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Ok, I’m going to get over my head pretty quickly here, but I’m wondering what features a Part 15 AM transmitter would have if we could design it with everything we like. This may be another of those things nobody wants to participate in but me, but here’s what I think for starters, anyway:
1. I like rack mount equipment for organizational purposes. So, my perfect transmitter would have it’s inside the control room portion rack mounted. I’d like some meters on the front to monitor signal strength, modulation and frequency stability, if possible. There is that place that custom makes rack mount front panels so maybe something like the ISS can be rack mounted anyway. I have a Comtek BST-25 for 87.7 FM that does have a rack mount conversion available. I think its $85, but I’ll get one sooner or later because I think rack mounting is the way to go whenever possible.
2. I do like having the final circuits of the transmitter mounted at the antenna itself, like the ISS extended range set up so we don’t have to subtract the coax length from the length of the antenna. Good to have an antenna tuner, anyway.
3. I’d also like the final amplifier to be as efficient as possible so we can get the most out of that 100 mw input as we can.
4. If we can put part of the transmitter up on the tower just under the antenna, what can we do to get the ground connection of the transmitter down at ground level? I’m also interested in ground wire tuning – if it will actually help our signal.
5. I’m undecided about audio processing. Should it be internal or external?
I know lots of people here know a lot more about tech matters than I do. I’d be interested in knowing what others think the best features to have on a LP transmitter would be.
John
W9LWA
John,
This has potential to be a very useful discussion. I suggest we look at features and functions separately, e.g. a feature is the transmitter is indoors rack mounted, and function is to produce maximum radiated power. I hope we don’t get wrapped around the axle and distracted by ground leads for now and just explore what can be possible.
From the what is possible category, I have a design for a transmitter which has a measured, not simulated, efficiency of 85 percent so we know this can be achieved. I have a design for a base loading coil with a RF resistance of 18 ohms so we know this is possible. I know from measurement that my ground system RF resistance ranges from about 20 to 40 ohms. From this we know what is possible but these data in no way limit what can be developed, they only serve as a starting place for what exists today and what can be realistically built.
For your wish to have the final at the antenna site and the “transmitter” rack mounted, this can be done with my design with only a few components (a transistor, a couple of capacitors, a resistor or two, a coil or two) at the antenna base with the power, frequency synthesizer, and audio circuits indoors in the rack. The connection between the two subsystems can be CAT 5 cable deferentially driven to prevent radiation. Though I have not implemented this, my point is your one desire for an indoor transmitter rack mounted is feasible with technology which is well known.
The greatest loss in an AM Part 15 system, the ground resistance, awaits a breakthrough and will be the most significant enhancement to range.
Let’s all kick around some ideas, wild or not.
Neil
Hello Neil,
Thank you for very good comments. I also hope others will join in. I’d especially like to know what kind of metering we can reasonably have. I’m of the age that I started out reading the meters and logging the results every 30 minutes. I probably didn’t appreciate doing it at the time, but at least I knew if the transmitter was working or not.
I guess I failed to mention I’d like to see a transmitter have whatever it is that helps with networking more than one transmitter. I don’t know if I’ll ever do that, but I’d like to be able to do so. I wonder how we can have meters to monitor for those remote transmitters…
John
W9LWA
I’m going to take a slightly different perspective here.
Most of these types of discussions end up focusing on those factors maximizing range.
Unfortunately, the FCC (and Industry Canada) rules were designed to limit range. And ultimately, range depends more on location factors (ground conductivity, topography, background noise, even weather) than it does on the transmitter. I’ve used pretty much every certified AM transmitter available, and I’ve found that for a given install location, there’s not really that much difference in range. Some, to be sure, but it’s usually measured in tens or low hundreds of feet, not miles.
I also don’t think that you’re ever going to get past the long ground lead, radiating coax cable (or CAT5) potential legal issues. If you ever do manage to design something that blows away other transmitters, and gets miles of range, the FCC will likely just change the rules.
To me, the perfect transmitter has other qualities. Sound is the most important. I want a transmitter to have the maximum bandwidth possible to get the best sound. It also needs to have the ability to over modulate the +ve peaks if loudness is what you want.
I don’t think that on board audio processing is important. If you really want or need it, you can always add external processing. Why should you add expense to a transmitter with something that might not be desirable, or good enough, for users.
I agree with John that metering is important – perhaps external metering as in the amateur radio transceiver FT-857 would be possible (allowing the transmitter to be outdoors).
To me, there already is a close to perfect transmitter available (at least in the U.S. – it’s not certified in Canada) and that is the Rangemaster. Add the metering, and you’ve pretty much got something as good as it could get. The best sounding and the highest field strength (as measured in the AM Transmitter test conducted by Hobbybroadcaster).
A note about the field strength of the Rangemaster – it’s probably the highest because you can tune it exactly to 100 mw input to the final stage through measurements. Other, certified transmitters don’t allow this, and so need a ‘fudge factor’ so that they don’t accidentally go over that limit due to variances in the manufacturing process.
On a another note, from what I’ve read and understand, attempting to network transmitters on a single frequency without interference is probably a pipe dream. There are also FCC legal questions about that (I can’t recall the exact wording, but the sum total output of all transmitters cannot exceed a legal, single, one if I remember correctly). If they’re on different frequencies, essentially multiple, different radio stations, then that would be OK.
