Low Power FM Radio
Setting up a Low Power FM Radio station in NZ
I have been asked to set up a LPFM Radio station in northern Christchurch. Here is my blog:
July 2011:
I took a look at the site - it is actually in a storeroom and the intention is to partition off one end for the radio room. Some of the equipment has already been purchased off Trademe; there are 3 Computers running XP, a Transmitter and antenna, and an Axel Technologies Oxygen 3 broadcast console. Well, it's a start.
So what is involved in getting on air? Hook a CD player up to the transmitter via the mixer and switch it on? I had a hunch there is a bit more to it than that so I started to investigate.
Sure enough, there is a few things to get sorted:
1. There are regulations enforcing any broadcasting in NZ, including LPFM transmission. The MED Radio Spectrum Management governs these. In particular they are:
Unwanted Emission Limits Frequency Range from carrier Spectrum Analyser Resolution Bandwidth
-25 dBW 128 to 240 kHz Not to exceed 10 kHz*
-35 dBW 240 to 600 kHz Not to exceed 100 kHz*
-56 dBW > 600 kHz 100 kHz
* The spectrum analyser shall be set for 5 minute maximum hold.
Ok, I'm going to need the expertise of a Radio Technician (more on this below).
I also note the requirement to announce the owner's name and contact details every hour.
Additional information is available from the Radio Spectrum Management website.
2. Unless all the material being broadcast is original or in the Public Domain, we are going to need copyright clearance. This is dealt with by paying an annual licence fee to two organisations:
That covers the legal aspects. Now let's take an initial look at the equipment required. The Oxygen 3 mixer appears to be the real thing - it even has two channels with phoneline connection. We will not be using talkback anytime soon but it could be needed in the future. The station can be automated so the bare essentials to get on air will be: PC running scheduling software, the console, limiter, transmitter, and antenna. If the station gets manned then a broadcast mic, headphones, and a professional dual CD player will also be needed.
Scheduling Software
The station is a community effort so there is not much of a budget. I have scratched around and found three free programmes. These are Direttore, ZaraStudio, and A:B:J.
Direttore looks like this:
July 2011:
I took a look at the site - it is actually in a storeroom and the intention is to partition off one end for the radio room. Some of the equipment has already been purchased off Trademe; there are 3 Computers running XP, a Transmitter and antenna, and an Axel Technologies Oxygen 3 broadcast console. Well, it's a start.
So what is involved in getting on air? Hook a CD player up to the transmitter via the mixer and switch it on? I had a hunch there is a bit more to it than that so I started to investigate.
Sure enough, there is a few things to get sorted:
1. There are regulations enforcing any broadcasting in NZ, including LPFM transmission. The MED Radio Spectrum Management governs these. In particular they are:
- Siting of a broadcast transmitter: Within a 25 km radius of any broadcast transmitter there must be no more than one low power FM transmitter broadcasting substantially the same programme.
- Identification: Low Power FM transmitter operators must broadcast the contact details (name and address or phone no.) of the person responsible for the transmissions at least once every hour.
- Broadcast content: only transmissions that are broadcasting, as defined in the Broadcasting Act 1989, are permitted. All programmes must comply with the BSA (Broadcasting Standards Authority) and (if applicable) ASA (Advertising Standards Authority) regulations.
- Permitted transmission frequencies (MHz): 86.7, 87.7, 87.8, 87.9, 88.0, 88.1, 88.2, 88.3, and 106.7, 106.8, 106.9, 107.0, 107.1, 107.2, 107.3, 107.4, 107.5, 107.6, 107.7.
- Maximum Power: The maximum radiated power shall not exceed 0 dBW (1 W) e.i.r.p, and the field strength shall not exceed 95 dBμV/m based on a measurement at a distance of 100 metres from the transmit antenna.
- Permitted transmission bandwith: 256kHz
- Antenna polarisation: Emission polarisation shall be vertical.
- Transmitter carrier stability (frequency tolerance) must be maintained within +/- 5 kHz.
Unwanted Emission Limits Frequency Range from carrier Spectrum Analyser Resolution Bandwidth
-25 dBW 128 to 240 kHz Not to exceed 10 kHz*
-35 dBW 240 to 600 kHz Not to exceed 100 kHz*
-56 dBW > 600 kHz 100 kHz
* The spectrum analyser shall be set for 5 minute maximum hold.
Ok, I'm going to need the expertise of a Radio Technician (more on this below).
I also note the requirement to announce the owner's name and contact details every hour.
Additional information is available from the Radio Spectrum Management website.
