My Fm Transmitter Query

xitronics · 4th September 2005, 05:02 AM

Hello friends.

i have a 1WATT FM Transmitter schematic, to which i design a PCB using Express PCB soft..

at the test, transmission clairity is very good but only for an OVER THE AIR distance of 50-55 mtrs max.. surely much less than my expectation of around 500-600 mtrs atleast...

i used a dipole antenna for transmission with a decent RG8 cable. And the class C amplfier 2N3866 doesnt disspiate significant amount of heat. using a scope i observe no amplification of the osc. freq. arcoss its o/p.. can anyone suggest some modifications to be to the design..

i have posted the blurred schematic of my Tx.. I feel the need for greater inductance across Class C biasing.. and removing Trimmer 2; the one just before the Tx o/p..

Please advice..

________________
Prasanna.

Expectation leads to disappointment...
More expectations lead to more disapoinments.

Randy Knutson · 4th September 2005, 06:42 AM

What are the element lengths of your dipole antenna? Is the antenna near anything which might detune it? Are you sure your output impedance matches the antenna's input impedance?

-=Randy

xitronics · 4th September 2005, 07:03 AM

Sir,

The total dipole length is around 2 meters (1 + 1 mtr). Impedance of the cable is 75 Ohms, as rated with the o/p impd. of the transmitter.. The tx. is tuned to freq. of 102.3 MHz.

And if i use a simple 100cm aerial, then too the range is around 15-20 meters.. not much diff. as compared to the dipole range..

________________

phase_accurate · 6th September 2005, 07:12 AM

Some thoughts: Wavelength at 100 MHz is 3 meters approx so a half-wavelength dipole is 1.5 meters and a quarter-wavelength aerial is around 75 cm.

When using the dipole then use is vertically, since your receiver's antenna is most probably also vertically polarised.

Have you ever checked the output power of your TX into a resistive load ?

Regards

Charles

TwoSpoons · 6th September 2005, 07:49 AM

Get yourself a VSWR meter so you can tune your antenna properly.

xitronics · 9th September 2005, 11:13 AM

Quote:

Originally posted by TwoSpoons
Get yourself a VSWR meter so you can tune your antenna properly.

Could you elaborate more on that pls..

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
PC interferes with FM transmitter	Vermonter	Everything Else	17	19th February 2009 11:53 AM
FM transmitter / PA	Studio1	Tubes / Valves	4	17th July 2008 12:25 PM
My sub is a radio transmitter.	mashaffer	Subwoofers	6	7th April 2006 06:08 AM
FM transmitter	kamathajit2002	Digital Source	2	3rd January 2006 05:01 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

4th September 2005, 06:42 AM	#2
Randy Knutson diyAudio Member Join Date: Mar 2003 Location: Willmar, Minnesota	What are the element lengths of your dipole antenna? Is the antenna near anything which might detune it? Are you sure your output impedance matches the antenna's input impedance? -=Randy

4th September 2005, 07:03 AM	#3
xitronics diyAudio Member Join Date: May 2005 Location: Mumbai	Sir, The total dipole length is around 2 meters (1 + 1 mtr). Impedance of the cable is 75 Ohms, as rated with the o/p impd. of the transmitter.. The tx. is tuned to freq. of 102.3 MHz. And if i use a simple 100cm aerial, then too the range is around 15-20 meters.. not much diff. as compared to the dipole range.. ________________

6th September 2005, 07:12 AM	#4
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	Some thoughts: Wavelength at 100 MHz is 3 meters approx so a half-wavelength dipole is 1.5 meters and a quarter-wavelength aerial is around 75 cm. When using the dipole then use is vertically, since your receiver's antenna is most probably also vertically polarised. Have you ever checked the output power of your TX into a resistive load ? Regards Charles

6th September 2005, 07:49 AM	#5
TwoSpoons diyAudio Member Join Date: Oct 2004	Get yourself a VSWR meter so you can tune your antenna properly.