31 December 2012

IFR, Knob evolution

2012 Xmas season has taken me back to the IFRK code, so that transverter functions would be finally included, paving the way to a long-awaited public release. Curiously, after almost 3 months without looking at the source code, I was able to identify a simple way to support the transverter math.

The current IFRK state-of-the-art is:
  • frequency computed down to 10 Hz resolution, like the FT8x7 display
  • transverter LO 10 Hz precision
  • maximum shown output frequency is above 21.4 GHz
  • tuning knob supported!
  • tuning knob has 11 steps and "fast" 10x mode
  • direct dial; in transverter mode, only kHz digits can be inserted (1296.xyz.000)
  • LO value <> memory location mapping
  • FT817 proprietary functions for power level control and A/B/C repeat on IFRK display
In order to summarize current key mappings I have compiled a table with key functions (opens in new window).

Besides some cosmetics on the display and a thorough testing, I am planning to output in binary form the LO position and/or the band selected (2 bits each). These last features would control unused pins on the ATmega168 chip, so there will be no impact on existing IFR(K) circuits.

HNY 2013!

18 December 2012

Beach40 - oscillator waveforms

The Beach40 is a simple QRP DSB transceiver for 40m, designed by Peter VK3YE who released 4 youtube videos about it. In the first video Peter draws the schematic diagram, which has then been re-drawn in electronic form and shared through the Minimalist_QRP_Transceivers Yahoo group.

It is a simple circuit, whose development can be monitored with the 100 MHz equipment of my shack/lab (oscilloscope, frequency counter). So I dediced to give it a try.

After I built the oscillator, buffer and diode-ring mixer I checked waveforms on two "test points" as identified on this modified schematic diagram:

On TP1 the waveform is almost a sinewave. The small knee close to the top occurs both with a ceramic resonator and a quartz. It also gets worse when the resonator is pulled upwards: what is causing it? How to fix it?
Probe was 10x, so 2V/div, AC coupling

Then I measured voltage on TP2, with diode ring mixer installed but without the output transformer; the effect of diodes is evident:

Probe was 10x, so 2V/div, AC coupling

And finally a glimpse at my ugly Manhattan style (probe on TP1):

17 December 2012

ADS-B with RTLSDR devices

The team behind SDR# application has released a lightweight receiver software for 1090 MHz ADS-B signals that uses an RTLSDR device right away. The ouput in AVR-like format (whatever that means), available over a TCP/IP connection, can be used by most common airplane tracking software.

From my shack and using a simple vertically polarized dipole sticked against the window I could receive pings from airplanes as far as 140 km.

I also tried a properly cut biquad antenna without reflector (which is bidirectional) but did not notice big improvement over the dipole. Since the whole system is 100% digital, I miss the analogue feedback that helps identifying signal strength, not counting that transmitters move continously ... and fast!

I will not go much further into this monitoring activity, but it was interesting to notice how little security is built around airborne airplane position!

12 December 2012

CAT Bluetooth for FT-890 and FT-840

I have been asked if the CAT Bluetooth dongle for FT-8x7 could work with an FT-890 too in this configuration:
  • one dongle owned
  • either FT817/FT857/FT897 or FT890 active at once
  • one computer active at once
In other words: you move the bluetooth dongle from one radio to the other, depending on which one you want to use.

BT dongle and Y-adapter for FT-890
FT-890 has serial data on the CAT port and voltage supply on BAND DATA and TUNER rear ports. So, it turns out that it is possible, with a relatively simple adapter, to swap the bluetooth dongle between these transceivers. One requirement is that both CAT port and BAND DATA or TUNER sockets are available. Alternatively the voltage supply can be derived right at the FT-890 PSU.

Another requirement is that CAT rate on both 8x7 and 890 is set to 4800 baud since FT-890 does not offer other choices.

Incidentally the FT-840 has the same connectors of FT-890, so swapping and/or using a CAT bluetooth dongle is possible too.

Last but not least, it is possible to build a CAT-to-Bluetooth adapter natively for FT-890/FT-840 which takes DC power supply either from one of those ports or the 13.8V PSU. It can even be "dongle shaped".

