LPFM – Page 2 – Engineering Radio

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 the 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 planning 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, electricity, 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	Used for call-in/on air
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 the 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.

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:

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.

And:

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.

Micro Radio goes to Occupy Wall Street

I read a very interesting article from John Anderson regarding the Occupy Wall Street movement’s use of media, specifically low-powered radio. Being a native New Yorker, the demonstrations are of some interest to me. To date, the demonstrators have placed a wide variety of grievances at the feet of “Wall Street,” some justly and some not. What I found interesting about it is this:

Last week, the Occupy Wall Street encampment established a microradio station at 107.1 FM. The station simulcasts the 24/7 live stream which provides coverage of life inside Zuccotti Park, as well as street-level reportage of daily protest actions in New York City’s financial district.

One of the reasons for this is the City’s ban on the use of amplified speakers and or public address systems. By using a micro radio station, persons in a crowd too far away to hear the orator can use a small FM radio or even their smartphones to listen to the speech. Another reason is the idea that large corporate media has been controlling the narrative for far too long, to the detriment of the average citizen.

Zuccotti Park is in lower Manhattan, about two blocks away from Wall Street itself. It is described as 33,000 square feet, which makes it about 3/4 of an acre. A part 15 FM radio station (47CFR 15.239) can easily cover this area and more. Even with the station limited to 250 µV field at 3 meters from the radiating element, generally thought to be 100 mW TPO, the reliable coverage area would be a radius of approximately 200 feet, depending on local interference. That makes the coverage area approximately 125,600 square feet or more. There are several other stations licensed to 107.1 in the greater NYC area; WXPK, WWZY are the closest and most likely to cause problems.

I am not sure how they are generating their live stream, but when listening to it for several hours over the weekend, I found it interesting and technically well done. They seem to be running circles around others, who are only grudgingly admitting that there might be something going on in some forty-odd cities across the US.

Micro Radio is a creative way to use the available technology and keep the public and protesters informed.