Decibels and Charts

[rfry]

>> Neil,
>> I think something like this makes it easier to estimate what
>>types of power one will expect to get in terms of db to
>>watts.
>> www.minicircuits.com/dg03-110.pdf
>> Radiopilot
Neil,
Nonsense, you are correct! Anyway if you look at the table in the minicircuits site, you'll see that 47uV equates to -74dbm approx. and the power output is somewhere around .05nw, does this sound familiar in my arguments in the previous posts about how much power the PCFM transmitter outputs! Not very much power but even with that amount of power on a well installed antenna will give you 200-300 feet of coverage, maybe more but for a high school radio broadcast system it's not too bad, as I said and it should comform to the FCC as far as compliance, I just don't understand sometimes why people make harsh issues of things when all they have to do is sit back and have a cup of Jo...
Radiopilot
_____________

Radiopilot,

You found a chart that says 45 µV is the voltage across 50 ohms at a power level of -74 dBm. The chart is right, but that chart is not directly useful to you to make your point. Here's why.

The output level of the PCFM transmitter is given in terms of dBmV, but the units in the column you used in the chart are in µV. In order for the chart to apply directly, the units in it would have to be shown in dBmV, not µV.

Here's how to use the chart to find the approximate output power of your PCFM tx. First, calculate the output voltage itself. I'll use +35 dBmV as its output level, as I think this is the spec shown for it on the Pico MACOM website.

Millivolts = 10^(35/20) = 56.23, or ~0.056 volts

Now look up the closest voltage value to this in the voltage column of the chart. It appears as the voltage across 50 ohms at a power level of -12 dBm.

To convert dBm to milliwatts...

mW = 10^(-12/10) = 0.063 mW, which is over 5,000 times more power than it takes to generate the maximum Part 15 FM field using a simple 1/2-wave dipole. So the output power of your PCFM tx is not ".05nw" as you concluded in your clip above.

Of course, this chart shows values for 50 ohm systems, and the PCFM output level spec is referred to 75 ohm systems (a cable industry standard). So using this chart doesn't strictly apply in this situation, but at least it will give you a rough idea.

And... I'm not wishing to be "harsh," just wanting people to have valid information. Part 15 issues are hard enough, even then.
//

 

[radiopilot]

> >> Neil,
> >> I think something like this makes it easier to estimate
> what
> >>types of power one will expect to get in terms of db to
> >>watts.
> >> www.minicircuits.com/dg03-110.pdf
> >> Radiopilot
> Neil,
> Nonsense, you are correct! Anyway if you look at the table
> in the minicircuits site, you'll see that 47uV equates to
> -74dbm approx. and the power output is somewhere around
> .05nw, does this sound familiar in my arguments in the
> previous posts about how much power the PCFM transmitter
> outputs! Not very much power but even with that amount of
> power on a well installed antenna will give you 200-300 feet
> of coverage, maybe more but for a high school radio
> broadcast system it's not too bad, as I said and it should
> comform to the FCC as far as compliance, I just don't
> understand sometimes why people make harsh issues of things
> when all they have to do is sit back and have a cup of Jo...
>
> Radiopilot
> _____________
>
> Radiopilot,
>
> You found a chart that says 45 µV is the voltage across 50
> ohms at a power level of -74 dBm. The chart is right, but
> that chart is not directly useful to you to make your point.
> Here's why.
>
> The output level of the PCFM transmitter is given in terms
> of dBmV, but the units in the column you used in the chart
> are in µV. In order for the chart to apply directly, the
> units in it would have to be shown in dBmV, not µV.
>
> Here's how to use the chart to find the approximate output
> power of your PCFM tx. First, calculate the output voltage
> itself. I'll use +35 dBmV as its output level, as I think
> this is the spec shown for it on the Pico MACOM website.
>
> Millivolts = 10^(35/20) = 56.23, or ~0.056 volts
>
> Now look up the closest voltage value to this in the voltage
> column of the chart. It appears as the voltage across 50
> ohms at a power level of -12 dBm.
>
> To convert dBm to milliwatts...
>
> mW = 10^(-12/10) = 0.063 mW, which is over 5,000 times
> more power than it takes to generate the maximum Part 15 FM
> field using a simple 1/2-wave dipole. So the output power
> of your PCFM tx is not ".05nw" as you concluded in your clip
> above.
>
> Of course, this chart shows values for 50 ohm systems, and
> the PCFM output level spec is referred to 75 ohm systems (a
> cable industry standard). So using this chart doesn't
> strictly apply in this situation, but at least it will give
> you a rough idea.
>
> And... I'm not wishing to be "harsh," just wanting people to
> have valid information. Part 15 issues are hard enough,
> even then.
> //
>