10 December 2012

Two beacons in one shot

I should consider myself lucky since I have a local 23 cm beacon to test my homemade biquad antenna. While aiming it, trying to discern reflections from the actual line-of-sight signal, the waterfall spread over 2 MHz showed another beacon, 500 kHz below the known one:

Without SDR I would not have noticed IZ1ERR/B. It was 10 dB S/N, even with the 23 cm dipole inside the house. We are in full line of sight, but it is pointing away from me (I am on his side)

I have recorded 50 seconds of baseband IQ signal with SDRSharp: if anyone wants it I will share a download link of the 404 MB file.

28 November 2012

Keyer "in crosta di sale"

CQWW CW contest is one of those events that can be tackled with a simple 2-memory keyer: callign in one, "CFM 599 TU" in the other. It also overcomes my "safe" sending speed limit of 20 WPM: in QRP the slower the better and send it right the first time!
After a couple of contacts I dug my trust keyer based on PIF16F84, opened it to insert the second AA cell required and I discovered that one battery had leaked on the circuit board covering the IC with salt.

Ouch! What I loved of this keyer was that it lasted forever on a couple of AA batteries. Unfortunately I am not able to program a 16F84 anymore, so I will have to switch to something else. Fortunately there is a fairly complete (and complex!) keyer based on Arduino/AVR boards by K3NG, so I am probably going for it.

27 November 2012

Troubleshooting the biquad

First thing I checked on the biquad was the continuity of the coax+antenna setup. Electrically the quad is a short circuit, so measuring resistance across the antenna plug in the shack should be as close to 0 ohm as possible.
Instead my DVM was reading ~10 ohm "round-trip", but measuring at the bare coax cable end returned a fraction of ohm...
The antenna plug has a screw for ensuring electrical contact, which I promptly secured with a solder joint. Electrical resistance dropped to a more meaningful value and incoming signal from the local beacon increased. The biquad is still beaming away from it, I need to move the antenna to ther side of the house so that it will be facing the beacon, but currently my only properly terminated coax cable is running through a wall :-)

Next weekend there will be a 23cm contest, so I will have other on-the-air signals coming through.

21 November 2012

Nothing beats the good ol' dipole(?)

Last night I monitored 1296 MHz with the RTLSDR receiver and the homebuilt biquad antenna, fixed in one direction.

Apart from a strong station, I could hear nobody else. Then the usual HB9 placed a CQ and he was weaker than expected, so I switched back to the indoor 23cm dipole and his signal was at least 5 dB higher: something is wrong with the biquad! Last night's test confirmed my suspicions.

The outdoor antenna should gain about 10 dB over the dipole. The cumulative coax and connectors loss could be 3 dB, leaving a 7 dB boost in favor of the biquad. But according to my late night observations the difference is 7+5 = 12 dB in favor of the (indoor) dipole!

Either the biquad I have built has a weird radiation pattern or something is really wrong. Troubleshooting begins.

16 November 2012

23cm biquad simulation

Before assembling my 23 cm biquad antenna I wanted to know what happens when loop-to-reflector spacing is reduced. In theory, at least.

The standard spacing is 1/8th of lambda, while I want to halve it to 1.5 cm which is about 1/16th lambda.
Why? Because it simplifies building the antenna since the double loop can then be soldered directly to the back of a BNC female head. :-)

3D model of biquad and wire mesh reflector
I use MMANA to simulate antennas. So I drew a biquad with a reflector spaced 1/8th lambda and simulated it (the .maa file). The result was encouraging; both Z and gain were within expected values.

Each simulation run takes 36 seconds in "free space" and 48 seconds if the antenna is said to be on "real ground", so I chose not to increase reflector density.

After saving to file the "far field" data, I reduced spacing to 15 mm (0.015 m) and re-run the simulation. In both cases the antenna was set to be over real ground.

