Actually, Epiglottis, I did not overlook the fact that you want component level chips and what not to "roll your own," so when I mentioned the Sony Wireless I was viewing those as component-level devices since they are small and essentially do what's being asked of them, as they could be the building block for further enhancement.
But I understand wanting to know what's inside so you can get down to open-scalp surgery and I have two steps to try...
First, I'll see if Sony publishes a Service Manual for the device. Oldtimers remember the days when all electronic devices had professional service manuals available by special order to service technicians. Those days may be long gone, but I'll look into it.
Step two, I'll examine the transmitter / reciever and see whether they can be busted open. If so, I'll go in with magnifying glasses and gather the needed data.
Carl, thank you for understanding. It almost seems that those interested in unlicensed operation in the broadcast bands now have more resources than non-corporations wishing to work in non-broadcast bands. Technology is a weird beast.
Neil - I can't for the life of me understand why Linx makes that chip fixed to one frequency and only one frequency. Even in fixed-frequency modules they usually offer a dozen different modules set to adjaent channels. Since I'm looking to make more than one of these that could be used simultaneous, and I don't want to get into a public safety band, I guess I can't use that module. I just don't understand some of these design choices. And it doesn't help I don't know much about RF theory or EE in general. Why is it harder to build a receiver on 900MHz than 90MHz if it's looking for the same signal on both, and there are no practical power restrictions on 900MHz? Seems to me that anybody who worked in 900MHz would run way more than 250uV/m, which would seem to suggest broadcast FM tuners need the more sensitive receiver.
I may have to just wait until the local economy gets better and hack the TI PurePath development modules.
Okay, so help me out here: Say I build a circuit that simply oscillates down a random wire at 88MHz, and a receiver to detect an 88MHz oscillation in the air nearby. Coils, transistors, PLLs, crystals, whatever, just an 88MHz sine wave at a certain power. Forget what we encode on it for now. Then say I build the same oscillator at the same power but this time it's sending a 916MHz sine wave down that random wire. Why is the receiver different in that case? Is it "easier" for basic electronics components to work with a lower-frequency signal? And since both receivers would divide it to the IF at 10.7MHz, is it just more difficult to deal with the signal at 916MHz and get it down to IF because of its frequency?
I guess when something is mass-produced I tend to think to myself, well, that problem has been solved, to a certain degree. So in my naievte, I think, well we're using pretty much every frequency from 0 to 5GHz these days, and I don't hear people talking about it being prohibitive to work in one band or another. So I guess in my limited knowledge I think there's a "thing" (circuit/module/chip/whatever) that sends a wave and a thing that hears that wave and that problem is long solved.
Maybe there isn't the demand for commodity modules or chips that I thought there was? Maybe I'm wrong that RF products don't have primarily custom-designed chips. Or maybe there are still enough old-timers in the industry that non-broadcast band devices are still more discreet than I think they are? Maybe I need to go back to college, lol?
Appreciate the continuted patience and information while I work this out.
ej
A man without patience is a child.
I guess that's a fair "saying," best I could do right now.
The behavior of radio frequency (RF) energy changes a lot from the long wave spectrum on up through MW, SW, HF, FM, UHF, microwave.
At least two aspects of frequency domain have ever different rules depending on operating frequency.
In blunt terms, low frequencies are non-directional and follow the ground.
Within the AM band alone tremendous power & sky-wave differences can be detected as frequencies increase.
Channel 2 TV has some characteristics of lower frequencies such as sky-wave and storm detection, whereas Channel 13 TV is more directional and free of such effect.
Higher the frequency the more directional things become.
The other aspect of frequency governs the designing of circuit layouts and lengths of connections, which is ever more delicate at high frequencies.
The difference between 90 MHz and 900 MHz is profound given these considerations.
e j,
The Linx modules which I have used (900 MHz) had switch selectable frequencies, eight in the same band. I was also surprised that these modules don't have this.
You asked about what is different between 80 MHz and 900 MHz receivers. Basically, they are the same block diagram wise. Even at "low" frequencies, the small signals, mixing, detection, and amplification are not trivial for good performance.
At "high" frequencies, about 100 MHz and above, so called parasitic effects become important. For example, the lead inductance of a capacitor can greatly increase the effective in circuit capacitance of the component. Higher Q front end filters are required. Circuit noise increases and this is why you don't hear receiver hiss on an AM broadcast band receiver yet you do on an FM or TV (analog) receiver. If it wasn't for the SMD technology we would be hard pressed to have affordable receivers operating above 500 MHz.
Neil
A word of caution: don’t piss off HAM’s.
In the 400MHz are there is a band of frequencies that allows 200uv/m @ 3m, 410-470MHz.
To me, that almost sounds perfect for in-ear monitors. That range corresponds to some cable TV channels.
To make a transmitter, you could start with a multi channel UHF modulator that can do cable channels 56-64. (A Channel Vision 3 Input Modulator CVT 3UB/UHF can do cable channels 59-86). You would want to disable the AM video portion of the modulated signals so you were just outputting the FM audio portion of the signals. Then you would pad the output of the modulator so with your antenna gain the field strength was 200uv/m @ 3m.
For receivers, you would need something that can receive FM modulated audio in the 400MHz range. I am not particularly familiar with receiver design, but it should be possible to change the oscillators and filters in an 88-108 design to work between 432-468 MHz.
