24 December 2007

The Joule Thief

I had it ready for months, but never finalized. This Xmas 2007 we needed a simple way to light the Nativity scene, so I took the chance to get it working.

I used the joule thief in its simplest form, as probably published November 1999 issue of EPE (Everyday Practical Electronics). It's a NPN transistor, one resistor, a bifilar transformer and a LED (any color). I found the diagram on the web and worked immediately.

Lighted using a dead saline battery.

Lighted using a dead saline battery. No flash.

The Nativity scene, with room lights ON.

The Nativity scene, with room lights OFF.

How did I wind the transformer? I saw many questions about it around the web. First of all, you need some luck since you're probably winding it on a core with unknown characteristics. I took some length of enameled copper wire (2 metres), bent in half and wound about 8 turns through the core. Windings are spread about on 80% of the core. The core is a ferrite bead recovered from WhoKnowsWhereLand. Try it first with a fresh battery. If it doesn't lit, add some turns and try again. If at 20 turns you still don't get light, then:
  • check your LED is wired properly
  • change the core
Don't forget to scrape off the insulation from the enameled wire at solder points!

Before someone asks, no, I have no spare cores to send around.

With the saline battery my joule thief produced noticeable light (in darkness) for 36 uninterrupted hours. I will measure how much current it draws at the next battery change.

11 December 2007

Driving a LED from TTL/CMOS

It's the first thing you learn about TTL/CMOS chips: they cannot (should not) drive a LED directly. A transistor driver is needed, and is shown at the right in its simplest form.
When the gate output goes high the BJT saturates and current flows through your LED. A limiting resistor is needed to control the LED current.

The table below shows R values vs supply voltage vs LED current.

Vcc R ohm R_ohm R_ohm
3,6 45 30 22,5
4,8 105 70 52,5
6 165 110 82,5
7,2 225 150 112,5
8,4 285 190 142,5
9,6 345 230 172,5
10,8 405 270 202,5
12 465 310 232,5
13,2 525 350 262,5

0,02 0,03 0,04
2 2 2
V_CE [V]
0,7 0,7 0,7

I will need these in my hi-brightness red LED optical MCW transmitter.

13 November 2007

CCD as infrared sensors

This might be obvious to many of you, but it wasn't to me.

CCD, the digital camera sensor, is sensitive to infrared light, such as the one emitted by all kinds of remote controls (if you don't consider prehistoric ultrasound models).

Webcams use CCD as well, so here's a screenshot taken with an old one to prove that it actually works.

The IR generator is a handheld device running the pre-installed IR remote control software.
You can see the lighted IR-LED, a reflection on the left (double-bounce?) and another spot near the top border of the picture.

You can reproduce this experiment aiming a remote control to a digital camera lens. Then press a key while looking at the display.

Perhaps a simple way to explain some physics to kids?

12 November 2007

Antenne Yagi per usi portatili - Q&A

Data la visibilita' che ha questo blog tramite alcuni motori di ricerca (e' una semplice constatazione), postero' qui in forma anonima le domande e risposte che ricevo sul mio articolo pubblicato su Radiokit Elettronica di novembre 2007.

La prima domanda riguarda il fissaggio degli elementi: c'e' un accorgimento particolare per evitare che ruotino attorno all'asse del boom?

No. L'incastro e' molto stretto, al punto che e' quasi impossibile inserire l'elemento a scatto senza farsi male, ma si deve farlo scorrere sul boom fino al punto previsto.

Avevo il problema della rotazione con i giunti a T forati, che dopo un po' perdevano di robustezza, ma con questi ad incastro gli elementi rimangono dove li metti. Il problema e' invece riuscire ad allinearli sullo stesso piano.

Bisogna tenere presente che comunque si tratta di antenne per installazioni temporanee, dove l'importante e' la rapidita' di s/montaggio e il peso. Il resto e' grasso che cola.

Eventualmente, se i propri incastri sono troppo laschi, si puo' montare l'antenna a testa in giu', con il boom in alto e gli elementi appesi come dei pipistrelli.

29 October 2007

Multiband beam (70 MHz)

I have no experience on this matter, so this is a purely theoretical post.

If looking for a directional antenna that covers 50 MHz, 70 MHz and 144 MHz, why not consider a log-periodic? With a boom of 4.5m, max width of 3.6m and 11 elements, three bands are covered. A matching system is needed.

Another version, probably with a better impedance range but lower gain, counts 15 elements over a 5m boom.

So, there's plenty of room to play with. Just need to put to work some simulation software and then cut lots of pipes...

22 October 2007

Antenna tuners are reversible

I'm back on posting after a few weeks without any shack or lab activity.

I had few minutes to spare, so I wanted to do a measurement on my homebrew LC switched antenna tuner. I wanted to see what kind of impedance range it can match. How? Read on...