Finally, let’s not forget the other half of the radio equation – the receiver. The work Thelegacy is doing with receving antennas demonstrates that those that really want to receive a low power station can do so far beyond what might be expected by 1) improving their receiver and 2) dramatically improving their antenna. That might not make sense for a casual listener, but are we going to get those casual listeners in any event?
If you really want to be heard, get the best possible transmitter, sure. But you have to let people know you’re ‘out there’, and you can also work with them in other ways so that they can receive your puny signal.
Not sure I can relate to the concept of rack mounting as being a major feature. These transmitters are small. Put them at the base of the antenna and be done with it. There’s no coax or antenna lead necessary, period. I installed my Procaster outdoors 6 years ago, on my third floor attic window frame (outdoors). During this six years it has suffered no ill effects. The first couple years I went up and opened it up to check and see if I might need to tweak the tuning for maximum output (as you do at initial setup) and every time it was still peaked as good as it gets. No variation or loss in power being outdoors in weather from -30 below zero in the winter to 100 degrees and high humidity, baking in the sun in the summer. And a check on a professional frequency counter and also a spectrum analyzer show the frequency to be rock solid. The audio portion of the transmitter remains in the studio. The in studio box ( a very small box I might add) contains the audio processing which you can adjust from the studio, and also accepts the DC power input which is then sent to the transmitter. The connecting cable sends power and audio, no RF. The meter for tuning your output is built right into the transmitter.
The legalities of the Range Extender befuddle me, but if it’s certified, then so be it. I notice that their certification numbers as provided show nothing about the range extender in the FCC database, and those numbers were issued in 1997 and there is no update or recertification related to that ID involving the range extender. Changes in transmitter designs, etc require recertification. It’s also my understanding that their range extender is passive — it uses no power source, so I don’t understand how it might contain the final circuits. But again, haven’t seen it in real life. I’m also a bit perplexed about the ability to adjust the power in the Rangemaster to exactly 100mw input. This seems to imply that this input power is adjustable and could be easily adjusted to more than 100mw input which would be illegal, and the ability for a user to do so should disqualify it from certification. But again, I don’t know all the details of their legalities.
So, the Procaster has built in processing which is adjustable. I’ve set it for 125+ 99- modulation peaks for most loudness. No need to spend hundreds more for external processing. But, if I wanted or felt I needed to you can set the included processing to be bypassed and send in your own processed audio if you like. So I do think that the ultimate transmitter would have the option of using built in or external. Note the cost between a Rangemaster and Procaster is not that far apart so it’s not like you’re paying hundreds more for the built in processing capabilities of the Procaster. In fact at this moment the Rangemaster is quite a bit more expensive, depending on the configuration you buy.
Also somewhat amused by the needs to have meters to monitor things. Now, I too have been working in commercial broadcasting since the olden days, and I still do — that’s my “real” job. I too remember taking meter readings all day every day, plate current, plate voltage, and on an FM frequency deviation and modulation, etc., even frequency stability, as well as base current readings at the towers, and loop currents at directionals, etc. I once worked at a daytime directional AM that required taking base current readings physically at the base of the towers (three of them) every day. These towers were in a swamp and I had to walk out there on 2×12 boards sitting on cement blocks to get there!
Nowadays readings are nearly nonexistent. In the last few years for the stations I work for, we’ve replaced two old tube transmitters with modern solid state transmitters. The readings are output in watts and reflected power. That’s it. And the FCC doesn’t even require transmitter logs anymore. And the reflected power reading is more for us being able to protect our equipment than any legal concern. The transmitters are ungodly stable and if they should go awry they call my cell phone, call the station phone, text me, and send me an email alerting me to the trouble and telling me what the errant reading is. Yes, I realize that the fun of old school meters and readings are a kick, but on a super low power Part 15 transmitter they just don’t make sense. Driving a power meter or mod meter from a transmitter will waste some of that tiny precious power you’re putting out. I monitor my modulation with an Inovonics mod meter. You have more than enough over the air signal to drive one of these and it uses zero of your output. I also use an old Nems Clarke field intensity meter to monitor my signal, which gives me an actual, meaningful reading. This also reads the signal out of the air, so uses none of the output power. I use a Potomac FIM to do field intensity readings around my coverage area now and then just to see if coverage remains constant. It does, with very minute variation, over the past 6 years. The idea of building this into a Part 15 transmitter would add greatly to the cost with no real benefit except the fun of metering.
For me, the Procaster comes as close as we’re gonna get to the ideal transmitter as long as we’re not adding bells and whistles just for the fun of it. The Rangemaster would be pretty close too. I provided a long list of reasons why that AM transmitter test was not definitive in any way, back when it came out. Just measuring field strength with no modulation is no way to test and here’s why….
People will tell you that modulation more (100 % or even 125% positive) does NOT increase your range or signal strength. Well, yes, it does. For one thing you can WATCH on an analog field intensity meter the signal peaking higher with more modulation. Sure, it’s a teeny tiny bit, but it is some. But what you’re NOT seeing is that the louder signal increases your range not by giving you more field strength, or by giving you more output, but by giving you LOUDER output that covers up more NOISE increasing your effective range, simply because you can be HEARD over the noise floor. When I was working on my initial setup, I have a test spot about 1 1/3 miles from the transmitter as the crow flies. This is what I consider to be the fringe of my coverage. When I drive past this spot I get an acceptable signal in any one of 8 different cars, and when I park there I can listed on a $4 portable transistor radio, to a boombox, to a GE Super Radio, to a Tecsun, etc. But if I reduce my modulation to 100% I start to lose it at this spot, and if I let it go down to 80% peaks the sound is lost in the noise — and I live in a tiny rural town with a VERY low noise floor. I have set up at this spot and had my wife adjust the modulation up and down back at the studio and I can hear the station come and go. While field strength for all practical matters remains constant, the increase in modulation greatly increases the ability to listen to the station, by increasing useable, listenable range.
