Just an update.
Testing is continuing on this project.
Much needs to be done on this kit I have as far as modifications goes.
Output impedance is one big issue here since there really is no output impedance to speak of at this point. It was designed for a simple 10 foot wire antenna.
Audio is not clear as I am told it is supposed to sound like by others who own this device.
Being that I bought my kit already assembled off of Ebay over a year ago, until now, I have only fired it up periodically to see if it worked e.g. transmitted a signal in stereo, therefore I have not attached an audio producing device to it until a week ago, so I am now testing it with a audio source for the first time.
It does suffer an AC hum, I have taken the 19 volt laptop power supply off of the transmitter for now, because that might be too much DC power input for the voltage regulator on the transmitter, I have switched in a Radio Shack multi-voltage (switched type) output wall wart running at DC 12 volts 300mA for now, but I still witness an AC sine-wave on the carrier that has to be eliminated.
I do not have a tunable antenna in the works as of yet, that is another whole project and a whole another whole can of worms I have yet to open.
There are some modifications I have been told about, that should help the kit operate with a cleaner audio carrier, like adding .1uF Mica caps to all the ICs at B+, to board ground and adding RF chokes of 100uH to 300uH at various stages of the PC board and perhaps adding a toroid coil near the RF output stage to give the kit a matchable impedance output that can be matched with the proper antenna e.g. 300 Ohms or 50 Ohms etc.
I will keep everyone updated as this project continues.
Some may ask, why not just buy an already to go AM transmitter with an attached antenna? Answer, because there is no learning curve to doing it that way and I want to experiment and learn by trial and error. That is what this hobby is all about to me, the curiosity and the mind expanding experience of it all.
Bruce.
Mr Bruce said: "Some may ask, why not just buy an already to go AM transmitter with an attached antenna? Answer, because there is no learning curve to do that and I want to experiment and learn by trial and error."
Mr. Druid said: "Some may ask, why operate an AM transmitter on 1710 kHz when one will get better performance below 1705 kHz? Answer, because there is no learning curve to do that and I want to experiment and learn by trial and error."
Mr Some: INSERT COMMENT(S) HERE
Okay, this Chris Cuff AM C-QUAM Stereo transmitter project is currently dead in the water. The biggest issues is getting a usable carrier out of this transmitter because of the lack of an output stage that creates a carrier that is capable of reaching more than 20 feet or so.
I am not capable of building my own output stages, such as pre-amp and amp because I lack that knowledge and test equipment and purchasing the only pre-built amplifier I could get my hands on reqiures a 50 ohm impedance input and some may refuse to assist me with rebuilding the Chris Cuff output stage to produce a 50 ohm impedance, because it might be felt I am constructing a transmitter with intentions of exceeding part 15 rules for the AM broadcast band. Thus asking and questioning why am I needed a 50 ohm impedance out the output?
The major issue I face is producing a 50 ohm impedance just for the sake of feeding the proper impedance into the pre-built amplifier.
The impedance of the output stages of the Chris Cuff transmitter are not known, nor was one important when Chris Cuff designed his transmitter kit, but, the major issue with the output is even if it is hooked up to a properly tuned antenna, its total range is only meant to reach several feet even with the so-called high power stage included that was a Chris Cuff after thought.
So, because, I can not get any usable range out of this kit with any possible mods and lack of room to add new stages to the current PC board layout, this project is currently dead in the water.
Bruce.
That's always been the way with the Alfredo/CCuff circuit, it's only intended to be a one room wireless broadcaster and demo stereo radios the way it is. It uses low millivolt signal levels on the NE602 ICs to avoid distortion, that's one thing.
The other is that since it produces an already complete AM signal at its output, it needs a linear amp to increase the signal. The best for 100 mw might be a simple single stage class A amp, or something with a push-pull output stage at a few watts if you're doing carrier current. At these frequencies, they're almost audio amps, no special devices needed.
Don't give up, try to learn some circuits, you'll be happy with the accomplishment. You have what I believe is currently the best, most authentic to Motorola's standard, CQUAM transmitter out there! It's not taking shortcuts like the others.
What you are doing is very impressive.
(A short message from my smartphone)
Broooce Part 15 Hartford CT
I have a prebuilt amplifier I already purchased, which is encased in a metal cabinet with heatsink included. It requires a 50 Ohm impedance at the input for it to work correctly.