Rfry,

I concurr on your rebuttal about the power, but in terms of the power of the unit compared to the power of even FCC certified transmitters you have to admit that .063mw... less tha .1mw is grand standing amount of power, and I can't see this being anymore a nuisance than some garage door openers or even some other part15 devices which produce much larger output than the Pico...

Even with a 3db gain antenna attached to this unit, I can't see it any more power than a 10mw Ramsey or Talking House transmitter...

Should I attenuate .063mw to get .01mw just to be the ballpark? What are we talking here 250' with .01mw verses .063mw and 330 feet? I think even the FCC agent would laugh at this...

My intention is not to break any laws but if the FCC wanted to stop all FM transmissions using 10mw transmitters or for that fact even 100-500mw transmitters the FCC enforcement logs would be filled with thousands if not hundreds of thousands of illegal activity with FM transmitter abuses, but we don't see that and I don't think you will... just in my area alone there are many FM transmitters being used to broadcast everything from religous to sports and foreign language programs using these part15 FM and AM transmitters... now I know the FCC agent has been here in my area more than once and I have not seen anyone carted away or equipment consficated or anybody being given the NAL.

The reality is we are making what seems to be a big issue out of something that's been done for decades.. even if the transmitters were not bought at some retail outlet, they were being homemade and putting out alot more power than the Ramseys, Talking house, Veronicas, etc. by able hams/experimenters, etc.
This is nothing new we are talling about, let's all put this issue to rest until someone here post a message saying he is broadcasting with 5-10 watts of power and think he can get away with it! Now THAT would be a pirate!

Just my say, and hope that the posts below does not confuse anyone to believe he or she is doing anything out of the ordinary.

Radiopilot

 

[rfry]

> Should I attenuate .063mw to get .01mw just to be the
> ballpark? What are we talking here 250' with .01mw verses
> .063mw and 330 feet? I think even the FCC agent would laugh
> at this...

The amount of power that the tx is capable of producing is not directly the issue. The real issue is the field strength that the Part 15 FM antenna generates, at a radius of 3 meters, with the power that is applied to it.

If that is greater than 250 µV/m, then the system is non-compliant. And the reality is that a simple 1/2-wave dipole needs ~11.4 nW of tx power to generate the maximum Part 15 FM field, and it doesn't take a tx rated for thousands of times more power to provide that (that is, tx powers of 10 mW or 25 mW, or even your PCFM's 0.063 mW).

Some Part 15 FM operators want to avoid the consequences of this reality, and apparently are doing so -- but at least they should recognize that the reality remains true.
//

 

[radiopilot]

> > Should I attenuate .063mw to get .01mw just to be the
> > ballpark? What are we talking here 250' with .01mw verses
>
> > .063mw and 330 feet? I think even the FCC agent would
> laugh
> > at this...
>
> The amount of power that the tx is capable of producing is
> not directly the issue. The real issue is the field
> strength that the Part 15 FM antenna generates, at a radius
> of 3 meters, with the power that is applied to it.
>
> If that is greater than 250 µV/m, then the system is
> non-compliant. And the reality is that a simple 1/2-wave
> dipole needs ~11.4 nW of tx power to generate the maximum
> Part 15 FM field, and it doesn't take a tx rated for
> thousands of times more power to provide that (that is, tx
> powers of 10 mW or 25 mW, or even your PCFM's 0.063 mW).
>
> Some Part 15 FM operators want to avoid the consequences of
> this reality, and apparently are doing so -- but at least
> they should recognize that the reality remains true.
> //
>


Rfry,

Unfortunately we don't have the luxury and I would say that no one on these boards have the means of obtaining the Potomic meter capable of measuring such levels and at the costs of thousands of dollars just to measure a 250uv signal or the power level of 11nw to insure that their transmitter is running at the proper level!