2. Unless all the material being broadcast is original or in the Public Domain, we are going to need copyright clearance. This is dealt with by paying an annual licence fee to two organisations:
- Copyright clearance licence from APRA (costs $255.12+GST)
- Mechanical royalties licence from PPNZ (costs $109+GST)
That covers the legal aspects. Now let's take an initial look at the equipment required. The Oxygen 3 mixer appears to be the real thing - it even has two channels with phoneline connection. We will not be using talkback anytime soon but it could be needed in the future. The station can be automated so the bare essentials to get on air will be: PC running scheduling software, the console, limiter, transmitter, and antenna. If the station gets manned then a broadcast mic, headphones, and a professional dual CD player will also be needed.
Scheduling Software
The station is a community effort so there is not much of a budget. I have scratched around and found three free programmes. These are Direttore, ZaraStudio, and A:B:J.
Direttore looks like this:
and ZaraRadio looks like this:
The A:B:J software looks like this. It is a bit different to the other two; being designed like a DJ desk with A deck, B deck, and a crossfader.
There is some other handy freeware that will help too. For an MP3 tag editor there is:
MP3DirectCut
MP3Tag
Simple MP3 Tag Editor
Media Monkey (also a librarian)
and other free utilities are:
Shuangs Audio Joiner
Audacity
Tobasco's Amazing Clockwheel
MP3DirectCut
MP3Tag
Simple MP3 Tag Editor
Media Monkey (also a librarian)
and other free utilities are:
Shuangs Audio Joiner
Audacity
Tobasco's Amazing Clockwheel
Hardware
Audio:
Broadcast limiters are available but at $2000 or so they are well outside the price-range of this exercise. I am hoping to find a good peak limiter on TradeMe. Over the past year there has been the occasional Aphex Dominator for sale, so I'll keep a look out. Without this we are just asking for trouble, as an over-modulated transmitter will send spurious frequencies either side of the carrier which will interfere with adjacent stations and/or communications channels. This is a big no-no.
RF:
A transmitter with antenna has already been bought. Initially I thought this was a good thing, but having looked into what is involved I fear they may have bought a lemon. It is a DB Electtronica FM Modulator TRN and was bought on TradeMe for $500. I Goggled DB Electtronica and it turns out they are an Italian company that manufacture many radio transmitters for commercial use (up to 30KW). However, there is no mention of this model and I suspect by its appearance that it is quite old. By this I mean that if it was built in NZ I would say for sure it was of 1970s vintage. Other Google searches reveal nothing, so I have exactly zero information - not a good start. With the cover off I can see 15 W on the power amp circuit board, and inside a tin can are some rotary switches mounted on vero board which probably set the transmit frequency. There is no indication of what the rotary switches need set to to get a specific frequency. Round the back is the coax connector (which I think is an N type), and two RCA phono inputs - labelled Mono, and MPX. Does this means it can encode stereo or is a separate box required? So, now I have some questions for the Radio Tech. - is this thing set for 1W, 0.5W, 15W output?, is it going to transmit stereo? How do I set the carrier frequency? Also, I read that in NZ we use 50µS pre-emphasis (whereas in the USA its 75µS) so that will need checked as well. What's pre-emphasis? Well, radio has a fairly poor S/N ratio so the high frequency end of the audio signal is boosted prior to modulation. This is reversed at the receiving end. If this transmitter is set for 75µS the programme will sound tinny when received on a receiver designed for NZ FM radio transmission.
