I have an AM C-Quam AM Stereo crystal controlled Transmitter which is hard wired for 1250 KHz to which I am considering an out door antenna for.
I looked at the antenna length for 1250 KHz and if I did it correctly it states 786.86 Feet is the total length for the main antenna radiator element.
I was curious what the results would be if I was to take several 10 Foot x 2" PVC pipes glued together and wrapped 786.86 feet of copper wire around the pipe from the ground up to the top of the antenna would this work? I have seen many antenna setups for AM broadcasting to which large coils are used and tuning capacitors to help tune the antenna, but most are tuned up to transmitters using the 1605 KHz to 1705 KHz part of the band which obviously require a MUCH shorter antenna.
So I was considering wrapping the copper wire around the pipe like a cork screw making the coils so they do not touch thus creating a solid rod but lets say a 30 foot pipe with 786.86 feet of copper wire wrapped around it.
For those who understand MW antennas better than I do, what do you think this antenna would do as far as performance goes compared to 10 feet antennas with large copper coils?
It would work as a regular helical antenna but a waste of money in all that wire. Using a single piece of wire the same length as the PVC pipes or better yet use metal pipes themselves as the antenna with an antenna tuner at the bottom would work equally well and be far cheaper. After all a tuner can be made with nothing more than a variable capacitor and tapped coil.
With shortened antennas what makes the largest positive difference is the top capacitive hat and a good radial system, in fact I would suggest to save all that wire for that specifically. Lay as much wire on the ground as possible for the radials and use a single piece of wire straight up as high as you can get. Add a capacitive hat (several wires going horizontally) at the top, or just go with the old fashioned Marconi T style antenna. Doing so will work far better than a short helical wound antenna as you are questioning about.
Helicals do have their place with short antenna designs when it would cost more for the extra capacitor and loading coil, but do not radiate any better than a short wire of the same vertical length with a tuned loading circuit. Also with high power they build up dangerous voltage near the end of the helical which can cause arcing and a good zap.
Really comes down to what cost more for you.. the wire or the extra parts? Also the helical needs to be cut to the exact right length and wound with a bit of vertical wire at top whereas with a tuned antenna any short length works and you can tune it up far easier w/o cutting wire by trial and error.
There are ham radio designs floating around on the web showing how to make a 160 meter helical. Just tack on some more wire for the windings to get it to resonate down to 1250kHz and it would work the same. You can get an idea of how well the antenna is working using the old lightbulb between the antenna and transmitter trick and add/cut wire until the bulb glows brightest just like with other MW antennas.
I was looking at various web sites related to "shortened verticals". The real pain here is the ground system required for such a wave length setup. The radiator is workable for height, but looking at how I would setup the ground system I see myself as being very limited.
The placement of the antenna would have to be in a wooded area behind my house, the guy wires have to have room to be streched out away from the structure. That leaves me with sticking one guy wire out into the main yard area. It is a shared yard since I rent an apartment. The big issue though, is setting up the ground system required for 1250 KHz. The ground here is both dirt and ledge. Some areas of my yard have large boulders in the ground which are sticking up, so no chance of stretching any ground wires in those directions, because they can't be safely buried below the surface to prevent issues with lawn mowing and trip hazards etc.
I have a coil / variable tuning capacitor that was included already built into the transmitter I am not sure how many times the coil is wrapped, but it is wrapped around what appears to be a cigar tube. The way this thing is wired is this way. The output transistor goes to the tuning capacitor, the tuning capacitor goes to an antenna clip, while the other wire comes directly from the output transistor and goes through the coil and then on to the antenna clip.
This thing has an output transistor to which I can not identify. All it has on it is
T Z
1034-01
414
I have not found any data on this transistor, it looks almost like a regulator package than it does an RF transistor. Mind you I did not build it, I bought it off ebay already built. It is a Chris Cuff design though, but his had a round transistor of an unknown value. Mine did not come with a schematic diagram and it has a crystal for 1250 KHz operation and supposed to be 100Mw.
Any ideas on that transistor or what should have been in there?
Use whatever you can as a ground, even if that means using your house wirings ground. A few ground rods in the soil a few feet apart can't hurt either. Believe it or not it is possible to get a good signal out with little to no ground. Part 15 operators do it all the time considering the FCC regulates them to count in ground lead length along with antenna length for the total length of the radiator, so normally they use no ground at all to get the most length of the main radiator!