So, while a Ringmaster may have a better signal strength by a smidge, with it’s lack of processing my money says it won’t be listenable at the same distance as a Procaster using it’s built in processor. Yes, of course you can add an external processor to the Rangemaster. But this adds quite a bit of cost depending on what you want.
So, the ultimate transmitter should have at least basic processing included, with the option to bypass and use something fancier if you so choose.
Of course, I’m not addressing FM at all as far as I’m concerned the idea of broadcasting to more than yourself on FM Part 15 is a waste of time. The field strength limits are what they are and anything to get more coverage must increase this field strength, which makes them illegal.
Personally I think we often spend too much time discussing range, transmitters, ground leads, and transmitters, when we should be spending more effort discussing creating programming that is sustainable, unique, and that people actually want to hear.
TIB
Well, there is certainly a difference between needs and wants. I don’t need meters but I like and want them. I don’t need any part of the transmitting apparatus to be rack mounted but I want that. It’s a place to put the meters, if nothing else. I think this topic from my perspective is a lot more about wants than needs.
I’m good with having the RF circuits and antenna tuning at the top of the tower. I think that’s where they belong as long as the allowed antenna length includes the lead.
And indeed, what about the ground lead? Is there something we can separate off the transmitter to have at earth level that we could connect to the earth with a short lead? Or, do we think we need a long radiating ground wire to get the range we seek?
The perfect transmitter for me is unlikely the perfect transmitter for everyone or maybe anyone else. I like bells and whistles and I guess I’m willing to over-pay for them. But, my technical knowledge is old. I’m hoping others have a lot better ideas about tech things than I do.
Thanks for your comments.
John
W9LWA
I think the on board compression etc is a great feature for the “perfect transmitter” and I wish the “perfect” FM transmitter, the Decade, which I use, had the on board compression, release, adjustable so I wouldn’t have to have a separate piece of gear for this. Also the “perfect” transmitter should have the power supply on board and not having to use a wallwart, which we all know a lot don’t work too good. At least the Decade has that.
If John wants to design and market a transmitter GREAT! as more choices would be a good thing as current ones won’t be around forever. Example…SSTran.
Thanks for commenting. If we come up with something that really is an improvement, I would indeed be willing to get the FCC approvals and get it put into production as I’ve been involved in manufacturing before. But, it wouldn’t have to be just me, if others want to be involved.
John
W9LWA
A few comments on the previous posts.
I have no issue with built-in audio processing in a transmitter, as long as it doesn’t add significant cost. It will definitely add some, and I’d rather that cost be put into better base transmitter components. Based on my experience, the Rangemaster (without built-in processing) sounds better than the ProCaster with its audio processing switched out. Both of those sound far better than the Talking House (as an example).
Re power supplies. Why not have the transmitter capable of being powered by both a quality, built-in AC supply, as well as an external 12 volt one (or have 2 different models, one for each supply). Powering the transmitter with 12 volts allows you to install it in places where there is no AC power (mobile, as an example, or in remote areas using solar or other alternative power sources).
I’m surprised that no one has mentioned AM stereo (C-QUAM). It would be ideal if the transmitter could broadcast in both mono and stereo.
Here is one of my dream transmitters… A battery powered transmitter (with built-in battery and solar charger), coupled with a built-in wireless STL, internet-based). This transmitter would have no wires that anyone could say would be radiating, other than its antenna. If mounted in the air, you would connect no ground wire, but I would imagine that you would get the best range with a ground mount over a good ground plane (such as radials). The transmitter would have Rangemaster-like mono audio quality, with the capability of C-QUAM.
Like I said, I can dream, can’t I?
timinbovey: The range you mentioned is FAR greater than what I’ve observed with the ASMAX2 C-Quam AM Stereo transmitter my broadcast engineer friend put together for me. I can tell that my modulation is around 125% with the Sean Cuthbert audio processor. I use HARD compression meaning I keep it LOUD but not to the point of distortion especially with Album Rock and too I have to be careful not to destroy the C-Quam pilot signal by over driving the transmitter. My engineer friend was very careful not to cause splatter on the AM band either by too much modulation but we did find 125% to be the magic sauce to achieve 1 1/4 miles to a Tecsun PL-380 with the Terk AM advantage loop. Toyota Cololla’s Radio’s sometimes heard me 2.9 miles out. but a $4 pocket Radio on my transmitter the way its set up now NO WAY maybe 1/2-1/8th mile tops. My Sony car Radio I hear it to the 7-Eleven at 0.9 miles with a barely readable signal. If I got my antenna up 20 or so feet like you maybe I’d do more like you.
