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It really doesn't matter what frequency the application is, modern
transistors have good gain well into the UHF range and VHF parasitic oscillations can occur even in an audio application Joe W3JDR "Paul Burridge" wrote in message ... On Sun, 05 Oct 2003 13:27:59 GMT, "W3JDR" wrote: John, Can you post a picture of your unit somewhere(top and bottom views) so we can see what the PCB & wiring layout looks like? Many times an improper layout can lead to parasitic oscillations that will raise DC power consumption without delivering RF on the proper frequency. It's worth a try, John. But 7Mhz is practically DC these days so strays and paracitics shouldn't be too much of a problem. One thing I meant to suggest in my earlier post was that the OP should try transmitting into a known good 50 ohm dummy load and seeing if his final tranny still gets as hot. That ought to be a real good clue as to whether he does have some probem with his matching/antenna/feedline etc.. -- "Windows [n.], A thirty-two bit extension and GUI shell to a sixteen bit patch to an eight bit operating system originally coded for a four bit microprocessor and produced by a two bit company." |
On Sun, 05 Oct 2003 13:50:43 +0100, Paul Burridge
wrote: snip I'm getting very little output. After tuning the transmitter, per the specs, and measuring the output using the method suggested by the author of the web page, I figure I'm getting 1 watt or less. How is this figure arrived at? How are you measuring it? 1W doesn't sound much, but it can go a long way on 40M., given an efficient antenna system with short, low-loss feeder and matched radiation resistance. Voltage is measured across my 50 ohm dummy load and rectified using a ..05 mfd ceramic disc cap and a 1N34A diode. Then I'm calculating thusly: Power = (Voltage x Voltage) / 50 I'm taking the author's word that this works for a ballpark estimate. I'm measuring 7 volts across the load, maximum, which works out to 1 watt or less. I've verified that my meter is accurate. I am running this into a dipole cut for 40 meters, which is 7 feet off the ground. That's *way* too low! As you must know for any ariel, you gotta get that thing up as high off the ground as you can and that's even more important at low frequencies like 7Mhz. We have a mess of power lines around the house, so it's hard to find a spot to even get it 7 feet high in a straight line. I'm thinking about trying it on the roof, which is about 20 feet high at the highest point, and mabye angling it in the center. One of the transistors (Q2) is supposed to be heat sinked. I have put a large homemeade heat sink on this, using plenty of heat sink grease, and it gets so hot I can barely touch it. Something's wrong, then. The heat dissipated in your final transistor should equate to the output power at the antenna if the system is matched properly. Sounds like your tranny's trying to dissipate rather more than a Watt. Are you sure you don't have a feeder/matching problem somewhere? Have you cut the ariel to the right length? Are you using a balun? Have you tried a substitute balun? The length of each element is 32' 11", which I calculated for use at 7110 kHz. There's no balun; I'm using coax, the shield is connected to one element and the center conductor is connected to the other. The coax might be 75 ohm. Pretty soon I'll have RG-58 for the entire run, but right now it's a mix of RG-6/U and RG-59/U. Get another ham a couple of miles away from you to give you a signal report. It might show up something useful. I will do that. Thanks. -- -John Sandin KC0QWE Remove the "T" to respond by e-mail |
I will try to do that sometime during the next day or so. The author
of the website says that the layout isn't critical, and his version of the project works great. But when I look at the original QST article and the photos of how they did it (all direct-wired), I'm amazed at how simple they were able to keep the assembly. So now I'm wondering why I bothered to use a printed circuit board in the first place. On Sun, 05 Oct 2003 13:27:59 GMT, "W3JDR" wrote: John, Can you post a picture of your unit somewhere(top and bottom views) so we can see what the PCB & wiring layout looks like? Many times an improper layout can lead to parasitic oscillations that will raise DC power consumption without delivering RF on the proper frequency. Joe W3JDR -John Sandin KC0QWE Remove the "T" to respond by e-mail |
I will try to do that sometime during the next day or so. The author
of the website says that the layout isn't critical, and his version of the project works great. But when I look at the original QST article and the photos of how they did it (all direct-wired), I'm amazed at how simple they were able to keep the assembly. So now I'm wondering why I bothered to use a printed circuit board in the first place. On Sun, 05 Oct 2003 13:27:59 GMT, "W3JDR" wrote: John, Can you post a picture of your unit somewhere(top and bottom views) so we can see what the PCB & wiring layout looks like? Many times an improper layout can lead to parasitic oscillations that will raise DC power consumption without delivering RF on the proper frequency. Joe W3JDR -John Sandin KC0QWE Remove the "T" to respond by e-mail |
The fact that the connection between the top of L2 and the base of Q2 is
marked as coax is probably a clue that layout is critical. ... "Roy Lewallen" wrote in message ... A hot transistor combined with low output power makes me suspect that the transistor is either parasitically oscillating or trying to produce a lot of harmonic energy. |
The fact that the connection between the top of L2 and the base of Q2 is
marked as coax is probably a clue that layout is critical. ... "Roy Lewallen" wrote in message ... A hot transistor combined with low output power makes me suspect that the transistor is either parasitically oscillating or trying to produce a lot of harmonic energy. |
Working people with one watt can be challenging, but certainly not