I run a MW setup along with my FM broadcast and simulcast both at the same time. Here I also have limited space and options for ground but I find that tying the ground lead to *anything* grounded outside helps. Just run a nest of wires. It does not have to be pretty spokes coming out from your antenna, though the direction of the radial does project the signal somewhat more that direction, but house wiring, plumbing, large metal objects, metal fences, all those things can work. The other goal should be to get the main radiator as high up as possible. Bend it into an L if you have to, or go for the T type antenna if you have two tall structures. Another grounding option may be cable TV lines, using their ground on the cable. The boxes themselves are almost always grounded with a rod and travel a good distance from most properties. However I have no idea as to the legality of that alone. It is possible for 10' radiators with no ground at all to get out 1/4 mile on MW with nothing more than 100mw for Part 15, so for pirating your options greatly expand
"Any ideas on that transistor or what should have been in there?" No idea but considering it is MW and only 100mw just about any power transistor would work there. At those frequencies most transistors will amplify just fine, even ones only designed for audio amplification.
"The output transistor goes to the tuning capacitor, the tuning capacitor goes to an antenna clip, while the other wire comes directly from the output transistor and goes through the coil and then on to the antenna clip." If you could draw out what you are talking about that would help. Sounds like the output tank is a standard one used for Part 15 legal unlicensed transmitters so they can directly load up a 10' whip antenna without any other necessary tuning. If that is the case then you will need to bypass the output loading coil/cap to load up a longer antenna than is designed for legal operation.
Take a look at this old ebay auction from CCUFF for this transmitter to which this topic is based upon. click the link below and if you need to, click 'see original auction' if my link does not already bring you there. Click one of the three images and mouse over the larger image. This should give you an idea what my transmitter looks like.
NOTE: Make sure you scroll down the page at that link to see the original auction!!!!!!!!!
The output transistor is located in the upper LEFT corner of the circuit board. In one image (The One with the circuit board in the plastic case), the transistor looks flat like just like mine does, it's a TO-202 design and the other image (The one with just the circuit board) shows a TO-39 design transistor.
I'd like to replace the RF transistor with something that will work with this unit that has higher gain output. The markings on the included output transistor aren't anything that can be cross referenced because I believe those numbers are not the transistors identifying numbers.
The seller told me that Chris Cuff built this unit was supposed to send the seller a higher gain transistor but never did. Now of course the output does not include any filtering circuits either, so this means harmonics and spurs are very possible.
My efforts to contact Chris Cuff have not been successful either. What I'd like to do is find an output board that can be connected to the RF output stage that includes filtering and power gain at the same time. Any suggestions on something like that that works with the AM broadcast band?
I'd like to replace the RF transistor with something that will work with this unit that has higher gain output. The markings on the included output transistor aren't anything that can be cross referenced because I believe those numbers are not the transistors identifying numbers.
The seller told me that Chris Cuff built this unit was supposed to send the seller a higher gain transistor but never did. Now of course the output does not include any filtering circuits either, so this means harmonics and spurs are very possible.
My efforts to contact Chris Cuff have not been successful either. What I'd like to do is find an output board that can be connected to the RF output stage that includes filtering and power gain at the same time. Any suggestions on something like that that works with the AM broadcast band?
Bruce.
Using a higher gain power transistor in the output stage sometimes will not work properly because you need to also drive more modulation to achieve the same 100% modulation level and some transmitters just don't have the modulation power to really support a stronger RF transistor. Ramseys AM transmitters comes to mind where people have tried this without success for that very reason. Besides any RF power gained will be insignificant to really get a signal out further. Only exception to this is transmitters that already have a linear RF output where they are modulated low-level (before the RF stage). You would need to get from 100mw to at least 1 watt to even see twice the broadcast range. The best bet would be to add a linear amp to get from those milliwatts to a few watts of power or more if you want the additional broadcast range. Very few companies sell low power mediumwave linear amps. You could use a converted 160m ham linear amp, or just dig around on ebay until you find something that works.
That would do the trick. Keep in mind 60 watts is not toy power. RF burns can become an issue at those power levels if you touch a live antenna matching coil or antenna wire.
Hard to tell from the PDF but if that is 60 watts PEP then you will actually get 15 watts carrier (carrier = 1/4 of 100% modulated). It`s possible you may need to attenuate your signal a little before going into the amp. You almost need an oscilloscope to test that sort of thing but with luck you may get by w/o one.