I have schematics of the Chris Cuff AM Stereo C-Quam transmitter, I can ask Chris if he has any issues with me publizing the section that relates to the output stage.
The schematics I have are well drawn not like the ones that have already been published on the web.
A few mods have been presented to me by someone who is familiar with this particular transmitter, trouble is, the directions leave me with some guess work to do and the person seems to have dropped off the face of this Earth, because repeated emails have gone unanswered.
I can't work with guess work, specially if it involves soldering in the wrong parts, only having to remove them afterwards causing damage to the PC board traces and the IC chips.
The mods invloved are to clean up the audio hash and to produce a cleaner signal before the amplifer and also to produce a 50 Ohm impedance to satisfy the external amplifier's need for a 50 Ohm imedance at least at the input.
The amplifier is a MW linear amplifier which is wide band, so the signal needs a little doctoring before the amplifier to assure there is a clean signal before the amplifier input stage.
A balun was suggested, the issue with that, is the Chris Cuff transmitter's final output stage transistor's impedance has to be known in order to make a successful BALUN transformer.
The likelyhood of a 2N3035 final output transisitor would be used, but it is not clear to me as to how to wind a BALUN for that transistor to come up with 50 Ohms.
The directions are as follows: (As far as the output impedance of that final....it is at the impedance of the amplifying device's collector to emitter resistance.
As you can see from the schematic and the unit itself..there is no impedance matching circuit there.
Best approach is to use a toroid transformer and wind the primary side based on the device impedance,
and wind the output of the toroid to match what load you want...ie 50 ohms or 300 or whatever)
The biggest concern with adding parts is the mention of adding .1uF Mica caps to all of the B+ pins of all of the IC chips to help clean up any hash.
Directions are: Your first step is to eliminate the hash noise with the .1 mica caps from each B+ point at each IC to ground. Then install 100uH to 300uH chokes at the voltage regulator in's and out's.
You will also want to add RF chokes before and after any voltage regulators on the board.
I found that chokes in the 100uH to 300uH range works good.)
Issues are I can't find any .1 Mica caps and I'm not sure if .1uf is what is required.
So there remains a mystery as to what exactly is required.
Another circuit was suggested that uses two IF cans from AM radio receivers, the ones with the RED slugs and 3 electrolyic capacitors, 1000uf/3000uf/1000uf.
This circuit consists of a 1000uf cap, a coil, the 3000uf cap, a coil and finally the 1000uf cap.
The two cans are supposed to be tuned for maximum output to the amplifier.
Sounds simple enough, but for me that is not the case, specially with those mica caps, they are required to be soldered to every IC B+ pin to ground, and if I purchase the wrong caps and have to remove them, I risk damaging something including the ICs if I use the wrong capacitors from the get-go.
So, this brings me to a stand-still until I know exactly what I am supposed to be purchasing before hand.
Bruce.
I do have the feeling you're in a dilemma right now Mr. Bruce, all of these engineering types are going to be telling you different ways to go about it, because there are a number of ways, and everyone has their opinion, and there's no one completely right way!
I didn't know you were having hash noise, and you'd want to find the cause of that first. One thing to do is put the transmitter on a 12 volt battery by itself and see if it's still hashing.
They probably mean ceramic disk capacitors, or more likely molded ceramic, like this for example.
http://www.ebay.com/itm/MilSpec-Molded-Ceramic-Capacitors-1-uF-50-V-qty-25-/361763815874
That link folded over, hope it works... The issue is, .1, (100 nF) is an uncommonly high value to be found in a mica capacitor, in fact I've never seen one, and I think it would be huge!
What kind of power input does your linear amp take, either for full output, or is there a range of inputs with an adjustable input selector? The power should be expressed in watts or milliwatts.
In regards to the .1 mica caps, those instructions were given to me and Station8 and yes, looking for .1 mica caps has left me at a dead-end.
The specs for the amplifer are as follows:
The working frequency of 100 KHZ - 40 MHZ
The input power 0 DBM
37 DBM output power, that is, 1 watts
Harmonic suppression (typical) - 20 db
Working voltage 12 -- 15 v
The working current 0.8 A
Input and output impedance 50 euro
This amplifer was the lowest power I could find with the unit already fully put together, since I couldn't etch a board for an amplifier if my life depended on it, so I was stuck purchasing one already assembled and will have to go with carrier current.