The LC circuit is a bidirectional quadripole, so it can be used in any direction: close one end on 50 ohm and measure R-jX on the other.

I used the MFJ-259B to do measurements, so I have no idea if "X" is inductive or capacitive. I closed the antenna side on a simple 50 ohm resistor (2x100 ohm in parallel) and flipped switches all around to see what the instrument showed.

On all HF I could read low R with highX (probably the equivalent of a short whip) as well as moderate R&X (a long non resonant, non half-wave, wire). I was concerned the capacitance swing was somehow wrong, but my feelings were wrong and the tuner actually does the job.

28 September 2007

Closed for holidays

About to take a short vacation, with lots of open projects:
  • FT-817 hands free adapter
  • Finishing 4m TX #1
  • Rebuilding 4m TX #2 (it has a short Vcc-GND on the ICS512 adapter)
  • Put into an enclosure the NiMH constant-current charger
  • Adapt two relays for 7A13 Tek plugin
  • Put into an enclosure the Cisco 7960 headset adapter
That's it for the circuits laying on the workbench. Pending circuits list is much longer...

25 September 2007

Controlling canned oscillators

For a number of projects it might be interesting to control the frequency of a canned oscillator. Some of them have a control pin, others an enable pin, others... no option.

There are two possibilities, one of which should always work:
  1. controlling the voltage supply
  2. controlling the load capacitance
The latter works only if the module does not include an output buffer. Most recent canned oscillators should be insensitive to load C variations.

The voltage supply control apparently works on all canned oscillators. You'll need to map your oscillator behavior vs. voltage, but a few Hz shift can be achieved, say 200Hz at 30 MHz, that is 0.06%.


17 September 2007

Tektronix 7A13: broken relays

Relays sit on sockets, so it's very easy to test them outside the original location. Pinout is printed on one side and, before you worry, they're reversible. Surprise: they have 8 pins per side, but row spacing in just 1 pin, so they don't fit on the breadboard as an IC would. So I built an adapter...

If you notice my adapter has 4 pins on one side and only 3 on the opposite: it's because I ran out of pins. But these Tek beauties are reversible, so 5 pins would be enough.

Result of testing 2 relays: out of total 4 switches, they all show continuity in the rest position and only one in the switched position. All others do "click" but don't close the contact. #@£!!

These DPDT relays are Tek 148-0034-00, 15V 600 ohm. No chances to get a direct and new replacement.

But the 7A13 plugin has two other relays with the same part#, used to reduce the bandwidth to 5 MHz. The default position (relays in "rest") is "full BW", that is what I am more likely to use (RF vs. LF). I did not check these K480 and K490 for proper operation, but a self-transplant restored 2x and 5x V/div ranges.

If no other relay is available, use a short jumper to close the contact of interest and live with it.

14 September 2007

Tektronix 7A13, debugging

I have a Tek 7A13 amplifier plug-in that shows a problem. The 1V:100mV:10mV/div ranges work fine, but others don't.

With both inputs at GND, trace centered on the screen, changing to a 2x or 5x voltage range brings the trace down a couple of divisions. If a signal is injected in 2x or 5x ranges, nothing happens. A signal can be injected this way:
  • bring to (+) 0.000V the internal voltage generator
  • set both inputs to GND and POSITION the trace on mid screen
  • set IN+ to Vc: you're now comparing the voltage generator to GND
  • slowly increase the voltage
If the range setting is working, the trace will move up and down together with the voltage. Return the generator to 0.000 and change range: if the trace jumps, there's a problem.

And here the original paper documentation becomes useful. Since only three ranges work on my unit, I started my search from board 1, where the selector is located.
Amongst all poles, there's one that drives two relays, namely K47 and K48, in all ranges except those that work. They control a resistive network on board 3. Ouch!, BTW, this is also described in the "Circuit Description" section of the manual!!!

So there is the possible culprit: a relay, a contact on the rotary switch or a connecting cable between boards.

I will inspect it soon...

07 September 2007

4m TX - foto

Ecco come si presentava il TX il 6 settembre 2007:

Da sinistra a destra: filtro C-L-C, BNC e rele', 74AC08, moltiplicatore x5 e, in alto, il regolatore a 5V.

Il rele' nella posizione di riposo (non alimentato) gira il segnale del BNC verso l'RX. Questo connettore di uscita verra' aggiunto quando il TX sara' inscatolato. Peraltro tra il rele' e il BNC vorrei inserire un filtro passa-banda o passa-basso. A circuito acceso il rele' manda in antenna il segnale del trasmettitore.

Il filo nero che si infila sotto il quarzo e' un rudimentale tasto CW. Il quarzo lo tiene a massa ("key up").