Comparison of 1/8th vs 1/16th lambda in free space.
The comparison of far fields for both antennas (1/8th is in black, 1/16th in green) show a reduced gain and F/B ratio for the shorter antenna. Gain difference is 0.5dB (theoretical), which is negligible for my final, RX-only, application. F/B looses 3dB and doesn't worry me too much, even if I will mainly use the front lobe beaming out of the balcony... I am going to build the biquad right off a BNC female head screwed to the reflector panel (a copper clad board about 20x30 cm).

Next, since I had some spare CPU cycles, I ran an MMANA overview over +/-40 MHz from the center frequency (1295 MHz). Z/Gain/F-B were computed in 5 points, SWR is interpolated. Apart from an impedance discontinuity at 1315 MHz, all other relatively flat values give hope for a normally performing antenna ... especially taking into account all my mechanical bulding errors.

Gain and other parameters comparison at various frequencies.

SWR interpolation over 80 MHz span.

Someone may notice in screenshots that SWR is computed for 75 ohm and not 50. The fact is that the RTLSDR dongle is meant for TV reception, whose impedance is 75 ohm. Also I will use a SAT-TV coax to reduce losses, so why not reason in 75 ohm terms?

14 November 2012

23cm biquad spacing

As 1296 MHz receive only antenna I have chosen to try a biquad (or dual-quad). It is composed of two full-size quadriangular loops (23cm perimeter each), set electrically in parallel and "touching" at one corner, the feedpoint.

Mechanically speaking, a 23cm biquad is simple to build, requiring a thick copper wire (1mm diameter or so) and a large reflector, say, 20x30cm, like a copper clad board. Loops-to-reflector distance should be 1/8th wavelength, which is about 2.9cm.

2.9cm ... that's the tricky part for someone like me that is not equipped to do mechanical work. I prefer what can be done with the soldering iron. So I wanted to understand what would happen to my biquad if the element separation would be of ~1.5cm, that is the height offered by a BNC female head screwed on the PCB/reflector element.

Online resources suggest that a change in spacing modifies forward gain and F/B ratio, but impedance doesn't vary too much. Anyway I have no means to measure SWR at 1200 MHz, so all I am interested in is a confirmation of the gain, amount and direction.

An MMANA simulation is on the way...

12 November 2012

10m and 30m are not harmonically related

Since a week I have switched my antenna from 10m to 30m, to be able to use some after-sunset propagation. On 30m it is composed of a 3.8m long radiator with a loading coil at the base, held horizontal out of the balcony with a telescopic fishing rod. Previous posts: [1] [2] [3] (all on this blog, open in a new window)

Then I remembered that the two HAM bands 10/30m are not harmonically related, which is a prerequisite for building a multiband "parallel" dipole. In my case it would be a parallel dualband monopole. Or three-band, since the 10m radiator could be used on 12m with acceptable SWR.

Since this is an experiment I have never tried before, I will check it out soon.

05 November 2012

RTLSDR as a (cheap) lab spectrum analyzer

While listening to a local repeater with RTLSDR (sdr# software) I spotted a strange oscillation in the output carrier.

I didn't measure the frequency oscillation width, but it was clearly visible at every silence. I suspected a sampling artifact, maybe in conjunction with an output subtone, because I had never seen the same effect on other NBFM carriers. As a cross-check I tuned another UHF carrier, which looked clean:

This unmodulated carrier, receiver over the air (see the signal disappear in the waterfall as I moved around the antenna), was clear and stable, which excluded an instability within the RTLSDR hardware.

Few days later I met the repeater technician (on the repeater itself) and he confirmed the PLL instability in the Motorola transmitter. So, it is not a sampling artifact but I was really looking at an unstable signal.

This oscillation is about 1 Hz, which is hard to spot on the equipment I have access to. But with the RTLSDR + waterfall software it was easy to see. Not bad for a 20 USD device that covers between 60 and ~1400 MHz. Good to know for my 70 MHz building activities.

30 October 2012

Bluetooth CAT for Yaesu FT1000 mark V

A HAM contacted me to have one of my CAT-to-bluetooth dongles for his Yaesu FT1000 mark V. Well, that's a transceiver I have only heard of, never seen either in real-life or pictures. I looked up the user's manual online and studied it a bit.