Here is the full instructions I was given for this transmitter:
Hi Bruce. I'll be happy to answer questions on that unit. It is a good little transmitter/exciter on it's own if it is to be feeding a simple wire antenna or a loaded coil antenna/atu combo. But range is limited to about 20 feet or so as is.
The carrier it produces is well above the noises it generates from the digital circuits. However since that unit's output is not a tuned circuit, whereas the tuned circuit is the antenna system, driving amplfiers becomes an issue because of two things.
1. The fact the output is un-tuned.
2. The un-tuned output when connected to a set impedance input such as 50 ohms, loads down the signal level at that output to almost the same level of the noises from the digital circuits...thus you end up with a very dirty signal and not a pure carrier signal and all that will pass thorugh to the amplifier, which is why the difficulty of impedance matching and lack of carrier drive.
Your first step is to eliminate the hash noise with the .1 mica caps from each B+ point at each IC to ground. Then install 100uH to 300uH chokes at the voltage regulator in's and out's. Third thing to do is use local oscillator coils found in AM radios...in this case the red slug coil. Using 2 of these coils and 3 fixed capacitors (or variables for finer tuning), your forming both a impedance matching network and a low pass filter...a tuned output. Caps to use here are 1000uf/3000uf/1000uf. The / are your tuning coils. See attached drawing.
The other option for the output is to use a balun transformer. This approach would turn the output of the unit to a "broadband" output. But you want to make sure that all of the filtering described above is done to eliminate all the hash, otherwise it will still be present at the balun output.
The balun would have to be wound with the output device impedance in mind for the balun input. So if the output device has a 10k impedance, you will need a high impedance input on the balun...ie a lot of windings. Using a TO-32 core wind #22 solid insulated coper wire 40 turns for the input. Then wind same wire type in between the first set of windings 10 times for the output.
You can combine both the tunable filter and the balun. Put the balun at the output of the unit, then the filter at the output of the balun. Tune filter for maximum drive into the amp.
What would also improve things is the last little driver stage before the 1 watt transistor had some tuning as well. Unfortunately there is no room on the board to install a tuning coil tuned circuit.
Anyway these initial steps can drastically improve that unit for amplifier driving.
(End of Instructions)
Keep in mind though, that this transmitter is designed as a bench top transmitter to near-by radio, not for extended range, that is why an external amplifer is needed to reach more than 10 or so feet with a well tuned 3 meter antenna.
Bruce.
It appears this thread went silent pretty quick.
Is it because of the mention of an addition of an external linear amplifier??
I am not trying to break any FCC rules here.
This kit does have exceptional audio quality built as it is, the only real problem is, it's author intended it to be a novelty and experimental kit and did not take into consideration that anyone would use it to broadcast at 100mW with it.
Filtering is good to excellent, but not at 100mW, which is legal for part 15 AM in the USA.
I am admitting that my education lacks too much know-how and information when it comes to building Radio Frequency output stages.
At 57 Years old, 4 years of tech school is out of the question and I lack local associates who fully understand the type of algebra that is used in the radio electronics field.
They look at it and say, "it's all japanese to me".
Still no word from the guy who emailed me the directions I posted earlier.
Unfortunately, I am like Troy, Thelegacy, I am losing my eyesight rapidly do to several eye dieases, my left eye far worse than my right from degenerative disc disease, this being irreversible at this point and time, which is why most of my posts contain typos, I can't make out the letters on the screen for typos. e looks like a and t like an i. Then from than, I can't see the typos unless it is large print which is after I post it on line.
Situation, project is still dead in the water do to lack of knowledge and understanding.
Bruce.
Ya know, we are lucky to have people like Phil Bolyn provide us with AM transmitters like the AMT-3000 and the 5000. For $100, the 3000 is a serious contender. It is in kit form. It builds into a perfect unit every time! This is my fourth build of this.
Why someone can't (or won't) make a C-QUAM kit in a similar fashion is beyond me. I need to ask Phil if he is interested...
Doug
Dugger, Glad that things are going well with the kit since you've been able to get one. I wonder if someone has tested both the 3000 and 5000 to see how much different they are, and what things are better with one or the other.
Right, I sense at least some desire for AM stereo in a higher power form than we have presently, or at least higher efficiency for use under tenth-watt rules in the US. There are higher power CQUAM transmitters available from Greece that could be used for carrier current, but at more serious prices, so I see a gap that could be filled there.
The problem is it could take some serious design work to make something to the CQUAM-quality specifications, and a company would have to decide whether there's enough interest to make it worthwhile to engineer and produce a more complex kit that will cost more.
