I have the Realistic TM-152 AM Stereo Receiver, it requires an external audio amplifier, such as a stereo receiver system, since it is simply an AM stereo radio tuner with RCA output jacks.
As for the Chris Cuff transmitter, I tried two different setups at the output feeding the external linear amplifier.
In one setup, I used the coil and tuning capacitor, a 2N3035 output transistor as the final. I left the rice bulb in circuit in this experiment, the output then fed the coil and tuning capacitor, then a 50 ohm RG-58 piece of coax fed to the SMA connector of the external amplifier's input.
I do not have a decently tuned AM broadcast antenna at this point in time, but I did take a roll of 100 foot coated 16 gauge wire and stretched it out into my yard, up into a tree as high as I could get it, drapped it across to another tree, then to another tree, until I had the full 100 feet stretched out, then I grounded the transmitter to an Earth ground I use for my outdoor scanner antenna since it is buried 8 feet in the Earth.
Now under these test conditions, things can be seen as illegal, since the transmitter is inside with a 10 foot piece of RG8 coax feeding a SO-239 coaxial connector and a grossly long antenna with a long ground lead due to the outdoor scanner antenna's long ground lead, but I did this as a quick test, because I still have to construct an antenna for the current frequency the transmitter is locked on which is 1250KHz, there is no tunable frequency with the Chris Cuff Transmitter, because it uses a single crystal for frequency selection and this kit came with a crystal that places it on 1250KHz.
I can buy a crystal from Digi-key and move the frequency to the upper AM broadcast extened band. My Realistic TM-152 does not tune much past 1605KHz, I have not done any mods to the TM-152, there are several out there on the web and I have those saved on my computer.
Those mods do require altering the exterior of the TM-152, by adding new toggle swtiches, the back plate is made of hard cardboard, and placing swtiches in the face plate require drilling holes and the adding of the switches.
These mods will forever alter the appearance of the TM-152, so I am hesitant about doing the mods. I used to do mods to USA CB radios back in the day, but often, I would place the switches on the back panel, which as made of metal or aluminum, not hard cardboard.
If I moved to a channel above 1605KHz with the Chris Cuff, I would have to alter the tuning range of the TM-152 to which the analog dial tuning scale would not match, since it stops at around 1605KHz or so.
Now as for the transmiter, when I used it, it did not take long for the amplifier to get real hot and the range to a portable AM radio was about 1000 feet before it died out into no signal at all.
I do not think that range can be seen as acceptable, being the mass antenna structure and the amplifiers output power to which at perfect extreme conditions could reach 5 watts. The transistor inside the linear amplifier, has for some reason, been altered to remove the identification numbers. They have been scratched off intentionally.
I tried another approach, I removed the tuning coil and tuning capacitor and fed the output transistor with rice bulb included in the circuit, directly into the amplifier, again, same results. The amplifier got hot after about 10 minutes of operation and very little range as the result, maybe 800 feet maximum.
I then tried by-passing the 2N3035 transistor all-together and fed the coupling capacitor that origianlly fed the 2N3035 transistor to the coaxial cable feeding the amplifier to see if there was any over drive issues, the results there were still even worse, 500 feet distance.
The whole issue I believe I am facing is the Chris Cuff transmitter has no output impedance built as it is and the amplifier is expecting at least a 50 Ohm impedance at its input stage, since the impedance is not known, it is impossble to determine what is needed to get a satisfactory impedance that satisfies the amplifier's input stage.
I lack the proper equipment to diagnose such issues at this point in time.
All I have is a frequency counter, my oscilloscope I had many years ago, died and I have no such equipment anymore on hand.
I do not own any meters that work this low in frequency, sure I have VOM meters, analog and digital ones, but nothing fancy that reads frequency or other odd values. Just your simple AC DC volts, Ohms, AC/DC Current and Diode tester.
I have tons of coils and chokes, from Radio Shack assortment packs, but I'll be damned if I know what their values are, since none of them are marked!!!