The "one thousand" has a CAT interface with RS232 levels (-12V/+12V), opposed to pseudo-TTL of FT8x7's (5V/0V), so my dongle cannot work on it.

But this characteristic makes the FT1000 easier to interface over Bluetooth, because there are ready-made adapters on the market. Their price varies from about 18USD to 70USD, depending on the source and packaging (you need a "slave" one, that's most common anyway). Those devices need a power supply, usually of 5 volts, that can be easily derived from one of the unused accessory ports on the back of the FT1000: I suggested to take 9V from the DVS-2 port and convert them with a 78L05 and a couple of decoupling capacitors. That's it.

Well, don't forget to configure the RS232-to-BT dongle at 4800 baud, 8N2, as detailed in the Yaesu manual. How-to do it depends on the Bluetooth adapter you've got.

And no, I am not going to build these adapters for FT1000, unless someone sends me a similar transceiver to test them on :-)

23 October 2012

Toshiba Tecra M2 recovery disks

Contact me if you need the recovery disks for a fine Toshiba Tecra M2 laptop.

Edit: the resulting system will speak Italian.

16 October 2012

Raspberry Pi from RS shipped, at last

Last night, while I was about to cancel my #2 RasPi order, RS wrote me:

"If you ordered a Raspberry Pi board as part of your order we are pleased to inform you that we have sent you the upgraded 512MB Revision 2 board to thank you for your continued patience."
That's a pleasant surprise, especially if this means I can run GCompris and Childsplay on it without noticeable slow downs.

15 October 2012

Counterfeit ICs—the Serious Problem that Only We Can Make Go Away - Tutorial - Maxim

Lately the Maxim-IC newsletter delivered to my inbox carried a link to an interesting document about Counterfeit ICs—the Serious Problem that Only We Can Make Go Away.
While as hobbysts we cannot do much about the phenomena, we are certainly pushing components to their limits and beyond (here I am thinking of the CW TX based on 74HC240 run at 7V, IRF510's as HF PA, ...): counterfeit components can be the cause of an unexpected failure.

25 September 2012

Back on the 10m waves

This antenna was easy to tune, since I have enough support to hold a 10m quarter of wave radiator (4m long fiberglass telescopic fishing pole).

I had a couple of hours to tidy up the shack-lab while putting out some CQ's.
First I tried on 10m WSPR at 0.5W, receiving report from DU and VK lands. Then, not satisfied with the gratification coming from an automated system since I was in the shack, I remembered of PSK31. I tuned down a little and managed 8 QSO's, including a new one OD Lebanon that came back to my call.

The antenna is fed with RG58 coax coiled up to form an RF choke. The choke is held in place with a clip-on ferrite bar. I have no idea if RF is flowing back to the shack. At the indoor coax connector the SWR is 1.5:1 on 10m and 2.5:1 on 12m, so the antenna is somehow a dualbander.

The fishing pole is long enough for a 15m quarter of wave radiator without needing loading coils, so I might give it a try.

22 September 2012

How it all began

After my initial interest in electronics (will be in another post), sometime in 1980's my brother and I were given a pair of 27 MHz walkie talkies. I could have been 8 or 10 years old.

Those walkies worked on 27.145 MHz, an "alpha" CB channel used also for remote controls. The microphone was the loudspeaker itself. The receiver was broad, very broad but sensitive: I could hear truck drivers on channel 5 (27.015 MHz) from kilometres away.

With no understanding of frequencies or channels, my mother and grandparents took me along the truckers' road trying to talk with them. No success, of course.

I don't remember if it was the very same Summer or the next, I got a 3 channel portable CB, then followed by a CTE Alan 48 which gave me my first sporadic-E DX on channel 34 FM with an Austrian station.

Yesterday my mother asked me what to do with those walkies, "Gig Bravo 2000": no way they're going to the recycle bin!

I am tempted at replacing the XTAL and try some extreme HF AM portable operation...

13 September 2012

HVPP fusebit doctor for AVR's

Great job did these Polish guys that created the High Voltage Parallel Programmer (HVPP) for Atmel AVR microcontrollers. HVP programming is the only way to regain control of an AVR uC that has received wrong "fuse" settings, like I did with RSTDISBL=on.