Moving on now... to getting the signal from the transmitter to the world (to the suburb of Papanui, actually). Bob (let's call him Bob, because that's not his real name) has already stuck up the aerial and is about to drill a hole in the roof for the cable...hmm. If only it were that simple! There are actually several types of antenna used for FM - dipoles, folded dipoles, yagis... all I know is the idea is to radiate the RF energy isotropically (ie in equal amounts in all directions). Practical antennas at FM frequencies don't quite do this so the coverage pattern is not in a circle, so things get a bit complicated. At this stage I am thinking it would be far easier to do Internet Radio, and this is probably true. Internet streaming does require a large data bandwidth so a standard ADSL connection is not going to work. This all adds up to it costing quite a bit, whereas the ongoing costs of broadcasting are very small. Apart from the financial considerations it just seems more radio-ish if people actually tune in. Anyway, back to the antenna. It needs to be vertically polarised, meaning that the radiation is mostly horizontal to avoid transmitting up into aircraft flightpaths. In other words it will mounted vertically rather than horizontally. As the maximum power radiation allowed for LPFM is 1W (it used to be 0.5W until 2010) the coverage is going to be too small if there are any inefficiencies. On the other hand some antennas give an effective gain so it is also possible to end up transmitting more than 1W and hence go outside the regulations. I would say the antenna in question is mounted high enough because it is sticking up from the building roof which must be at least 10m off the ground. This is good but the aerial pole itself is not that high off the roof and I'm wondering what effect a huge sheet of iron (which might be earthed, not earthed, or partially earthed) will have. Then there is the matter of the cable between the transmitter and the antenna. This came with it and all that can be said is that it is some form of coax. At 88-108MHz the cable is more than just a pipe, it has its own personality, and this is called Characteristic Impedance. This needs to match the transmitter at one end and the antenna at the other (ie if all three were say 100Ω that is a good thing, because maximum power can be transferred). Most likely the transmitter is 50Ω as this is a common value for radio. Most common however is 75Ω as this is the one used for TV. So who's to say the supplied cable isn't a bit of TV Coax (and maybe from Dick Smith Electronics, which will make it worse as they only sell low grade cable)? Does it really matter? Well, yes, as any mismatch will send energy bouncing back toward the transmitter instead of going off 'into the ether'. OK, so lets use 50Ω cable, and while we are at it select quality stuff (eg Belden). One problem is that there are 30 or so 50Ω coax cables to choose from. But wait, there's more...the aerial itself has an impedance and this needs matched to the cable. Also we are going from unbalanced to balanced so a thing to do both matching tasks is a Balun. Do I need one? And what about lightning arrestors so the Radio DJ doesn't get zapped in a storm? There is also a thing called an isolator; maybe I need one of those too. These radio waves are tricky - I really am going to need a Radio Technician. Not just someone with experience who knows all this stuff, but who has the right test equipment. There's SWR (Standing Wave Ratio) and Impedance tests to check that as much power as possible is getting sent (rather important since we are limited to 1W). Then a Spectrum Analyser is required to check for any naughty emissions, and a Field Strength meter to check that we are still within legal limits once the radiowave has left the antenna.
Audio:
Broadcast limiters are available but at $2000 or so they are well outside the price-range of this exercise. I am hoping to find a good peak limiter on TradeMe. Over the past year there has been the occasional Aphex Dominator for sale, so I'll keep a look out. Without this we are just asking for trouble, as an over-modulated transmitter will send spurious frequencies either side of the carrier which will interfere with adjacent stations and/or communications channels. This is a big no-no.
RF:
A transmitter with antenna has already been bought. Initially I thought this was a good thing, but having looked into what is involved I fear they may have bought a lemon. It is a DB Electtronica FM Modulator TRN and was bought on TradeMe for $500. I Goggled DB Electtronica and it turns out they are an Italian company that manufacture many radio transmitters for commercial use (up to 30KW). However, there is no mention of this model and I suspect by its appearance that it is quite old. By this I mean that if it was built in NZ I would say for sure it was of 1970s vintage. Other Google searches reveal nothing, so I have exactly zero information - not a good start. With the cover off I can see 15 W on the power amp circuit board, and inside a tin can are some rotary switches mounted on vero board which probably set the transmit frequency. There is no indication of what the rotary switches need set to to get a specific frequency. Round the back is the coax connector (which I think is an N type), and two RCA phono inputs - labelled Mono, and MPX. Does this means it can encode stereo or is a separate box required? So, now I have some questions for the Radio Tech. - is this thing set for 1W, 0.5W, 15W output?, is it going to transmit stereo? How do I set the carrier frequency? Also, I read that in NZ we use 50µS pre-emphasis (whereas in the USA its 75µS) so that will need checked as well. What's pre-emphasis? Well, radio has a fairly poor S/N ratio so the high frequency end of the audio signal is boosted prior to modulation. This is reversed at the receiving end. If this transmitter is set for 75µS the programme will sound tinny when received on a receiver designed for NZ FM radio transmission.
