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FM Transmitter and Receiver

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missy

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I had two FM circuits

1)Wideband FM VHF Transmitter and Receiver 80MHz to 110MHz and
The tranmitter will output approximately 250mV of RF power. Its ranges can be achieved 5km.

2)Narrowband FM Xtal Controlled VHF Transmitter
it will output approximately 250mW of RF power and can operate between 75 and 146 MHz. It can detect voices 40 feet away. Its ranges is over 5 km. The receiver will tune between 70 MHz and 170 MHz.

Which one is better? :?
Which fm transmitter is better, mono or stereo? :?

Anyone out there could give me any advice?
 
Well, for voice only transmissions, a mono transmitter is simpler and uses less bandwith. Why would you need stereo unless you are transmitting music?
 
missy said:
I had two FM circuits

1)Wideband FM VHF Transmitter and Receiver 80MHz to 110MHz and
The tranmitter will output approximately 250mV of RF power. Its ranges can be achieved 5km.

2)Narrowband FM Xtal Controlled VHF Transmitter
it will output approximately 250mW of RF power and can operate between 75 and 146 MHz. It can detect voices 40 feet away. Its ranges is over 5 km. The receiver will tune between 70 MHz and 170 MHz.

Which one is better? :?
Which fm transmitter is better, mono or stereo? :?

Anyone out there could give me any advice?

#1 is a joke. I'm with #2.

How could a 250 millivolt transmitter (solar cells provide more than 250mV) transmit 5km? :lol:
 
heathtech said:
Well, for voice only transmissions, a mono transmitter is simpler and uses less bandwith. Why would you need stereo unless you are transmitting music?

Well, that's really help.
In your opinion, which one is better? Either Wideband FM Transmitter and Receiver or Narrowband FM Transmitter and Receiver?
 
In my dictonary mW stands for miliwat and stands for power. mV is milivolt.

250 mW is qite some power.
 
Anyone out there could give me any advice?[/quote]

#1 is a joke. I'm with #2.

How could a 250 millivolt transmitter (solar cells provide more than 250mV) transmit 5km? :lol:[/quote]

I'm not sure about that and I'm not test the circuit yet. My lecturer wants me to examine both circuits and decides which one is better. Could you tell me why the first one is a joke??? :?
 
Well, it all depends on what you are transmitting. I think good engineering in FM radios requires that you use only the bandwith REQUIRED for the information you are transmitting. Stereo requires transmitting information for two channels, left and right speakers. This is overkill if all you need to transmit is your voice. I might add too that broadcasting mono FM voice only requires the amount of frequency bandwith that can understandably recreate voice tones, not the full range of audible frequencies. I can't expertly tell you what bandwith this is, but it is fairly narrow. where as good musical reproduction requires significant bandwith to reproduce all of the harmonics associated with music, at least for it to be clear and enjoyable.

I am assuming that you understand what "bandwith" means and implies........
 
Someone Electro said:
In my dictonary mW stands for miliwat and stands for power. mV is milivolt.

250 mW is qite some power.

Sorry, I guess I had been mistakenly writing that. ~Spelling Error~ :oops:
 
#1 is better for music and very clear speech, #2 is better for not so clear speech. I hate narrowband speech. Half the communication is, "What did you say?". Airplane pilots must say, "Sam-Charlie" instead of, "SC" because narrowband SC sounds like, "ehh-ee".

Disregard that the narrowband transmitter can "detect voices 40 ft. away". Any microphone can with a suitable high gain preamp. The transmitter type has nothing to do with it.

You don't say if the wideband transmitter is Xtal Controlled. It easily could be like in Silicon Chip's Micromitter project.
 
This is all true, Audioguru, but I think her instructor might be asking her to think about how to go about designing her FM transmitter, and stricly speaking about good engineering, it is a good practice to limit the bandwith of a transmitter to only what is necessary for the mode of transmission. If she is talking about an FM walkie talkie, it would be overcomplicating to build a stereo transmitter I think. That is, If her teacher is looking for that kind answer
 
My narrow band VHF transceiver (2 meter amateur band)has incredibly good audio quality - maybe not music quality but much more than necessary for intelligible speech.

I would consider that the mV might have been meant to be mW, otherwise the sentence where mV is used doesn't make sense - mV is volts not power.