An OM asked me to program a couple of ATmega32, he sent them over but they were not reacting to my serial programmer. A quick check with the Engbedded AVR Fuse calculator swapping high and low fuse bytes suggested that the previous owner had mixed them up, locking the chip to HVPP.

So I built the Polish circuit using an ATmega168 as the fusebit doctor on the protoboard. Pictures show the mess of wires, but it worked nevertheless. While I was at it I also recovered my locked 2xATmega168.
Green LED = chip rescued!

05 September 2012

Adding contact information to digital storage media

Following my own year-old post about backing up digital contents (pictures/videos) while on the go, I want to share a simple idea against the physical loss of digital storage media.

Unlike a mobile phone, when a digital (video)camera is forgotten somewhere, there is usually little or no means of getting it back to the owner. While the electronic device itself can be easily replaced, it is not the case for the digital content that has been stored on it. So, how about adding your own contact information to your digital storage media? If it falls in friendly hands then there are good chances it will be returned.

I came up with these ways of making our digital belongings:
  • handwrite an email address on the storage card (SD/SDHC, CF, TF, xD, ...) with a permanent marker, if there's room for it [your mobile phone may have been lost/stolen together with the camera, so just a phone number is not a safe idea]
  • create a README.txt or OWNER-INFO.txt file in the root folder of the storage card containing contact information, return info, reward, ...
  • create a digital picture containing contact information (the same of the README.txt file) and place it amongst your other pictures
The latter suggestion comes in handy if who rescues your lost device decides to browse through the content instead of plugging it to a computer. Imagine this: you find a digital camera on a bench, you check the content and find a picture showing owner's phone number, you call/text that number and return the device right away.
Oh, by the way, you don't have to edit the picture on the computer: write everyting on a large piece of paper and take a picture of it ;-)

Writing your details on the digital camera may make it less attractive for a future sale, but it can work as well as long as the card is not removed (i.e. for a sale). Remember that your main concern is to recover your memories, not the device itself.

03 September 2012

RasPi from RS delayed

Not that I am longing for another Raspberry Pi, but I got an email from RS that my order with them will be shipped about 4 weeks later than expected. Weird, since Farnell was weeks early! Maybe there is an unbalance of orders they receive?

This is a good chance to cancel my order with RS, unless someone in a hurry wants to buy it from me (how much I paid it + S&H to your doorstep).

23 August 2012

How to measure coax cable velocity factor

A recent (2010 AD!) discussion on an Italian forum tried to answer the question: "how to measure coax cable velocity factor?" Depending on the cable dielectric and size, vf is between 0.6 and 0.9.

If you have an antenna analyzer, such as the MFJ-259, it's easy, since the device will do it for you. Just follow the instructions on the user's manual.

If your instrument doesn't allow that, then you will have to proceed with trial and error. For example connect a known non-inductive impedance (resistance) on one end and look for the frequency where the same impedance is shown on the other side of the unknown cable. This condition occurs at multiples of lambda/2, so choose your frequency accordingly. The resistance must be different from the line impedance.
Edit 2013-10-22. OM Don adds that due to the intrinsic feed line attenuation, the resistance seen at the generator's side will be less than the face value. Obviously "how much?" depends on line length and test frequency, but could be in the order of ohms or fractions.

With a two-channel oscilloscope another comparison can be done, on two sections of the same cable, same length. Feed cables with a power splitter and observe the signal at both far ends: if waveforms are out of phase, then your two cable sections have different vf.. From this point you can use your imagination to work out other measures the o'scope can provide...

09 August 2012

Raspberry Pi arrived and tested

My RasPi from Farnell arrived 3 days after the shipping notificaton. It came with regular mail from UK.

Setting it up was not so straightforward:
  • pushing the operating system ISO to the SD card was not so easy with MS Windows
  • I had no USB keyboard at home
  • I have no HDMI-capable screen, at home
  • I had no DHCP-enabled network to connect it to
With the help of a colleague I got a working SD card and put my RPi on the net. I ran few apt-get's to update it and install gcompris and childsplay packets. Unfortunately there isn't much choice of software ported to the ARM processor. No problems to get a vncserver running at a decent resolution or 1280x900 over the 100 Mbps network link.

