part 15 FM.....your opinions???

[carlvenorden]

I'm curious as to your opinion on Part 15 FM. We already know a lot of things: the LPFM licences went to the churches, and the translators are taking over the little free space available on FM.

Part 15am allows about 25mW, which is about a yard sale.

Personally, I see no reason to allow part 15 operators some decent power, or antenna height, ON A CLEAR FREQUENCY, to cover a basic neighborhood. For part 15 operators, a decent neighborhood could be a block. Other hand, I advocate a longer antenna, or better power for part 15AM.

I'm bringing this up for a reason. I have inside information that this information is being discussed within the FCC this week.

The argument is that FM is the million dollar frequency and letting it loose will cause interference; if that happens, more licencing will occur. I believe that arguement.

However; using the following scenario, can we argue FOR part 15 FM that can be heard beyond your yard???????????

Providing there is a clear frequency in your yard, and extending for one mile without interference (or interference of a frequency that really can't be understood or listened to),
why can not part 15'ers use that frequency with a power of 100mW and an antenna that sent out a one mile circular signal?

Of course if a commercial station were licenced to your frequency you would have to vacate it (you would have to anyway, it just wouldn't work).

The FCC is all about religeous programming right now; the homegrown community is totally ignored, and pays all the fines related to pirating. So, what is the problem?
In this country all are created equal except in broadcasting. Unless you are a big broadcasting company, a small-just-entered-the-religeon-broadcasting-biz, own a translator (which will belong to a big broadcasting company), or are a college station, you have no business applying for a public frequency or using it, lest you get found and fined.
Mother Russia!!!!!!!!!!!!!

Lets establish a REAL part 15-type broadcasting service in an organized way.
1. Register it.....frequency, power.
2. Agree to abandon it if a commercial is assigned.
3. Serve your community with programming not available on the locals.

Now that is local radio and that is just my opinion.

for part 15 ground systems and coils, email:
[email protected]
carl

 

[phatdaddy]

I honestly think its a great idea but it simply won't happen. It's all about the money! The NAB, PBS, and the Clear Channels of the country have too big a vested interest in the status quo to ever permit any substantial changes to the suffocating Part-15 FM specs as currently written. Consider how the NAB is currently whining about the mobile satellite radio receivers interfering with FM stations due to either excessive power or improper installation. Does this sound like a group that is going to stand still for any relaxation to their precious 250 uV rule?

It seems to me that the best chance for the community broadcaster is in the upcoming low power AM proposals. The 100 mW rule should be trashed in favor of a 1 Watt limit which would also require the operator to register his station with the local FCC field office. It should still be license-free but the FCC should know where these stations are due to their increased potential to create interference. This 10 dB power increase would roughly double the coverage area of current 100 mW installations and make them more useful to the communities they are trying to serve.

Just some more food for thought......

 

[dbdigital]

There are many other issues the FCC should be discussing and making decisions on before the idea of a Part-15 500mw service can be entertained. Among these are the LPAM proposal and LPFM-10 service both of which have been gathering dust on the FCC docket. The 2003 translator invasion has yet to be resolved as well as freeing up the Channel 6 spectrum and what to do about those broadcasters who refuse to give it up (or, I guess at this point, are not required to). The matter of letting AM stations have FM translators and allowing FM translators to originate programming are also issues that have not yet been decided.

So, as you can see, the FCC has much on its plate but is chewing and digesting very little where radio broadcasting is concerned.

db

 

[Grrrradio]

I keep up on the FCC news for pirate radio, and have read of stations being busted for running a quarter-watt into a car antenna, as well as a station in Oklahoma with a measured field strength of 77 uV/m at 183 meters (i.e. 37 dBu at 600 feet -- just outside the blue contour on a Radio-Locator map -- "tolerably weak" at best, even on a good car radio. I'm no engineer, so I can't do precise math on this one... but from what I remember of some early shot-in-the-dark experiments as a teenager, it seems like about what you'd get out of a tenth of a watt into a very long wire, i.e. at multiples of lambda.) I've also heard some stories on this board of VERY overzealous Part 15 enforcement.

