Finally measuring the frequency of my HB-100's

Yesterday I wired up the LNB to a TV-spectrum analyzer to check that the preliminary setup would work. Besides an occasional short into the coax that trips the power-over-line circuitry, the LNB noise is visible. Then I fired up my HB-100 transmitter, that has been sitting in a box for months: its modulated signal peaked at 621.45 MHz on the screen.

So, if the LNB L.O. is at 9750 MHz, my TX is at 10371.45 MHz. That's well within HAM allocation.

Then I measured the HB-100 I had used as a receiver, which sat at 694.70 MHz = 10444.70 MHz. This confirms the delta of 73 MHz I observed in May 2017 when doing my first experiments.

Last I measured an apparently untouched HB-100, my third and last sample, and it could be received at 676.35 MHz, meaning 10.42635 GHz. Knowing me, I think I had left this spare radar module untouched, as a reference.

So, if the assumption of 9750 MHz LO is correct, all my HB-100 modules fall within the 3 cm HAM band (10.0-10.5 GHz), even if I was expecting a "brand new" one to be at 10.525 GHz. Hypothesis: I bought off eBay HB-100 modules that were rejected because they did not meet the spec on the operating frequency, and luckily were too low. Unfortunately I haven't found someone that published a measurement of their frequency.

I need a beacon of known frequency to confirm these relative measurements. Fortunately there is a beacon in L.O.S. from home and QO-100 satellite few degrees away. It will not give me accurate frequency values, but enough "ballpark precision" to allow a fellow HAM to quickly tune on my TX frequency and complete a QSO.

Returning to 10 GHz

I am again doing something at 10 GHz.

During the journey to Montichiari HAM fair, fellow Pino JNS showed us how easy it is to receive the geostationary satellite QO-100 with a PLL-LNB and a small dish. The "last mile" is then done with the ubiquitous RTL-SDR.

Now my HB100 radar modules have a valid RX companion, so a 10 GHz RX-TX setup can be built and operated. It will be WFM or CW (A1A), but at 10 GHz and with very simple RF parts. The total cost for RF is about 30 euro.

I will initially try to receive QO-100 and a 10 GHz LOS beacon. Once I confirm the LNB is stable and spot-on frequency, I will tune my HB-100 modules into the 3 cm HAM band to a known frequency. Then again a short distance test, 200 metres "DX", and who knows what will be next.

Thinking out of the box Telecommunication test for millennials in IT

I've just done this at work, using some tricks that were daily routine back in the days of dialup. I wonder how a sysadmin half of my age would tackle this problem.

You are logged into a Linux server through a sort of corporate menu-driven shell proxy and you need to get a 10 MB binary file out of it for local troubleshooting purposes. The shell proxy and firewall do not allow your unprivileged account to ssh/sftp directly into the machine and you don't know its password either. There is a webserver but your unprivileged user has no write rights to its folders. You try to mail the file to yourself with the "mail" utility, but the test message you try before going all the way never reaches your mailbox into the organization. The server cannot do outbound ssh/ftp either.

So, how do you get the file on your local computer? Ask for further details and share your ideas in comments (moderated).

GPS Week Number Roll Over, 2019 edition

I discovered this detail of GPS raw signal in 2010, when my Garmin Geko 201 showed a wrong date. The guys behind GPS (not Garmin) implemented the transmission of a 10-bit weeks counter value that rolled over in 1999, so that some devices began showing a date that was 1024 weeks behind.

It will happen again at the end April 6th, 2019 (UTC).

(Somehow) The week counter has been upgraded to 13-bit, 157 years (but week #0 is still back in 1980-01-06). Probably most devices using GPS location data built in the last 19 years have a software way to handle the rollover, so you will not be affected. Probably. Hopefully. I know too many lazy developers to be 100% sure all my devices will not be affected.

Unless the device is tested with a fake GPS signal ahead in time, all we can do is to wait for the first full weekend of April 2019.

What's worse, the device might have an embedded lookup table "GPS week vs real week" that is 19.5 years long and would roll over any time in the future. And, in most cases, all these devices are unlikely to get a firmware update.

See you in week #0 :)

Weird behavior of ZS-042 RTC modules (DS3231)

First of all: all these ZS-042 RTC modules were paid about 1 USD each and come from not-certified sources. 

One night I decided to measure the 32K output of some DS3231 ZS-042 RTC modules. I wanted to see what difference would make if I retouched the aging register. This experiment lead to few unexpected discoveries.

1) Maxim DS3231 datasheet mentions 32K output and 32.768 kHz interchangeably. Alright, it is a digital device, so 32K equals 32768 if K=1024 as used for bytes. But we are talking of Hz, not bytes, so I think should be K=1000. Proof? Search for "768" in the datasheet.