Moving on now... to getting the signal from the transmitter to the world (to the suburb of Papanui, actually). Bob (let's call him Bob, because that's not his real name) has already stuck up the aerial and is about to drill a hole in the roof for the cable...hmm. If only it were that simple! There are actually several types of antenna used for FM - dipoles, folded dipoles, yagis... all I know is the idea is to radiate the RF energy isotropically (ie in equal amounts in all directions). Practical antennas at FM frequencies don't quite do this so the coverage pattern is not in a circle, so things get a bit complicated. At this stage I am thinking it would be far easier to do Internet Radio, and this is probably true. Internet streaming does require a large data bandwidth so a standard ADSL connection is not going to work. This all adds up to it costing quite a bit, whereas the ongoing costs of broadcasting are very small. Apart from the financial considerations it just seems more radio-ish if people actually tune in. Anyway, back to the antenna. It needs to be vertically polarised, meaning that the radiation is mostly horizontal to avoid transmitting up into aircraft flightpaths. In other words it will mounted vertically rather than horizontally. As the maximum power radiation allowed for LPFM is 1W (it used to be 0.5W until 2010) the coverage is going to be too small if there are any inefficiencies. On the other hand some antennas give an effective gain so it is also possible to end up transmitting more than 1W and hence go outside the regulations. I would say the antenna in question is mounted high enough because it is sticking up from the building roof which must be at least 10m off the ground. This is good but the aerial pole itself is not that high off the roof and I'm wondering what effect a huge sheet of iron (which might be earthed, not earthed, or partially earthed) will have. Then there is the matter of the cable between the transmitter and the antenna. This came with it and all that can be said is that it is some form of coax. At 88-108MHz the cable is more than just a pipe, it has its own personality, and this is called Characteristic Impedance. This needs to match the transmitter at one end and the antenna at the other (ie if all three were say 100Ω that is a good thing, because maximum power can be transferred). Most likely the transmitter is 50Ω as this is a common value for radio. Most common however is 75Ω as this is the one used for TV. So who's to say the supplied cable isn't a bit of TV Coax (and maybe from Dick Smith Electronics, which will make it worse as they only sell low grade cable)? Does it really matter? Well, yes, as any mismatch will send energy bouncing back toward the transmitter instead of going off 'into the ether'. OK, so lets use 50Ω cable, and while we are at it select quality stuff (eg Belden). One problem is that there are 30 or so 50Ω coax cables to choose from. But wait, there's more...the aerial itself has an impedance and this needs matched to the cable. Also we are going from unbalanced to balanced so a thing to do both matching tasks is a Balun. Do I need one? And what about lightning arrestors so the Radio DJ doesn't get zapped in a storm? There is also a thing called an isolator; maybe I need one of those too. These radio waves are tricky - I really am going to need a Radio Technician. Not just someone with experience who knows all this stuff, but who has the right test equipment. There's SWR (Standing Wave Ratio) and Impedance tests to check that as much power as possible is getting sent (rather important since we are limited to 1W). Then a Spectrum Analyser is required to check for any naughty emissions, and a Field Strength meter to check that we are still within legal limits once the radiowave has left the antenna.
Below is a chart of folks who are already broadcasting on LPFM in this neck of the woods. Sadly, a few have knocked out due to the earthquake. The one to note is Rapid FM on 88.1MHz as the Waimairi School is only abut 700m away (as the crow flies). Maybe we should aim at transmitting from the top end of the band (106.7-107.7).
You are not alone.
While investigating, I discovered that there is a NZ LPFM Society. There is also an FM Broadcast Community. And a guy named Tony Mulcher can tell you exactly how to set up an FM station (for a fee). These are all NZ connections (Tony does International work too), and this is important because there is a lot of local knowledge involved.
So how are we going to proceed? I have about 10 people interested in doin' some radio so that's a start. Bob is very keen to get it on air, but I think we should get everyone busy generation programme material (having identified how varied that might be), setup the PCs and run the station off-air for a week or two. This will let me iron out any bugs in the software, and allow everyone to get up to speed so they can produce stuff week after week. At the same time a Radio Tech could start getting the RF side of it working. Great, I have a plan (now watch it all go pear-shaped).
August
There are two Dell computers to use. I powered one up but there was no OS installed, so I have installed Windows XP. For some reason the video resolution is stuck on 640 x 480. This means that the Direttore software won't run.
Ok, I have now investigated the problem and it seems that this lowest resolution is all that can be got off the motherboard (I'm a Mac user so I don't have these issues). There is no videocard, so I need to find a couple of AGP cards for these 2004 vintage computers.
September
Michael Duncan, who has just retired from CPIT Broadcasting School has kindly offered to help with the RF side of things. He has had the transmitter away for testing and it is going to do the job. The power has been set down to 4W which should give 1W at the antenna. A further inspection inside revealed the frequency markings by the miniature switches on the PLL circuit board so it is easy to set the transmit frequency. It was decided to use 88.0 MHz after scanning the FM band in the Papanui area. As the transmitter is mono, a stereo multiplexer has been ordered from the USA, and a peak limiter.
Bob (whose name I can now tell you is actually Steve) has organised a launch date for the 2nd Dec. with some CPIT students organising the event. He has chosen a name: PC Radio. I mentioned that PC stands for so many thing that it will be confusing, but he's mad keen to call it that. Oh, well. The cupboard has been divided with a new wall so there is now a separate space for the equipment. There is also a design going on the wall. Meanwhile, there are several interested parties starting to think about getting programmes together.
For a computer we have decide to use a newer PC that is coming free from one of the offices. This should be more reliable.
October
I came across another website with useful information for setting up and operating a community radio station here.