Just remember with linear amplifiers you do not want to overdrive their input or else your signal will splatter badly causing interference to adjacent stations.
I have been researching this PM62FDC device I mentioned above, being it is from the other side of the big Atlantic Ocean, the cost for me is almost $100.00 USD.
What concerns me about this board is the lack of any transformers or heat sinks which is common on RF linear amplifiers and I am not sure if this can really be used on any application. Perhaps those toroid coils are the transformers? I am curious if this board will work since it is also designed to work with the PLL Exciter Board SDH203M. It has a 6 pin interface and I am concerned that the board may not fire up unless those connections are jumpered in some way. I am not sure what paper work comes with the unit.
Chris Cuff also sold his transmitters with an NPN 2N3053 transistor as the output transistor, those are round, while mine is square and the output wire on mine is soldered to the tab on the transistor.
If you really want to know more about this transmitter Chris has his own Youtube channel regarding his transmitter.
Here is a starting link;
Kage, I seen you built an amplifier in another thread related to MW, so you might have a better understanding of this unit in question.
Now the unit sates it runs at 28 Volts @ 3.30 Amps. Most power supplies I seen out there are around 13.8 Volts. I prefer since the transmitter is an MW type and subject to interference from noisy transformers, that I have a clean power supply with no harmonics introduced into my transmitter's audio circuits. Any suggestions on what is out there that would work well with my transmitter?
Lastly, I have read Chris Cuffs directions for changing the frequency from 1250KHz to another higher one, by getting a custom Oscillator from Digikey that is four times the operating frequency, so I plan on getting one of those Oscillators and moving up into the 1605 to 1705Khz region since a shorter antenna is possible and it is also quieter up there as well.
I have a Realistic TM-152 Analog AM Stereo tuner I won on Ebay on it's way to me. Probably by the time you read this, I'll have already received it. This will allow me to monitor my AM Stereo signal. I'll keep you updated on that part.
Now, I do not plan on purchasing that amplifier until September, so would like some advice on it and suggestions on a clean power supply.
I would love to move the AM Stereo transmitter board into a professional looking rack mountable metal case, the trouble with that part is how the hell does one punch holes for things such as stereo LED VU meter units? I have one I took out of a stereo VCR and the thing has both the left and right channels at -13 to +3 scale, it has the chips included to drive 30 colored LEDS per channel, The LEDs range from green to yellow then red for over modulation. The meter is 3/4" high and 3 3/4" wide and 1/2" deep. Would look nice on the front of a metal case, but making a rectangle hole in metal does not sound easy to do without a hack job mess resulting.
By the way that LED meter is not an original part of the AM Stereo transmitter because it has no modulation meters.
28 volts * 3.30 amps = 92.4 watts from the power supply. This suggests that the RF output is 60 watts *PEP* power, or 15 watts carrier of that linear amp. Even then you will probably want a beefier power supply. More amperage can never hurt and will reduce any possible power sagging. A regulated switching type power supply would work nice for this application but most online are 24 volt models. If you search around you may find one at 28 volts at the amperage you need or higher. I would definitely opt for even higher rated supplies to give some headroom. It would be much cheaper to use a switching power supply instead of transformer based.
When you start getting past 50 watts RF the supplies usually go up in voltage. It is quite common to see linear amps go beyond 28 volts since it is usually cheaper to design both the power supply and the amplifier to use higher voltage and lower amperage rather than higher amperage and lower voltage. This is why, for example, car stereo amplifiers usually have DC to DC converters built inside of them to boost the voltage from 13.8 volts to much higher voltage required by the parts because it becomes a chore to get high power levels at such low voltage.
Either way the old rules apply to power supplies for RF, make sure to choke off any RF along the power wires going into the supply with toroidal cores and maybe some RF blocking capacitors of both 0.1 and 0.01uF. Stiffening capacitors can help with both hum and voltage sagging, the lower the microfarads the better. I used 13,600uF on my supply and it helps greatly at smoothing the power and load variations. Power supplies for AM transmission really do not need to be complex to work well, the idea is to get smooth power that does not vary much under load. You may get away with just connecting the amp right to a good switching supply with no other modification and work just like plug and play.
