15 May 2019

Tools for planning 10 GHz "expeditions"

Activity on 10 GHz means portable operations. If you live near some mountains, it is a matter of finding a panoramic spot, clear of vegetation, open to possible correspondants. Besides asking for advice to "who has already been there", technology and Internet help a lot.

Street View on Google Maps allows to survey many places directly from home. You can get an idea of the possible presence of vegetation, parking place, pic-nic table or grass field for stuffing the equipment.

Once you're done you can run a coverage simulation with Radio Mobile online. You'll need some practice in order to get meaningful and reliable maps, but I am sure there are many tutorials to choose from.

Last but not least, the wonderful peakfinder.net website lets you name mountains/peaks surrounding any location of the world: without running a simulation you will know if two remote locations can "see" each other and stand chances for a 10 GHz QSO. This is also useful if someone will operate from home and wants to know if the portable station is visible.

06 May 2019

Just another 10 GHz test transmission

Yesterday I wanted to test again my HB100 signal and the online receiver 30 km away. No dish on either side. This is the result of my WFM signal modulated with a square wave (which generates two parallel traces on the waterfall).

Three beacons and me on 10 GHz.

My transmitting setup.
I did not leave it transmitting for long given its strength on the waterfall and the frequency too close to beacons. Moreover the TX beam was 60 degrees off, at least according to the theoretical/datasheet radiation pattern. 

Simply amazing.

29 April 2019

32 km on 10 GHz

Still one-way, but it is quite outstanding: my bare HB100 signal could be received by a bare LNB at 32 km distance with a 13 dB S/N margin. I could increase the signal by adjusting the TX direction, but the RX side is fixed on a remote location (remote SDR receiver).

Also I think that the strong wind was waving some vegetation into the path because the signal would disappear with heavy QSB.

What is even more interesting is that the bare LNB is receiving a 3 cm beacon 300 km away! At least now we know a remote site where we could try a super-HB100-DX!

23 April 2019

Distorted readout on Tektronix 7603

I got to use my Tektronix 7603 analog oscilloscope over the weekend and started worrying.

I usually fire it for few minutes to check a signal and then off it goes for weeks. Not long ago, during longer operation, I heard a "clunk!" and with side-vision I saw the CRT display going blank and then back again.

Last weeks the "Trig'd" lamp on the timebase plug-in broke, but it triggers just fine.

Fast-forward to this weekend... when switching vertical plug-ings left-to-right I noticed the Tek was using a different font for readout:

Wait a moment! That's 1970's hardware, it cannot change font!

I am afraid I need to start troubleshooting from the PSU. This calls for a way to see PSU signals, that means I need another oscilloscope.

And dilemma: keep it or let it go? It will hardly sell as a single piece (to be re-capped, the least). I might sell individual plug-ins, 2x 7A18, 7A13, 7B80 (doesn't sweep), 7B53A. Or keep the beast since I can configure it to provide 4 channels at 100 MHz BW.

13 April 2019

8,85 km on 10 GHz

I've made it! Today 2019-04-13 at 11:20Z my bare HB-100 WFM TX was received with a bare LNB at 8.85 km (5.50 miles) over a pure line-of-sight path. Then I added the parabolic dish on the RX side and the signal became very, very strong. BTW, nobody was aiming the TX side, so the signal could have improved a bit.

The current world record is 204 km (HB-100+dish to LNB+dish) and I am longing for it. :)

10 April 2019

The Gunnplexer Cookbook (1981)

The Gunnplexer Cookbook was published in 1981 (and can be found online in PDF form, but I am not sure if it has been relased into the public domain). In 2019 we are playing with HB-100 and low noise SAT-TV LNB's rather than Gunn diodes, but I think that book contains good old wisdom that still applies nowadays. Temperature stabilization, a simple and mechanical way to estimate a frequency at 10 GHz (useful for HB-100 transmitters too) as well as other pearls to enrich one's knowledge of microwave bands.

Have a look at it if you are interested in GHz operations.

07 April 2019

Welcome to GPS Week #0

The second GPS Week Number Rollover (do a web search for more info) has just happened. Your GPS device might think it is in 1980, or in 1999. The first symptom would be the long time to acquire a GPS fix. Then a wrong date is shown.

How's yours?

