- June 21, 2019 at 4:43 pm #111613
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.
W9LWAJune 21, 2019 at 6:33 pm #111615radio8zSenior Moderator
Total posts : 237
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.
NeilJune 21, 2019 at 7:27 pm #111617
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…
W9LWAJune 22, 2019 at 8:39 am #111621ArtisanRadioParticipant
Total posts : 499
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.June 22, 2019 at 9:41 am #111624timinboveyParticipant
Total posts : 661
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.
TIBJune 22, 2019 at 10:32 am #111626MarkModerator
Total posts : 548
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.June 22, 2019 at 11:01 am #111628
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.
W9LWAJune 22, 2019 at 11:06 am #111631
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.
W9LWAJune 22, 2019 at 11:23 am #111633MarkModerator
Total posts : 548
Also Canadian approval, so we can use it here. The problem with a lot of these transmitters is they are no good here. Me, I’m not a technician or have any engineering knowledge, just know some basic electronics, so I don’t know how I could be of help. I’m also not in the USA.June 22, 2019 at 3:36 pm #111635ArtisanRadioParticipant
Total posts : 499
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?June 22, 2019 at 5:07 pm #111637
Well, perhaps it could be modular with different options such as processing on separate boards that could be included or not as the operator desired?
W9LWAJune 22, 2019 at 5:48 pm #111639ThelegacyParticipant
Total posts : 283
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.June 22, 2019 at 7:05 pm #111641
So, C-Quam is pretty important to have for a transmitter to be top of the line? I’m familiar with it of course, but must admit around here in Indiana I’ve never heard anyone speak of it.
But, would there be any downside to having it on the transmitter?
W9LWAJune 22, 2019 at 9:07 pm #111643ThelegacyParticipant
Total posts : 283
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.June 22, 2019 at 10:14 pm #111645
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.
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