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FM transmitter module test result.

B

Boki

Jan 1, 1970
0
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.
 
J

Joel Kolstad

Jan 1, 1970
0
Boki,

Boki said:
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 ?

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

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

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

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.
 
R

Rich Grise

Jan 1, 1970
0
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.

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:
http://www.ntia.doc.gov/osmhome/allochrt.pdf

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
 
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