So I am at a stand-still here, I may have to send this crap out to someone who knows what is what with this stuff, I have the Chris Cuff transmitter in an old Asus computer mid-tower case, as I did not like it being in a plastic project case.
The board here, does not allow me to add now photos to this topic, which is sad, because I would like to add new photos to this topic. A picture tells a thousand words.
Bruce.
Bruce,
Have you tried to connect an atu to the output ?
Reason i am thinking is that this would give some flexability on ip/op matching ?
You really need to get a schematic drawn out, this would clarify things.
Paul.
I have a complete well drawn schematic diagram of the Chris Cuff Transmitter circuitry, the whole thing. The whole road map is professionally drawn out.
I have to ask Chris Cuff if he has any issues with me posting it on line and, then there is the issue with not being able to add attachments to this thread, since my edit options have expired and I can't add any images to this thread hosted on part15.us
I do not want to host them in file sharing sites or image sharing sites for obvious reasons. But I would like to add them to this thread once permission is granted to share them here. They are in .png format, so sharing them is easy.
Bruce
If you get permission from Chris Cuff,and if you want me to host the files on my own domain, so they are added here, just ask.
Paul.
Hello all I just got word from Chris Cuff and permission was granted to publicize the entire Chris Cuff AM C-Quam Stereo schematic diagrams in this forum.
Here is what he said to me in Facebook chat.
Hey Bruce- I have no problem with anyone using my design. They already copied my board in Greece. (I used some oddball values in certain areas and they copied it directly) -have fun! Chris Cuff
BOARDMAKER I can email you the images and you can put the images in this topic, contact me at [email protected] with your email and I'll email them to you.
Please let me know when you have emailed me.
I have decided to share the images in another topic posted here at part15.us.
Please refer to this topic for the images, they include the Chris Cuff RF Power OutPut Stage, so now you know how it is designed.
Bruce.
Just posted in the other topic, before reading here !
Yes Chris's comments about copying looks about right !
The Cyprus C-Quam exciter that has many similarities, such as pilot tone circuit, the problem i have with that design, is whilst oversampled, the waveform clearly shows the oversampled steps on the scope, so hardly a decent sinewave !
I suppose this practice is considered as acceptable, due to low power use ?
The Cyprus tx does use a balun transformer on the o/p stage, to match it to 50 ohm.
Paul.
The SeanC C-QUAM transmitter I have doesn't appear to have distortion issues, I believe every so often Sean would make minor changes to the transmitters in an attempt to keep improving them. It could be the version I have isn't the same as Boardmaker's, I still have mine though its been off-air for awhile now. Coverage was meh at best, then again I've been completely spoiled by my Rangemaster at this point. IIRC the SeanC transmitter went about 800-1,500 feet for me.
That's kind of funny, a little subterfuge, over the guys in foreign countries trying to copy his design as a cheap way out, versus someone like Chris who really cares about promoting AM stereo and selling at a fair price.
One thing about the stairstep waves, I'd like to see them on a spectrum analyzer to look at what the harmonic profile is like. A direct method of testing might be to kill the 555 oscillator, then inject a 25 hz real sine wave into the system at the same level and hear what it does on your receivers, and if the noise is lower.
I've looked at Sean's transmitter too and thought about getting the kit, at least his seems to come at a reasonable price for an AM transmitter, AND it's stereo.
I just don't like to spend hundreds for a tenth of a watt, I'd rather spread the dough around and try more transmitters 🙂
Nate,
Sean's uses a single mod ic for the phase mod, it is not vector, but i seem to remember sean saying the distortion for stereo reception is low though.
I have just drawn out the Cyprus (Lesvos) exiter, it is identical to Chris's circuitry, except the final output transistor is a BD135 with broadband matching transformer using a binocular ferrite wound construction.
What is unusual is that the primary winding is centre tapped, with this tap going through a series cap and resistor back to the base of the final transistor !
The oversampled pilot waveform is sinewave overall, but you can clearly see the step transitions, so does need a l/p filter to remove these.