I wasn't aware I had pissed off any hams. I sinerely apologize for any discomfort I have caused.
200uV/m@3 is less than FM broadcast, or did you mean to say 200mV/m@3?
I'd love to know what's in that Channel Vision unit that does the modulation and see if the parts are still available. But as you said, finding a 400MHz range receiver is the problem. IEMs did operate in this band for awhile. I figured ISM bands would be the way to go as they don't have these ridiculously small field strength limitations.
Neil, do you think the version of the modules you used are good and gone? These chips seem to get discontinued very quickly; if you don't develop and manufacture something during their lifecycle, you have to start over.
The Linx transmitter I use is model TXM-900-HP-II. The last I looked, these were listed as discontinued. Too bad since they were easy to wire and had the multi-frequency capability.
I just checked the popular web auction site and there was a listing for one of these but it was sold.
Neil
EJ,
I think you are saying that you would like to build a discrete circuit version that would insulate you from the crazy dynamics of the chip/module market. A discrete TX or RX operating at 900 MHz would be difficult or impossible due to component geometries at microwave frequencies. The chip/module devices are so small that they can overcome the severe limitations of the super high frequencies.
What selection of modules are offered on the market at any particular time is a function of the volume of devices that are projected to be sold. The fixed development cost is very high, so they need to sell a minimum of say 50k or hopefully way more to spread the fixed cost and arrive at a unit price that is affordable. The market is in complete chaos, with new devices and new applications coming up almost monthly, and disappearing at the same rate. Look at the cell phone market. They may design a super chip set and sell 100,000,000 for a year and then its on to the next chip set. Obsolete chips are everywhere in the trash dumps.
If you want to disconnect from the comings and goings of whiz bang chips/modules, you'll need to go with lower frequency TX/RX discrete circuits in roughly the FM band. Don't even try to build anything with discretes for the 900MHz region. You will be frustrated.
Thanks, but I never said I wanted to go discrete. I said I see a lot of consumer and pro gear that can't possibly be all in-house custom proprietary chips operating in license free bands from 400MHz-2.4GHz that push audio over wireless, most as multiplex FM, and I wanted to know what the chips are. I'll build the circuit, design the board, and have the board made. I love ICs. I don't understand why there aren't more. And SoCs too. If your average consumer still won't buy bare chips why not put modulators, oscillators, buffers, amps, ADCs and DACs, and an RF amp all in one DIP or SOIC instead of 6 2mm^2 QFNs?
I'm seeing $900 IEM systems that modulate MPX FM on 900-something, and I can't help but think those are commodity parts in that circuit, and if I don't need the brand name, the warranty, the Ethernet port, the capability to run 32 of them in the same room, and a pretty over-engineered enclosure, I bet those commodity ICs that do all the heavy lifting are $15 of the total cost.
But what I'm seeing is that nobody makes analog latency-free RF parts anymore, and no, I wouldn't bother going discrete at 1MHz much less 900 or 2400. The only chip that does anything near what I want is the TI PurePath series; which require an external ADC/DAC depending on direction, and an external RF amp. But they run with 20ms latency, full digital up to 96k sampling, and auto-hop in the 2.4GHz band so as not to cause or accept interference. I just can't get it through my thick skull that that's the only thing being manufactured right now. I thought I just didn't know where to look. I'd like the experience building something but I don't need 96k sampling over microwave. But I also don't know if I can just buy any old frequency synthesizer and any old FM encoder and hook them together, and I don't know if I can do something analogous to that on the receive end. I feel like I'm working on Vostok I and nobody has ever put a man into orbit before and you'd be an idiot to expect there were parts available. I just didn't think a 900MHz audio link in 2015 would be like that.
e j,
I just finished a build with the RN-41 module. Thought this might give you some ideas.
I started with a piece of printed circuit board and cut it to size. After cleaning it with copper cleaner and a wipe down with lacquer thinner I used an artist's brush to paint the traces with lacquer paint. I kept it simple with only traces for the connector, LEDs, resistors, capacitors, and the 3.3V regulator.
After painting, the board was etched in ferric chloride and when etched the paint was removed with lacquer thinner. The board was then tinned with solder.
The SMD parts were salvaged from a scrapped PC motherboard using a temperature controlled hot air gun. These components were then soldered to the board and the module connections were made with wire wrap wire.
It worked first time!
This is quite involved and I have lots of experience with fabrication but nonetheless I hope it encourages you that it can be done.
Here's a picture which you can click for a larger view.
Neil
Edited to post a better picture.
That is a beautiful bit of craftsmanship Neil/Radio8Z.
As a pastime while listening to the radio (my own station) I hunted for more info on the Sony Wireless Mics I talked about earlier.
1st thing I tried was to get into the egg-like encasement, removed two micro-screws, but the rest was snapped with very delicate plastic edging no doubt designed to break, so I replaced the screws and moved to...
2nd thing was to do an FCC Site search for FCC ID: AK8WCS990T which took me to the 1-line description indicating "There are no documents on file for this device." Sometimes they have circuits, but not for this.
3rd I searched for and located the Service Manual PDFs for both WCS-990 and WCS-999, but a subscription is necessary to download them, so I'll link it if anyone else wants to go after it:
http://www.nodevice.com/manual/Sony/page148.html
@post20/21
I wasn’t saying you had, I was just giving a heads up in general, and a warning that my suggestion in the 400MHz could catch their attention so be mindful of field strength.