OK I think if the Procaster had C-Quam AM Stereo it would have been the perfect transmitter and honestly that was why I had my broadcast engineer friend put together the ASMAX2, tune it with his spectrum analyzer and for good measure add extra filtering to block harmonics that the Talking House generated at a further range. I have a Ham operator who asked me to be careful not to generate interference on 3480, 3280, or spurs on 80 meters as he said he was worried about when I advertised on the Deltaville, VA Facebook page. I assured him this time I had a Broadcast Engineer helping me to be sure I was not wreaking havoc on the HF spectrum area nor MW.
The agent that visited me I keep in contact with at times told me he did like the Procaster AM transmitter and as he put it if I wanted to do Album Rock that transmitter was what I was to aim for as far as a fully assembled FCC approved unit that would give off that sort of audio quality because of the built in processor. If it were not for my friend the engineer Procaster would have been my choice for a Rock solid transmitter that would do what I wanted. This is why I tried to get Procaster to make a C-Quam AM Stereo version of that transmitter. We see where that went but I tried.
Are you powering your ASMAX2’s at 12 volts or at 24 volts? If you have experimented with both, was there any noticeable difference in range? What do you use for antenna tuning? I built the classic vertical antenna setup for the SSTran AMT3000/5000 and used it with the ASMAX2. For tuning I used a home brewed field strength box connected to a DDM but it is cumbersome, especially when you are mounting three transmitters on different frequencies on the same chimney.
During the first week, with the first ASMAX2 (powered at 24 volts) the range and audio quality were excellent, but it deteriorated after that. The third ASMAX2 had the worst range and it eventually failed completely. All three ASMAX2’s are now on their way back to Greece for repair and testing. My guess is at 24 volts 24/7, they are not reliable.
I agree… the ultimate Part 15 AM transmitter would be a Procaster with C-Quam stereo, better audio quality, and the elimination of the the anomalies you run into in fringe areas when other signals are available on your channel. (From your description, it seems like TalkingHouse/Iam Radio might also have this problem?) If Chez Radio addressed just these three issues, it would be a total no-brainer. Procasters are already the easiest to install and tune and are as stable as tanks.
As for any downside for having C-Quam AM Stereo on a perc 15 AM transmitter there are no downsides that I have experienced nor my broadcast engineer have experienced. Unlike the FM stereo signal when you get further away from it and the signal is weak and you get that terrible hiss you don’t get the noise with C-Quam AM stereo so broadcasting in Sequim does not degrade your signal in any way in fact if anything it even helps it mono because it seems that the signal is even cleaner in mono.
The only possible downside and this might have been a fluke on a couple of songs I had that Were Somehow recorded with some sort of spatial expander technology when you heard those on a mono AM radio The Voice seemed to Echo as because of the spatial expander technique that they used which was crossing the bass and the treble to give you the Wide Stereo effect messed with the mono signal a bit. I didn’t even know that the song was recorded that way but 99% of my songs we’re not affected in any negative way on a model AM radio.
The pros certainly would outweigh any cons because I have not seen any cons whatsoever and broadcasting in C-Quam does not degrade your range like it would if you transmit FM stereo vs. FM mono. So again I don’t see why procaster did not consider a sequin version of that transmitter because after all if you want to get rid of FM piracy for the album rockers that are out there that is the only way you’re going to do it. The radios are out there if you look yes there are little hard to get but someone who really wants a great sound can get them as they are starting to come back thanks to the C-Quam AM stereo Facebook page. In fact a well-known radio station in Texas turn down there stereo signal because of the demand for this to be returning. The more people that demand C-Quam AM Stereo the better the chances that both radio manufacturers and radio stations will make its return thus making AM radio better than it ever was in a long time.
I guess at this point, this is what I’m thinking, so far, regarding John’s better than average transmitter:
1. Transmitter belongs outside on top of the tower.
2. Controls, meters and the better-than-average power supply will be rack mounted, although that is not a necessity. John knows where to get professionally made front panel so it will look like whoever made this knows what he’s doing – even if John has to do it himself.
3. Processor might as well be in the rack mounted unit, if used and not already part of the transmitter elsewhere.
4. Meters aren’t necessary either. But, even though a source of amusement to some, John likes meters – so such would at least include voltage out to the transmitter to make sure power supply is working. A vu meter is also desired to make sure levels are ok going to transmitter. There is an old portable radio around here with something like an S meter on it. John will wire that into a front panel meter, too, if possible. Unlikely this signal strength meter will actually give a meaningful reading but it should show if the strength is about what it usually is, relatively speaking.
5. As for transmitter itself, a range master or procaster would be perfectly acceptable, although if something winds up being hand made, C-Quam would be a desired addition.
6. John further acknowledges that we want this signal to sound good and the transmitter chosen or built should reflect that. The transmitter is also desired to have efficient circuitry that delivers as much power as possible to the antenna.
7. John would like to further state that he is not trying to get into the transmitter business, but if the project becomes something worth building, he would at least be willing to shop around for printed circuit boards to allow those so inclined to put it together as a kit with relative ease.
Further suggestions much appreciated.
John
W9LWA
FWIW here’s my follow up to John’s “So Far”
1. Agree completely the transmitter belongs where the antenna is. Be it ground mounted or elevated. This eliminates any issues with the legalities of a long feed line to the antenna, and eliminates any signal loss through this lead. Although presently there is no legal way to ground it when elevated. Which is working fine for me.
