Calling all radio hams!! - Page 2 - Electronic Circuits Projects Diagrams Free

**Nigel Goodwin** · 19th October 2005, 03:59 PM

Quote:

Originally Posted by pike

The oscillator should work. I pulled it out of the circuit audioguru designed here, the mod4 version that is: http://www.electro-tech-online.com/v...ic.php?t=14899. If it works at vhf I cant see why it wont work at 25.3mhz.

We'll have to wait and see :lol:

That configuration isn't normally used at lower frequencies, perhaps increasing the feedback capacitor might help?.

It's also (as already suggested) fairly vital that both the receiver and transmitter are crystal controlled! - free running oscillators are NOT a good idea!.

Quote:

The first diagram I drew looks iffy, probably because the resistor on the base was supposed to be a capacitor.

Yes, it wouldn't have worked.

Quote:

To save space, I decided to go with a simple prewound choke and capacitor in a series resonant filter setup. The reactance of the capacitor at 36mhz is about 550 ohms where as for the inductor it is about 490. Will this 60 ohms difference matter??

Well it won't resonate at the correct frequency, but the main problem is it won't work very well either! - use another 36MHz transformer as suggested - the Q of the circuit will give magnification of the signal.

audioguru · 19th October 2005, 04:41 PM

Hi Pike,
Harry is a ham and also does some FM transmitters with printed coils. He has a wealth of info on his site and some new ones:
http://web.telia.com/~u85920178/

pike · 20th October 2005, 07:12 AM

Yeh harry is a good man, kind enough to share his ideas. His site was the main basis of this project. Most of the stuff i pulled together has come from his site.

From the reactance formula, i can figure that at 25.3mhz that 10pf capacitor has about 600 ohms. Does that sound high for a feedback capacitor??

*back to the drawing board. :x

EDIT: seeing that if I used the transformer on the aerial, do I just connect the base to the secondary output or do i connect it onto the primary. Connecting it onto the secondary sounds like it will be more attenuative, and have lower gain.

**Nigel Goodwin** · 20th October 2005, 09:33 AM

Quote:

Originally Posted by pike

Yeh harry is a good man, kind enough to share his ideas. His site was the main basis of this project. Most of the stuff i pulled together has come from his site.

From the reactance formula, i can figure that at 25.3mhz that 10pf capacitor has about 600 ohms. Does that sound high for a feedback capacitor??

*back to the drawing board. :x

EDIT: seeing that if I used the transformer on the aerial, do I just connect the base to the secondary output or do i connect it onto the primary. Connecting it onto the secondary sounds like it will be more attenuative, and have lower gain.

Try looking at Harry's site - specifically the TBA120 NBFM receiver!.

BTW, I'm currently playing with PIC Manchester wireless routines, which could be useful if you get your radio working.

pike · 20th October 2005, 12:26 PM

Well I built that oscillator after dinner. It was a 5 minute job but yes it did work!!!, under my freqency meter, the 18mhz signal varied about 7khz. For narrowband this wouldn't be acceptable.

Better stick with crystals.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

19th October 2005, 04:41 PM	(permalink)
audioguru	Hi Pike, Harry is a ham and also does some FM transmitters with printed coils. He has a wealth of info on his site and some new ones: http://web.telia.com/~u85920178/ __________________ Uncle $crooge

20th October 2005, 07:12 AM	(permalink)
pike	Yeh harry is a good man, kind enough to share his ideas. His site was the main basis of this project. Most of the stuff i pulled together has come from his site. From the reactance formula, i can figure that at 25.3mhz that 10pf capacitor has about 600 ohms. Does that sound high for a feedback capacitor?? *back to the drawing board. :x EDIT: seeing that if I used the transformer on the aerial, do I just connect the base to the secondary output or do i connect it onto the primary. Connecting it onto the secondary sounds like it will be more attenuative, and have lower gain. __________________ www.winpicprog.co.uk - Great PIC language tutorials.

20th October 2005, 12:26 PM	(permalink)
pike	Well I built that oscillator after dinner. It was a 5 minute job but yes it did work!!!, under my freqency meter, the 18mhz signal varied about 7khz. For narrowband this wouldn't be acceptable. Better stick with crystals. __________________ www.winpicprog.co.uk - Great PIC language tutorials.