FM transmitter module test result.

Hi All,

I just got a FM transmiter module from supplier, after my test, its every channel occupy almost 0.5MHz of range.

For example, when I tune to 100MHz, I can hear it from 99.7MHz~100.2MHz and only 99.7MHz didn't show "Stereo" tag on screen, others (

99.8~100.2MHz ) all show "Stereo" tag.

How is this quality ? I test general FM radio music, the range is not so big. ( about 0.2MHz~0.3MHz.) and only 0.2MHz range with "Stereo"

The FM module occupy 0.5MHz range, is that too big for worldwide use?

btw, I can feel the quality is not as good as FM music radio, does that mean the FM module chip's audio quality is not good enough ? it seems that I didn't see the quality spec ( SNR ...etc ) on FM module specification.

BR/ Boki.

Reply to
Boki
Loading thread data ...

Boki,

It's impossible to say from the information you provided. Off-the-cuff, for a cheap FM transmitter I'd say your results are about average, but that makes many assumptions about the receiver you're using, how far your transmitter and receiver are separated, etc.

The only way you're going to make objectively meaningful measurements on an FM transmitter is with a spectrum analyzer or service monitor or similar.

Commercial FM stations have legal requirements they need to comply with that are far stricter than what someone building an unlicensed, low-power transmitter does (low-power unlicensed transmitters are often governed by rules that aren't much stricter than, "if you keep the power below such-and-such a field strength at a certain distance, we don't care how messy your signal is"). The commercial stations have people who regularly monitor the exact frequency content of what's going out to their antennas, as well as people who drive around and perform similar measurements of their radiated signal in the field.

Ask the module manufacturer. They should know in which countries their module works in.

Good enough for what? Manufacturers will happily build you modules that are as good (in audio quality) as commercial FM stations are, but there are also plenty who'll sell you lesser quality modules that are still "good enough" for many people and cost less.

Reply to
Joel Kolstad

Boki, I want to first say, congratulations on your English studies - this is very understandable! :-)

OK, now here's the thing. As usual, we need to know more specific information. Like, for example, you say that your receiver can hear your transmitter over a fairly wide range of its dial. Well, FM receivers can do that. Have you tried attenuating your transmitter's output so that it's closer in signal strength to the other broadcast channels that you're using for your reference? It could simply be "swamping" your receiver, that is, giving it such a strong signal that the receiver hears it anyway even if it's not tuned right spot-on.

I don't know about the bandwidth specification, but there is a chart, which is a quite big .PDF:

formatting link

But I have heard numbers like 100 KHz and 200 KHZ and stuff.

So, OK, given that you know the response of your receiver, then you start looking at the bandwidth of the transmitter, like freq. stability, deviation, modulation index, and all sorts of arcane stuff that you'll need special books and stuff for. ;-)

Good Luck! Rich

Reply to
Rich Grise

By Carson's rule of thumb, commercial FM stations take up "about 180kHz" -- hence the 200kHz dial spacing. See:

formatting link

Reply to
Joel Kolstad

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.