23 May 2017

My firstpcb.com's first PCB's have arrived!

Finally! After a slooooow journey across the world, my first PCB's have arrived! Ten pieces of a board holding 4x ZM1332/5870S Nixies, the driver IC and transistors. The tubes are supposed to be multiplexed offboard.

There is a lot of free board space, I know. I could have packed many more components, but I really wanted something as general purpose as possible that would simply hold the tubes in place at a proper distance. And, a PCB that would work right away (test still pending).

These PCBs were designed in KiCad and fabbed by www.firstpcb.com. I haven't found a problem but, as I said, these are simple two-layer boards.

In case you want to give a try at the whole PCB production process, you may want to register through my referral link https://www.firstPCB.com/mi_odrCr8 which gives both of us a 10 USD bonus (new customers get it nevertheless).

The boards packed in vacuum. Cool.



19 May 2017

My review of "57° Mercatino di Marzaglia" - May 2017

Top quality from the past!
For the first time I attended the famous Mercatino di Marzaglia near Modena (57th edition, May 2017). I believe it is the largest Italian radio-electronics flea market event, only for private sellers and used items. No cheapo Chinese modern stuff, no drones (not even in the air!), not much computers either. It takes place in a large camping site twice a year (mid May and mid September, on Saturday): bring sun lotion, baseball hat, water, ... Free entrance and parking for visitors, small contribution for exhibitors.

What was there? A lot of vintage valve radios in excellent conditions. A lot of 80's and 90's audio equipment. The usual assortment of valves ("NIB" conditions) and maybe overall 15% tables with pure HAM radio stuff (RTX, antennas, accessories), components. Few instruments, very little retrocomputing, some militaria.

I bought (memo to my future self): a 200Vdc Wester Electric voltmeter (without resistor!), 3x IV-21 VFD tiny displays, some HV electrolytic caps for Nixie PSU's. I haven't found other display technologies as spares (Nixies, VFD, early LEDs). The list of things I have not brought home is too long, but I do have good memories.
Parking lot - 7 A.M.!

I arrived at 7:00 am and most stands were already displaying their stuff. I think you shouldn't arrive later. Overall I walked 3h30' and I think I haven't missed a stand, but I have skipped over those sellers that were not calling for my attention. With reference to Friedrichshafen 2015 (1,75 halls) and 2016 (1.5 halls) flea markets, it seems to me that Marzaglia has the same size if not larger. Exhibitors in Marzaglia are mostly Italian. I spotted two Hungarians, two Germans and a French, not counting those that were selling stuff I was not interested in and I didn't even get close.

It has been a positive experience, combined with enogastronomic and cultural tourism in the area (Modena, Reggio Emilia, Parma). I encourage interested visitors to get there early, so sleep over in the area. You better get there by car or stay at the campsite if you're that kind of traveler (you need to bring your own tent/caravan/camper). I have no comments about eating on site because I left early, but it probably gets really crowded at lunch time, so bring your own food. Also, the bar/restaurant building is at the campsite entrance. Plan a stay of at least 5 hours if you want to do some serious business and see everything. Add chat time!

Personally I will attempt a second visit to Marzaglia and perhaps skip FN2017: I fear too few exhibitors will go there in mid-July!
Need some valves?
They were playing "Stayin' Alive" and dancing :)
Six Dekatrons in a row. Rare instrument I dare to say.

Keep on walking. I took this picture and I
missed interesing stuff on the grass!
More, more, more sellers!


18 May 2017

HB-100 300 metres "DX" and opaque windows

When the first "long distance" 10 GHz reception test failed (about 300 m as the crow flies), I knew something was utterly wrong. Based on the indoor NLOS SNR I recalculated the link budget and determined I had enough signal to cover a much longer distance.

The setup was as follows. TX in a plastic box outside at the far away site. RX indoor at home, with RTLSDR and laptop. Just bare HB100 radar modules. Full optical visibility.

No reception at all. I suspected broken wires and cold joints, so I re-checked everything and successfully re-tested at home.

For the second attempt the RX station was on the balcony and I replaced the RTLSDR with the spectrum analyzer: ta-da! My transmitter' signal was there, at 74.8 MHz I.F. as expected. It was fun to notice how millimeter waves bounce everywhere if you're surrounded by concrete buildings and combined with the broad radiation pattern of HB100 antennas I could not get a null.

Then a doubt arose: could the RTLSDR dongle be too insensitive at that frequency? So I powered up the laptop on the kitchen table, the dongle and the receiving module. This time the door to the balcony was open, and I was standing between it and the nearby closed window. Since I was holding the RX in my hand, I moved it around looking for a peak on the spectrogram and noticed it would appear and disappear, loosing 20 dB down into the noise. What was going on? Just five minutes before I couldn't get a null and now the signal was gone still pointing the antenna at the right direction?!