At home I used the composite video out to test how functional it can be, but the result is not encouraging. Both childsplay and gcompris require a minimum screen resolution that is larger than what is available on TVout, while they run OK on the existing home computer + LCD screen.

On the other hand it may work as a digital media center with OpenELEC, but I haven't had the time to test it in the real world. But I can imagine the burden of wires around/behind the TV if an external hard-disk is added, then a USB-to-WiFi adapter, a powered USB hub ... not charming at all!

My RasPi test drive impressions are that it has enough computing power to do interesting things, with an excellent performance/price ratio. I am a bit skeptical about its usefulness in bringing youngsters closer to in-depth computer science and programming. And I doubt I will have much use for it. :-(

24 July 2012

Raspberry PI from Farnell

Yesterday I received an email from Farnell stating that my RPi had been shipped (order #ORP051xxx). Since I ordered it the same day I submitted my order to RS, I was expecting a similar 11 weeks delivery time. But it got on my way about 50 days early. Could the recent increase in production capacity have something to do with it? Or most people ordered their copy from RS, since the communication was a tad better?

There is apparently no way to know which express courier Farnell used, nor to get a tracking number. On the other hand, RPi @ RS was paid right away, while Farnell charged my card on the shipping day.

Still no shipping news from RS, though.

21 July 2012

DX's EzTV668 lacks ESD protection diode too

It is amazingly easy to open the EzTV668 RTLSDR USB dongle bought at DealExtreme: make a little pressure with a small flat screwdriver on both sides of the USB connector and the cover will pop up.

I wanted to check whether my dongle has the ESD protection diodes installed...

I was not surprised to find an empty U7 location next to the antenna connector. BAV99 should be the part missing, which costs next to nothing. Plus shipping, of course.

19 July 2012

I.F.R. current

After adding the tuning knob and on request of a fellow builder, I checked the IFR current. The DVM read 16mA with a LCD without backlight. If you need a backlight then add the LED current, 10 to 20mA.

In cases where the power budget is strict, select an LCD that can be used in both cases (like the classic black/green) and add a switch for controlling backlight (or a trimpot).

29 June 2012

Raspberry PI: ordered

The "invitation to order" email came one day late and I have just paid for my RasPI. Order #127xxx, despatch expected within 11 weeks (or 77 days, or mid September).

(up here is a countdown widget in Flash, in case you don't see it)

27 June 2012

avreal32 and lock bits

I feel dumb. I was expecting to see AVR's lock bits LB1 and LB2 amongst FUSES in avreal32 programmer, so I never saw that there is a dedicated option for preventing the readback of the chip content.

The command for locking an ATmega168 is (add your usual programmer definition and options):

avreal32 +mega168 -l2 (programmer parameters)


22 June 2012

SDR# on a Centrino CPU

Not a big achievement, but I want to report that I could use the RTLSDR dongle with SDR# on a laptop running WinXP with an Intel Centrino 1.6 GHz CPU. I have reduced the sampling to 1 Msps and the machine was running at 50% CPU: not bad for a 2004 computer! I listened to both WFM and SSB signals. There is probably room for a higher sampling rate, but keep in mind I have been listening to decoded output and not fed it over to another software (which in turn uses its share of CPU cycles).

20 June 2012

23cm activity

These heard stations on 23cm SSB are some of the local big guns. Well, not so local given the DX distance of 136 km and my antenna consisting of an indoor dipole! But the HB9's were using 200W or more...

HB9BCD at 136 km

I1NDP and another QSO at 1'296'250 kHz

HB9SV at 136 km.

I do not like those aliasing products (or intermod?! or receiver overload?!), which then disappeared when I fiddled with SDR# settings. That effect requires further investigation.

My RX setup was not QRP either, since the i5 core laptop eats up a good deal of energy too (50W or so). I have already shaped up a biquad antenna. Now it needs a reflector and a support, then I am ready for the next 23cm event. Unless I manage to get a signal out of that SAT-TV PLL...