In any event, they've apparently got the time, resources, and willingness to fart around making sure that Part 15s aren't going 20 feet further than they're supposed to (saints preserve us!)... and to dig for fractions-of-a-watt signals above Part 15. That tells me they've damn sure got the time and resources to investigate at least a 250 mW station, or even 500 mW, especially where the process would be complaint-driven (just as with pirates). I don't buy the idea that it would be any more of an administrative burden on the FCC than the current Part 15 service is, nor that there would be a terribly increased risk of interference, especially where *existing* pirate and Part 15 radio enforcement is complaint-only to begin with. (I.e., if a complaint comes up on an expanded-15 station, they'd investigate it the same way they already investigate pirates -- all an expanded Part 15 service rule would really have to do is require the FCC to have an actual-interference basis, or the established power exceeded, before being able to shut down the station.)

Since it wouldn't complicate the actual investigative process (i.e. would only limit the number of people the Feds could shut down after the investigation), I have to take Phatdaddy's view -- that the only thing really holding back an expansion of Part 15 is political. The large radio conglomerates have willfully abandoned any kind of localism, but still know a real competitor when they see it... and a station with even weak service out to a mile or so could easily cover most small towns. (Out here in the Midwest, where there are few topological barriers to the even spread of city growth, this could even cover a mid-size town of 10 or 12 thousand people!)

 

[radioboy]

It seems to me that the best chance for the community broadcaster is in the upcoming low power AM proposals. The 100 mW rule should be trashed in favor of a 1 Watt limit which would also require the operator to register his station with the local FCC field office.

The low power AM proposals are probably the ONLY chance left for the community broadcaster.

In my area, there are at least 6 Christian stations. Coming from a commercial Christian broadcasting career, that in itself doesn't bother me - but then the LPFM goes to - a church!!?? Relly..LPFM is a joke for most of the country. A few folks, like Chuck and Gene(WRPO), who contribute to the board, have developed real community stations. But for most of us..

A 1-watt AM was proposed some time back through Radio Ready to Grow although I don't remember all the details of that proposal.

In my area, the FM dial is so full that probably nothing can be added to it. Not all of those signals are local..several are rimshots, or are just close enough to make the channel useless. AM is actually pretty clear here beyond the 4 local AMs. Actually there's 5 but one is silent..owner wants a fortune for a license with no assets or business.

I think a lot of what the FCC does now has only one purpose: to bring in money to the government. Many
violations that they can issue fines for are minor, trivial, and frivolous.

This is basically a good idea that will never be allowed to happen.

When veteran broadcasters and the average American are shut out or priced out of the market/business, it's no wonder little stations spring up!

Mine will be springing back to life later this summer if all goes well. With a Rangemaster and Carl's ground system.

 

[Tom Wells]

For a while, I used a C Crane FM modulator to put the same signal as my AM on FM.
It stopped modulating audio about a year ago, and I haven't replaced it.
My AM is flat to 15khz, and I far prefer the sound of the end result to FM's sound.
No matter how I fiddled the audio, I couldn't seem to get same pure sound on the FM.
And the truly compliant AM would seem to have better coverage than a compliant FM.

I would be very happy to see an authorized 1-w AM service instituted, but I hold little hope of this
ever occuring.

 

[Black_Shire]

For a while, I used a C Crane FM modulator to put the same signal as my AM on FM.
It stopped modulating audio about a year ago, and I haven't replaced it.
My AM is flat to 15khz, and I far prefer the sound of the end result to FM's sound.
No matter how I fiddled the audio, I couldn't seem to get same pure sound on the FM.
And the truly compliant AM would seem to have better coverage than a compliant FM.

I would be very happy to see an authorized 1-w AM service instituted, but I hold little hope of this
ever occuring.

With a good antenna/ground system, a range of tens of miles is possible with 1 watt. The pirate radio ship MV Ross Revenge, the home of Radio Caroline, is still broadcasting today and is now doing so legally, under Britain's RSL (Restricted Service License) low-power radio licensing plan. The vessel is moored in Southeast England and broadcasts on Medium Wave, using 1 watt ERP through a Marconi "Tee" wire antenna which is suspended between two towers on the deck.

The radio and heavy horse enthusiast Derek Norry visited the ship/radio station, and he photo-documented and chronicled his visit here: www.heavyhorses.co.uk . (Click on "Pictures" on the first screen-page, then click on "Page 96 MV Ross Revenge" at the very bottom of the "Pictures" page.) Derek reported that the station is "getting 20 to 30 miles, which in the south east of England is a lot of folks."


