New Zealand License Free LPFM

[edarmsttrong]

Did anyone else notice that New Zealand just changed rules for it's version of Part 15 FM as of June 1st, 2010?

They shifted their FM band down to 87.5 Mhz. LPFM operators are allowed to use 87.6 through 88.4. The old band was 88 to 88.8 Mhz.
The upper band, 106.7 to 107.7 Mhz is unchanged.

They also allow 1 Watt E.I.R.P. now!

Surely, if the good people of New Zealand can follow simple rules, the citizens of the USA could, too. Why a service like this can't exist here really
baffles me....

Read all about it here:

http://www.rsm.govt.nz/cms/policy-and-planning/current-projects/broadcasting/lpfm-gul-consultation-2010/lpfm-gul-consultation-paper-march-2010/attachment-c-proposed-lpfm-gusl

 

[Ai4i]

With no antenna hight limit.

 

[druidhillsradio]

Surely, if the good people of New Zealand can follow simple rules, the citizens of the USA could, too. Why a service like this can't exist here really
baffles me....

Not me. It's called the NAB. They lied about interference potential by distributing phoney audio CD's to members of Congress. They get shlock operations like NPR to scare the public about the dangers of LPFM's to full power stations, many of which stared out as 10 watt operations.

 

[Ermi Roos]

The increase to 1 W EIRP, and the additional channels, do not apply to license-free broadcasting, but to "General User Spectrum" licensees. Previous documents from New Zealand's Radio Spectrum Management mention a "transition period" to implement the changes to the rules, and a Temporary General User Spectrum License that is good for the transition period.

The General User Spectrum License appears to be very trivial. No frequencies are assigned, and the licensees are supposed to work out interference issues among themselves. If the present interference problems in the major population centers (like Aukland, Wellington, Christchurch, Hamilton, etc) persist, maybe the temporary licenses will not be renewed after the transition period. From what I have read, LPFM is really screwed up in the population centers, with several stations on each available channel.

Other proposals RSM may consider is allowing only mono in "saturated" areas, and requiring at least a 2 km spacing between LPFM stations.

In the US, the EIRP allowed for Part 15 FM is 18.75 nW. 1 W EIRP is a gain of 77.3 dB!

 

[wkbam1690]

In the US, the EIRP allowed for Part 15 FM is 18.75 nW. 1 W EIRP is a gain of 77.3 dB!

Where specifically do the rules state 18.75 nW for Part 15 FM?

 

[rfry]

Where specifically do the rules state 18.75 nW for Part 15 FM?

For Part 15 they state 250 µV/m maximum field measured 3 meters from the antenna. Doing the math shows that this field is generated when 18.75 nW is radiated by an isotropic antenna.

Of course, an isotropic antenna does not exist in the real world. A more useful reference is a 1/2-wave dipole, which does exist, and which produces the FCC maximum Part 15 FM field with about 11.43 nW of applied power.

RF

 

[wkbam1690]

Where specifically do the rules state 18.75 nW for Part 15 FM?

For Part 15 they state 250 µV/m maximum field measured 3 meters from the antenna. Doing the math shows that this field is generated when 18.75 nW is radiated by an isotropic antenna.

Of course, an isotropic antenna does not exist in the real world. A more useful reference is a 1/2-wave dipole, which does exist, and which produces the FCC maximum Part 15 FM field with about 11.43 nW of applied power.

RF

So, in theory, one could mount a dipole on a mast and calculate the loss necessary to arrive at 11.43 nW of power getting to the antenna. If you have a small transmitter with an output of, say 50 mW, you would need a loss of around 66.4 dB from the transmitter output to the antenna input. This could be realized with 2 30 db attenuators, a 6 db attenuator, and roughly 0.4 dB loss from the coax.

 

[pianoplayer88key]

Where specifically do the rules state 18.75 nW for Part 15 FM?

For Part 15 they state 250 µV/m maximum field measured 3 meters from the antenna. Doing the math shows that this field is generated when 18.75 nW is radiated by an isotropic antenna.

Of course, an isotropic antenna does not exist in the real world. A more useful reference is a 1/2-wave dipole, which does exist, and which produces the FCC maximum Part 15 FM field with about 11.43 nW of applied power.

RF

What would the approximate level be for a part 15-compliant FM (250µV/m @ 3m) if you run the transmitter without an antenna connected, or at most something a tiny fraction of a millimeter or maybe a few micrometers (i.e. won't protrude at all past the antenna terminal) if you have to have something? Also, this may be a bit OT for this thread, but what would similar power levels be for 15,848µV/m @ 30m at 13.56MHz, 10,000µV/m @ 3m at 27MHz and 49.86MHz, 50,000µV/m @ 3m at 915MHz, 2.44GHz, 5.8GHz, and 250,000µV/m @ 3m at 24.125GHz?