2. There aren’t that many controls. However using a better quality power supply is always a good idea, although I’ve not found any noise or issues with that supplied with my Procaster, but there are indeed much better ones available. As for rack mounting it would be a piece o’ cake to add a volt meter to the power supply output and rack mount it. You could certainly mount the supply and on/off switch to a rack mount if desired.
3. There are many perfectly wonderful rack mounted processors that are dandy for Part 15 AM. You could choose to use one with just about any respectable Part 15 transmitter. If you were to use the built in at no additional cost processing in the Procaster you could, if you were so inclined, wire up your own remote panel for the controls for the built in processing. The controls are all in the small studio interface box that remains in the studio. Controls are all either PC mounted potentiometers, or small pin jumpers to set up compression, input gain, modulation, and turning processing on and off. Of course with a Rangemaster and many others, if you’re using processing you’ve purchased a separate unit and it’s probably rack mounted anyway.
4. I too like meters. I’ve never felt a need to monitor the power supply voltage to the transmitter, but again this is easy and you could choose from a wide variety of great looking panel meters for this. VU metering would best be on the audio source, be it a vintage control board or computer (there are some fun VU meters for computer screens). In my case I purchased a very inexpensive rack mounted LED VU meter device where the LED VU lights run the full span of the unit. In my case I have them monitoring the final part of my audio chain which I won’t explain in detail, but it’s the audio level into the cable TV system that also carries my programming. If those lights are blinking and the levels are right, they’re correct on the air and to the cable TV. As for signal strength, it’s really easy to build a very basic field strength meter – doesn’t have to even be tunable that at close range would easily indicate your signal on a panel meter. It would completely not provide any actual field intensity, but it would show signal present. you could even calibrate it so that, say, 100% on the meter would be your typical signal strength, and should there be any drop in signal the meter would drop accordingly. You’d get nice, useful, relative field strength. And it could be made to look great. The circuit is pretty basic and can be build right on the back of a two space rack panel. You could easily build it on a one rack space panel but that wouldn’t leave room for a really neat meter.
5. These two transmitters are generally considered to be the cream of the crop. I’m not a C-Quam fan, simply because it will never see a comeback. Never. AM will go all digital before C-Quam makes a comeback. That said, if there were a top quality C-Quam Part 15 transmitter made — on the same quality level of the Procaster or Rangemaster, with similar construction and features, I’d consider it — just because there are no real disadvantages and some minor advantages. There are simply no readily available C-Quam receivers available to the general public that are quality units.
6. Obviously the most efficient transmitter design is desired. I like to think that the makers of the top units available today have done the best they can, and not simply said “that’s good enough” when designing their transmitters. But as technology and parts availability changes, so do possibilities. It would also have to be affordable. If a transmitter cost $800 and was 85% efficient, would you spend $1500 to have one that was 91% efficient? Would this make a noticeable difference in coverage area? I have no idea what the efficiency of the top units are, but I like to think they’re the best they could do taking all the variables into consideration.
TIB
Thanks for the comments. They sound about right to me. Here are a few things I might throw in, be them right or wrong:
1. Regarding processing, I do have an ART Pro MPA II 2-channel Tube Microphone Preamp and the matching Pro-VLA II 2-channel Opto Tube Leveling Amplifier. I’m not even sure what all these things do, but I got them for virtually nothing. Do you think they would have any application here?
2. About grounding, what do we really need? I remember someone complaining that the TH transmitters ground through the power supply. Wouldn’t they all? Then there is that ground wire from the transmitter to earth. Do we indeed need them both? It doesn’t sound like your set up has the latter of the two. I’d thought about building a ground lead tuner connected at the transmitter and having the insulated output wire from the GT run down inside one of the tubular legs of the tower. I’ve heard doing something like that helps a bit.
3. On the other hand, could we put the power supply at the tower base in a weather proof enclosure and then ground that with a short lead to the earth and radials?
4. Not that I think such grounding shenanigans are really necessary as the legal definitions of ground and ground lead are not necessarily the same thing.
5. Well, I kind of hate to admit, but given the choice of 85% efficient for $800 or 91% efficient for $1500, I’m afraid I’d go for the 91%.
Here’s to putting together the best Part 15 stations as we can.
All comments are welcome and encouraged…
John
W9LWA
1. Your ART Pro units are quite useful. The Mic pre-amp is just that. Is used to bring mic level up to line level to input to a mixer, etc. Most mixers have some mic inputs already with built in pre-amps that are perfectly functional for broadcast use. But, musicians especially, and those who record them, will go crazy trying different mic pre-amps for the perfect sound, minimal noise, perfect gain, etc. Mic pre-amps can cost from about 50 bucks to many thousands. I do use a dbx 286S mic pre-amp for some of my voice over work, most clients want dry, unprocessed voice if they’re project is for broadcast use. Every station I’ve worked at in over 45 years has never used an outboard mic pre-amp — what was built into the console was fine. But that’s a nice unit and could probably be used to get a nicer sound than a built in, but if that’s necessary for broadcast is up to debate. I tend to go with the theory that if you’re processing your audio on it’s way to the transmitter you’re better off to NOT be applying any additional processing before that in the audio chain.
Your leveling amp is most often used in a recording setting, but could easily be used for compression/limiting in a radio audio chain. But won’t have the ability to give you asymmetrical modulation or any of the other features specific to broadcasting. But it’s the sort of thing I’d use in a back up situation should a stations main processor bit the dust, and I needed a quick substitute while repairs were completed. It would be set up to give solid loudness while preventing over modulation.