Il rele' e' collegato direttamente all'alimentazione a 12V, dato che usando un RX separato l'oscillatore deve essere spento durante la ricezione. Ecco perche' a riposo il contatto ruota l'antenna sul connettore che ancora non c'e'.

Comb Generator - measured

I built the circuit in about one hour. With an accurate selection of NOR gates usage, the signal can be routed through the 74HC02 simply bending pins inwards:

This build is a preliminary version to verify my assumptions (the theory). I used a 14.000 MHz XTAL and I didn't care to keep leads short or add bypass capacitors: the more noise the better.

The 100 MHz frequency counter could measure the 14 MHz signal at the oscillator but went crazy when picking up the output, showing 3.8 MHz or so. Perhaps the glitches were too fast?

On the spectrum analyzer the output looked like this:

45-150 MHz, marker 70 MHz

150-450 MHz, marker 210 MHz

Comb teeth are 14 MHz apart (XTAL frequency, not XTAL/2 as stated in a previous post). Measured harmonic levels are as follows:

MHz dBm
42 -14
56 -14
70 -13,4
84 -14,4
98 -12
112 -15
126 -13,3
140 -17
154 -16,5
168 -18
182 -20
196 -21
210 -23,3
224 -28
238 -28
252 -34
266 -35
280 -43

Note: 42 MHz is estimated.

Up to 150 MHz levels are quite constant. The further quick decrease is probably amplified by the attenuation of RG58 cable used for measurement.

I cannot explain the notch at 294 MHz (lambda ~= 1 meter), maybe some series resonance in the measurement setup? Or an expected zero on the spike spectrum? Higher harmonics are between -35 and 40 dBm up to 450 MHz.

Conclusion. Although the comb is obviously not leveled it is useful for comparative measurements on VHF/UHF filters:
  1. take note of levels without filter
  2. insert the filter between the comb generator and the spectrum analyzer
  3. tune the filter and measure harmonic levels and compare with step 1
Add-on. A small trimcap on the output of the delay gate may vary the output duty-cycle, thus modify the theoretical spectrum roll-off in case measurements fall in the ~300 MHz range.

06 September 2007

Comb Generator - simulated

After checking few times the paperwork with logic states to confirm the expected behavior, I tried simulating the comb generator circuit.

I used NOR gates instead of NAND because I will build it with a 74HC02 and not a 74HC00, but the effect is the same.

I found a Java-based logic simulator called logsim. It does not produce output vs. time plots, so a D flip-flop is added to evaluate the effect of propagation delay (as described in logsim manual).

Here is the diagram. Don't forget to RTFM.

Results so far: in theory, it works. Simulated, it work. Will it work?

05 September 2007

Comb generator, preliminary

This is a preliminary circuit diagram of a comb generator using a 74HC00/74AC00:

The first gate is biased as a XTAL oscillator. I picked 10 MHz but any HF junkbox rock will probably do. Pretty standard stuff.

The second gate is a simple buffer for the oscillator output. Makes sense.

The third gate delays the signal of few nanoseconds, enough to produce -hopefully- a glitch in the 4th gate output. Will it work?

The R-R-R network is a simple ~10dB ~50ohm attenuator pad to match the impedance to 50 ohm loads (D.U.T. - Devices Under Test - mainly HF/VHF filters in my case).

According to my paperwork the comb peaks should be separated of half the XTAL frequency.

I've always wanted to put to a good use TTL gates propagation delay! Let's see...

Filtro passa-banda per i 70 MHz difettoso

La realizzazione presenta una attenuazione di 80dB alla frequenza fondamentale. O c'e' una saldatura fredda o ho sbagliato qualcosa.

Primo passo di debug: rimuovere uno dei due condensatori da 100pF usati per arrivare a 212pF. Forse il compensatore usato (fonte: cassettino dei recuperi) e' di capacita' troppo elevata.

Se la situazione non migliora abbozzo al volo un filtro passa-banda LC riciclando i due C da 100pF e l'induttore di cui gia' dispongo:

Se proprio non ne esco, ripristino l'uscita dell'antenna a valle del primo filtro originale e controllo che la potenza sia quella di prima (21dBm).

C'era una saldatura fredda! Diamine! In realta' si era staccato il collegamento tra l'uscita della porta NAND e il primo LPF. Ovviamente avevo gia' fatto tutto il debug indicato sopra.

Il "finale" non si e' bruciato, e infatti all'uscita del primo LPF ci sono ancora 21 dBm.