I would guess that more power in less bandwidth, all other things being equal, would be more effective in terms of range. There must be some RF, broadcast engineering or other communication reference that addresses this - maybe that's what your professor is fishing for. Could your professor want you to look at path losses for the various frequencies - they are different. Antenna requirements for different frequencies are different too. Without knowing about the construction of the transmitter or receiver it's hard to comment on the rather wide range of frequencies. On the receive end, the wider the frequency coverage the more troublesome the receiver becomes - as it's front end is designed to accept a wider bandwith. These will be susceptable to overloads or desensing - less sensitivity. That is not to say that some fine receivers haven't been built with wide frequency ranges - it just takes a more complex/expensive design. All of this speaks to what one might mean by "better" - it all depends on what you mean by better.

Aircraft used to be AM, at least the VHF stuff.

I would expect professor would like the right answer - or maybe the professor wants you to explain how you arrived at the answer - that would be more of what I'd be expecting.
 
As everyone else has agreed, 'best' is totally relative - wideband FM is 'best' for broadcast programs, because that's what it's designed to do - it gives high quality, has the bandwidth capability for stereo, but (due to the wide bandwidth) has a much shorter range.

NBFM, as commonly used on the 2M amateur band, gives EXCELLENT voice quality, 'audioguru' is wrong about that - and aircraft use very low quality AM, not FM - for compatability reasons it's never been changed. The narrow bandwidth used gives far greater range for the same power, 1W on 2M is 'line of sight' - limited by the curvature of the earth, or more likely hills in the way :)

It's common to work 60-70 miles with a 1W handheld on 2M.

For a suitable simile?:

Which is 'best' - a skate board, or a large truck?. This is the sort of 'nonsense question' you've asked!.
 
Missy, I think you probably punched in the wrong letter making me think that it is mV instead of mW. Watts = voltage * current, and Voltage = Voltage.

If you haven't made a mistake, then I'm still for #2 :lol:

If I were to be honest with you, I can't give you a true answer upfront because I don't know what is required in a transmitter you consider optimal, but here are some things to consider:

Wideband and Narrowband are two basic descriptions of bandwidth.

Wideband means that more channel space can be picked up at a time. This is good for audio broadcasting, and high speed data transmissions. The drawback is that if you are transmitting in the FM band, you could jam some signals that are several Mhz below and above your transmitter frequency, provided your transmitter is strong enough to reach the receiver.

Narrowband can partially eliminate the problem because Narrowband transmitters occupy less space. I think they are only useful for small data transmissions, or basic morse code.

I think crystals make transmitters or receivers more stable, but I have never used one yet.

Which is 'best' - a skate board, or a large truck?. This is the sort of 'nonsense question' you've asked!.
A large truck :lol: j/k.

As for you missy, if you need to make a transmitter and you are stuck, tell us what you have sone so far, and then we can help you.
 
I think narrow-band audio takes some getting used to. I never got used to it because I usually communicate live.

When telephones were invented they chose to limit the audio from 300 to 3kHz. It was to reduce crosstalk, and reduce the awful distortion caused by the transducers (carbon mic and vibrating tin earphone) and amplifiers of the time. AM broadcasting and 78RPM vinyl (or those wax things) records were the same. No high audio frequencies that make voices sound clear and live. I measured a spoken "sss" at 14kHz, and some people have it peaking at 18kHz.

When I worked with telephone systems I measured the frequency response on a call from my office to my office. 3Khz was down -14dB! I complained to Bell who said it was the round-trip distance that reduced the high audio frequencies, and that it was fine because their spec was -15dB. If I called the company next door I could hardly hear what they were saying.
Every time I demo'd my telephone conferencing system "equalizer", it was sold. It made voices sound much crisper and clearer. It peaked audio at 3kHz by 10dB (don't tell Bell).
When my home's telephone exchange was converted to digital, it made an enormous improvement in bandwidth and clarity. It is still fairly far away.

My cable-TV company has a new voice-activated attendant. When I repeat over and over into my phone the word "service", it trashes its brains trying to find what is "ervihh". It usually gets the word "accounting" correct. It thinks my spoken "zero" was a Greek emperor. :lol:
 
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