-- Black Shire

 

[rfry]

With a good antenna/ground system, a range of tens of miles is possible with 1 watt. The pirate radio ship MV Ross Revenge, the home of Radio Caroline, is still broadcasting today and is now doing so legally, under Britain's RSL (Restricted Service License) low-power radio licensing plan. The vessel is moored in Southeast England and broadcasts on Medium Wave, using 1 watt ERP through a Marconi "Tee" wire antenna which is suspended between two towers on the deck. ... Derek reported that the station is "getting 20 to 30 miles, which in the south east of England is a lot of folks."

Note that 1 watt ERP on 530 kHz produces a field strength of about 1 mV/m over a sea water path of about 6 miles. A 1 mV/m signal is about the minimum needed for fairly noise-free reception using a cheap indoor AM receiver in an urban area.

So even if the soil conductivity of southeast England was as good as sea water, wouldn't the effective range of this setup be a lot less than claimed?
//

 

[radiopilot]

With a good antenna/ground system, a range of tens of miles is possible with 1 watt. The pirate radio ship MV Ross Revenge, the home of Radio Caroline, is still broadcasting today and is now doing so legally, under Britain's RSL (Restricted Service License) low-power radio licensing plan. The vessel is moored in Southeast England and broadcasts on Medium Wave, using 1 watt ERP through a Marconi "Tee" wire antenna which is suspended between two towers on the deck. ... Derek reported that the station is "getting 20 to 30 miles, which in the south east of England is a lot of folks."

Note that 1 watt ERP on 530 kHz produces a field strength of about 1 mV/m over a sea water path of about 6 miles. A 1 mV/m signal is about the minimum needed for fairly noise-free reception using a cheap indoor AM receiver in an urban area.

So even if the soil conductivity of southeast England was as good as sea water, wouldn't the effective range of this setup be a lot less than claimed?
//

This is where REAL WORLD experimentation and actual measurements differ from calculations done on a computer even though the physics claim otherwise.

No matter what the outcome is on your NEC software and you're adherance to the data collected over decades of FCC testing... the real world is alot different, that's why in science one takes the theory and performs real experimentation and adjusts the numbers to match...

I do this all the time in my field of work... no matter how much I calculate pressures, temperatures, vibrations, etc. the real experimentation and test results proves otherwise.

So perhaps he's getting tens of miles as the article states and actual listeners describe, even though your calculations suggest 6 miles at best.

Radiopilot

 

[rfry]

This is where REAL WORLD experimentation and actual measurements differ from calculations done on a computer even though the physics claim otherwise. No matter what the outcome is on your NEC software and you're adherance to the data collected over decades of FCC testing... the real world is alot different, that's why in science one takes the theory and performs real experimentation and adjusts

The 6-mile range to the 1 mV/m contour for 1 watt ERP on 530 kHz over a sea water path is essentially equal to the inverse distance field for those parameters. (The inverse distance field is the field produced over a path having no groundwave loss, whatsoever.)

Propagation conditions in the real world can reduce this 1 mV/m field intensity for this ERP and frequency, but it can't increase them. There is no groundwave propagation path on earth with conductivity greater than sea water.

Theory and real-world experience are not in conflict here. They give the same result.
//

 

[Black_Shire]

With a good antenna/ground system, a range of tens of miles is possible with 1 watt. The pirate radio ship MV Ross Revenge, the home of Radio Caroline, is still broadcasting today and is now doing so legally, under Britain's RSL (Restricted Service License) low-power radio licensing plan. The vessel is moored in Southeast England and broadcasts on Medium Wave, using 1 watt ERP through a Marconi "Tee" wire antenna which is suspended between two towers on the deck. ... Derek reported that the station is "getting 20 to 30 miles, which in the south east of England is a lot of folks."

Note that 1 watt ERP on 530 kHz produces a field strength of about 1 mV/m over a sea water path of about 6 miles. A 1 mV/m signal is about the minimum needed for fairly noise-free reception using a cheap indoor AM receiver in an urban area.

So even if the soil conductivity of southeast England was as good as sea water, wouldn't the effective range of this setup be a lot less than claimed?
//

No. It isn't uncommon for the state Sea Grant Part 15 AM radio stations set up at marinas and seaside national parks to achieve ranges of up to 3 miles, and they're only using 100 milliwatts into coil-loaded 2.6 meter tall CB whip antennas.

