Tracking a transmitter - Electronic Circuits Projects Diagrams Free

bkamalnivas · 7th January 2009, 01:18 PM

I need to design a FM receiver to receive a FM signal of specified frequency....and thereby reach the transmitter's place...

what are the things that i need to take into account while designing my Fm receiver....

audioguru · 7th January 2009, 01:53 PM

It is difficult to track an FM transmitter because the FM radio's modulated sound is always at the same level regardless of the signal strength (if the radio is good).
An AM transmitter that is received on an AM radio has its modulated sound fading when the signal strength is low and the sound level increases with increased signal strength so an AM radio needs to have automatic-gain-control.

There is an FM tracking circuit on the internet that rapidly switches two antennas. When the signal on each antenna is the same level then they add. When the signals are so that one antenna is close and the other antenna is farther from the transmitter then the signals cancel. The problem of not knowing if you are facing the transmitter or if it is behind you is solved by adding some phase shift.

flat5 · 7th January 2009, 01:53 PM

An Attenuator. A signal strength meter. A very directional antenna.

Good luck on your T-hunt :-)

RadioRon · 7th January 2009, 05:34 PM

You need to make sure the receiver is well shielded. When you are close to the transmitter, the signal can be picked up by the receiver circuit board directly if it is not shielded and then you lose all of the directional value of your antennas. Prevent this by putting the receiver into a metal box.

Menticol · 7th January 2009, 06:09 PM

Quote:

Originally Posted by audioguru

There is an FM tracking circuit on the internet that rapidly switches two antennas. When the signal on each antenna is the same level then they add. When the signals are so that one antenna is close and the other antenna is farther from the transmitter then the signals cancel. The problem of not knowing if you are facing the transmitter or if it is behind you is solved by adding some phase shift.

Aircraft VOR receivers work that way

KMoffett · 7th January 2009, 06:34 PM

Quote:

Originally Posted by Menticol

Aircraft VOR receivers work that way

No, not VOR. VHF omnidirectional range - Wikipedia, the free encyclopedia

You must be thinking of ADF: Radio direction finder - Wikipedia, the free encyclopedia

Ken

Menticol · 7th January 2009, 06:41 PM

You are 100% right Ken, sorry!

Nice system by the way

stevez · 8th January 2009, 11:50 AM

Amateur radio operators and others participate in fox hunts (there are probably other names for this activity). You might google there.

In amateur radio handbooks there are relatively easy to build attenuators that might improve the usefulness of a normal FM receiver given the concerns expressed in audioguru's comment.

A reflected signal might confuse or complicate your direction finding efforts.

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7th January 2009, 01:18 PM	#1 (permalink)
bkamalnivas	Tracking a transmitter I need to design a FM receiver to receive a FM signal of specified frequency....and thereby reach the transmitter's place... what are the things that i need to take into account while designing my Fm receiver....

7th January 2009, 01:53 PM	#2 (permalink)
audioguru	It is difficult to track an FM transmitter because the FM radio's modulated sound is always at the same level regardless of the signal strength (if the radio is good). An AM transmitter that is received on an AM radio has its modulated sound fading when the signal strength is low and the sound level increases with increased signal strength so an AM radio needs to have automatic-gain-control. There is an FM tracking circuit on the internet that rapidly switches two antennas. When the signal on each antenna is the same level then they add. When the signals are so that one antenna is close and the other antenna is farther from the transmitter then the signals cancel. The problem of not knowing if you are facing the transmitter or if it is behind you is solved by adding some phase shift. __________________ Uncle $crooge

7th January 2009, 01:53 PM	#3 (permalink)
flat5	An Attenuator. A signal strength meter. A very directional antenna. Good luck on your T-hunt :-)

7th January 2009, 05:34 PM	#4 (permalink)
RadioRon	You need to make sure the receiver is well shielded. When you are close to the transmitter, the signal can be picked up by the receiver circuit board directly if it is not shielded and then you lose all of the directional value of your antennas. Prevent this by putting the receiver into a metal box. __________________ RadioRon

7th January 2009, 06:41 PM	#7 (permalink)
Menticol	You are 100% right Ken, sorry! Nice system by the way __________________ La Rotta If you have a problem... If google translate can't help... And if you can find it... Maybe you can use... MS PAINT!

8th January 2009, 11:50 AM	#8 (permalink)
stevez	Amateur radio operators and others participate in fox hunts (there are probably other names for this activity). You might google there. In amateur radio handbooks there are relatively easy to build attenuators that might improve the usefulness of a normal FM receiver given the concerns expressed in audioguru's comment. A reflected signal might confuse or complicate your direction finding efforts. __________________ stevez