What concerns me about this board is the lack of any transformers or heat sinks which is common on RF linear amplifiers and I am not sure if this can really be used on any application. Perhaps those toroid coils are the transformers?
That really depends on the parts used. Some RF transistors require very little cooling, especially if they are far overrated for the job at hand. Most RF amps made today for <30MHz use toroidal transformers on their output to match the antenna load and impedance of the output transistors. Often with low power transmitters the antenna output is tied right to the collector of the transistor. 2N3053 is rated at 5 watts so it would probably run cool without a heatsink only making the legal 100mw power of part 15.
It would be much cheaper to use a switching power supply instead of transformer based.
Chris Cuff included a piece of paper with his transmitters that includes recommendations for what type of power supply to use. He says, "DO NOT use a switching type power supply, too much noise."
I have to consider whether to have one power supply power both the AM Stereo transmitter and the PM62FDC and have both inside the same cabinet, or power each one separately.
The transmitter was built into a plastic project box, I would prefer a metal one, but then again, metal is not easy to work with when adding some externally viewed hardware such as the LED VU meter. That would require a rectangle hole punched into the face plate. I don't even own a drill press and a hand drill would result in a hacked up cabinet from the drill riding the surface before it grabs and digs into the metal. But it would be nice to have some visual idea of the peak levels of each stereo channel.
My Realistic TM-152 AM stereo receiver came in a week ago, I could not find any AM stereo stations that were coming in, however, the receiver was doing quite well with great reception and low noise. It does not tune above 1605Khz though, so if I was to choose a frequency above 1605Khz, it won't be able to pick it up.
So, there is no local stations transmitting in stereo, however, when I powered up my AM Stereo C-Quam transmitter without any audio source attached to it, the stereo light on the TM-152 switched on and just like with FM stereo, I could also hear a difference in the carrier signal, just like how the FM carrier sounds with FM Mono Vs. FM Stereo.
I did pick up a few stations in the night time skip hours that lit the light up, but of course those signals were a bit unstable and faded in and out, but for the few moments, I could hear the high fidelity sound just as if it was FM.
Just think, I'll be the only AM Stereo radio station in my area.
There are some modification schematics on the web for that TM 152 receiver which expands the IF filter from it's stock 4.5Khz to 10Khz, wide/narrow switch, 75us de-emphasis (NRSC curve), synchronous detection (better quam envelope detection) and better pilot tone detection with co-channel filtering. As is the TM 152 provides a good sound, but can be far better like the RS ST-JX220A (Canada Model sporting 12Khz IF)and the Denon AMAX receivers. www.amstzone.org/ about 3/4 down the page. I recommend doing the modifications so your monitor captures the full bandwidth of CQUAM. Trust me...think that transmission sounds like FM now....listen to it through a wide IF filter receiver or an AMAX receiver!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
A few notes on the C-CUFF CQUAM unit. Install .1uF mica caps across each IC B+ pin to ground. This will eliminate the digital hash noise generated by the circuits, which unfiltered results in a huge spectrum mess if amplified by an external linear. The entire unit is unfiltered from front to back, and some of that digital hash even gets into the L-R audio path and produces a "hiss" at the upper audio frequencies received.
The unit will work well with just about any video driver transistor for the output, like those found in the old 19 inch or smaller analog tv's. The stock "hi power" model produces enough juice to drive an LPB 30 PA, so it will drive that 60 watt pallet amp with the final it comes with. From about 3/4 turn and up on the power pot on the transmitter, you will find that the linear response out of the final will begin to crush audio because the final has a set bias. Replace the bias resistor with a pot to make it adjustable. Kage threw up a neat little linear probe some time back for adjusting transmitter linearity response and will work here.
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Replace the bias resistor with a pot to make it adjustable. Kage threw up a neat little linear probe some time back for adjusting transmitter linearity response and will work here.
You're referring to the BIAS resistor on the PM62FDC circuit board correct?
Where is this linear probe posted by Kage? Is it an RF probe using a diode and coupling capacitor that you are referring to?
The current output transistor in my C-Quam is marked with the following markings:
T Z
1034-01
414
Not sure which number identifies that transistor, none of my cross reference books comes close to what the casing looks like.
I suppose I could get a NPN 2N3053 transistor and replace that unknown generic with such, that is the transistor Chris shows off in his videos.
BTW, thanks for the mention of that TM-152 mod, might give that a try.