As Gerry Herlinger observed while he was developing the TalkingSign www.talkingsign.com Part 15 AM transmitter, the Automatic Gain Control (AGC) characteristics of modern AM receivers enable them to receive low-power AM transmitters at considerably greater distances than one would expect, when the transmitter is operated on a quiet channel.

The MV Ross Revenge's Marconi "Tee" antenna is a much larger and more efficient radiator than the 2.6 meter tall CB whip antennas used in outdoor Part 15 AM installations, so I'm not at all surprised that it can achieve broadcast ranges of 20 miles - 30 miles using an ERP (effective radiated power) of 1 watt.


-- Black Shire

 

[rfry]

The MV Ross Revenge's Marconi "Tee" antenna is a much larger and more efficient radiator than the 2.6 meter tall CB whip antennas used in outdoor Part 15 AM installations, so I'm not at all surprised that it can achieve broadcast ranges of 20 miles - 30 miles using an ERP (effective radiated power) of 1 watt.

ERP is the product of the antenna gain and the input power applied to the antenna. It doesn't matter in this setup what combination of antenna gain and input power is used to produce that ERP. It could be 1/2 watt of r-f input to an antenna with a gain of 2, or 1 watt input to an antenna with a gain of 1, etc.

And if this system effectively radiates 1 watt on 530 kHz from a vertically-polarized tee antenna, then the radius to its 1 mV/m contour over a path having the conductivity of sea water will be 6 miles. This value is based on accurate field strength measurements going back many decades, and also is supported by antenna theory and propagation analysis. It's not really open to debate.

It would be possible for radio listeners beyond 6 miles to tune in this station as long as they can tolerate the increasing noise and/or interference levels. My choice of 1 mV/m was based on a fairly noise-free signal on a cheap indoor receiver in an urban area.

For reasonably clear paths this 1 watt ERP would generate about 0.3 mV/m at 20 miles and about 0.2 mV/m at 30 miles (for salt-water paths). Those fields could produce a listenable signal on a good receiver, depending on the tolerance of the listener to the added noise and possible interference. Note that receiver AGC circuits can't improve the signal-to-noise ratio -- they only keep the audio output of the receiver fairly constant for a wide range of signal+noise input levels.

Once the radio wave crosses the shoreline from sea to land, it will be subject to the same groundwave losses for that overland path as a land-based transmitter generating that field at that shoreline would have. So the distances to the land-based contours would be less than those in my paragraphs above.
//

 

[phatdaddy]

This discussion on field strength points out another important fact. It is usually necessary to run more compression or processing on a Part-15 signal due to it's comparatively low field strength. Make sure the modulation is as near 100% as possible and if your transmitter supports asymmetrical modulation, get those positive peaks up near the 120% range, then set compression to keep the average modulation up near that level. If you can afford it, install an NRSC processor like the 222 to limit transmitted bandwidth and put more RF into those audio sidebands which can actually be heard in today's sick AM receivers. This is AM and we are going for "maximum smoke". It is possible to achieve high audio density and still have decent quality which doesn't fatigue the listener after a few minutes of listening. It took me a lot of tweaking on my Part-15 but is worth it. If the receiver can hear my carrier at all, the audio is "right there" and can be easily heard.

 

[Black_Shire]

The MV Ross Revenge's Marconi "Tee" antenna is a much larger and more efficient radiator than the 2.6 meter tall CB whip antennas used in outdoor Part 15 AM installations, so I'm not at all surprised that it can achieve broadcast ranges of 20 miles - 30 miles using an ERP (effective radiated power) of 1 watt.

ERP is the product of the antenna gain and the input power applied to the antenna. It doesn't matter in this setup what combination of antenna gain and input power is used to produce that ERP. It could be 1/2 watt of r-f input to an antenna with a gain of 2, or 1 watt input to an antenna with a gain of 1, etc.

And if this system effectively radiates 1 watt on 530 kHz from a vertically-polarized tee antenna, then the radius to its 1 mV/m contour over a path having the conductivity of sea water will be 6 miles. This value is based on accurate field strength measurements going back many decades, and also is supported by antenna theory and propagation analysis. It's not really open to debate.