Now I know that if 'Joe's FM transmitter certified' at 10mw PASSED the FCC certification, using a telescoping whip, and getting the 200-300 range, that anyone using a transmitter with far less power or for that fact more power than 10mw is not still compliant as long as the signal does not propagate further than the limits stated by the FCC, which to me is ridiculus since that FCC test is done on a bench 45 inches high and the recieving antenna is only 3 meters away on perhaps another table 45 inches off the ground that the signal can't go further than 3m is ludicrous. That 250uv/3m signal may wind up being further than that if they placed the receiving antenna say at 30 feet away or even 100 feet away, not to mention if the unit were say mounted 50 foot high, how far would the signal go during this test? Should there be another meter measuring the signal at 30 feet away to insure that the signal isn't indeed 250uv at that point, or 50 feet, 75 feet, etc.? Surely the 10mw transmitter is definately putting alot more range than 300 feet!

What I'm saying is and I believe I said it before... attest to the fact that if there were broadcasters out there who have been approached by the FCC for using a 10mw - 1 watt transmitter, what was the outcome? Surely out of the thousands if not hundreds of thousands of broadcasters using the FM transmitter there must be one or two that were cited by the FCC to either turn down the power, use a smaller or unity antenna, or shut down completely... where are they? Now we are not talking about the Free Radio Berkley's, or the Free Olympia Radio, or the recently shut down station noted on this board earlier all using excess power, some over the LPFM power levels of 10-100 watts, but small scale part15 broadcasters even if you choose to decline to call them part15 level broadcasters.

I'm willing to take that consequence if it ever comes, no different than when I choose to drive 60mph in a 55mph highway everynow and then, we all do it!

Radiopiot

 

[rfry]

> Unfortunately we don't have the luxury and I would say that
> no one on these boards have the means of obtaining the
> Potomic meter capable of measuring such levels and at the
> costs of thousands of dollars just to measure a 250uv signal
> or the power level of 11nw to insure that their transmitter
> is running at the proper level!

That isn't necessary. Just buy an FM system (tx with an attached antenna) that is FCC-certified as a system under Part 15 FM, and use it unmodified. The manufacturer has done all that power setting and field strength measuring for you, during the certification process.
//

 

[radiopilot]

> > Unfortunately we don't have the luxury and I would say
> that
> > no one on these boards have the means of obtaining the
> > Potomic meter capable of measuring such levels and at the
> > costs of thousands of dollars just to measure a 250uv
> signal
> > or the power level of 11nw to insure that their
> transmitter
> > is running at the proper level!
>
> That isn't necessary. Just buy an FM system (tx with an
> attached antenna) that is FCC-certified as a system under
> Part 15 FM, and use it unmodified. The manufacturer has
> done all that power setting and field strength measuring for
> you, during the certification process.
> //
>

Now I speak for my self and perhaps others feel the same way, but experimentation and playing with gadgets, antennas, radios, transmitters, building my own electronics, breadboarding, etc. is a personal enjoyment, to have to 'buy' a system complete out of the box is not my cup of tea...

Some may like it that way, it's not what I'm teaching in my class of high school kids, if we don't train them to love radio, it'll be gone, they already listen to less radio than any other generation with the advent of CD's, computers, and now Ipods, they will surely be the downfall of radio if we don't continue the learning process, otherwise radio will be antiquated.

Radiopilot

 

[radio8z]

> That isn't necessary. Just buy an FM system (tx with an
> attached antenna) that is FCC-certified as a system under
> Part 15 FM, and use it unmodified. The manufacturer has
> done all that power setting and field strength measuring for
> you, during the certification process.
> //
>
Hello all,

I ask if anyone here has a real certified FM system and can tell us what range they get with it. The impression is that 200 feet or so is the range to expect, but does anyone have any experience to share?


Neil

 

[WCWalker]

Panaxis makes the ACC 100. It's a FCC Type Accepted Part 15 FM transmitter. www.panaxis.com Ernie Wilson's been around for years and has a reputation for being a decent marketer of low power radio gear.


