Chris Cuff AM C-Quam AM Stereo Transmitter

First of all is there a way to peak the output for any given frequency?, an adjustment of some kind? Without that it's just broadband and the range will never be very much. Nowhere do I see a tuneable circuit anywhere at the output. If you check other AM transmitters max range can only be had with a way of peaking the signal....or wait...at the bottom of pic I see what looks like a tuning cap.? which tunes the large coil? Sort of half out of the picture.

If that peaks the signal on each frequency(you have to know when peaked) then the only other advice I can give is longer isn't nessessarily better for the antenna. Usually a certain length is ideal with the tuning circuit. The part 15 rule says 3 meters. Could also be this transmitter is very low powered.

Mark

Yup that is the a variable capacitor connected to the output transistor and the coil on the right side of the picture.

Bruce.

Given the loading coil visible in the picture, the output may be designed to work with a 3 meter antenna wire.  If that's the case it probably won't tune up properly with a 100 foot long antenna wire.

Have you tried tuning into a 3 meter antenna?

I found a few web hits on this part number. Here's a link to a catalog listing (click on the Discontinued Transistor Data Book 1975 link):

http://www.datasheetarchive.com/1034-datasheet.html

And a link to a NTE replacement:

http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=121-1034-01

If you want to try to replace this I would suggest doing so with a 2n3904. There is probably no need to have a power transistor here unless this is the modulator rather than the RF output (I can't tell from the photo. Modulator transistors can run hot.)

Edit to add: looking again at the pictures it doesn't appear that the power transistor is the RF output transistor since it doesn't have any RF components nearby. You mentioned that the tuning cap is on the right side of the board so that is probably where the RF output transistor is located.

Neil

I downsized the picture trying to keep it below the size limit for this site, so it does cut the image  down not showing the whole circuit design.

Yes, I tried a 3 meter wire antenna. Tuned the vari-cap until the light bulb in the first image went dim, meaning a perfect tune. Range was 10 feet maximum line of site range and dropped out completely.

What is not clear in my photos is that there is a wire soldered to the tab of that 1034-01 transistor, from there it goes over to that variable tuning capacitor. At that variable tuning capacitor, a second wire soldered to that same terminal goes to the coil located on the right side of photo number two. The output terminal on the vari-cap has a wire going to the antenna output which also has a second wire attached to it which comes from the coil.

That 1034-01 transistor is the output transistor, please try to note the black wire attached to the tab, it is soldered on the opposite side of that tab out of view. I realize there is a red and black wire in that area of my view, making it difficult to distinguish where the wires are going. Those other two wires are the DC power input wires. Near that transistor is a light bulb, it has a black wire crossing over its view, that is there to protect the output transistor from mistune damage.

Reading part 15 AM transmitter rules and RF power output allowances in the USA, the range I should be getting is just not there. It is hard for me to explain, but I know this transmitter was built with a limited distance in mine, perhaps as an in home entertainment system, where the proposed output signal was purposely intended to be 10 feet or so.

Imagine how far are 10 feet is, if other FCC certified AM transmitters are allowed to reach a one mile distance legally, then obviously, this transmitter isn't even close to what it can legally put out. I am not asking questions to get an output that is illegal, I am asking questions to at least get the power output up to that point where it is still legal.

Hopefully everyone here understands that I am saying that built as it is, I can not get a range greater than 20 feet, at 20 feet the signal is just barely noticeable on an AM car radio.

Bruce.

Bruce,

I now understand about the black wire. If you are willing and able measure the DC voltages at the three leads of this transistor with respect to circuit ground. This might give a clue to a problem.

Neil

Radio8z, I believe that this transmitter was built properly since it was built by it's designer not an inexperienced kit builder.

I believe that transistor was intentionally used. My attempts to contact Chris Cuff have led to no such luck.

The person I bought the transmitter from said Chris Cuff was going to send him a higher power output transistor, but never did. So basically, he originally intended to include a transistor that had a very limited output.

This kit does include a variable resistor for power output adjustment. Looking at image #2 you  can see it in the middle upper left corner just above that IC chip. With that turned in the direction for the highest output, it reaches those outputs I listed above. In the opposite direction, that output signal is almost none existent close by.

I can take readings using a digital LCD readout VOM meter and post my readings later.

Bruce. 

Bruce,

I did some net snooping and found that the "low power" transistor used in this transmitter is a 2N3053.

I also found that the collector goes to the light bulb. I can't tell from your picture but you might check that the center pin (the collector) of the power transistor is connected to the light bulb and the beveled end pin (the base) goes to a resistor and capacitor. There is no guarantee that whoever wired this knew what they were doing (especially since the tab is soldered to the black wire...unusual to do this).

Apparently Chris just took the connection to the antenna directly from the collector and your unit has the additional coil and variable cap installed. Maybe you should disconnect this and connect your short wire antenna to the collector and find out what this does for range.

Neil

Here are a bunch of Youtube videos created by Chris Cuff in his kit he included that 2N3053 transistor you mentioned, in this kit I have, he used that strange tabbed 1034-01 transistor for some reason.