It would be possible for radio listeners beyond 6 miles to tune in this station as long as they can tolerate the increasing noise and/or interference levels. My choice of 1 mV/m was based on a fairly noise-free signal on a cheap indoor receiver in an urban area.

For reasonably clear paths this 1 watt ERP would generate about 0.3 mV/m at 20 miles and about 0.2 mV/m at 30 miles (for salt-water paths). Those fields could produce a listenable signal on a good receiver, depending on the tolerance of the listener to the added noise and possible interference. Note that receiver AGC circuits can't improve the signal-to-noise ratio -- they only keep the audio output of the receiver fairly constant for a wide range of signal+noise input levels.

Once the radio wave crosses the shoreline from sea to land, it will be subject to the same groundwave losses for that overland path as a land-based transmitter generating that field at that shoreline would have. So the distances to the land-based contours would be less than those in my paragraphs above.
/

At the time of Derek Norry's visit, Radio Caroline was broadcasting at 1278 kHz aboard the MV Ross Revenge. At that frequency, the "Tee" antenna would be much more efficient than it would be at the 530 kHz frequency you plugged into the equations.

In any event, I see no reason why Derek Norry (a retired RAF officer) would make up the 20 mile - 30 mile range figure, as he doesn't work for Radio Caroline.


-- Black Shire

 

[rfry]

At the time of Derek Norry's visit, Radio Caroline was broadcasting at 1278 kHz aboard the MV Ross Revenge. At that frequency, the "Tee" antenna would be much more efficient than it would be at the 530 kHz frequency you plugged into the equations.

Your posts stated that the ERP from this system was 1 watt, so the carrier frequency, antenna input power, and the radiation efficiency of the antenna system are irrelevant. Whatever that combination was, it resulted in 1 watt of ERP. The combination will be different for 1278 kHz than for 530 kHz, but the ERP at 1278 kHz will still be 1 watt (by definition).

Therefore the inverse distance field strengths from this setup on 1278 kHz are the same as on 530 kHz. The only difference when using 1278 kHz is that groundwave losses will be higher, which will reduce the distances to the field strength contours I posted earlier in this thread.
//

 

[rfry]

The following links will give some insight in to what happens to radio waves when propagation paths change from salt water to land, as in the Radio Caroline situation. These links apply to a broadcast station on Santa Catalina Island, serving the Los Angeles area.

The first link shows the shape of the radiation pattern as it is launched from the antenna system. Note that it is a directional pattern, with maximum gain toward the population centers on the mainland.

http://www.fcc.gov/ftp/Bureaus/MB/Databases/AM_DA_patterns/305355-2453.pdf

The link below shows the affect of groundwave path conductivities on three field strength contours produced by this station. Notice how the distance to the contours to the east is much less than to the south, even though the ERP toward the east is much higher than toward the south. Once that radiation reaches and crosses land, it is quickly reduced by the relatively poor ground conductivities of those overland paths.

http://www.radio-locator.com/cgi-bin/pat?call=KBRT&service=AM&status=L&hours=D

//

 

[Black_Shire]

At the time of Derek Norry's visit, Radio Caroline was broadcasting at 1278 kHz aboard the MV Ross Revenge. At that frequency, the "Tee" antenna would be much more efficient than it would be at the 530 kHz frequency you plugged into the equations.

Your posts stated that the ERP from this system was 1 watt, so the carrier frequency, antenna input power, and the radiation efficiency of the antenna system are irrelevant. Whatever that combination was, it resulted in 1 watt of ERP. The combination will be different for 1278 kHz than for 530 kHz, but the ERP at 1278 kHz will still be 1 watt (by definition).

Therefore the inverse distance field strengths from this setup on 1278 kHz are the same as on 530 kHz. The only difference when using 1278 kHz is that groundwave losses will be higher, which will reduce the distances to the field strength contours I posted earlier in this thread.
//

If equations could predict perfectly the performance of antennas and ground systems in the real world, there would be no anechoic antenna test chambers or outdoor antenna test ranges.

Radio Caroline is a commercial radio station, which is in business to make money. They would not have gone to the trouble and expense of obtaining a Restricted Service License from the UK government broadcasting authority if their broadcast range and signal quality weren't good enough to reach (and keep) enough listeners to make it financially worthwhile.