> > > Unfortunately we don't have the luxury and I would say
> > that
> > > no one on these boards have the means of obtaining the
> > > Potomic meter capable of measuring such levels and at
> the
> > > costs of thousands of dollars just to measure a 250uv
> > signal
> > > or the power level of 11nw to insure that their
> > transmitter
> > > is running at the proper level!
> >
> > That isn't necessary. Just buy an FM system (tx with an
> > attached antenna) that is FCC-certified as a system under
> > Part 15 FM, and use it unmodified. The manufacturer has
> > done all that power setting and field strength measuring
> for
> > you, during the certification process.
> > //
> >
>
> Now I speak for my self and perhaps others feel the same
> way, but experimentation and playing with gadgets, antennas,
> radios, transmitters, building my own electronics,
> breadboarding, etc. is a personal enjoyment, to have to
> 'buy' a system complete out of the box is not my cup of
> tea...
>
> Some may like it that way, it's not what I'm teaching in my
> class of high school kids, if we don't train them to love
> radio, it'll be gone, they already listen to less radio than
> any other generation with the advent of CD's, computers, and
> now Ipods, they will surely be the downfall of radio if we
> don't continue the learning process, otherwise radio will be
> antiquated.
>
> Radiopilot
>

 

[radiopilot]

> > That isn't necessary. Just buy an FM system (tx with an
> > attached antenna) that is FCC-certified as a system under
> > Part 15 FM, and use it unmodified. The manufacturer has
> > done all that power setting and field strength measuring
> for
> > you, during the certification process.
> > //
> >
> Hello all,
>
> I ask if anyone here has a real certified FM system and can
> tell us what range they get with it. The impression is that
> 200 feet or so is the range to expect, but does anyone have
> any experience to share?
>
>
> Neil
>

Neil,

T have an X-File XFT-40 model FM digital PLL (FCC certified) transmitter (FCC ID: RA6NFM-40T) is the registration number, this unit goes out 100-200 ft max on a good day on a clear frequency, not bad but the unit is not meant for serious broadcasting, I'd say it's equivalent in terms of an EDM10 but with less power, perhaps 1-5m....

I also have several Belkin Tunecast II FM transmitters which I used for experimentation purposes (FCC certified) and they have about -22dbm as measured on Belkin's test, about .05mw of power, it has about about 50 feet range, these are made for car FM accessory applications.

Surely there are those here that have the FM certified transmitter that can give us definate results.

Radiopilot

 

[radiopilot]

> Panaxis makes the ACC 100. It's a FCC Type Accepted Part 15
> FM transmitter. www.panaxis.com Ernie Wilson's been around
> for years and has a reputation for being a decent marketer
> of low power radio gear.
>
>
>

WCWalker,

Thank you, I'd seen their website before, they are very similar to the Talking House transmitters, maybe better quality.

I don't see how if the transmitter I'm using has less power and the antenna is not a high gain antenna, ie. maybe 1.5-2.5db gain antenna, that my signal is somehow illegal in terms of the 250uv/3m rule... just the 100ft 75 ohm cable is attenuating the signal roughly in half before it gets to the antenna alone. The school campus is around 3-4 acres, so if the signal fades out after 300-350ft, who cares, as long as the transmission is clean and free of interference.

Radiopilot

 

[rfry]

> I ask if anyone here has a real certified FM system and can
> tell us what range they get with it. The impression is that
> 200 feet or so is the range to expect, but does anyone have
> any experience to share?
____________

Signals from a certified Part 15 FM system aren't all that puny. Below is a table showing what to expect over a clear, reflection-free path from the tx antenna to the receive antenna.

Without interference, a decent car radio should receive a usable Part 15-compliant FM signal well beyond a 1,000 foot radius from a tx antenna radiating the maximum legal Part 15 FM field in all compass directions.

Feet > Field, µV/m
9.84 > 250.00 (this is the field defined by the FCC at 3 meters)
19.68 > 125.00
39.36 > 62.50
78.72 > 31.25
157.44 > 15.63
314.88 > 7.81
629.76 > 3.91
1259.52 > 1.95
2519.04 > 0.98

//

 

[WCWalker]

***R. Fry is even more anal than I am. He's got too much time on his hands and wants to nitpick the finer points of the technical aspects of part 15 broadcasting even when it conflicts with FCC views or protocol.

You are going to get much greater range with one of these units if you mount it up in the air. I know a guy in Indiana that did this and his range on a typical car radio was 2/3rds of a mile in three directions and half a mile in the other.

He mounted the unit 40 feet up in the air and got it away from most trees in his yard and it performed quite well. Range for home based radios was only about two to three blocks but he had full quieting in a car radio for the afformentioned distances.

