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Sensitive fm radio

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takne007

New Member
Hello

i have a FM radio. i want to make it sensitive. its sensitivity will be around 15µv. How can I make it more sensitive? is there any stable preamp circuit to increase the sensitivity to 1µv? i have built many bipolar transistor preamp circuits. but they only add noise, and make the signal much worse. could anybody give me an idea/schematic?

thanks in advance.
 

EN0

Member
blueroomelectronics' idea is good, start with a efficient antenna. Then you can feed the signal from the antenna into a preamplifier to make it more sensitive. In addition, you might want to adjust your FM receiving tuning circuit, so that you have a thin tuning bandwidth. For an antenna, I would suggest a dipole to start out with and see how well that works.
 
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audioguru

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The extremely simple "FM preamp" might increase the sensitivity of your FM radio if you are on Mars where there are no strong local signals to overload it.

In a city you will have all the stations cross-modulating all over the dial and all will be heard at the same time.
 

EN0

Member
The extremely simple "FM preamp" might increase the sensitivity of your FM radio if you are on Mars where there are no strong local signals to overload it.

In a city you will have all the stations cross-modulating all over the dial and all will be heard at the same time.
That's why I suggested him to narrow the receiving bandwidth of his demodulator. It would certainly help.
 

transistor495

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DG MOSFETs are best for this purpose such as BF981. They won't add noise as like BJT amps.

Regarding overloading, a combination of such a pre-amp with a professional quality receiver may become extremely sensitive and should give excellent results. You cannot test the preamp performance using a low quality Chinese receiver.
 

audioguru

Well-Known Member
Most Helpful Member
A half-decent receiver is sensitive enough so it doen't need a preamp. It tunes the antenna signal then amplifies the narrow-band signal then tunes it again.

A cheap radio does not have the tuned circuit at the antenna so its RF amplifier gets all the local stations at the same time which results in overloading. Then the design of the cheap radio reduces the gain so that the effects of overloading are reduced.
 

audioguru

Well-Known Member
Most Helpful Member
A TV amplifier frequently has a notch filter to remove FM radio frequencies from overloading it.
A cheap TV amplifier is overloaded by all the strong local stations.
A very expensive TV amplifier works very well.
 

morseindustries

New Member
most tv amps have a notch filter selection via jumpers i have never had any problem with tv amps for this purpose of amplifying vhf fm , if they have a notch filter they can be disabled by cutting the notch coils and caps out of circuit. and of course most tv amplifiers also have a gain selection via jumpers or a variable resistor to decrease stage gain to stop overloading. as posted before a good antenna with the amp would be suitable either a vertical dipole / groundplane would be suited the best
 
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flat5

Member
A good used fm tuner can be bought for less than the price of a good preamp. An fm tuner that lacks sensitivity probably is lacking in other areas of it's design.
A tuner that appears to lack sensitivity (has noise) may in fact be dealing with other problems such as overload or poor selectivity.
In any case start with a good antenna.
 
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transistor495

Member
Forum Supporter
Reception of FM wave sometimes depends on the location of the receiver regardless of how sensitive the receiver is.

So an outdoor antenna with a preamp should definitely pull in maximum strong/weak signals available on that area.

A gain control is needed to treat them for optimal reception and hence no overloading.
 

audioguru

Well-Known Member
Most Helpful Member
Why are we talking about using an outdoor antenna and a VHF preamp to make a cheap FM radio pickup distant stations? It is a cheap clock radio! It has no sensitivity. Maybe it is a super-regen or a crystal "radio".

Why not use a very sensitive hi-fi tuner or car radio?
 
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