Alla fine ho lasciato solo il filtro BPF ad un polo indicato nella figura ed ho ottenuto i seguenti livelli:

[MHz] [dBm] [dBc] [dBm] [dBc] [dBm] [dBc] [dBm] [dBc]
70 14 0 14 0 21,5 0 13 0
140 -35 -49 -38 -52 -19 -40,5 -45 -58
210 -40 -54 -40 -54 -19 -40,5 -46 -59
280 -52 -66 -49 -63 -26 -47,5 -69 -82
350 -47 -61 -35 -49 -24 -45,5

470 -50 -64 -56 -70 -28 -49,5

La potenza e' scesa, di moltissimo. Il filtro al momento non e' sintonizzabile... urge costruire un "comb generator" per misurarne l'effettiva risposta in frequenza.

04 September 2007

Cosa manca in un'auto

Hai acquistato un'auto nuova o usata ad estensione del parco macchine, non in sostituzione di un veicolo: cosa le manca per renderla confortevole?
  • giubbottino catarinfrangente (obbligatorio per legge)
  • ombrello
  • stracci per i vetri
  • tappetini
  • parasole da parcheggio
  • carta e penna
  • cartine stradali della citta'/zona (se non si dispone del navigatore satellitare)
  • auricolare del cellulare
  • (supporto per) telepass
Se si e' radioamatore:
  • base magnetica
  • antenna
  • cavo di alimentazione RTX dall'accendisigari (controllare la polarita'!)
Se si hanno bambini:
  • seggiolino/rialzo (obbligatorio per legge)
  • giochi
  • tendine parasole
E probabilmente altro ancora...

31 August 2007

Filtro passa-banda per i 70 MHz

Usando RFsim99 ho progrettato (fatto progettare al programma...) un filtro passa-banda centrato a 70.3 MHz con larghezza di banda di 15 MHz:

Richiedendo una larghezza inferiore i valori di alcuni componenti diventano molto critici e difficilmente realizzabili.

Gli induttori sono realizzabili con:
  • 24,153 nH: dia 5mm, len 7mm, 3 spire
  • 1,061 uH: dia 8mm, len 18mm, 19 spire
Date le basse potenze in gioco i condensatori saranno semplici ceramici affiancati da comuni trimmer capacitivi.

Questo filtro avra' il doppio compito di abbellire il segnale trasmesso e di filtrare un po' le stazioni radio FM verso il ricevitore.

29 August 2007

Confronto filtri di uscita

Prima di chiudere definitivamente il progetto del TX QRP per i 70 MHz ho voluto provare un altro tipo di filtro di uscita, quello a pi-greco. Entrambi sono descritti in un documento trovato in rete.

Cosi' ho sostituito il LCL con un RCLC, dove R era di 100 ohm in serie all'uscita della porta AND. La potenza risultante era nuovamente di 14 dBm (25mW) su 50 ohm e si notava un leggero peggioramento sulla risposta alle alte frequenze (colonna "LPF pi").

Ho poi rimosso la resistenza da 100 ohm pilotando direttamente il filtro con la porta logica. Non so quanto essa gradisca il trattamento, ma la potenza di uscita e' balzata a 21,5 dBm, circa 140mW. Peccato che le armoniche siano solo 40 dB sotto la portante (colonna "LPF pi NO R").

[MHz] [dBm] [dBc] [dBm] [dBc] [dBm] [dBc]
70 14 0 14 0 21,5 0
140 -35 -49 -38 -52 -19 -40,5
210 -40 -54 -40 -54 -19 -40,5
280 -52 -66 -49 -63 -26 -47,5
350 -47 -61 -35 -49 -24 -45,5
470 -50 -64 -56 -70 -28 -49,5

Il grafico mette a confronto i tre tipi di filtro di uscita fino alla sesta armonica:

Altri valori misurati. Su "sonda a RF" 1,16V efficaci, ma a questi livelli di potenza e' un valore poco significativo.

L'assorbimento in TX e' passato da 44 mA a 60 mA. Considerando i 33 mA in stand-by, 5*(0,06-0,033) = 0,135W IN. Qualcosa non quadra in questi calcoli, ma forse ci vorrebbe il dettaglio dei singoli assorbimenti.

Provero' ad aggiungere un ulteriore LC per attenuare le armoniche.

28 August 2007

Telescopic VHF/UHF antenna

This is a 30 minutes project that I did in the pre-Internet era. I wanted an antenna for my VHF handheld that would outperform the rubber duckie.

Easy: take something metallic some 50cm long that is self-supporting vertical.

I had a telescopic antenna whose length reached 50cm. Its base diameter fit loosely into a PL-259, so I screwed a thick wire to the antenna base and soldered the other side to the connector pin. I kept the antenna away from the outer ring, and vertical, with some pieces of rubber (probably RG58 black coating) pressed in with a screwdriver.

When closed the antenna is about 12cm long, including the PL259. Of course the size of any reproduction will depend on the telescopic antenna used.