I asked two different sources at the FCC about this and they see nothing wrong with it. 'nuff said.



> > Panaxis makes the ACC 100. It's a FCC Type Accepted Part
> 15
> > FM transmitter. www.panaxis.com Ernie Wilson's been
> around
> > for years and has a reputation for being a decent marketer
>
> > of low power radio gear.
> >
> >
> >
>
> WCWalker,
>
> Thank you, I'd seen their website before, they are very
> similar to the Talking House transmitters, maybe better
> quality.
>
> I don't see how if the transmitter I'm using has less power
> and the antenna is not a high gain antenna, ie. maybe
> 1.5-2.5db gain antenna, that my signal is somehow illegal in
> terms of the 250uv/3m rule... just the 100ft 75 ohm cable is
> attenuating the signal roughly in half before it gets to the
> antenna alone. The school campus is around 3-4 acres, so if
> the signal fades out after 300-350ft, who cares, as long as
> the transmission is clean and free of interference.
>
> Radiopilot
>

 

[radio8z]

> Neil,
>
> T have an X-File XFT-40 model FM digital PLL (FCC certified)
> transmitter (FCC ID: RA6NFM-40T) is the registration number,
> this unit goes out 100-200 ft max on a good day on a clear
> frequency, not bad but the unit is not meant for serious
> broadcasting, I'd say it's equivalent in terms of an EDM10
> but with less power, perhaps 1-5m....
>
> I also have several Belkin Tunecast II FM transmitters which
> I used for experimentation purposes (FCC certified) and they
> have about -22dbm as measured on Belkin's test, about .05mw
> of power, it has about about 50 feet range, these are made
> for car FM accessory applications.
>
> Surely there are those here that have the FM certified
> transmitter that can give us definate results.
>
> Radiopilot
>
Radiopilot,

Are the Belkin units certified with an antenna? I haven't seen these units.

Also, somewhere I read that you broadcast on a campus. You might want to look at Part 15.221. It appears that one could put a fairly high power unit in the center of campus and if the field strength limits are met at the campus perimeter, then a really good AM signal would result beyond the borders.

My only experience with campus radio was with carrier current AM, and we had a transmitter in each dorm. Couldn't hear it very far away but inside the dorm, it boomed.

Neil

 

[rfry]

> You are going to get much greater range with one of these
> units if you mount it up in the air. I know a guy in
> Indiana that did this and his range on a typical car radio
> was 2/3rds of a mile in three directions and half a mile in
> the other.
>
> He mounted the unit 40 feet up in the air and got it away
> from most trees in his yard and it performed quite well.
> Range for home based radios was only about two to three
> blocks but he had full quieting in a car radio for the
> afformentioned distances.
_________________

There is nothing in Part 15 limiting the height of Part 15 FM antennas, and I have never written that there was. The performance you report above is not unexpected even from compliant Part 15 FM systems, as I posted earlier in this thread (pasted below):

+ + +

Signals from a certified Part 15 FM system aren't all that puny. Below is a table showing what to expect over a clear, reflection-free path from the tx antenna to the receive antenna.

Without interference, a decent car radio should receive a usable Part 15-compliant FM signal well beyond a 1,000 foot radius from a tx antenna radiating the maximum legal Part 15 FM field in all compass directions.

Feet > Field, µV/m
9.84 > 250.00 (this is the field defined by the FCC at 3 meters)
19.68 > 125.00
39.36 > 62.50
78.72 > 31.25
157.44 > 15.63
314.88 > 7.81
629.76 > 3.91
1259.52 > 1.95
2519.04 > 0.98

//

 

[radiopilot]