 

[Ai4i]

What would the approximate level be for a part 15-compliant FM (250µV/m @ 3m) if you run the transmitter without an antenna connected, or at most something a tiny fraction of a millimeter or maybe a few micrometers (i.e. won't protrude at all past the antenna terminal) if you have to have something?

If said transmitter in question is located within a 100 percent shielded and grounded cage of pure silver one meter thick and is transmitting into a dummy load within the same environment, that transmitter should probably run less than one million watts in order to remain part 15 compliant ;D

 

[rfry]

So, in theory, one could mount a dipole on a mast and calculate the loss necessary to arrive at 11.43 nW of power getting to the antenna. ...

While that is true, that is not "the whole story" concerning compliance with the FCC Rules for Part 15 FM. For example:

• That 250 µV/m field is the calculated, maximum, free-space field for radiation from the dipole, itself. But near the earth the measured field can vary by maybe +6 dB to maybe -20 dB as a result of reflections. Measuring the field only 3 meters from the Part 15 FM antenna may reduce the contribution of these reflections to the measured value somewhat, but not enough so that the reflections may be ignored.
  
• If coaxial cable is used as the transmission line between the transmitter and a dipole antenna, then unless means is provided to prevent it, r-f current will flow on the outside of the outer conductor ("shield") of the cable, which will produce radiation that combines with the radiation from the dipole. It could either add or subtract from the dipole radiation, depending on how the cable and dipole are physically oriented with respect to each other, and the physical location where the net field is measured.
  
• Even if the coax outer conductor does not have any r-f current on it conducted by a wire path directly from the transmitter, r-f current may be induced on it by radiation from the antenna, which can change the net radiated field in a manner similar to when a direct connection to the outer conductor does exist.

Measuring such fields and/or such total, transmitted power levels as are needed to produce them takes specialized and expensive test equipment that the average person has no access to.

So for those wanting some assurance that they meet Part 15 FM they might be better off buying a system (including its non-removable antenna) that has been granted FCC certification, and has the FCC identifying label appearing on its case somewhere. Probably that will not be a unit rated for output powers of a milliwatt and more, because such power is much more than can be radiated even by a short "whip" antenna to be compliant with Part 15 FM.

On another website, Part 15 operator "Neil" (radio8z) has posted some practical guidance about adjusting the length of a whip or wire antenna to whatever it takes so that the FM signal cannot be received on a good FM receiver over a clear, unobstructed path for much more than 200 feet. That is the free-space distance from a Part 15 FM system just meeting the Rules to a field intensity of about 10 microvolts/meter. That still will be no guarantee that the system would pass an FCC inspection, but the chance of such an inspection would be rather unlikely for such a system.

The link below leads to a chart of free-space field vs. power radiated by a 1/2-wave dipole (only).

http://i62.photobucket.com/albums/h85/rfry-100/6417f684.gif

RF

 

[Ai4i]

What would the legal condition be of taking an FCC certified device and antenna and placing them at the focal point of a reflector or near the primary winding of a transformer connected to a high gain antenna?

 

[rfry]

What would the legal condition be of taking an FCC certified device and antenna and placing them at the focal point of a reflector or near the primary winding of a transformer connected to a high gain antenna?

That is a judgment call, but one approach an FCC field inspector might take is that if the radiated field measured some distance away from that setup, say 100 meters or more, is higher than could be expected for a system radiating the peak legal field 3 meters from the driven antenna in that same direction, then the system is non-compliant.
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[wkbam1690]

What would the legal condition be of taking an FCC certified device and antenna and placing them at the focal point of a reflector or near the primary winding of a transformer connected to a high gain antenna?

That is a judgment call, but one approach an FCC field inspector might take is that if the radiated field measured some distance away from that setup, say 100 meters or more, is higher than could be expected for a system radiating the peak legal field 3 meters from the driven antenna in that same direction, then the system is non-compliant.
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What assurance is there that a certified unit which met Part 15 specs in the certifying lab's anechoic chamber, will still meet them in a real world installation, given the additive/subtractive nature of the direct to reflected waves. In other words, isn't it entirely possible that a unit could exceed the specs depending on the environment it is operated in?

 

[rfry]

What assurance is there that a certified unit which met Part 15 specs in the certifying lab's anechoic chamber, will still meet them in a real world installation, given the additive/subtractive nature of the direct to reflected waves. In other words, isn't it entirely possible that a unit could exceed the specs depending on the environment it is operated in?

Yes, that is possible. Proving the error would be very difficult, though.

Usually the FCC doesn't issue FM NOUOs in cases where there could be any doubt that the operation is non-compliant (including field reinforcement by reflections).

For example, a measured field that is 5 X or more greater than could be expected from the free-space field of a compliant system probably did not get that way because of reflections and/or measurement error.

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