Since most of Radio Caroline's program content is music, the audio quality of their AM signal must be quite good or people wouldn't listen, since they have plenty of music programming alternatives available on FM and DAB (Digital Audio Broadcasting) radio.


-- Black Shire

 

[rfry]

If equations could predict perfectly the performance of antennas and ground systems in the real world, there would be no anechoic antenna test chambers or outdoor antenna test ranges.

However test ranges/chambers are most practical at VHF frequencies and above, not at MW frequencies and below. Standard practice for MW broadcast antenna systems is to measure their real-world field strengths using a calibrated field meter, after the antenna system is installed. For directional AM broadcast stations the power and phase at each radiator can be adjusted to produce the measured fields in various compass directions as required for that station by the FCC.

At the time of Derek Norry's visit, Radio Caroline was broadcasting at 1278 kHz aboard the MV Ross Revenge. In any event, I see no reason why Derek Norry (a retired RAF officer) would make up the 20 mile - 30 mile range figure, as he doesn't work for Radio Caroline.

I did a little web reading on that. The Ross Revenge was tied up at a dock at the time of these RSL broadcasts in 2004. The RSL license they were operating under allowed 1 watt e.m.r.p. (effective monopole radiated power), and was good for 28 days.

In http://www.ofcom.org.uk/radio/ifi/rbl/rsls/rslapps/notes.pdf, Ofcom (the British FCC) says this about the coverage expected for these stations:

Coverage area and power levels
1.6 In order to make optimal use of the spectrum available for this type of licence, and satisfy as far as is practicable the level of demand from applicants, S-RSLs are issued for a restricted coverage area as well as being restricted by duration, and are for small-scale community use. Licences are issued for coverage of a town or part of a city, typically a 3km (2 mile) radius in an urban area, or a 5-7 km (3-4 mile) radius in a rural area. Power levels are set accordingly, with account also taken of interference levels, which limit coverage of the service. Coverage areas and transmitter sites, particularly for the higher power levels on FM, will be scrutinised carefully.

As for the claimed coverage range of 20-30 miles -- I happen to know one of the engineers from Radio Caroline when it was operating at high power while anchored offshore. I asked him to comment on this RSL operation, and here's part of what he wrote back:

Transmitter power is not limited, the stipulation is no more than 1 watt radiated. In fact that tends to be rather casually enforced, and sometimes that "One Watt" does surprisingly well. When the ship was broadcasting on 1278 KHz, the transmissions were audible over a radius of about 25 miles. I think the radiated power was probably nearer 100W !

So maybe this explains why their coverage was greater than reasonably could be expected for 1 watt ERP.

PS: The only reason I keep posting about this is so that people will not be left with the expectation that 1 watt of MW ERP can produce a coverage radius of 20-30 miles, and expect to achieve that themselves.

Enthusiasm is good, but it doesn't replace realism.

//

 

[Black_Shire]

R. Fry wrote:

<PS: The only reason I keep posting about this is so that people will not be left with the expectation that 1 watt of MW ERP can produce a coverage radius of 20-30 miles, and expect to achieve that themselves.>

The real reason is that you don't want to feel outmoded and irrelevant in your dotage, but whatever floats your boat...

I'm glad to hear that Radio Caroline has remained true to their pirate radio heritage, doing what they can get away with when the authorities aren't looking.


-- Black Shire

 

[rfry]

R. Fry wrote: <PS: The only reason I keep posting about this is so that people will not be left with the expectation that 1 watt of MW ERP can produce a coverage radius of 20-30 miles, and expect to achieve that themselves.>

The real reason is that you don't want to feel outmoded and irrelevant in your dotage, but whatever floats your boat... I'm glad to hear that Radio Caroline has remained true to their pirate radio heritage, doing what they can get away with when the authorities aren't looking.

But note that proven science does not become outmoded or irrelevant, no matter the dotage of those who first discovered/described it, or those who now refer to it.

Anyone with provable evidence showing errors in the statements I've made are welcome to present same for verification by scientific methods.

I'll quickly admit to, and correct all proven errors I've made in my posts in this, or any other thread.

In fairness -- will that also will be true for you, Black_Shire?

Your comment about being glad to hear that Radio Caroline is "doing what they can get away with when the authorities aren't looking" tells us quite a bit about you, does it not?

//