The FCC LPFM plan

FCC moves ahead on a couple of different fronts in the LPFM battle.  Cliff notes version:

  1. The 2003 translator filing window question.  The FCC has more or less stuck with it’s plan to keep a minimum number LPFM channels available in the top 150 markets.  This also includes a 50 application limit for the country and no more than one application per market per applicant.  Where conflicts occur, translator applicants get the chance to demonstrate how their application would not preclude LPFM opportunities.
  2. Modifies (eventually eliminates) the May 1, 2009 cut of date for cross service (AM to FM) translators.
  3. The establishment of new LPFM allocations under the criteria of disregarding the third adjacent channel contours.
  4. More stringent requirements for local programming and ownership, especially as a determining factor for mutual LPFM applications.
  5. Allows LPFM stations to own translators.
  6. New class LPFM is established; the LP250.  The 250 watt LPFM stations are designed mainly for areas outside of top fifty markets or for previously licensed LP-100 stations that want to upgrade provided the minimum separation contours are met with existing stations.

The FCC has included the proposed rule changes as appendix A of FCC 12-28.  Standard FCC comment and reply windows apply.

Looks like things are moving along pretty fast.  Others have speculated at a filing window sometime later this year, I’ll not do that.

Cost of Starting a LPFM vs Cost of Internet Streaming

I have been watching the LPFM proceedings with some interest. The FCC has not exactly promised to have a filing window by end of 2012, but indicates that it might try to do that. In comparison to such evolutions in the past, this is moving pretty fast. Those that want an LPFM station need to start planing now.  As in previous LPFM windows, the availability is for non-profit organizations only.  This does not mean all hope is lost; NPR stations are all non-profits and most of them are very successful.

One of the biggest questions is: How much will it cost?  Like all things, it varies greatly.  If I were to put an LPFM or internet radio station on the air, there would be certain minimums, such as the use of professional audio equipment, a new antenna, and some type of redundancy.

Generally speaking, radio stations and internet stations both need some type of office/studio space.  This can range from large and opulent to a closet.  The costs for these would depend on the type and quantity of equipment installed, whether the equipment is new or used, the building, the area, etc.  Those facilities also have monthly reoccurring costs such as rent, electric, telephone service, internet service, etc.

Since internet radio stations and traditional terrestrial over the air radio would use the same type of studio equipment, those costs will be similar.  Here is a breakdown of the studio equipment:

Nomenclature Cost new (USD) Cost used (USD) Comments
12 Channel professional audio console $6,000.00 $2,500.00 Analog, 4 buss, telephone mix minus
Studio Furniture $5,500.00 $1,000.00 Can also be fabricated locally
Microphones, RE-20 or SM-7B $250-350 $100-150 Per unit, several required
Monitor Amp $250.00 $100.00 Can also use consumer version
Monitor speakers $500.00 $200.00 Can also use consumer version
CD Player $500.00 $200.00 Professional unit with balanced outs
Computer w/ professional sound card $1,500.00 $500.00 For automation and sound file storage
Computer, general use $700.00 $300.00 General information web browsing
Computer, Streaming w/sound card $900.00 $400.00 Sound card should be good quality
Studio Telephone system $1,900.00 $300.00 Used for call in/on air
Barix remote box $240.00 (x2) N/A Used for IP remote broadcasts
Comrex Matrix POTS codec $3,200.00 $700.00 Used for telephone line remote broadcasts
Misc wiring, hardware, ect $1,000.00 $800.00 Connectors, mic booms, wire, etc
Total $21,780.00 $7,930.00

Some equipment is not available used such as Barix boxes.  Of course, not all of this is required for a radio station, however, most local radio stations would want the capability to do remote broadcasts, take phone callers on the air, have multiple guests in the studio, etc.

For a traditional LPFM station, the transmitting equipment would entail:

Nomenclature Cost New (USD) Cost Used (USD) Comments
300 watt transmitter and exciter 4,400.00 2,000.00 Smaller transmitters with higher gain antennas can also be used
2 Bay ½ wave spaced antenna $1,900.00 $700.00
125 feet ½ inch coax $350.00 N/A
100 foot guyed tower and installation $4,000.00 $3,500.00 Not needed if station is on tall building or leased site
STL; IP radio w/ barix boxes $850.00 In lieu of standard 950 MHz STL
STL standard 950 MHZ $6,500.00 $3,500.00  Used in lieu of IP STL
STL antennas, transmission line $2,500.00 $1,500.00
FM Processor $10,000.00 $1,200.00 Can also use software such as Breakaway Broadcast
Misc connectors, grounding kits, etc $1,100.00 N/A
EAS unit $1,900.00 N/A Fully operational CAP compliant
Processing software, Breakway broadcast $200.00 N/A In lieu of standard FM processor
Total $12-24K $8-12K

This is a generic station, most will be somewhat different due to antenna supporting structures, transmitter powers and antenna types.  For the best possible signal, a circularly polarized antenna should be used.  A two bay, 1/2 wave spaced antenna will give the maximum signal density, while minimizing downward and upward radiation.  The upward radiation is simply wasted energy, as no one in space is listening to FM radio.  The downward radiation reduction is key if located in congested areas.