2) There are two quite different devices that share 6 characters of the part name - DS3231 - and are distinguished by their suffix: M or SN. The former "M" is 5 ppm with MEMS resonator, while the latter "SN" is 2 ppm with TCXO. In simple terms, "SN" is better than "M". But you can't choose when buying ZS-042 modules and you will receive either model

"M", "SN", "M":notice the deeper blue PCB of "SN"

3) All my ZS-042 modules with DS3231M output a frequency close to 32.700 kHz, while those with DS3231SN are close to 32.768 kHz. The "M" would be loosing 180 seconds/day, 1.5 h/month, but none of them does! Actually I have one DS3231M in my longest running Nixie clock and it is within 5 ppm specification.

Measuring "32K" output of DS3231M.

So, let's forget DS3231SN that are most likely second-hand/pulls but legit. How can a DS3231M that outputs 32700 Hz be so accurate as I observed? If it is genuine, Maxim has a way to calibrate the chip once, before it is sold. If it is a fake, then it is microcontroller with proper firmware and calibration to count the correct number of interrupts. I could sacrifice one and decap it, but then I lack the microscope to examine the silicon die.

Conclusion. Buy the DS3231SN if you need an interrupt rate of 32768 Hz. Otherwise for hobbyist use, they are both worth it.

Timebase for homemade clocks, 1 pps

I am currently into a minimalist approach to building (Nixie) clocks that does not include a user interface. The are several reasons, like simpler and less buggy firmware, straightforward user interaction, less hardware, fewer holes to drill in the case. Since these are one-offs "products" without commercial intents, I can afford it.

I am after a simple way to get an accurate 1 pps or integer fractions of it so that the microprocessor can count the elapsed time.

The most elegant way would be to clock the AVR microprocessor with a purposely chosen XTAL, feed that timebase into a divider and use it as timekeeping interrupts. I've got plenty of 11059200 Hz crystals, but they don't divide well into suitable interrupt counts.

Another way is to take advantage of the AC line at 50 (60) Hz, but that means a special power supply (AC-AC) and additional circuitry to get DC voltage for the logic and the booster in case of Nixies. No, I don't want to use the direct-AC method!

How about a watch crystal at 32768 kHz and a 4060 divider? That would work, indeed.

But when you take into account both the additional wiring and the cost of each of these solutions, it turns out that modern RTC chips (at 1 USD shipped, already on breakout boards) are equally cheap, maybe even less complex to wire, output a 1 pps signal and offer greater upgrade possibilities if you ever want to, like battery/supercap backup, date, power loss warning. And their SOIC package is probably not too difficult to hand-solder either.

By the way, how to set the time on a interface-less clock? Well, it always starts at an agreed time, and you simply have to plug it in at that time. We are surrounded by clocks and "my" device doesn't aim at being the time reference standard.

Windows 10 1803 failed update week-long nightmare

In December 2018 I bought a laptop with Win10 (Asus, for the records, but I think it doesn't matter). It has been little responsive since the beginning, so I let it run all updates for 24 hours: at least it stopped using the hard-disk like crazy.

But it still complained that there were pending updates, the "Windows 10 1803", that had already failed three times to install. I don't know which version was running, probably it had arrived to 1709 (that is Fall 2017).

Microsoft forums already gave the workaround: skip the 1803 update and go for 1809. Alright, but how? As of January 2019, Microsoft-provided tools would not do it.

After a week of wasted evenings I was successful with:

1. downloading the [correct] 1809 ISO from the the Microsoft downloads site pretending not-to-be a Microsoft browser (do it from Linux or use the documented trick for Internet Explorer/Edge); it is a circa 5 GB file
2. burning the ISO into an USB pendrive (min 8 GB) with Rufus tool under Windows
3. going into the laptop BIOS and disabled Secure Boot
4. from the BIOS forced to boot from the USB pendrive
5. installed the update by choosing to keep existing files

Step #5 took few hours (overnight) and my files were not lost. Do yourself a favour and backup first, just in case!

I dare to say it is not for the unexperienced user; friends confirmed that there is no Microsoft-ish way out if 1803 update doesn't install: it would go on forever killing your HDD, CPU and Internet bandwidth.


Tip. If you want to control when Win10 downloads and installs updates, find the way to mark your connection as metered.

Good luck.

Taking control of HP 9403A

The HP 9403A odyssey might be close to an end. After tracing most connections on the "DVS Program I/O" connector to corresponding ICs, thus understanding if they are inputs or outputs (they all end up into an HP 1820-0107 level adapter), I begun to take control of the device:

HP 9403A: first signs of human control after 40 years.

I know which are control lines and which are data lines. There is no serial protocol, but just plain parallel negative logic. If I want to do something with the bulky piece of equipment I will need a microcontroller with lots of I/O lines, or some serial-to-parallel (open collector) converter.