06 April 2019

800 metres with HB-100

Since I have discovered that from home I see a parking space 600 m away, I have just completed two tests with HB-100 TX and TV monitor+LNB RX.

At the parking spot the signal was loud and clear with plenty of SNR, so I can go further with this setup.

Then I took a longer route home and I stopped 800 m away on the same direction, and the signal could be received through reflections, but very very weak. Well, the TV monitor instrument is not as sensitive as an RTL-SDR, but there was no clear path between "me" and me.

NB: no dish was used on either side!

While measuring the distance on Google Maps I noticed that if you zoom in on the drawn path the line is black on "clear" and grey when there is an obstacle: helpful!

03 April 2019

HB-100 RF polarization

The test at 200 meters distance with HB-100 TX and LNB RX helped me:
  • to confirm once again that the 10 GHz signal can travel long distance
  • identify which position corresponds to horizontal polarization
Two years ago I could communicate one-way HB-100 to HB-100. I did it again but this time I had an LNB on the receiving end: plenty of signal to try a longer distance. Unfortunately as long as I am alone doing these experiments, it is either 200 m or 8 km.

Then, since the LNB has a known polarity, with no bounces off the room walls I determined (I am 90% confident) the polarization of the radiated 10 GHz signal. The rule is: polarization is given by the position of the line joining the two mounting holes. Incidentally it is rotated 90° with respect to the position of patch antennas.
So, when the longer side of HB-100 is horizontal, you should expect horizontal polarization.

22 March 2019

HB-100 vs Voltage

Having built a DFCW modulator for the HB-100 controlling the operating voltage, I could observe that a difference of +130 mV in the supply voltage causes about +200 kHz shift. The higher the voltage, the higher the frequency.

Besides the lack of temperature stabilization, switching voltages affected negatively the resulting RF frequency, causing all sorts of short-term drifts. Most likely I will switch to FM-modulated CW (audio tone over the carrier) once I want to have a real QSO and not just a reception test.

21 March 2019

HB-100 vs Temperature

My simple observation of a single HB-100 module is that the frequency increases as temperature decreases

I think it has gained 150 kHz while cooling of 15 °C, so -10 kHz/°C. That's just one test of one specimen, YMMV, even MMMV. In any case the temperature should be stabilized as much as possible, at least for short term variations, by adding thermal insulation.

I wonder if the relationship between temperature and frequency is deterministic, therefore either parameter can be inferred if the other is known: frequency-based thermometer, or temperature-based frequency estimation.

15 March 2019

There is life on 10 GHz around here

I am really excited: I received HAM signals on 10 GHz!

I needed to add a T-bias to my RTL-SDR box and the longest part was drilling a hole for the pass-through capacitor.

Here's the quick setup on my crowded desk: can you see the LNB and the RTL-SDR?

What did I receive, beaming free-hand the LNB out of the window? Three beacons! And two of them were bouncing off the mountains surrounding Torino.  The recording has HB9EI/B ID signal at 147 km while both the LNB and the RTL-SDR were warming up, so it drifts:

Cool! Next days I will try QO-100 satellite, but I need to move everything on the other side of the house.

14 March 2019

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.

13 March 2019

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.

01 March 2019

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).

25 February 2019

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 :)

15 February 2019

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.

02 February 2019

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.

19 January 2019

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.

05 January 2019

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.

02 January 2019

HP 1820-0107 pinout

I have finally found some documentation about HP 1820-0107 custom IC from 1970's. It is (hidden) in the HP 3720A manual.
HP 1820-0107 as documented in HP 3720A manual.

That document describes it as "Interface buffer gate" and draws the chip pinout as follows:
Well, I've never seen a NOT gate with two inputs. I confirm Vin is a Vcc pin (+5V in my case). In a custom chip Vout could make sense, but why so close to the Vin pin?!

In the next page of the same document I see this:

which makes more sense considering two Voltage pins and the NOT symbol. Further down the manual, the schematic diagram the corresponding ICs (A6MC21, 25, 31, 33, 35) are drawn as interface inverting gates:

Alright, now this makes sense! It explains the presence of resistors on data lines in various places of the HP 9403A. But, most important:
  1. the 1820-0107 is not a flip-flop of any sort (easier to reverse engineer the circuit)
  2. the input pin requires pulling down to ground (which explains why I haven't found yet a common +V line on connectors towards the external world)
 Back to the PCBs now!