Your proposed antenna sounds nice. The telescoping sections are a good idea. I would think that 2-3 sections would be sufficient, while minimizing production costs. In fact, an advantage of my modified SSTRAN antenna with the in-line coil is that the whole thing collapses to about 9ft (minus the mast).
As an aside - at these low power levels, how much worse is aluminum vs copper as a radiator? Since we're dealing with skin effect, I would think the copper would be better.
The Litz wire is also a nice idea. I would be interested in seeing a direct comparison of identical antennas and xmitters, one with a Litz wire coil and the other with solid copper (like the SSTRAN antenna). I have only seen Litz wire used in things like fancy crystal radios, but the rule of reciprocity would indicate that it would also work well in transmitting.
Any idea what your antenna might cost?
Hi Gerry, I'm not sure that the fully assembled circuit board wouldn't take it into being a manufactured unit that would need FCC approval and out of the "kit" category. I don't really know enough about how such units are viewed.
Now, if the tricky parts only were preinstalled? That might accomplish some of the same goals you listed for "fully assembled" without it taking it out of kit category.
Sounds like an interesting unit you have in mind, from your description. I don't know how big the market is for part15 gear, really. I consider a Rangemaster out of my price range, and the Sstran low enough priced that it's a serious temptation even though my inclination is towards homebrew I can tinker with. I'm not typical I don't think, though. I have a small home recording studio, spent years in bands and my college degree is in music and recording, so I have things already like compressors and limiters. Most people don't, though, and if I didn't, the Sstran kit would be beyond just tempting since it has a very nice little audio section from what I hear. LOL
Daniel
You will have to give some thought to the telescoping sections of your antenna. I live in the Southwest, where the Spring winds can be quite high. In fact, we have already had a few days of early wind. My SSTRAN antenna is still standing, thankfully.
I'm not sure what to recommend to secure the telescoping sections. The homemade SSTRAN uses hose clamps, spaced 3" apart. While they hold beautifully, they lack in esthetics. I doubt you'd want to use them on a manufactured product.
Another comment about the use of aluminum. Cheap aluminum alloys can be prone to stress fractures. Although weight bearing will not be an issue, wind loading will.
Just more food for thought. I like your proposed kit idea and would like to hear more.
Here are some comments to suggestions made...
May get the unit FCC approved once I see the demand is there or there is a need for a ready built unit. Meanwhile the PCB will have the surface mount parts installed and the thru hole parts would have to be added which should be easy to do. Then the transmitter would be final assembled.
The main oscillator will be adjustable over a certain range in order to null out beating between adjacent transmitters. It seems to me that the easiest and best way to create large coverage with several transmitters is to use a device like the Exstreamer from Barix (www.barix.com). This device can be set up as a "streaming puller" feeding from a server. Because the bitrate is low for the bandwidth required by AM, the server loading is quite small. Using the Internet also allows your radio station to be heard over the Internet also.
If the transmitters are set up such that their fringes coincide, and their oscillators are set to "zero beat", then coverage will be continuous. There may be some slight echo at the fringes due to audio arriving at slightly different times through the Internet. This would be small because the Internet delay over these short distances should be very small. You can see this when you "ping" an IP address and watch what the delay in the package returning. Efficiency of Litz wound coils versus solid copper: I have tried both and the Litz is definitely better due to lower RF losses. Also using the most efficient output stage possible for Part 15 does add to the ERP of the unit. The losses are so huge in Part 15 devices that everything helps.
The antenna is not telescoping but 3 sectional tubes of different diameters (5/8" dia. at the base) attached to each other with self tapping screws. It's light, strong, radiates well and looks OK. I have tested this antenna in Canada during the winter with storms and ice and it has not failed. Trees came down, but not the antenna 😉
The antenna also mounts to a sturdy aluminum bracket (which also holds the weatherproof transmitter) that fits directly on top of 1.5" dia. piping so there is no extra hardware to buy. The entire transmitter is compact, lightweight and reasonably inconspicuous. The audio/power cable and contentious ground can also be fed down through the mast pipe making them invisible resulting in a very tidy installation. The idea behind a sectional aluminum antenna is that it can be shipped worldwide and it's light.
Gerry
Daniel,
Interested in a Panaxis AM100 "kit" with many of the parts needed to construct a second transmitter (cheap)? Things at work have changed and I'm no longer interested in trying to convince people that part15 might work, so I'm giving up on this stuff. endlerg AT sunyocc.edu
I think you're missing an opportunity by not having the capability to sync carriers between multiple transmitters, like the Rangemaster. Zero-beating carriers is not enough, as previously discussed here.
Also, assuming that every installation could use the internet for audio feed is a mistake. There will still be need of an STL type feed in many circumstances. Another problem with an internet feed is that it is not 100% reliable and latency can be highly variable.
You ideas sound great and I would love to see your new kit when it is available. However, if you don't have any more functionality than the SSTRAN kit, why should I buy your kit at a higher price? Now, your antenna is a different matter, as no one else has a pre-fab antenna available.