(pictures not in scale)




Connector detail, FWIW

So I have 12 to 50 cm of radiator, which equates to a 1/4 lambda between 140 and 625 MHz. So it covers both VHF and UHF (and 220 MHz) HAM bands with a simple movement, and anything in between or above. It is not a multiband antenna: you need to retune it for a band change.

This antenna has now turned into a VHF/UHF facility that permanently sits in my car, together with the magmount base. The fully extended whip did not mind travelling at 130 km/h.

As a bonus you can use a similar antenna as a signal pickup on a monitor receiver when testing homebrew transmitters.

27 August 2007

Air core coils. An update

I'm willing to try a different output filter topology on my 4m TX, so now I need a 113 nanoH coil. I would also like to fit the transmitter into a metallic box to see if RF leakage during stand-by becomes more acceptable.

113 nH is 5 turns on 8mm diameter (drill bit), about 10.5mm long.

I decided to try with a thicker wire, say 1mm diameter. Even if I wound it using some good finger pressure, it did spring back. But they are only 5 turns, so once the support was removed I tightened the coil with a circular finger/hand movement.

Now I have a self-supporting 8x11mm coil whose inductance can be adjusted by stretching/compressing it.

So the coil wire diameter vs. coil diameter plays an important role on the need for a permanent coil former. How to find out? I haven't come up with a rule, sorry! Try and see, and YMMV.

23 August 2007

Misure sul TX per i 70 MHz

Il TX e' ultimato, o almeno diciamo utilizzabile se si dispone di un'antenna per i 70 MHz.

Ho scoperto di avere accesso ad un analizzatore di spettro (45-1200 MHz, step 50 kHz), non propriamente pensato per i segnali "CW", ma che almeno mi permette di tarare il filtro di uscita e stimare la potenza RF generata.

Il test e' stato effettuato usando 4-5 metri di RG58 tra TX e analizzatore, l'unico cavo a 50 ohm che ho intestato con BNC al momento. Questi sono i valori ottenuti:

[MHz] [dBm] [dBc]
70 14 0
140 -35 -49
210 -40 -54
280 -52 -66
350 -47 -61
470 -50 -64

Circa 14 dBm alla fondamentale, su 50 ohm, sono 25 mW. Sinceramente speravo qualcosa di piu', ma i dati sull'assorbimento di corrente l'avevano preannunciato:
  • 33 mA in stand-by
  • 44 mA in TX
Sono 11mA di differenza a 5V, ovvero 55mW IN. Efficienza del 50% sulla singola porta AND del 74AC08, non male.

Se si va a "scavare" nei bassifondi dei dBm sull'analizzatore si vede che c'e' moltissimo rumore sotto i -60dBm, portanti varie, ... l'oscillatore e annesso moltiplicatore per 5 non sono proprio silenziosi...

Ho anche notato una certa fuga di segnale verso l'analizzatore di spettro quando il circuito e' in stand-by. Si misurava -47dBm a 70 MHz e -61 dBm alla seconda armonica. Forse con un po' di schermatura il problema si risolve.

Ecco il circuito:
La bobina a sinistra fa parte del filtro passa-basso a pi-greco (v. post successivo).

Chi vuole tentare il QSO? :-)

20 August 2007

Air core coils. Yeah, sure!

"Yeah, sure!" was the typical answer of my friend Urska when our requests were too awkward.

For my 4m TX I computed number of turns vs diameter vs length for a couple of air-cored inductors (output filter) using "mini Ring Core Calculator" software.

I picked round diameter values (10mm, 20mm) and adjusted length until I had an integer number of turns. Took adequate lengths of enameled wire and started winding on drill bit. 1 2 3 4 5 turns, done, release finger pression... CLANG! The coil springs back to a wider diameter and fewer turns.

Changed wire with a thinner one, same result plus a more instable coil.

Lesson 1: a coil former is needed. It will hold the wire in place, forever.

But I don't have any 10/20mm former!

Lesson 2: compute the coil according to available coil supports.

I have spare 16/25mm PVC pipe cut-offs. 16mm was behind the door (literally) and large enough. Re-computed coil lengths, cut the pipe to host the wire plus some extra as support.
I also cut a strain relief guide on both sides of each former that keeps the wire in tension.

Il TX per i 4m prende forma

Ecco come appariva due giorni fa, prima che aggiungessi il driver/PA:

La basetta ramata e' quella da cui ho ricavato l'adattatore SOIC, il chip e' un moltiplicatore di clock ICS512. Acceso con una batteria da 3V c'era un bel segnale a 70.308 MHz.

17 August 2007

SOIC to deadbug extender

The "SOIC to DIP adapter" presented here actually is a "SOIC to deadbug extender", since I never spoke of drilling holes and adding pins. Did I?

In the final version I also drew diagonal cuts towards the adapter corners so that the two inner pads have a larger, triangular shape, which is much easier to handle.