Most little AM transmitters you can buy are based on classic circuits that have been floating around for years are are tried and true. CQUAM is a less-known art that would require more design work time and prototyping.
I find it interesting that Asia hasn't attached itself to the AM broadcast sector yet, like they have with FM and hamradio, etc.
C-Quam is definately a big challenge for part 15 !
Design would be low level balanced modulators, and linear amp final stage (with lower efficiency), or phase mod the carrier frequency coupled with class d/e final stage, with high level mod for the mono part.
Design of a frequency agile tx could easily cause phase noise/jitter, that gets decoded as noise on a c-quam receiver.
I have added a switch on my Denon TU-680NAB, for forced stereo, this is handy for hearing pll tx noise.
I have a Delta Electronics ASE-2 exciter, i am going to wire this up to the SSTRAN AMT-5000 tx, this should match up well, due to the excellent response of the AMT's modulator.
Paul.
At least for me, I just hadn't gotten the time to answer until the weekend.
The specs are a little confusing with the amp, but there might be light at the end of the tunnel with driving the amp at least. 0 dbm would be 1 milliwatt, and and your C. Cuff transmitter should drive that easily!
For now I'd consider putting aside the transformers and other parts between the transmitter and amp, and keep it simple. I'd use a circuit with just a coupling capacitor and pot, with some coax and wire.
Hopefully my proposed circuit will attach to the post. (edit: no dice) I'd lay out the transmitter board on the table, with the pot circuit attached, then to a few feet of coax to the linear, with a 50 ohm dummy load on the output. If it's 5 watts peak power on the amp, then see if you can adjust the signal for about 1.25 watts into the dummy.
The circuit is simply a pad, with a DC blocking capacitor. Later you might see what other coupling you could do, but if you're limited on resources, you could try this for now.
Hi Boardmaker, I've been mulling this stuff over, and think the linear amp idea could work, at least for carrier current use. I don't like how the current circuits are using low signal levels, essentially receiver levels since the NE602s have to operate without overloading. There's a lot of amplification going on in the C-Cuff lineup, even to get 10 milliwatts.
I think you're right about it having to be class D or E, maybe C. That shouldn't be too hard to do, since it could be done when retrofitting a mono station that was never designed for stereo, when AMS was new. I wonder if longwave stations in the UK ever modulated in stereo?
I was wondering the same thing about using the usual PLL that small transmitters use, and wondered about the phase noise exactly! Is it possible to get rid of it and most all of the 9/10 khz tone, keep it to acceptable levels for stereo?
I'd try, but am almost sure that a DDS board controlled by a micro would be the better choice. Great that you have that Denon, said to be the reference tuner for AM stereo, that would make a good mod monitor. 🙂
Nate,
Both the ASMAX-1 and the Cyprus c-quam exciter use DDS boards,but the phase mod still comes from a johnson couter method.
So the dds board just produces the reference 4X frequency agile source,so this has very low phase noise.
The sean cuthbert tx uses 4x frequency agile pll oscillator, and given this, the noise is fairly low, my big concern is microphonics of the coil.
The ASMAX-1 is interesting as it uses an intermediate frequency, the modulator is at a lower fixed frequency,passed through a bandpass filter, and then mixed with the dds agile osc.
The advantage here is that the whole band coverage requires one fixed filter on the rf output stage.
The Denon tuner is over rated, certainly not a reference tuner to me.
This tuner uses a basic 25hz notch filter, and lowpass filter after the decoder ic, the response is not flat at all.
I also have a Carver tx-11a, that is superior in the frequency response stakes.
I bypassed the Carvers 10k notch filter, and the flatness of the audio is exceptional !
The Carver does not use a 25hz notch filter, but instead extracts the phase pilot reference from the decoder ic, then mixes this out of phase with the audio channels, so cancelling the residual 25hz pilot from the audio.
Also another good design by carver is the excellent design of a eq circuit, that flattens the audio response by compensating for the 30khz bw 450khz if filters rolloff.
I have swept the audio response of the carver, and it is within 1db from 20hz to 15khz, yes that is right +/- 0.5db flatness !
The switchable de emphasis filter is really useful when sweeping a tx/antenna setup for audio bandwidth.
This is my reference tuner, as far as frequency response goes.
I am fortunate to have 2 Denon TU-680NAB tuners, one i am keeping original, and the other i am starting to modify, to improve it's specs.
Paul.