Slow down Paolo. Repeating my movements I could see that the signal was lost when the receiver was behind the window, and present when looking out of the open door. What?! Wow!

The window is made of double-glazing and I know it contains some form of Sun shield: my home windows are also a very effective 10 GHz filter!!

Now I can look for a longer LOS path!

14 May 2017

10 GHz TX ready for the first mission

Now that I have completed, debugged and tested the WFM modulator for HB100 radar modules, it is time to try an outdoor transmission. Since I will place the transmitter at my parent's place I needed an enclosure.

Peter PA1SDB (probably him) measured the attenuation of various materials, and plastic was found to introduce negligible attenuation at 10 GHz. So I bought a plastic box for food at the Chinese shop around the corner (1.19€) and this is the first result:



I love working with plastic because most of the time it can be drilled by hand. So far I have secured the HB100 module (TX only), while the breadboard is a tight fit in there.

The modulator is based on DJ7OO circuit and was built with parts that were in the junk/parts box. Main difference is that the tone generator is built around a NE555 and potentiometer P2 on the voice chain has been connected properly. The NE555 might be replaced with a microcontroller so that more functions can be executed, like bitonal beacon and MCW ID.

What's missing before the test in the outside world is a DC socket and a power switch. Then a beacon/voice toggle and a microphone input too.
The test transmission is scheduled for Tuesday.

10 May 2017

A ionizing experience

In 1987 Italians voted against the use of nuclear power plants to produce electricity on the Italian land. This meant an immediate shut-down of all four nuclear plants and the beginning of a long decommissioning phase. Few years later, real decommissioning works could begin (around 1994) and since few years ago the former nuclear sites are safe enough to be visited by the general public.

SOGIN, the company owning the plants and handling the whole decommissioning process, opened their gates last weekend (6-7 May, 2017) with two possible guided tours: unrestricted and controlled zones. I managed to get a seat in the remainings of the controlled area tour.

Taking pictures was strictly forbidden, so this will be a blind blog post.

The plant in Trino used a PWR reactor build between 1960 and 1964. We dressed up covering shoes and wearing gloves, helmet and white coat. Some participants were given a dosimeter, while the staff wore their own. We climbed up four floors to see the pools from above (still full of water), then moved to the area that was above the reactor (temperature during operation: 60-70 °C). The top position offered a clear view of the vessel from above. Then we went outside to a temporary storage of nuclear waste, full of drums, some already categorised, some not. Probably this was the most active area visited even if the highly active material (reactor fuel) has been moved to France and UK for reprocessing. Lastly, before leaving the controlled zone, we removed all the protective clothing and got two full-body scans for possible contamination. Everyone was clean.

It was a really unique experience. It showed how complex and costly is to decommission a nuclear power plant, regardless it happens after its useful life or before. It was clear that the technology itself is safe, as long as a human error, human stupidity mixed with bravery (Chernobyl disaster) or natural event (Fukushima) do not interfere with the operation of the plant. In my humble opinion the largest problem of this technology is the kind of waste that is produced, which requires ages to become safe. Don't forget that the same kind of waste is produced by nuclear medicine and research centres, even if in smaller quantities.

I asked the tour leader if, in two years from now - the possible next Open Gates event - there will be something left to see in the uncontrolled zone. She nodded. Dismantling the Trino plant will end somewhere near year 2030.


09 May 2017

First WFM on 10 GHz (HB100 radar)

The transmitter of this test.
After fiddling for a while with the modulator circuit by DJ7OO, I managed to transmit audio using Wide-FM through a HB-100 radar module. The single-tone beacon was already working (with a NE555), even though I should try to widen its resulting RF bandwidth (which means increasing the amplitude).

The ability to increase the receiver's bandwidth on an SDR automatically compensates for the short-term frequency instability of the HB-100. At least for "operations" within indoor conditions, that are pretty much static.

The test setup was as follows. RX: RTL-SDR dongle receiving the IF output of a stock HB-100 module. TX: retuned HB-100 driven by my own version of DJ7OO modulator (LM317). No external antenna aids, no real line-of-sight but a loose zig-zag in the house for a total of about 10 metres. There was also a slight polarisation mismatch.

My WFM signal at about 10.452 GHz, as received on another HB-100 radar sensor.
In the conditions described above the signal is about 30 dB peak above noise. I think the peak could be higher if LOS could be established over the same distance. But now it is really time to test it over a longer distance!