arduino code for this Open Source? Glenn n6gn |
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Hello Glenn
I have not measured it specifically for FST4W. But it should be relative to the general phase noise/jitter. Please see values here: https://rfzero.net/documentation/rf/ The S/W is open source. Bo www.rudius.net/oz2m :: www.rfzero.net |
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Steve KD2OM is transmitting FST4W-300 on 20M with his RFZero and receiving with his GPS-aided KiiwSDR and reports mostly under 40 mHz of spectral spreading.
But there are outlier spreads which I don't think a due to the Kiwi. Open http://logs1.wsprdaemon.org:3000/d/4xvGwI97z/wspr-and-fst4w-comparisons?orgId=1&var-receiver=DI&var-sender=KD2OM&var-band=20&var-rx_id=KD2OM&from=now-24h&to=now to get this page and change the rx site to see who receives him and with what spreading.  |
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Glenn Elmore
That looks pretty good. I'm not too concerned by the outliers since GPS-aiding is expecting good short term Kiwi Clock performance. The aiding only corrects every couple of seconds (if it is set that way in admin) and during a -300 symbol time, it is expected that nothing bad will happen. That may not be guaranteed in any given environment.
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I'm just starting to look at the Arduino code that generates RFZero FST4W. All this seems hopeful that the QDX *can* be made to work on HF FST4, at least if an external clock is used. I did try playing with the configuration on my QDX but was not able to improve it, in fact I wasn't able to see any effect. Maybe I screwed up. On 10/13/22 16:14, Rob Robinett wrote:
Steve KD2OM is transmitting FST4W-300 on 20M with his RFZero and receiving with his GPS-aided KiiwSDR and reports mostly under 40 mHz of spectral spreading. |
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Glenn Elmore
Furthermore, I've already spotted Steve in Colorado, one-hop I suppose, with a reported spread of 40 mHz which is characteristic of 'stable' conditions.
I think it's probably working OK.
On 10/13/22 16:28, Glenn Elmore wrote:
That looks pretty good. I'm not too concerned by the outliers since GPS-aiding is expecting good short term Kiwi Clock performance. The aiding only corrects every couple of seconds (if it is set that way in admin) and during a -300 symbol time, it is expected that nothing bad will happen. That may not be guaranteed in any given environment. |
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Rob Robinett
I just thought to look at Steve's Kiwi GPS pages and found that all three of them are tracking only 1 or 2 satellites. That would expect the outlier events shown in the previous charts.
I also failed to look at all three of his Kiwis. With the RFZero transmitting on a vertical antenna, the Beverage Kiwi reports +30 dB SNRs while as one would expect, the Dipole and Vertical Loop Kiwis -20 to 0 dB SNRS. So Steve's outlier reports almost certainly don't reflect a problem with the stability of the RFZero, just poor GPS RF feeding to the Kiwis. I have an RFZero on backorder and look forward to getting one in the not too distant future. |
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I have improved the gps feed. There still is a variance between the kiwis but much better than before. Now the radios and RFZero are all being fed with the same antenna. Steve On 10/15/22 11:35, Rob Robinett wrote:
I just thought to look at Steve's Kiwi GPS pages and found that all three of them are tracking only 1 or 2 satellites. That would expect the outlier events shown in the previous charts. |
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Rob Robinett
Hi Steve, Thanks for working on this. You have dramatically improved the GPS RF signal levels so much so that your Kiwis are now tracking 10-12 sats and locking on 4-6 of them. At my sites I am able to track and lock on 10-12 satellites, but all 3 of those sites (KPH, KFS, and AI6VN) have clear views of most of the sky. It is my impression that the Kiwi's oscillator frequency correction improves somewhat when a Kiwi with 6 locks gets 10-12 locks with a better RF feed. But we will know more about the improvement to your site after the Kiwi runs for a few more hours. Since your RFZero signal is much stronger on the Beverage, I have been watching your Beverage Kiwi's spectral spread on Gwyn's Grafana page: http://logs1.wsprdaemon.org:3000/d/4xvGwI97z/wspr-and-fst4w-comparisons?orgId=1&var-receiver=BE&var-sender=KD2OM&var-band=20&var-rx_id=KD2OM&from=now-1h&to=now 73, Rob  On Sat, Oct 15, 2022 at 10:36 AM KD2OM <steve@...> wrote:
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