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AM Transmitter

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chickens1127

New Member
Yes, AM is measured by wattage, going into the antenna, but I also said FM was measured by signal strength from antnna.

And for god's sake, AM get's better range then FM! End of question! The best lower power FM transmitters got 200 yards witha great antenna, vs 2 miles with a good antenna and an AM transmitter. There's two forums dedicated to this, so Hero don't claim FM is better. When you find as easy of a circuit as the one I posted, with the range it can get, with FM, please post it. I don't mean this negative. I'm just saying, people have made this exact circuit, put a good antenna on it, and gotten 1 1/2 miles + with great sound quality at over a mile.
 

Hero999

Banned
Yes, AM is measured by wattage, going into the antenna, but I also said FM was measured by signal strength from antnna.
No, the Effective Radiated Power (ERP) is what's important because the antenna won't radiate all the power sent to it, some will be released as heat.

And for god's sake, AM get's better range then FM! End of question! The best lower power FM transmitters got 200 yards witha great antenna, vs 2 miles with a good antenna and an AM transmitter. There's two forums dedicated to this, so Hero don't claim FM is better.
What frequency?
DSB SSP?
FM mono/stereo?

Sorry don't believe you, please post some references.

All things being equal (power, frequency and path) FM will go further than AM DSB.

As I said before, if you're comparing MW (530kHz to 1700kz) to VHF (88MHz to 108MHz) then there will be other factors as well as being able to bounce round the earth's curvature off the ionosphere, for example longer wavelengths will probably be able to bounce round obstacles better than shorter wavelengths but that's not a level playing field.

Compare an FM transmitter working on 150MHz with a DSB AM transmitter on the same frequency with exactly the same average ERP and the FM transmitter will go further.

FM gives better reception at a lower signal to noise ratio.

If FM wasn't so efficient then why do you think people are moving away from AM towards FM?

AM could theoretically give just as good sound quality as FM if the bandwidth were increased but notice that this has not happened and we have FM instead?

When you find as easy of a circuit as the one I posted, with the range it can get, with FM, please post it. I don't mean this negative. I'm just saying, people have made this exact circuit, put a good antenna on it, and gotten 1 1/2 miles + with great sound quality at over a mile.
The simplest solution is to buy it, which is what has already been half done in the circuit you posted. The circuit inside that little metal can is at least as complicated as the circuit I posted above: it will contain at least a few transistors and a crystal.

There are much simpler FM transmitter circuits but they all perform very poorly compared to the one I posted.

Here's an example but it's very poor quality. I say if you want to build your own transmitter then you should at least want to make a decent one.
FM Voice Transmitter
 

chickens1127

New Member
Most people get 200-500 yards with OK quality, and rarely detectable at 1/2 mile with the BEST fm transmitter.

http://hobbybroadcaster.net/smf/ind...d81f9ffda&topic=377.msg2313;topicseen#msg2313
Read the whole thread. Period.
VS.
These guys are using $35-$90 kits with a home made antenna. They get easily 1-2 miles, sometimes more in winter.

Variety AM1640
mighty1650.tk
Troubadour 1700 AM - Part 15 Radio Station in Shirley, MA USA


Now, thes guys are using 1600-1700, which is now what I plan to use if I can find an oscillator of that frequency on Jameco or some other electronics store. And before you even say this, I am NOT using those very basic plans on the website I linked. I'm talking w/ a guy who has built his own and it's gonna hopefully be like the SSTran 3000, used by most of the LPAM stations I posted.
 
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Hero999

Banned
As I said before, you're comparing chalk with cheese, you've not disproved the fact that, all things being equal, FM travels further than AM.
 

audioguru

Well-Known Member
Most Helpful Member
The range of my home-made fairly simple FM transmitter depends on whether something blocks the signal and the sensitivity of the radio.
My FM transmitter has a range of more than 2km over a huge river valley to my very sensitive home hi-fi tuner and very sensitive car radio.
Its range is 300m to my cheap Sony Walkman portable stereo radio.
Its range is 80m to a cheap clock radio.
Its range is across the street (30m) to a very cheap radio from The Dollar Store.

Homes, hills and maybe trees block the signal.
 

