Indoor FM boost with no cables?
 

amdx wrote in :

PS, I'll bet both of you stations stream on the internet. If you
have wifi, that will eliminate your noise problem.


I get capped at 10GB per month, and that costs far too much. If I saw the
costs of the bandwidth to do this I might scream loud enough that even my
neighbours might have a noise problem. :) Besides, good FM totally beats all
internet quality. Radio 3's best HD sound falls well short, equivalent to a
192 kbps MP3 at best, from what I have read and heard about it. FM in the UK
is extremely good quality, nothing else has been any better yet. Which is
probably why obituary after obituary gets written for broadcast FM radio, btu
it never dies, the 'swicth-off date' is forver being set back, and it likely
won't happen once peoplerealise the costs of allocating bandwidth foe that
kind of quality ona per-person basis! That's a mind-stunning financial and
technical calculation no matter how we look at it.

Indoor FM boost with no cables?
 

On Fri, 01 Aug 2014 15:22:10 -0500, Lostgallifreyan
wrote:

Jeff Liebermann wrote in
:

For FM tuners, it's dBf (dB over 1 femtowatt) usually into 300 ohms
but sometimes into 75 ohms:


The Tecsun PL-390 uses dBµ (micro).

Yep. The Tecsun PL-390 uses a Silicon Labs SI4734 DSP chip. I've
done some work with similar chips and think they are wonderful.
http://www.kaitousa.com/PL390.htm
https://www.silabs.com/Support%20Documents/TechnicalDocs/Si4730-31-34-35-D60.pdf
One of the chief benefits to all an all digital receiver is the nearly
"brick wall" IF filter, which works nicely at keeping HD Radio crap
out of the receiver. I'm not sure if you have that problem in UK:
http://www.telegraph.co.uk/technology/8071209/BBC-launches-HD-radio.html
but if you do, the SI4734 should remove the junk from the adjacent
channel. Note that the HD Radio occupied bandwidth is about 400 KHz,
while conventional FM is a bit less than 200 KHz.
http://802.11junk.com/jeffl/crud/KCSM.jpg
Too bad the PL-390 won't do synchronous AM or SSB. The chip can do
it, but it's only available in the later PL-880 receiver.
http://www.kaitousa.com/PL880.htm

I'm not sure where the dBf stuff came from, but my guess(tm) is that
it was used to simplify the sensitivity specs so that the numbers came
out positive integers.

Most of this is new to me, but I read
that Tecsun's dB referencing makes them useful to EMI and RFI engineers,

We call it EMC (electromagnetic compatibility) in the US.
http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/ElectromagneticCompatibilityEMC/default.htm
I don't think using dBµ will make much difference as I'm constantly
converting from various field strength units to voltages and powers.
If you're into this, you might want to save this page:
http://802.11junk.com/jeffl/coverage/VZW-water-plant/Field%20Intensity%20and%20Power%20Density.pdf
I forgot which book I stole it from.

and
one related radio beign especially useful for tracing noise, having a plug-in
rotatable magnetic loop antenna as well as a long(ish) whip.

Direction finding is fine for finding the general area. However, for
close up, one needs a "sniffer". For that, I use an Alinco DJ-X2 AM
receiver with the stock 17 cm antenna. It's not very sensitive but
good enough for finding unwanted emitters. Your Tecsun PL-390 would
probably work equally well.

At this point pouring scorn or praise on Tecsun radios is interesting to me
either way, because for the first time in a while I have found a radio I care
enough not to be indifferent to it.

I guess that means you like it.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Indoor FM boost with no cables?
 

Jeff Liebermann wrote in
:

If you're into this, you might want to save this page:
http://802.11junk.com/jeffl/coverage...%20Intensity%2
0and%20Power%20Density.pdf


Thankyou. That's a good looking reference. For now it passes swiftly
overhead, but I get the point about converting to SI units ASAP for best
anchorage. I did see the Wikipedia page, but I think studying that file you
posted will work better for me.