Here's a SketchUp of the chip and extender:

Got the picture now? And, by the way, it works as expected! I soldered the SOIC8 with a 0.6mm RoHS Sn and 15W iron (1mm tip or so). No flux, no other helper: just a steady hand, a lot of patience and some luck.

16 August 2007

Cheap eBay XTALs

In April 2006 I bought a batch of XTALs via eBay from a Chinese shop. The shop is still open (16 August 2007) but currently does not list XTALs.

I took 2x7030, 4x14060 and 4x14020 kHz: 10 XTALs for 18 US$ shipped. Good deal! Not so...

I recently planned to use those XTALs for my homebrew 4m TX , which started to come to life on August 14th, 2007.

On a Colpitts test oscillator, the 14060k XTALs was resonating on 14020k. OPS! The 14020k was close to 14060kHz. I tested a couple more crystals and the mis-marking was confirmed. The 7030k rock went on at 7028kHz, which is reasonably close to the marked frequency, and perhaps my oscillator was pulling it a bit.

Lesson learned? Be careful with cheap components on eBay!

09 August 2007

SOIC to DIP homemade adapter - w/pictures

You didn't ask for it, but here is my process described with pictures.

NB: I take no responsibility for whatsoever damage you may do to any animated or inanimated object. Do it at your own risk.

Sit the IC (or an identical one) on the board and hold it in place with a crococlip, near a corner of the board.

Mark on the PCB empty areas between pins using a permanent marker with 1mm tip.

With a SOIC-8 you'll get 3 marks per side

Very carefully with a cutter and a ruler draw connections between
twin marks on each side of the IC, and extend them beyond your marks

Then etch. Note the original marks...

With the cutter also etch a line across in the middle, so that you'll have 8 pads once you cut the copper clad board with your favorite method so that the PCB is composed of 8 pads

Last but not least, check insulation between adjacent pads with an ohm-meter, "dig" more with the cutter if you measure zero ohms. I discovered that you can emboss the etch if you hold the cutter slightly diagonal.


08 August 2007

SOIC to DIP homemade adapter

Got the ICS512 chips for the 4m TX and I suddenly have to deal with a SOIC-8 package. I remember seeing some solutions around the web for adapting SOIC to DIP, to which I'll add my own:
  1. Sijosae's DIY Gallery, scroll down to "Tip"
  2. commercial adapters (search for "Browndog", or check what Futurlec or eBay offer)
  3. The saltwater etch process
  4. my own cutter etch process
I cannot quickly buy the commercial adapter. I also seem unable to use Sijosae's method(s), and I don't want to abuse the chip since I've gotten very few of them. So I'll go for the 4th method.
  • Take a piece of unetched PCB.
  • Sit the IC (or an identical one) on the board and hold it in place with a crococlip, near a corner of the board.
  • Mark on the PCB empty areas between pins using a permanent marker with 1mm tip. With a SOIC-8 you'll get 3 marks per side. The result:
__ __
__ __
__ __

  • Remove the chip
  • Very carefully with a cutter and a ruler draw connections between twin marks on each side of the IC, and extend them beyond your marks:

  • With the cutter also etch a line across in the middle, so that you'll have 8 pads once...
  • ...you cut the copper clad board with your favorite method so that the PCB is composed of 8 pads
  • Check insulation between adjacent pads with an ohm-meter, "dig" more with the cutter if you measure zero ohms
  • Pre-solder pads
With a little patience and firm hand you can produce several adapters in a row.

That's it. Hopefully I'll add some pictures of the process.

06 August 2007

Finally on the air with 5 elements

In mid-July 2007 I tried the 5 element VHF Yagi out on the field.

Supporting mast was the lower section of a fiberglass fishing rod ("telescopocket 4"). Antenna performance was good. Beamwidth not much tighter than the 4 el., but I did notice better signals and reports were encouraging.

There's still one goal to reach: use a telescopic fishing rod as boom, but given its conical shape I can make up a good element-to-boom fixing harness.

03 August 2007

Transverter 4-10 di OZ2M in kit

A questo link ci sono tutte le informazioni per comprare o riprodurre un transverter 4-10 metri in kit: http://rudius.net/oz2m/70mhz/transverter.htm

Il costo indicativo e' di 125 euro + le commissioni di pagamento (bancarie o PayPal).

In ogni caso lo schema elettrico e' pubblico e vi si puo' attingere per le proprie realizzazioni.

31 July 2007

Chip interessanti

Prodotti dalla IDT, ovviamente non disponibili in Italia, ma recuperabili da fornitori internazionali:
  • ICS672-02: "quadrature delay-buffer"
  • ICS512: "clock multiplier"
Con il primo, partendo da un riferimento HF XTAL o TTL si puo' ottenere un output fino a 200 MHz con fattori di moltiplicazione fissi. In piu' l'integrato fornisce l'output moltiplicato con le quattro fasi per pilotare un QSD (RX SDR, slurp!).