> > Neil,
> >
> > T have an X-File XFT-40 model FM digital PLL (FCC
> certified)
> > transmitter (FCC ID: RA6NFM-40T) is the registration
> number,
> > this unit goes out 100-200 ft max on a good day on a clear
>
> > frequency, not bad but the unit is not meant for serious
> > broadcasting, I'd say it's equivalent in terms of an EDM10
>
> > but with less power, perhaps 1-5m....
> >
> > I also have several Belkin Tunecast II FM transmitters
> which
> > I used for experimentation purposes (FCC certified) and
> they
> > have about -22dbm as measured on Belkin's test, about
> .05mw
> > of power, it has about about 50 feet range, these are made
>
> > for car FM accessory applications.
> >
> > Surely there are those here that have the FM certified
> > transmitter that can give us definate results.
> >
> > Radiopilot
> >
> Radiopilot,
>
> Are the Belkin units certified with an antenna? I haven't
> seen these units.
>
> Also, somewhere I read that you broadcast on a campus. You
> might want to look at Part 15.221. It appears that one
> could put a fairly high power unit in the center of campus
> and if the field strength limits are met at the campus
> perimeter, then a really good AM signal would result beyond
> the borders.
>
> My only experience with campus radio was with carrier
> current AM, and we had a transmitter in each dorm. Couldn't
> hear it very far away but inside the dorm, it boomed.
>
> Neil
>

Neil,

The Belkin is FCC certified with a small antenna embedded with the audio cables, if you carefully pry out the antenna wire (10 inches) and hang the unit like you would the AM transmitter at about 50 feet, you'll have some very nice range, equal in quality to any FM out there, but the range is small as it's certified for 150uv/3m and not 250uv/3m... but it's a clean PLL 88-108mhz transmitter, very nice too!

I have the Radio Systems TR20 20 watt AM transmitter made for TIS/HAR with the carrier current adapter and have used it but it interferes with the audio/visual systems of the school (arts/performing school), anyway I cannot use it and the kids just will not listen to AM period! AM for young kids is dead! Unless you REALLY get them motivated it's very hard to get them to understand there is something other than Ipods and Internet radio.

Radiopilot

 

[radiopilot]

> ***R. Fry is even more anal than I am. He's got too much
> time on his hands and wants to nitpick the finer points of
> the technical aspects of part 15 broadcasting even when it
> conflicts with FCC views or protocol.
>
> You are going to get much greater range with one of these
> units if you mount it up in the air. I know a guy in
> Indiana that did this and his range on a typical car radio
> was 2/3rds of a mile in three directions and half a mile in
> the other.
>
> He mounted the unit 40 feet up in the air and got it away
> from most trees in his yard and it performed quite well.
> Range for home based radios was only about two to three
> blocks but he had full quieting in a car radio for the
> afformentioned distances.
>
> I asked two different sources at the FCC about this and they
> see nothing wrong with it. 'nuff said.
>
>
>
> > > Panaxis makes the ACC 100. It's a FCC Type Accepted
> Part
> > 15
> > > FM transmitter. www.panaxis.com Ernie Wilson's been
> > around
> > > for years and has a reputation for being a decent
> marketer
> >
> > > of low power radio gear.
> > >
> > >
> > >
> >
> > WCWalker,
> >
> > Thank you, I'd seen their website before, they are very
> > similar to the Talking House transmitters, maybe better
> > quality.
> >
> > I don't see how if the transmitter I'm using has less
> power
> > and the antenna is not a high gain antenna, ie. maybe
> > 1.5-2.5db gain antenna, that my signal is somehow illegal
> in
> > terms of the 250uv/3m rule... just the 100ft 75 ohm cable
> is
> > attenuating the signal roughly in half before it gets to
> the
> > antenna alone. The school campus is around 3-4 acres, so
> if
> > the signal fades out after 300-350ft, who cares, as long
> as
> > the transmission is clean and free of interference.
> >
> > Radiopilot
> >
>

Right now range is not the question, the transmitter does it's job, I have no problem using it and the kids love it, they enjoy the 'programming and DJ' part of and the mixing tunes, making sweeps, and the general feeling of it all. Trying to get the kids to listen to what they just programmed is good for a couple of days, then back to the Ipods.... I may just have the kids do Podcasting as this is what they want to do....

Who knows, but I can sure tell you IBOC and HD radio is not the answer, just go ask the generation of kids this is going to impact and they'll just think it's a joke!

Radiopilot

 

[wkbam1690]

> Panaxis makes the ACC 100. It's a FCC Type Accepted Part 15
> FM transmitter. www.panaxis.com Ernie Wilson's been around
> for years and has a reputation for being a decent marketer
> of low power radio gear.

I seem to recall a website several years ago where someone was using one of the Panaxis units mounted in an enclosure made of PVC, and located on a mast and was claiming to cover most of a small community in, I believe it was rural Indiana.