Whilst this exciter is frequency agile with a dds board, the fixed l/p filters after the low level modulators are the same value as the C Cuff values for 1200khz and above.
Paul.
Here is the Cyprus c-quam pilot tone waveform, this picture is from the maker, and of course it is identical to c cuff.
Would a properly tweaked LPA1 boost the signal enough? I think all it needs is 10mW of input for its 1 watt. I suppose it could be used for Carrier Current or somehow pad it down to only spit out 100mW. I suppose if it was incorporated into the actual finals of the transmitter it would stay compliant with .219
To add, what is missing from the Chris Cuff schematic diagrams is the antenna tuning circuits.
This is a discriptive explanation of the way the antenna tuning circuit is designed. The output of the final transistor is wired to one side of a tuning capacitor (a two terminal tuning capacitor, perhaps a single AM radio receiver type tunning capacitor), on that same leg of the tuning capacitor is a wire that goes directly to the output of the transmitter for the connection of an antenna wire, perhaps 10 feet in length, the opposite terminal of the tunning capacitor goes to a wire wound coil, in this case, an empty cigar tube was used as the base for the coil, the number of wraps of coated magnet wire (wire gauge unknown) around the core is unknown, as I did not want to unwind the coil and have issues with rewinding it again. The opposite end of the coil goes directly to the same antenna output terminal as the other magnet wire. The antenna ground is simply a wire soldered to PC board (DC -)
Most antenna tuning coils I have seen (correct me if I am wrong) are wired to both antenna hot and antenna ground. I know a visual diagram says a thousand words, but again, I am restricted here and would have to host that image somewhere else for addition to this topic.
Missing from the schematic diagram of the final output stage is mention of the 2N3035 transistor, perhaps that was an over-sight, since Chris Cuff used that transistor in a lot of his kits.
What needs to be done here for part 15 .219 is to redesign the output stage.
Now mention was made in the schematic topic here at http://www.part15.us/forum/part15-forums/transmitter-talk/chris-cuff-am-c-quam-stereo-transmitter-full-schematics-here by BOARDMAKER that the fianl output transistor is wired incorrectly in the diagram.
BOARDMAKER Said in That topic:
The rf output stage looks wrong,
The diagram shows the transistor base is biased from a 56k resistor to the 12-20v supply ?
I would have at least expected the base bias to come from at least 2 resistors, so without rf drive, the collector would sit at half supply, as this has to be a linear amp.
Also the rf out has no matching network to load the antenna properly.
An oscilloscope is essential here.
BTW, most of this circuitry is VERY similar to 2 other c-quam exciters i have !
Paul.
MrBruce continues with:
I added that post to this topic, because this is the discussion topic for AM C-Quam Stereo and the Chris Cuff transmitter.
BOARDMAKER Do you still feel that the output transistor is wired incorrectly in that schematic diagram?
I have many more things to discuss here, so this topic has a lot to offer, but I'll cover one thing at a time here, to allow a decent flow to the reader.
By the way, can a mod, when they have time, edit and add a link to this topic to post #1 of this topic http://www.part15.us/forum/part15-forums/transmitter-talk/chris-cuff-am-c-quam-stereo-transmitter-full-schematics-here ? I forgot to include a link to this topic, when I posted those schematics to the site, since this here thread is my prefered discussion topic. Many thanks!
Bruce.
Bruce,
I would expect the final stage to look something like this.
The input cap is the cap on the previous op stage,the base bias is straight forward, diode in4007 or similar, and the op stage is a series blocking cap, say 1nf, then the usual series loading inductance, and a small trimmer capacitor to ground, as in the amt5000 op stage.
The 10 ohm resistor from emitter to ground could be decoupled with a 1nf cap to increase gain, if it needs it.
Just noticed a fatal flaw, the bias line to the base of the transistor needs a series rf choke to pass the bias but to block rf !
That's what happens when i rush the job !
Anyway, after the addition of the missing choke, it should be good to test.