2-3. What we really need for grounding is debatable for eternity. And what is legal is equally debated. FCC says ground lead and antenna can max at 3 meters combined, total. Clearly there are various interpretations, various oddball scenarios that have somehow been certified, and those who have their own beliefs. Best, most common case is a ground mounted transmitter with a 3 meter antenna. Transmitter is grounded at the Earth. In my case I have an elevated transmitter and have attached no ground lead at all. The only wires to it are audio and 12V from the supplied wall-wart. I get the coverage I need. I may do better with a ground. I would certainly do better with a 30 foot ground lead going from the transmitter to the earth, but that would clearly not be legal. Some say I must have some radiation from my power/audio cables, or a ground through them, or some such. I don’t really know. I know it was certified with this audio/power cable in use. And I know that even if it were ground mounted the same 50 feet of cable would be between the transmitter and the studio, so it wouldn’t really make any difference. I’ve never worried about grounding the transmitter case, the circuit itself, or anything else. I suppose it would be wise, legal and possible to mount a spark gap at the antenna so if it was hit by lightning it would jump to ground (this is how commercial AM towers are set up) but I haven’t bothered. The wall-wart is plugged into an APC UPS to protect it from power surges, etc and it also has enough back up power in it to keep the station on the air for a day (at least) during a power outage. It a power supply is grounded (say you opt for a separate 12V supply, something high quality like one would use for a ham transmitter) with a 3 prong plug, does that ground carry through on the 12V wires to the transmitter? Methinks not. I opted for an elevated transmitter because ground mounted it would be under 6 feet of snow 6 or more months out of the year.
5. I’d have to do the math and see what the actual gain would be for the cost.
TIB
I think we may be losing the forest for the trees.
What makes Part 15 broadcasting unique? Playing the Top 40 hits along with all the other thousands of stations (no matter what genre you’re in)? Reaching massive numbers of people like the much more powerful, licensed stations?
I think it’s being unique. Unique programming. A unique sound (such as AM stereo). I applaud Thelegacy for his work with C-QUAM, regardless of whether it will take over the world or not. It’s caring about the few users that you might actually have in your tiny listening area. Caring about the community which you serve. THAT’S how we can make a difference, however small.
I understand that this is a technical discussion, but the technical aspects of Part 15 are some of the least important, imho.
Why approach the problem of the ‘perfect’ Part 15 transmitter with the same sort of eyes as the big boys?
I think the issue is first deciding what you want your station to do, or be. Then, and only then, drill down on what is needed to produce those results. It may be (and I certainly believe it) that for most people, transmitters already exist that entirely fill their needs.
If you don’t solve the problem in this fashion, you risk having a wish list a mile long, most of which isn’t really necessary or even important.
For me, as I’ve stated earlier, sound quality and following from that, AM stereo, would be the two things I’d most like to see on a transmitter (one that is certified).
I can go across the AM dial in my area and hear exactly one licensed station that has decent sound, as listened to on my car radio. All are talk stations but even then, I find it difficult to listen to muddy and/or tinny audio. The one station that has my ear cares about how it sounds, and even when it plays musical interludes, it sounds great. The rest of the stations obviously don’t care how they sound. No wonder AM radio is losing listeners by the droves.
As to some of the other features being talked about, there are a lot of ‘nice to haves’, but nothing that would further my objectives in doing Part 15 broadcasting. Maybe someone else’s, but not mine.
I don’t even care about transmitter efficiency. I’ve found there are too many other factors that affect range to focus on that one particular thing. Locate your installation in the right place and you’ll get great range. Locate it in a bad place, and your range will suck. It doesn’t matter whether you’re using a Rangemaster/ProCaster or a Talking House (with large differences in efficiency between the two), or even a ‘perfect’ transmitter. When I was on Bowen Island, my Rangemaster was lucky to be heard 1/4 mile away on a car radio, because of the poor ground conductivity. That same Rangemaster, in a similar installation in Pitt Meadows could be heard at least a mile away in all directions, and much more in some, because of the good ground conductivity (and other factors that some have debunked here).
In the Pitt Meadows installation, even my Talking Sign and Talking House transmitters were getting a mile and more range. Noisier in the fringe areas than the Rangemaster, to be sure, and not as far for any given direction, but still comparable.
My 2 cents, anyway.
I especially agree with Artisan’s perfect transmitter with two ways to power. Household A/C with the transformer and filtering on board just needing an A/C cord or a second power input for using D/C like a battery. The onboard power supply would be much better than wallwarts which degrade the sound quality except for the block style computer ones.
Yes range is as much dependent on location and the radio but it should be the max. power allowed.
And importantly Certified for Canada also as Industry Canada read me the riot act about using transmitters with FCC approval only…..no good here.
The Decade has all the features of the perfect transmitter except for not being able to work with D/C but the design to need a plus and negative D/C voltage, needing an A/C supply is how the excellent sound quality is achieved as I was told by Decade.
As for us being unique, if I was to sound just like commercial stations what would be the point of doing my own. I would just listen to them.Well, I do agree that the transmitter should sound really good. Not just kind of good, but really good. I don’t think that’s mutually exclusive with having the highest possible output in pursuit of the best range. I’m ok with stereo, although I suppose that rules out the Rangemaster and Procaster which everyone seems to tell me are otherwise the two best transmitters on the market presently.