Il secondo invece serve semplicemente da moltiplicatore di frequenza 2x, 2.5x, 3x, 3.333x, 4x, 5x, 5.333x, 6x, 8x con output fino a 200 MHz.

Entrambi sono in contenitore SOIC, ancora saldabile con le normali attrezzature casalinghe.

Ecco risolto il problema della moltiplicazione in frequenza per arrivare a 70 MHz partendo da un quarzo, oppure per pilotare un transverter!

30 July 2007

Homebrewing for VHF

Seen this article list on GQRP list, compiled by Mr. Sholto. Mainly AM TX/TRX, which can obviously become CW equipment. On 4m too!

The 2T/2M (2 Transistors on 2 Meters)
QST p31 1968 September
R. J. Schlesinger, K6LZM
12v 2 transistor AM phone transmitter. 1.2W

The Connecticut Bond Box
QST p11 1968 August
Doug DeMaw, W1CER
A solid state transceiver for 144 Mc.
AM phone 0.25W @ 12v.

The 2-Meter QRP Mountain Topper
QST p11 1970 May
Richard Preiss, W7HCV
Solid state 2W compact phone rig.

A Featherweight Portable Station For 50Mc
QST p25 1964 November
Edward P. Tilton, W1HDQ
A complete 50 Mc phone rig including power supply. 50-100mW

A 2-Meter Transmatch With SWR Indicator
QST p39 1969 March
Doug DeMaw,W1CER
Transmatch with forward & reverse power measurement

Mighty Four On Six
73 Magazine p24 1967 November
E.R. Davisson, K9VXL
A low cost, 4 transistor AM transmitter for six meters.
Looks to be around 300mW at 12v

More Power On 144MHz With Transistors
QST p11 1969 August
David F. Becker, WA6BWP
A 7W@12v (28W@28V) 2M exciter and matching modulator and psu.

6 Meter Exciter
73 Magazine p52 1968 September
Kenneth W. Robbins W1KNI
Hybrid 6m exciter with 6CL6

Six Meter Transceiver
73 Magazine p62 1968 September
D.P. Bryan, W2AJW
Solid state 2W AM phone rig for 50MHz.

2N2 Receiver
QST p11 1965 January
Douglas A. Blakeslee, W1KLK
A simple 144 Mc Superregenarative receiver.
2 Nuvistors for 2 meters

23 July 2007

Per cinque per i quattro - simulazione

Ho provato a simulare con RFsim99 il circuito proposto dalla Wenzel per moltiplicare tramite porte HCMOS la frequenza di un quarzo. Ho ipotizzato 5 ohm come impedenza di uscita e 50k quella di ingresso di una porta.
Il condensatore da 4pF in parallelo all'uscita rappresenta la capacita' di ingresso di una porta logica 74HC/74AC.

La curva rossa riporta la risposta del filtro, con un bel picco a 70 MHz. La curva blu e' invece l'adattamento all'ingresso, ma e' poco rilevante al fine di questo circuito.

Un induttore da 827nH lo si puo' realizzare:
  • in aria con 9 spire su diametro 20mm lunghezza 30mm
  • con 16 spire su T50-10
  • con 4 spire su FT37-61
Il Txx-6 (giallo) va bene fino ai 50 MHz, cosi' come il FTxx-43.

20 July 2007

70.100 MHz NBFM dalle parti di Torino

Leggo sul sito dell'ARI di Torino di uno stream mp3 della frequenza 70.100 MHz NBFM.
Ho avuto qualche problema ad aprire il file con Windows Media Player, che non capisce che si tratta di uno stream continuo. Ho scaricato parte del file con wget sotto Linux, convertito in formato wave e analizzato con Spectran (impostazione QRSS3):

La registrazione ha molto rumore e si sente la compressione mp3. Ma forse ho solo beccato un momento di molto QRM.

17 July 2007

Una precisazione importante sull'IC706MKiiG in 70 MHz

Una precisazione sull'IC706, prima che troppi semiconduttori vengano sacrificati invano.

L'apparato esteso in TX, se mandato in trasmissione a 70 MHz, da' l'impressione di emettere qualcosa. Misurando la potenza emessa su carico fittizio probabilmente si rileva della radiofrequenza.

Cio' non significa che l'apparato stia effettivamente generando RF a 70 MHz. Il wattmetro potrebbe misurare la potenza delle armoniche generate, magari attorno a 140 MHz.

Il responso definitivo lo si puo' solo avere osservando il risultato con un analizzatore di spettro. E' quindi necessario un opportuno approfondimento strumentale prima di dichiararlo usabile sul 4m.