About the PL-390, yes, I like it. :) It crashed, locked like a brick within
days of buying, but despite that nasty event (and the even nastier twenty
minute wait that ensueth before the power fades enough to let me regain
control) that small radio impresses me every time I use it. I hope to figure
out a fast reset modification though, and I'm also wondering if I can find a
TTL serial based board for making my own project radio using the same IC, and
allowing me to use the old Psion Organiser II XP as a controller and display,
but I think that might be more expensive than I'd like despite the cheapness
of those Organisers these days.

Indoor FM boost with no cables?
 

Jeff Liebermann wrote in
:

I'm not sure if you have that problem in UK:
http://www.telegraph.co.uk/technology/8071209/BBC-launches-HD-radio.html
but if you do, the SI4734 should remove the junk from the adjacent
channel. Note that the HD Radio occupied bandwidth is about 400 KHz,
while conventional FM is a bit less than 200 KHz.


Not yet, so far as I know, but forewarned is forearmed.. :) I can't help
thinking that the extra demand for bandwidth might end up making FM look like
the better option...

Indoor FM boost with no cables?
 

Jeff wrote in :

The point that Jerry is missing is that the in-car devices that link an
MP3 player, and the like, to a car radio are being received by just
that, a car radio; so if the deviation were as low as 5 or even 15kHz
then the level of audio coming out of the radio would so so low as to be
unusable.

The deviation of the transmitters must match the bandwidth of the
receiver being used, ie the normal FM broadcast band deviation of 150kHz
of more.

I am not sure what the FCC power limit for such devices is, but in the
UK is it is 50nW erp in the FM broadcast band, yes 50 nanowatts. I
expect that the devices sold in the US are similar output power.

Jerry does not seem to take on board that this is an international
group, not a group of ex-US cable technicians who slovenly misuse dBm to
mean dBmV, when the rest of the world uses dBm correctly to mean dB
relative to a milliwatt.

Jeff


Thanks, that looks clear, and fits with other things I read, especially the
dBm bit and the 50 nW.

One thought: Does the bandwidth match have to be exact? Or is there a case
for some reduction on the transmitter to allow more of them to make
potentially less local competition between each other when lots are used? Is
there some compromise that doesn't afflict the sound too much, while reducing
both the occupancy of the spectrum and the need for power for some given
reach of distance?

(I don't intent using one, but they do interest me strangely...)

Indoor FM boost with no cables?
 

On 8/2/2014 6:12 AM, Jeff wrote:
On 02/08/2014 00:13, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrgvk8$5er$1@dont-
email.me:

I won't get into the math here, but due to the sidebands (yes, FM has
sidebands, also - the number and strength of the sidebands is
proportional to the deviation and modulating frequency), frequency
response of the modulated signal is proportional to the bandwidth of the
channel and deviation. A 5 kHz deviation can theoretically pass up to
about 5Khz of audio, but in practice it's limited to about 3 kHz (to
avoid adjacent channel interference). This is fine for voice, but does
not work well for music (try listening to music on the AM band, for
instance).


Thankyou, that's great help. I'll have to be careful about buying one of
those widgets... I did suspect that something that had a narrower
bandwidth
would reduce frequency response (based on playing with the AR-3000 on
narrowband FM). That's one reason I was wondering about boosting the
broadcast signal directly for low level rebroadcast in a building, to
keep
what fidelity I can as best possible.


The point that Jerry is missing is that the in-car devices that link an
MP3 player, and the like, to a car radio are being received by just
that, a car radio; so if the deviation were as low as 5 or even 15kHz
then the level of audio coming out of the radio would so so low as to be
unusable.


Wrong. These are operating in the commercial FM band, and use 75 kHz
deviation. I never said otherwise.

The deviation of the transmitters must match the bandwidth of the
receiver being used, ie the normal FM broadcast band deviation of 150kHz
of more.


Again, incorrect. The deviation is 75 kHz (deviation is measured from
the center frequency). Bandwidth is 150 kHz.

I am not sure what the FCC power limit for such devices is, but in the
UK is it is 50nW erp in the FM broadcast band, yes 50 nanowatts. I
expect that the devices sold in the US are similar output power.


Again, incorrect.

