30 December 2009

Calendario Contest VHF/UHF/SHF Italia 2010 per agende elettoniche

Finalmente, dopo due anni di pausa, per il 2010 sono riuscito a pubblicare il calendario dei contest VHF&up in formato vCalendar che consente l'importazione sulle più diffuse agende elettroniche: online, su computer e su telefonino (direttamente o tramite sincronizzazione con il PC).

Si può scaricare il file dalla home page del mio sito www.paolocravero.tk. Ho anche approntato una miniguida per chi usa il Google Calendar, prelevabile in PDF allo stesso indirizzo.

(EN/US: I have published in vCalendar form the Italian VHF&up Contest Calendar 2010. It's on my main website. It allows to load contest data into electronic organizers, online, local or handheld.)

17 December 2009

Stuck with 50 MHz QRP TX

I have been thinking for a week how to proceed on my 50 MHz TX and I haven't decided yet.

I have one fixed frequency transmitter that puts out some 30mW CW that I could turn into AM (or DSB). This would mix digital circuits with analog transistors.

I have another transmitter on a single chip, XTAL based so that it can work on FM. It's a neat design, it doesn't want to emit a proper 50 MHz harmonic but rather generates weird multiplication factors.

I have spent a good amount of time trying to make the FM TX work, actually to multiply correctly, but I also want to get on the air with an homebrew voice transmitter and AM is the closest...

I will have few more sleeps on this :-)

11 December 2009

Back to WSPRing

These days my RTX setup is collecting dust, mainly because 30m are closed when I would be able to use them (after 22Z). So I decided to spare some electricity and see who could be received in WSPR in this season.

After seeing always the same calls on 30m I tuned to 40m and with my surprise there were a lot of signals, even if my antenna is supposed to be single-band for 30m. On 40m I decoded both Brazil (5W) and Australia (10W).

One disappointment: most reported stations were announcing power levels of 5W or more, with one WSPRing at 50W, wiping out the braves running 1W or less.

WSPR is not a QRP mode. QRP is in operator's brain! Sirs, turn down your power!

09 December 2009

cdzservices.exe hanging mobile devices (mSuite sync problem)

Note: this is a service information not really related to my usual lab activities, but I found no mention elsewhere in the net. I hope to help someone...

On 2009-11-19 the mSuite client on my Windows Mobile smartphone stopped synchronizing. Worse, something hanged the device eating up all its CPU, making it very non-responsive, almost useless.

Looking at running processes I saw that cdzservices.exe was the culprit. It belongs to Commontime mSuite software. It hangs because the Commontime CA certificate has expired on ... 2009-11-19!

So, work with your internal helpdesk and find the new certificate, install it on the mobile device and hopefully it should start synching again. I haven't gotten the new certificate yet! No mention on the Commontime website!

Please post a comment if this post helped you. Thanks.

07 December 2009

My 6m FM TX

Looks like I have finally gotten around the proper deviation for a 50 MHz FM TX, but many problems still have to be tackled down.

I tried to "select" the desired harmonic with the RLC circuit found on a paper online and I had to play a lot with L and C values. The L was wound on a T50-6 core, while C was a 3-16pF trimmer. On the frequency meter I could read 2x XTAL fundamental and a weird 2.5x, depending on trimmer position. After removing almost half of the originally planned turns and making extensive use of the oscilloscope, the output frequency is now steady on 50 MHz.

I even noticed that the frequency changed when loading the "PA" (note that a buffer gate is between harmonic selector and PA), so I did the fine tuning with a 7dB 50ohm attenuator pad and a 50 ohm dummy load.

On the oscilloscope I can read almost 3V peak on the dummy load, which is about 80mW or +19dBm. Given the 7dB pad ... +19+7 = 26 dBm that is 400mW of RF. Not bad for a 74HC240 chip pulled at its operating limit!

In order to minimize stray capacitances I moved components around and now both AF and RF sit on the same copper ground.

It's time to add an LPF and ask for an online report! After a check at the spectrum analyzer, of course!

02 December 2009

Which RX for my 50 MHz QRPp FM TX

I received this question from Pedro, a LU HAM: "What are you planning to use for the 50 MHz FM project receiver?" Here's my answer to him.

Originally I planned to use the TDA7000 chip but configured at NBFM it is not good according to SM0VPO.

Then I switched my mind to TBA120, an FM IF chip from TV sets that works better but it works up to 10 MHz (or somewhere there). Since my TX is single-frequency, as the original SixBox, I thought of using a 50.0 MHz canned oscillator to feed a mixer and tune my IF at 800 kHz (my TX XTAL is 16.934 MHz or so).

Last chance is to use a direct conversion receiver and agree with the other station will reply in SSB or AM, so working a mode-split QSO. I am not planning to build two (R)TX to talk together!

I don't have a diagram of the TX yet. It is based on 74HC240 chip:
- one gate oscillator
- one gate buffer with LC output tuned on 3rd harmonic
- one gate buffer
- 4 parallel gates as PA

The second buffer could be removed but then the 4 parallel gates give about 14pF or capacitance, which is too much for the LC.

I have measured about 28mW at the output of a single 74HC86 gate, so hopefully 4 HC240 in parallel can deliver more, even if at 50 MHz (operating limits).

Let me know if you have some ideas for PA and/or RX!