Technically, a partially assembled transmitter is still just a collection of parts. It's not a transmitter until it's finished and working. Maybe having the board mostly assembled with some of the simpler parts left off to be soldered by the end user would be better.
Any possibility of AM stereo for your TX kit?
C5
I was thinking over your proposed project, Gerry, and I got to thinking. How are you going to do a 600 ohm blanced audio via a 4 wire phone line for both the audio and the supply voltage? Phone wire isn't really optimal for carrying sound over any distance in the first place, since it's unshielded and can pick up quite a bit of noise. 600 ohm balanced audio cable is two conductors inside a braided shield. Usually with XLR connectors on the ends, sometimes 1/4 inch diameter Tip/Ring/Sleeve, but not many people use those for a number of reasons.
Also, what do you mean by "auto power adjust"?
Daniel
by MRAM 1500 kHz
Radio stations have used leased telephone lines for many years to carry broadcast audio from the studio to the transmitter site. Our City Public Safety radio system used this method for 50 years. We're talking miles of unshielded wire. The telephone line (pair of wires) is used as a balanced line.
Balanced audio lines exhibit great noise immunity due to the nature of the "balancing act" they do. It's referred to as common mode rejection. Since the two wires of a pair are subjected to the same induced noise fields, the noise field creates voltages of equal polarity and amplitude in each wire of the pair. As such, the noise signal created is rejected because the receiving end responds to a difference of potential between the two wires unlike the noise signal which is common to both wires.
The telephone company routinely keeps a small amount of DC current running with the audio to help prevent corrosion where the wires are spliced. The DC is separated from the audio at both ends by their interface and has no effect on the audio. It also provides them a superviory signal in case the circuit is broken. We can do the same when using a pair of wires to supply both audio and DC power to the transmitter.
As for frequency response of the long circuits, the phone company equalizes the circuit to provide the proper characteristics to work with the audio. This was done with coils and capacitors to compensate for the frequency loss. More recently it's done with active components.
The phone company invented balanced 600 ohm audio transmission. Phones lines have been used for years in broadcast for different things. Radio mostly used specially equalized lines for transmission. Other portions of TV and Radio used what's called "dry pairs", and you just connect the two audio portions and leave the ground disconnected. Most sports stadiums still have a dry pair loop though them for broadcasters to connect line level devices. It's smart to put a transformer on each end of the dry pair just to make sure there aren't problems.
CAT3 phone cable has 2 twisted pairs. Use one pair for 12V power and the other for audio. Connect a 600 ohm transformer on one pair and with appropriate drive, you get excellent audio feed over long distances with no hum (no ground loops). I don't know how far you can go, but I have tried 200ft and noticed no difference compared to 0ft.
Auto power adjust means there is circuitry that will maintain power input to the final stage so that 100mW is not exceeded.
That's is my intention: supply the surface mount parts already assembled on the board; just add the thru hole parts and do the final assembly and it's done.
AM stereo - never thought about it. How many folks are interested in this?
Gerry
I'm not that familiar with this requirement and wonder how many people would want to do this?? - I don't know enough about it. From what I have read, it is complicated to set up and there is the expense of extra equipment and recurring charges for STL feeds etc.
As far as the kit goes as compared to SSTRAN, this transmitter would be expressly designed for external use and the antenna is part of the transmitter (it's not separate). The extra mechanical parts do add to the cost as they are custom designed and manufactured. The SSTRAN was designed for indoor use and I have noticed that many people have installed them outside in weatherproof cases and have added more efficient antennas in order to make them broadcast further - this adds cost. Somewhere on this forum I noticed that all these costs had been totalled up to show what was spent. It's a lot more than just the SSTRAN kit alone. So it depends what you want to do. My goal is to offer a top-notch quality product at a reasonable price. I appreciate all this feedback as it will help me produce what people are looking for.
Gerry
Cool, cool! Thanks folks, I've never seen such a thing. Learn something new every day here!
My confusion comes from recording studio and live sound support where microphone cable (and cables used to connect boards and devices, ideally, if the distance is more than maybe 20 ft) usually are low-z shielded cable which definitely has a heavy braid around the pair, and the locking XLR type connectors. It's just what I'm used to seeing, I use that sort of cable even for fairly short runs in the studio. Like from my Marshall MXL mic to my little Behringer board (which is only about 5 ft) I used Belden 8412 cable. That's a bit of "overkill", but with something like a vocal mic (especially if you do multitrack recording) you go to some pains to make sure the signal stays as clean and as low-loss as you can get it.
So wow. It never occured to me that radio stations might use anything else, or that telephone wire could actually deliver a good signal. Neat! Though I'll probably stick with what I know. LOL
Daniel
Shielded cable is still far better, but dry pair works for line sources if shielded cable is no possible. I wouldn't recommend running a microphone down dry pair.