I’d mostly been thinking in terms of add-ons to current transmitters and I’m not sure what it might cost to have an engineer or some other competent person design our dream transmitter. If it’s affordable enough, perhaps those of us interested could then build our own or get them from China. Some things like power supplies and processor boards are already so available that there seems little need to reinvent the wheel for those.
I don’t know if we can foster enough improvement over current products to make this worthwhile, but I’m good to look into it further.
I wonder if those Greek processor boards are any good?
John
W9LWA
Bluetooth Audio receiving at the transmitter will END the issue with long audio cable acting as a raiding element and thus making a transmitter non compliant (Geez problem solved there.
Less power loss at the final does not mean the FCC will change the rules because your making the most out of 100 mW
Some folks really need to read Michelle Bradley’s forum on Facebook because she is part of RECNet and I popped the question about the old ATU and the new ATU for the Talking House as well as Procaster and Range. Honest Engine answer a gentleman on that very forum said his range to a Pocket Radio was still listenable at 4 miles No Terk AM Advantage Loop to receive better and at 2 miles the signal was still Very Clear. So again many I know have been vague about Range because of Fear after a certain individual pressed the issue with ground. Don’t worry about your certified unit getting out even the FCC knows all about this issue.
Back to transmitter design I think it should be able to run on solar power so when power goes out you can announce emergency information to your listeners. Its very important to be able to stay on air if there may be a long period of no power. If your station gets in good with officials you can give updates on the progress and maybe where one can take shelter from extreme cold or hear or severe weather.
Thanks for the comments, Legacy.
Wouldn’t any transmitter work with a solar array? I wonder how much an array would cost to power a 100 mw transmitter? It couldn’t be that much, could it? I wouldn’t mind using solar power just for the novelty of it.
I’m not concerned about audio cables radiating. Or anything else that isn’t a ground lead, antenna or transmission line for that matter. If the FCC cared about audio cable they’d have included it in the regulation…
John
W9LWA
Hi John,
I bought a 100 watt solar array from Harbor Freight for 149 bucks. Comes with a controller and all interconnects. 100 watts is overkill for a Part 15 transmitter but it can certainly be done for a few bucks. This setup kept my 12 volt battery topped off for all of Field Day using a 100 watt PEP transceiver.
Well, that sounds easy enough. I was thinking solar because I think the best place for my tower would be at the back of the property and I wouldn’t have to run a power line back there. Indeed, with a good battery, something like you have should work fine.
Thanks for telling us about it.
John
W9LWA
Random comments before I head for work:
“Wall Wart” does not immediately mean crappy. There’s a big difference between a good quality supply and a cheap Chinese one. People see a 12V supply for $50 and have a cow at the price, and pop on Amazon or eBay and grab one for $3 then bitch because they’re crap. We have racks of professional broadcast equipment at work that run on quality “wall warts” some of which have been in service 25+ years with no issues.
Solar transmitter power. Wouldn’t take much. What do you plan on feeding that transmitter with? Have a mixer? Where’s your music and other programming coming from? A computer? Running a processor? All that stuff is going to need power. The transmitter itself uses a tiny amount of juice. It’s the other stuff that takes all the juice. I have a APC UPS supply. It runs the station for 3 days with no AC. At least that’s the longest it’s had to run the station. It would probably run longer. Faster, easier, more power than solar. Solar up here isn’t too handy. It’s only daylight from about 8 AM – 4 PM up here in the winter. And you’d have to go clean snow off it every couple days.
I can’t say that I’ve EVER heard of someone having an issue with a radiating audio feed or DC power feed. I can’t find a NOUO that cites that. That only seems to come up here when I mention I get about 1.3 miles with NO ground lead attached to my Procaster. There’s always someone who pipes up and says “then you’re getting ground from your audio / power leads”. If that’s the case so is the owner of every Procaster or other transmitter ever put on the air. We all have power and audio going to our transmitters. And every certified transmitter was certified with power and audio leads attached. At least the Procaster was. It’s all there in the lab photos that were submitted for certification. I assume that other certified units were powered up for their certification tests.
Bluetooth to the transmitter? If it’s close enough. And if you have the power at the transmitter. And it creates another link that can have issues. If you need to, fine. Nothing beats the simplicity and durability of wire.
Don’t dig the concept of AC operation with an onboard power supply. Who wants to run 110 volts out to their transmitter? Further, introducing high A/C voltage into the same case brings a huge potential for noise, heat and other issues into the transmitter box. There’s nothing wrong with an outboard power supply. Not to mention one of the most prone failure components are electrolytic capacitors. No need to put filter caps inside the transmitter box for power. Keep that stuff out of there. You wanna pull your transmitter down every few years to change the caps that failed because they’ve been running 24/7 and roasting in the summer sun? These are reasons why so much professional gear has an outboard supply these days. Keep the noise, heat and extra components out of the area of the audio or other sensitive circuits.
Off to work.
TIB
Tim, to change the subject just for a minute, you said you have this…..”I have a APC UPS supply. It runs the station for 3 days with no AC. At least that’s the longest it’s had to run the station”.
My station consists of a small 11″ laptop running with screen off and flash, not hard drive, small mini compressor, and the Decade MS-100 transmitter. That’s it. What model of APC back up do you have?
I always thought that these things would only work for 1/2 an hour or so.