AM Stereo transmitter Final RF assy part 1

AM stereo transmitter RF out part 2

AM Stereo transmitter RF out part 3

AM stereo transmitter RF out part 4

AM Stereo transmitter kit testing part 1

AM Stereo Transmitter kit- Demo & adjustments

Transmitter troubleshooting

AM Stereo transmitter orders

Each video takes you through the steps of assembling his kit.

Would that 2N3053 transistor cause this transmitter to transmit above FCC part 15 allowed power output? Is this possibly the reason why that odd ball transistor was used?

Maybe you can contact Chris Cuff and get an answer to your wanting more power.

Oh yes just saw you already tried that!

Mark

Bruce wrote: "Would that 2N3053 transistor cause this transmitter to transmit above FCC part 15 allowed power output? Is this possibly the reason why that odd ball transistor was used?"

As far as operating above the FCC limits goes I don't know. The operating power of such a transistor is set mostly by the supply voltage, bias conditions, base drive, and load and not so much by the transistor itself. It is commonly thought that a higher power rated transistor in a circuit will yield higher power but this is not the case unless the other conditions I mentioned are changed. Perhaps this TO-220 transistor was put in by someone who thought this would boost the power.

Here's the deal. If one increases the supply voltage and bias then the transistor will dissipate more power and could overheat so in this case a transistor capable of higher power dissipation is needed. Just swapping transistors won't change the power unless the other circuit parameters are changed.

Neil

See guys, there is no question that I am asking questions here with the intent of possibly going back on the air with a legal AM transmitter since trying FM got me a lot of bad press from HobbyBroadcaster. I'll try AM, but I want to go on the air as an AM C-Quam Stereo station.

I'll worry about adding a 102" steel whip later, but I want to get the output stage where I can cover an area not in conflict with the FCC rules.

 I can understand my trying FM may have caused a jealous FM station to go after me just to get me off 87.9Mhz.

Everyone in involved in this hobby, including Bill Defelice claims AM is the way to go for part 15 radio, I'm hoping this time around, I don't go through this crap again that I went through trying FM! But I will give it a try.

Before I re-buy any processing equipment or other studio related equipment such as a mixing board, I first want a transmitter setup that is legal to use in the USA and I want it to be AM stereo. I know not many people have an AM stereo receiver at this point, but I still want to go that route.

I do have a Radio Shack Realistic TM-152 AM stereo receiver that has the Wide AM and Narrow AM 'mod' done to it, so I can monitor my carrier in stereo.

As an extra added plus for our new listeners, I'd like to boast about transmitting in glorious AM stereo!

I just need to get my C-Quam AM stereo transmitter to cover more than my living room with an 102" steel wipe attached for an antenna. Right now, the antenna length is not the deciding factor here, it is the final stage output transistor that is limiting the signal.

Once I get one transmitter on air, I'll try doing the radio network thing again with AM instead of FM and see if I can convince a few people to house an AM stereo transmitter at their home carrying my Internet feed like I formally did with FM.

Bruce.

Here is what I really hope is not going to happen here. Okay I really want to make it clear, I am here asking for advice to run a LEGAL AM radio station. I am not looking to open the door for putting myself to be in the PIRATE spotlight again and hope my asking for advice here, is NOT going to put me there!!

Bill Defelice was always stating that the FCC watched his web site for pirates and some websites are notorious for being trap sites that exist only for the purpose of catching law breaking pirates.

I have no intentions of operating a pirate radio station and have no intentions of operating a radio station in violation of any laws. I want to be legal and nothing else.

So I am seriously hoping that everyone HERE understands my intentions before I go through what I did at HobbyBroadcaster and the Broadcastingengineering website before that. Many typos I posted at those two forum boards got me into a position of being looked down on and the accusations start being thrown left and right. I'm not going through that aggravation again.

Simply typing a sentence wrong or omitting a key word can make you sound like your intentions are to break a law. A simple sentence like "I DIDN'T use 1000 watts" typed "I DID use 1000 watts" can be used against you in a heartbeat simply because you forgot to add that compounded word didN'T. Trust me, I type typos and my typos get me into hot water! One means your guilty and the other means your innocent of such.

So let me make it perfectly clear here at this site, whether my real identity and location is already known, I am here to ask for advice on how to operate a legal law abiding radio station and nothing else.

Not that anyone here accused me of such....yet...but I just wanted to make it clear to everyone here and anyone who sees my posts on the Internet. If you view me differently than that, that is not my fault as I never came here asking otherwise.

I fear that once word gets out that I am considering going back on the air again, I'll have NUT CASES sitting outside my house with FIM-41's and spectrum analyzers looking to accuse me of something illegal again.

Thank you for understanding.

Bruce.

MrBruce, I have been here at part 15 dot u-s for years, and have not witnessed any accusations or suspicions about the intentions of those who post here. That means you also can probably relax, feel safe, and be taken at your word -- you are not a pirate and neither am I and neither are we (if I may speak for everyone who posts here).

The only negative thing I have seen is a few members became disappointed when they realized that the part 15 rules do not allow enough power to do what they hoped to do, but other members are running amazing success stations with legal power.

What you are doing now with the c-QUAM AM is a good way of re-claiming your legal right to broadcast under part 15.

I think there are two things left to do...

1.)  Get the input to your final RF stage up to 100 mW;

2.)  Match the 3-meter antenna for resonance.

That's it.