Friday 25 October 2013

AD9850, a Direct Digital Synthesizer IC

If you search on eBay for AD9850 you will find a lot of modules equipped with this nice DDS (Direct Digital Synthesizer) IC. Most of those modules incorporate a 125 MHz Xtal oscillator. The modules are offered often for less than $5.
With this module you are able to build your own sine/square wave generator
that runs from 1 Hz till 40 MHz in steps of 1 Hz.

There is some control required. Homebuilders often use a PIC (for example 16F628A).

VK5TM describes some AD9850 generators on his website. Here you will also find the
required hex files for PIC programming:

Some specifications for the AD9850 chip:

The AD9850 is a highly integrated device that uses advanced DDS technology coupled with an internal high speed, high performance, D/A converter and comparator, to form a complete digitally programmable frequency synthesizer and clock generator function.
When referenced to an accurate clock source, the AD9850 generates a spectrally pure, frequency/ phase-programmable, analog output sine wave.


    125 MHz Clock Rate
    On-Chip High Performance DAC and High Speed Comparator
    DAC SFDR > 50 dB @ 40 MHz AOUT
    32-Bit Frequency Tuning Word
    Simplified Control Interface: Parallel Byte or Serial Loading Format
    Phase Modulation Capability

    3.3 V or 5 V Single-Supply Operation
    Low Power: 380 mW @ 125 MHz (5 V)
    155 mW @ 100 MHz (3.3 V)
    Power-Down Function
    Ultrasmall 28-Lead SSOP Packaging

Friday 18 October 2013

Worked All Continents Award

Doesn't that sound great ? "Worked All Continents". 
It is not that difficult to get this certificate on your "Wall of Fame". You only have to make 6 QSO's.

In  Oct. 2006 I applied for the basic WAC-certificate (mixed mode) with following contacts:

North America : W1ZS (14 MHz, PSK31)
South America : YV5AAX (14 MHz, PSK31)
Oceania : YB0JIV (14 MHz, PSK31)
Asia: RV9WP (14 MHz, SSB)'
Europe: SP6GOX (14 MHz, SSB)
Africa: EA8OI (7 MHz, SSB)

                                                  WAC on my "Wall of Fame"

Allthough I am not an award hunter, this award I treasure.

Here you can read everything about the WAC award and the application:

Saturday 12 October 2013

50 MHz SSB QSO confirmation from Bretagne

Since I do not have the proper outdoor antenna to work on the 6 m band I am not often "radio active" in this part of the radiospectrum. During sporadic E openings in the spring/summer however I sometimes divert to 50 MHz and use an improvised aerial (like an in-house dipole). Apparantly, 24 June 2009, more than 4 years ago, was such a day with Es openings. Today I received the eQSL from Alain, F6HRP from Bretagne, Cotes d'Armer (IN88kn) from the SSB QSO made that day.

A nice begin of the free saturday !

                                           eQSL F6HRP, 24 June 2009

Thursday 10 October 2013

BFG591, ATV amplifier for 1.2 GHz

Some blog entries ago I informed you about my intention to build a 1.2 GHz amplifier with a CLY15 RF mosfet. I ordered 3 of them and did extensive trials. But in the end I had to conclude these devices are to delicate for me. I demolished 2 of them in 5 minutes time and the third provided almost no RF power in my circuit. 
I decided to look for another semiconductor that could help me in the GHz range. Hans, PE1DWA, informed me that a bi-polar transistor, the BFG591 could be interesting. This semiconductor has an Ft of 7 GHz and at 23cm I should easily be able to get 500 mW RF from it. I ordered 5 of them at eBay for about 4 euros.
Yesterday I built this circuit:

                                500 mW 1.2 GHz amplifier with BFG591

Although I have no device to measure the power at this rather high frequency I think half a Watt is a fair estimate that the circuit is producing.
With a bi-quad antenna I could get my signal to the local ATV repeater PI6ZTM. It was verified that the videosignal that came from a DVD-player  arrived at the local repeater. Although signal strength is not high enough to get a clear picture I recognized the transmitted pictures, and they were even in color.

  PI6ZTM repeater picture; in the left hand upper corner my video signal at 1255 MHz

                                          Snapshot of the 1.2 GHz  \  500mW amplifier

This is a good step forwards. In the mean time I ordered an MRF284 which is able to provide 5 Watts at 1255 MHz. Another 3 weeks to wait until it arrives from China...

Note: As you can see, I drawed the circuit by hand. Although I have computer programs to generate a drawing I did it in the old-fashioned way: Pencil & paper. Including scanning this takes me about 10 minutes time. A computer drawing consumes in most cases more than half an hour.

Sunday 6 October 2013

Nice QSO with Sahara

This afternoon I was lucky to find Mohamed, 7X3FG on 28 MHz band in PSK31 mode.
The signal from Mohamed was strong in Holland. My 20 Watt signal on 28.120 MHz was received in good shape as well in Adrar, Algeria in the Sahara desert
Mohamed shows nice pictures of his QTH in Adrar, Algeria in the Sahara on .
Have a look yourself.

Thursday 3 October 2013

Medium Wave tube receiver

Some time ago, one of the members of the Zoetermeer local radioclub, Mans PA2GHJ showed a homemade tube receiver. 

I think it is good, that in spite of the availability of all type of new components these days like PICs, Si570, Atmel chips and so on, there are still radio fans who use the old valve technology.

The receiver is a design with one tube (EF80) and  was designed for receiving AM stations in the medium wave broadcast band. The circuit contains a surprise: The anode voltage applied is only 6 Volts DC. In spite of this low supply voltage the receiver is quite sensitive. Under normal circumstances at least 15 stations can be heard through the headphones.

Here some nice pictures including the circuit diagram:
MW radio with battery and headphones, design by PA2GHJ

Side view also showing Amroh 402 coil

Circuit diagram 1 valve receiver