I’m not where I can take a look at the backup UPS right now, but it’s a bug sucker. UPS units come in a million different sizes and capacities — and prices! Mine runs an older iMac (screen off) and the Procaster for quite some time. Longest was three days. The typical ones you get at a big box store or computer store will only run a typical computer for a few minutes — 15 – 30 minutes is common. They’re designed to keep your devices running and safe, not really work as back up power. They give you time to do a proper shut down before they conk out.
At work (commercial broadcast stations) we have three air studios, with a myriad of equipment and all together we have 8 UPS units. Although these only keep us running for about three hours, they’re running several computers, microwave STL transmitters, satellite receivers, control boards, etc.
These units come in sizes from a couple hundred watts to several thousand. Naturally the more back up power available, and the more features, the more they cost. I *think* the one I have in the studio is 5000 watts. (I’m abbreviating specs here, there are more details that go into it). it’s an older model with no bells and whistles. Nowadays you can buy ones with digital readout that tell you present current load, how much available run time you have in minutes, and when power events happened, etc. They can even connect to your computer to do an auto shutdown before back up power fails, email you to let you know what’s going on, etc.
Do a quick search on choosing a back up power supply, etc. and look at the various models available at online retailers and suppliers. Price, features and capability is very varied.
And of course they all protect your gear against power surges, brownouts, and all sorts of other evils.
Hope that’s helpful.
TIB
It wouldn’t have to run the laptop..the battery will do that for about 8 hours, just the little compressor and the Decade, not to much power between the two things…maybe 30 watts if that. But 3 days!, for one of these back ups, with all that running from it!
I’ll check it out.Now back to the subject.
Well, these things are options: solar power, C-Quam, metering, remote controls and all that stuff. It would be nice to have our transmitter as modular as we can. Not everyone wants the same thing – other than the best range and the best sound. I think we all want that.
In my case, I’d still like a rack-mount transmitter control panel, but with the transmitter – probably a Rangemaster – mounted at the antenna. I’d like such meters as may be realistic and switches for the the transmitter itself on the control panel and perhaps things like the switch for the tower lights.
I don’t know where to put the power supply. Either with the rack-mount or at the base of the tower so it would be located by the ground lead to keep it short just as we are keeping the transmission line short by mounting the transmitter just under the antenna.
I don’t know that it has to be more complicated than that, in my case.
All comments much appreciated.
John
W9LWA
Here’s another thing for designing a perfect transmitter and this is something my broadcast engineer did for me when I was using the Sean Cuthbert transmitter. What he did was make a remote control for the ATU. After several months of warm cool warm cool your capacitor is going to Need retuning. One can use a field strength meter and a remote control especially on the talking house ATU that should have had a remote control tuner for that.
This makes it easier for people who can’t climb all the time or for those that are visually impaired like me and have to have someone set it up for them.
Granted right now I don’t have a remote control ATU for the ASMAX2`s outside ATU but those things can come later. This will always make sure you have the utmost range you can get.
I am curious to find out how far off tune a procaster would be after 6 months to a year and having to retune that?
I can’t speak for all Procasters, but mine has yet to need any retuning. For the first 3-4 years or so that it was up I used to check the tuning every few months to see if there was any need to peak it again. Every time I checked it was still as peaked as it could get.
Mine has been mounted outside a third floor attic window for 6 years. it’s on the south side of the house which means it bakes in the sun all afternoon every day. Temperatures here go from around 95-100 in the summer to -30 below zero (that’s temp not wind chill) in the winter. It’s hard to imagine a more widely varied temp than that. I’ve checked it in the summer and in the winter. I’ve always tried to peak the tuning and it could never go higher than it was originally set for. So I’d say it’s holding up quite well.
I also keep tabs on the frequency as well, with a frequency counter in the studio that takes the reading out to 6 decimal places, and also checked it on a spectrum analyzer and the frequency remains very stable as well.
To access my transmitter I have to go to the third floor attic, open the large glass window that opens inward and swings all the way down, then remove the screen, which is in a wood frame and screwed into the window frame itself. Then I can easily reach out to the transmitter and open the front panel. Kind of a pain in the butt, but at least I’m not climbing anything outdoors! In the Procaster, tuning control and built in meter are right there inside the box, so it’s easy to adjust.
TIB
Wow at least that one is a great performer. Now only if the Talking House’s new ATU does that well those folks will have no reason to worry either.
Knocking on wood I think my home made ATU is holding up nicely. But my engineer friend called a few days ago and told me when he has time he wants to see about taking down the old satellite dish since its not in use and on the roof and see if he may be able to stop a possible issue with the antenna being too close to the satellite dish causing issues with my range since your doing so well with your Procaster Tim.
If everything goes well I hope to achieve the sort of coverage you get and that will help me get to the market 1 1/4 miles away to a good Radio or car Radio. It shows things will work well if you take the time and make sure your set up is well done.
That’s half the reason you pay so much for these like the Procaster and the Decade as it will work forever and not designed to conk out in a couple of years so you have to get another one. The Decade is also OK for outdoor mounting in all temperatures as per manual. I think Artisan will vouch for that.
Unfortunately the “big three” transmitter makers in our hobby(Procaster, Rangemaster, Decade) will be gone sooner or later as they get older and retire, or close the business. and someone has to take their place or there will be no more high end transmitters of this kind in the future. Just a thought.
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