For internet radio station, the following would be required:

Nomenclature Cost New IUSD) Cost Used (USD) Comments
Streaming Server 2,100.00 1,100.00 Includes professional sound card
Audio processing software 200.00 N/A Recommend software such as Breakaway Broadcast
Audio Processing, outboard hardware 650.00 400.00 In lieu of software
Audio Streaming aggregator  1,200 to 2,400 N/A Annually

While LPFM’s are much more expensive than internet only stations, LPFM’s have the advantage of built in marketing, which is the on air signal.  If it is broadcasting on the air, word will get out.  On the internet, some other type of marketing will be needed to spread the word.  Also, LPFM’s should also be streaming, which would incur the same costs above.

The long and short of it is, to put a technically viable LPFM on the air is not an inexpensive proposition.  It is worth the effort, however, because the advantages of an LPFM over an internet only station are great.

Low Pass Filter design

Every good transmitter, tube transmitters in particular, require harmonic filtering.  The last thing any good engineer or broadcaster wants is to cause interference, especially out of band interference to public safety or aviation frequencies.  All modern transmitters are required to have spurious emissions attenuated by 80 dB or greater >75 Khz from carrier frequency.  In reality, 80 dB is still quite high these days, especially in the VHF/UHF band, where receivers are much more sensitive than they used to be.  A good receiver noise floor can be -110 dB depending on local conditions.

The principle behind a low pass filter is pretty easy to understand.  The desired frequency is passed to the antenna, while anything above the cut off frequency is restricted and shunted to ground via a capacitor.

Low pass RC filter
Low pass RC filter

In this case, the resistor is actually an inductor with high reactance above the cut off frequency.  Often, these filters are lumped together to give better performance.  This is a picture of an RVR three stage low pass filter:

RVR three stage low pass filter
RVR three stage low pass filter

RVR is an Italian transmitter maker that sells many transmitters and exciters in this country under names like Bext, Armstrong, etc.  The inductors are obvious, the capacitors consist of a copper strip sandwiched between teflon insulators held down by the dividers in between the inductors.

Schematically, it looks like this:

Low pass filter schematic diagram
Low pass filter schematic diagram

For the FM broadcast band, a good design cutoff frequency would be about 160 MHz. This will give the filter a steep skirt at the first possible harmonic frequency of 176 MHz (88.1 x 2 = 176.2).

Values for components:

Capacitors Value Inductors Value
C1 20 pf L1 74.7 nf
C2 54 pf L2 75.1 nf
C3 54 pf L3 73.9 nf
C4 20 pf

The inductors are wire, or in this case copper strap, with an air core.  It is important to keep the transmitter power output in mind when designing and building these things.  Higher carrier powers require greater spacing between coil windings and larger coil diameters.  This particular filter is rated for 1 KW at 100 MHz.

Shocker: LPFMs have little or no impact on commercial FMs

The long awaited report, required by the NAB as a part of the Local Community Radio Act has concluded that LPFMs have little or no impact on commercial FM stations. No kidding?

The executive summary states that:

LPFM stations serve primarily small and rural markets and have geographic and population reaches that are many magnitudes smaller than those of full-service commercial FM stations. In addition, LPFM stations generally have not been in operation as long as full-service commercial FM stations, have less of an Internet presence, and offer different programming formats. We also found that the average LPFM station located in an Arbitron Radio Metro Market (“Arbitron Metro”) has negligible ratings by all available measures and has an audience size that lags far behind those of most full-service stations in the same market.

Followed by:

Although each of the stations differs considerably in its individual characteristics, the results of the case studies show that the selected LPFM stations generally broadcast a variety of programming continuously throughout the day, operate with very small budgets, rely on mostly part-time and volunteer staff, do not have measurable ratings, have limited population reach, and do not generate significant underwriting earnings. All but one of the station managers that we interviewed stated that the LPFM station is not competing directly for listeners with any specific full-service stations.


We conclude that, given their regulatory and operational constraints, LPFM stations are unlikely to have more than a negligible economic impact on full-service commercial FM stations.

Forgive my excessive block quoting of the FCC report titled: Economic Impact of Low-Power FM Stations on Commercial FM Radio, I found those portions of text far better than anything that I could write on the subject.

The NAB is reportedly “reviewing” the results, which the cynical me thinks is just another way of stalling a potential LPFM window later this year.