Mi dispiace di aver creato false aspettative ai possessori del 706.

Il ricevitore invece e' genuino, anche se non il non-plus-ultra.

Per cinque per i quattro

La mia idea per i 70 MHz e' molto semplice: utilizzare al massimo
quanto si ha gia' "in casa" e ridurre all'osso la complessita'
circuitale. Una volta che si e' in ballo, l'acquolina vien mangiando e
si puo' complicare a piacimento. Siccome abbiamo pochissimo tempo
(tutti per la sperimentazione, e io per pacioccare), preferisco una via
rapida. Ecco cosa ho in testa.

"In casa" ognuno ha molto probabilmente un (R)TX HF: io lo vedo come un
generatore di segnali modulati. Quindi in un primo tempo si puo'
sfruttare il TX di stazione per pilotare un TX-transverter, senza
impazzire in oscillatori da stabilizzare, modulare, ecc ecc

Alcuni avranno anche un RX che copre i 70 MHz, solo in FM o multimodo
(io ho l'IC706MKiiG). In una Sezione sicuramente ne reperite piu' di

Come arrivo in TX sui 70 MHz? 14.020, 14.040 e 14.060 MHz, se
moltiplicati per cinque cadono nei tre "canali" assegnati. Un
moltiplicatore per cinque semplice l'ho visto qui:
www.techlib.com/files/hcmos.pdf . La potenza RF disponibile e' sotto il
mezzo watt, ma tanto la "stagione E-sporadico 2007" sta per finire.
Descrivendo lo schema a blocchi che ho in testa vedo:
  • TX 20m CW/FM (il moltiplicatore non e' poi cosi' lineare); per l'AM si puo' eventualmente modulare il segnale a 70 MHz
  • attenuatore per avere massimo 5Vpp (con l'817 a 0.5W basta poco)
  • moltiplicatore di frequenza
  • opzionale: amplificatore RF per arrivare a qualche Watt
  • filtro passa-banda a 70 MHz (eventualmente condiviso con l'RX)
In alternativa il TX 20m CW puo' essere autocostruito con un quarzo per
le frequenze QRP 14.060 MHz, reperibile in Internet (USA) a costi

Sto sbagliando da qualche parte? Ripeto, ci sono sicuramente delle
soluzioni piu' eleganti, come i transverter, ma l'impegno che
richiedono non porterebbe a dei risultati conseguibili in cosi' pochi mesi.

Questa sera compro un paio di 74AC08 (porte AND) per tentare la moltiplicazione.

16 July 2007

ARAC 4m Transverter

A questo indirizzo si trova la documentazione storica di un transverter 10-4 metri proposto negli anni '90: http://myweb.tiscali.co.uk/g4nns/ARACTVT.html .
Ci sono gli schemi della parte TX ed RX nonche' il manuale per l'assemblaggio di quello che era un kit. Dagli schemi si puo' prendere spunto per realizzare qualcosa di piu' moderno...

Ziplocking the FT817

I've come across a page describing 25 Uses for Ziploc Bags and since I happen to have one I've added a 26th use: sealing the FT817 when backpacking.

PS: Ziplock bags are not available in Italy. At least not under that name.

13 July 2007

Con cosa operare in 4m?

La bellezza e' che per questa banda non esistono RTX commerciali radioamatoriali. Al massimo si puo' recuperare qualche RTX di uso civile o militare, che pero' e' limitato all'FM e probabilmente canalizzato: bisogna aguzzare l'ingegno. E bisogna anche fare in fretta!
  • l'FT-817 con mio rammarico non copre i 70 MHz: la sintonia salta da 54 a 78 MHz. :-( Non so cosa accada per gli apparati con la TX estesa.
  • l'IC-706MKiiG riceve e trasmette in 70 MHz, pero' dubito che abbia dei filtri di uscita adatti. Si rischia di emettere spurie a non finire! Update 17/7/07: non e' detto che un 706 esteso in TX trasmetta effettivamente sui 70 MHz. Ci sono opinioni discordanti, quindi attenzione prima di fare modifiche affrettate!
Oltre ai transverter commerciali (in kit o assemblati) indicati sui vari siti, l'autocostruzione offre altre due possibilita':
  • moltiplicare per 5 un oscillatore a 14.060 MHz (frequenza per la quale si trovano facilmente i quarzi) ottenendo cosi' un TX in CW/AM/FSK
  • miscelare il segnale a 50.1-50.3 MHz (uscita a bassa potenza dell'FT817) con 20 MHz, un buon filtraggio a 70.2 MHz e si puo' trasmettere "all mode"
La prima soluzione richiede un RX separato; la seconda e' la base di un transverter.