Jerry does not seem to take on board that this is an international
group, not a group of ex-US cable technicians who slovenly misuse dBm to
mean dBmV, when the rest of the world uses dBm correctly to mean dB
relative to a milliwatt.

Jeff

Nope. I'm talking about what is commonly used here. But there are some
people from the U.K. who think they are experts on everything.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Indoor FM boost with no cables?
 

On 8/2/2014 6:27 AM, Lostgallifreyan wrote:
Jeff wrote in :

The point that Jerry is missing is that the in-car devices that link an
MP3 player, and the like, to a car radio are being received by just
that, a car radio; so if the deviation were as low as 5 or even 15kHz
then the level of audio coming out of the radio would so so low as to be
unusable.

The deviation of the transmitters must match the bandwidth of the
receiver being used, ie the normal FM broadcast band deviation of 150kHz
of more.

I am not sure what the FCC power limit for such devices is, but in the
UK is it is 50nW erp in the FM broadcast band, yes 50 nanowatts. I
expect that the devices sold in the US are similar output power.

Jerry does not seem to take on board that this is an international
group, not a group of ex-US cable technicians who slovenly misuse dBm to
mean dBmV, when the rest of the world uses dBm correctly to mean dB
relative to a milliwatt.

Jeff


Thanks, that looks clear, and fits with other things I read, especially the
dBm bit and the 50 nW.

One thought: Does the bandwidth match have to be exact? Or is there a case
for some reduction on the transmitter to allow more of them to make
potentially less local competition between each other when lots are used? Is
there some compromise that doesn't afflict the sound too much, while reducing
both the occupancy of the spectrum and the need for power for some given
reach of distance?

(I don't intent using one, but they do interest me strangely...)


In an FM transmitter, the amount of deviation is proportional to the
amplitude of the modulating signal. That is, the louder the audio, the
greater the deviation.

Transmitter bandwidth cannot be greater than receiver bandwidth without
loss of signal and distortion. Transmitter deviation can be less than
receiver bandwidth; this only results in lower audio. This is why
commercial FM receivers typically have a bandwidth of 170-180 kHz, when
deviation is only 75 kHz. It makes things less critical.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Indoor FM boost with no cables?
 

Jeff wrote in :

The bandwidth does not have to match exactly, but it it is too much then
it will distort as it exceeds the Bandwidth if the IF filters in the
receiver, and if it is too low the volume out of the receiver will be
low, so you would have to turn up the volume control when you used the
device. If it were extremely low then the audio would be very quiet
indeed, and if the signal strength were also too low you would loose
everything in noise.

The nominal max deviation in the FM broadcast band is +/-75kHz (150kHz
total).


Thanks. It looks like matching is best for compromise then, not some value
for transmission lower than reception, because what you gain in RF reach you
lose in SNR on output so striving for anything but a good match looks like a
game of diminishing returns.

Indoor FM boost with no cables?
 

Jerry Stuckle wrote in news:lriogq$kba$1@dont-
email.me:

In an FM transmitter, the amount of deviation is proportional to the
amplitude of the modulating signal. That is, the louder the audio, the
greater the deviation.

Transmitter bandwidth cannot be greater than receiver bandwidth without
loss of signal and distortion. Transmitter deviation can be less than
receiver bandwidth; this only results in lower audio. This is why
commercial FM receivers typically have a bandwidth of 170-180 kHz, when
deviation is only 75 kHz. It makes things less critical.


Ok, so a kind of 'headroom' exists then, but is there some agreeable degree
of reduction on transmitter bandwidth to gain a significant reach in RF
propagation and reduction in intrusion across the band, before the whole
exercise fails due to poor SNR on output? My guess is that there may be, but
the decision could be very different depending on whether speech or music
(let alone stereo) is wanted.

Indoor FM boost with no cables?
 

Jerry Stuckle wrote in news:lrio4f$fs4$1@dont-
email.me:

Nope. I'm talking about what is commonly used here. But there are some
people from the U.K. who think they are experts on everything.


To be fair to him, I'm in the UK and he may well have aimed that point at me,
knowing this from the message header or some earlier post of mine. I'm
also interesed in how the US conventions differ from ours.