Hero999

Banned
I posted a link to your transmitter on the previous page but he siad it's too complicated. :rolleyes:
 

JimB

Super Moderator
Most Helpful Member
As I said before, you're comparing chalk with cheese, you've not disproved the fact that, all things being equal, FM travels further than AM.
Sorry, but I really must take you to task on that statement.

AM and FM are modes of MODULATION, a way of superimposing information onto a carrier wave.
The carrier could not care less what form of modulation is used, a CARRIER wave of a given frequency will propagate with exactly the same attenuation and have exactly the same field strength at some given point from the transmitter irrespective of whether it is modulated with AM, FM or is just an unmodulated carrier.

What will make a difference to the quality of the received signal and the recovered information (audio) are the characteristics of the receiver particularly the noise factor which is mostly influenced by the RF amplifier and to a lesser extent the first* mixer, and also the detector.

*In dual conversion receivers, in single conversion receivers there is only one mixer.

JimB
 

Hero999

Banned
AM and FM are modes of MODULATION, a way of superimposing information onto a carrier wave.
The carrier could not care less what form of modulation is used, a CARRIER wave of a given frequency will propagate with exactly the same attenuation and have exactly the same field strength at some given point from the transmitter irrespective of whether it is modulated with AM, FM or is just an unmodulated carrier.

What will make a difference to the quality of the received signal and the recovered information (audio) are the characteristics of the receiver particularly the noise factor which is mostly influenced by the RF amplifier and to a lesser extent the first* mixer, and also the detector.
What I was saying is that FM can still be received when the signal to noise ratio is lower than the minimum required for AM to be intelligible. This means that FM effectively travels further because the receiver can still pick up the signal at a greater distance than an AM receiver.
 

JimB

Super Moderator
Most Helpful Member
Hero,
I assumed that was what you intended to say.
However I still disaggree with you.

I will agree that as the signal strength is reduced, the recovered audio from an FM signal will retain a good signal to noise ratio as the RF signal approches the minimum detectable signal when the recovered S/N ratio will rapidly degrade.
The AM signal on the other hand, the recovered S/N ratio will degrade as the RF signal is reduced, but at very low RF signal levels the AM signal will have a better (but very low) S/N ratio than the FM signal.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
What I was saying is that FM can still be received when the signal to noise ratio is lower than the minimum required for AM to be intelligible. This means that FM effectively travels further because the receiver can still pick up the signal at a greater distance than an AM receiver.
Wrong way round, AM is useable over greater ranges than FM - even narrowband FM requires more bandwidth than AM, and it's all down to bandwidth.

It's why AM used to be used on the HF bands by radio hams, before SSB took over as it's far more efficient than AM as well. CW of course is by far the most efficient, as it uses almost no bandwidth at all.
 

chickens1127

New Member
Thank you, Nigel!

And for the last time, I dont give a CRAP which one will travel further per a unit of power, all I care is that with the regulations set down by Part 15 of FCC, most notably part 15.239(go read it), allows the amplitude modulation transmitter, to us e100mW and that will probably travel 1-3 miles depending on conditions and season. However, the best frequency modulation kit out there can get 1/2 of a mile in excellent conditions.

I don't want a debate about this, many, many, many websites say that for the same relative power, AM will travel hundrads of miles, compared to the 50-100 miles of FM.
 
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transistor495

Member
Forum Supporter
AM travels more than FM for the same amount of power...that's the only advantage?! What about the quality and efficiency of transmission.

FM systems are bit more complex than AM, that's a fact.
 

chickens1127

New Member
Another person is agreeing with me, Hero. No offence, but please don't act like your an expert in radio. Your initial help was great, and I admit I'm a newbie too with radio, but just don't give false advice.


After all this, a member on another forum suggested I just go with the Ramsey AM1C kit for $35. Now I need to get the money...
 

Hero999

Banned
Al right, it looks like I was wrong.

I had learnt that FM goes further at college. It looks like I should apply more critical thinking and not take everything that was taught to me at college as fact without proof.

I think I now understand why FM requires more power. It has a wider bandwidth,, therefore more power is needed to produce the same signal over a range of frequencies. There's also more of a threshold at which FM fades and becomes unintelligible, where as AM undergoes a more graceful degradation.
 
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