Saturday, August 22, 2015

Pre-Mixed Oscillators

It was not possible to make the stable VFO due to many reasons, mainly lack of styroflex capacitor, not available suitable slug inductor, variable capacitor etc.

Then I wanted something which put me at a spot so that my QRP experiments can be built reliably.

I experimented with various designs , two VWN 40 meter transmitter, two my own CW /DSB transmitters etc.

The Xtals available which can be used directly on hambands are few.

1843 kc
3579 kc
7159 kc
14.318 Mhz
28.322 Mhz ( beware some are not fundamentals)
also 14166kc, 7050kc ,14060kc but very hard to find. They are special order xtals so costly.

But, I can find the 11059kc, 10mhz, 4000kc,4194kc,4433kc etc And using the mixer techniques we can arrive at some frequency which can be used easily.

This is the working module on 14194kc +/-10kc. {Of course it worked for a day on test bench he he... }
scrapped TA7358 mixer board
There is one xtal oscillator 4194kc, A gilber cell mixer in ic TA7358AP LO here is 10.0  Mhz. The output is amplified selectively and filtered.

One thing I learned from vu2dev is putting the pins for interconnections. This is new for me. As previously major fault with my projects were the interconnections become loose during the assembly or boxing. So that's good.

Schematics,,,, wait a little.... please 22aug2015
Stuck once again at the coils... it needs some tweaking. There is some problem .....

31August 2015:

To solve it I first scrapped the coil, amp stage then the ta7358ap stage itself. This DBM got rotten due to over drive from the oscillator. WTF.

Why this happened ???? due to my minor mistake of not using the 1k preset which I previously used in 40 meter mixer. This 1k pot was helping in reducing the power going into the chip. My buffer puts really big voltage. Scrapped above board. Making new board.. once again..... 

04september 2015:
Ohh my god this was the reason my DSB exciter 14194kc did not work.... I need to correct that one.... and use it... good idea...... Removed few parts. Making  it work.

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