impossible. In the course of a few years, I worked (and confirmed) all 50 states and 33 countries on 40 meters with about 1.5 watts output. Your antenna height is a big handicap. 7 feet is severely low for a 40 meter antenna. While you'll still be able to hear stations just fine, it'll produce a very weak signal from an already weak transmitter. If there's any way possible, make the antenna higher. I'd strive for at least 30 feet if possible; higher than that is better yet. Another option is to use a vertical. With even a poor to moderate ground system -- even a couple of ground radials (more would be better) -- it'll do much better than the very low dipole. A hot transistor combined with low output power makes me suspect that the transistor is either parasitically oscillating or trying to produce a lot of harmonic energy. That means that you could be producing only a tiny amount of power on the desired frequency -- much less than even a watt. Pull the antenna off your receiver and tune around. Does the signal from your rig sound hissy or hashy? Are the signals at harmonic frequencies as strong as or stronger than the signal at the desired frequency? Set up a sked with a ham that's a few miles away (whom you can locate through a local club), and have him tell you what your signal sounds like. Have him listen for harmonics, birdies, or other signs of instability. Finally, you need to be aware that a crystal-controlled transmitter can be a big handicap these days. People don't often tune off their own frequency to listen, and they're likely to have a pretty narrow filter, so you're not likely to get a response unless you're lucky enough to be very close to their frequency. That said, your success rate should be higher when calling someone than when calling CQ, since people are more prone to respond to a weak signal calling them than to one calling CQ. But only if you're on their frequency so they can hear you. I couldn't get the link to the URL to work, so couldn't look at the transmitter schematic. However, after you get the other problems fixed, consider modifying the rig to VXO operation (where you're able to move the frequency a bit) if it's not already VXO. There's no reason you can't substitute HC-6 crystals for FT-243 in a rig like this. Roy Lewallen, W7EL John Sandin wrote: I am a new technician with code privileges. I built the following CW transmitter for 40 meters: http://cs.okanagan.bc.ca/ve7ouc/eng/...nsmitter2.html It's a solid state 3-watter, based on an article in QST in June 1967. I used a printed circuit board instead of wiring everything together directly, as the QST article suggests. So, there are many wires running from various parts mounted on the chassis to the circuit board. I'm getting very little output. After tuning the transmitter, per the specs, and measuring the output using the method suggested by the author of the web page, I figure I'm getting 1 watt or less. I am running this into a dipole cut for 40 meters, which is 7 feet off the ground. I'm using fundamental frequency HC6/U crystals for 7110 and 7125 kHz. I've been trying for 2 weeks, at all hours of the day and night, and have had no indication that anyone hears me. I've called CQ, and I've attempted to answer CQ's. Nothing, after about 100 tries. I know it's impossible for any of you to know exactly what's wrong, but I'd like to see what opinions I can glean here. Is there any reason why I should use FT-243 crystals, as specified in the article and on the website? I used HC6/U crystals because they were easy to get. One of the transistors (Q2) is supposed to be heat sinked. I have put a large homemeade heat sink on this, using plenty of heat sink grease, and it gets so hot I can barely touch it. Also, the transmitter chirps a bit at the beginning of each transmission, but settles down after a few strokes of the key. Many thanks for any help you can give. -John Sandin KC0QWE Remove the "T" to respond by e-mail |
Working people with one watt can be challenging, but certainly not
impossible. In the course of a few years, I worked (and confirmed) all 50 states and 33 countries on 40 meters with about 1.5 watts output. Your antenna height is a big handicap. 7 feet is severely low for a 40 meter antenna. While you'll still be able to hear stations just fine, it'll produce a very weak signal from an already weak transmitter. If there's any way possible, make the antenna higher. I'd strive for at least 30 feet if possible; higher than that is better yet. Another option is to use a vertical. With even a poor to moderate ground system -- even a couple of ground radials (more would be better) -- it'll do much better than the very low dipole. A hot transistor combined with low output power makes me suspect that the transistor is either parasitically oscillating or trying to produce a lot of harmonic energy. That means that you could be producing only a tiny amount of power on the desired frequency -- much less than even a watt. Pull the antenna off your receiver and tune around. Does the signal from your rig sound hissy or hashy? Are the signals at harmonic frequencies as strong as or stronger than the signal at the desired frequency? Set up a sked with a ham that's a few miles away (whom you can locate through a local club), and have him tell you what your signal sounds like. Have him listen for harmonics, birdies, or other signs of instability. Finally, you need to be aware that a crystal-controlled transmitter can be a big handicap these days. People don't often tune off their own frequency to listen, and they're likely to have a pretty narrow filter, so you're not likely to get a response unless you're lucky enough to be very close to their frequency. That said, your success rate should be higher when calling someone than when calling CQ, since people are more prone to respond to a weak signal calling them than to one calling CQ. But only if you're on their frequency so they can hear you. I couldn't get the link to the URL to work, so couldn't look at the transmitter schematic. However, after you get the other problems fixed, consider modifying the rig to VXO operation (where you're able to move the frequency a bit) if it's not already VXO. There's no reason you can't substitute HC-6 crystals for FT-243 in a rig like this. Roy Lewallen, W7EL John Sandin wrote: I am a new technician with code privileges. I built the following CW transmitter for 40 meters: http://cs.okanagan.bc.ca/ve7ouc/eng/...nsmitter2.html It's a solid state 3-watter, based on an article in QST in June 1967. I used a printed circuit board instead of wiring everything together directly, as the QST article suggests. So, there are many wires running from various parts mounted on the chassis to the circuit board. I'm getting very little output. After tuning the transmitter, per the specs, and measuring the output using the method suggested by the author of the web page, I figure I'm getting 1 watt or less. I am running this into a dipole cut for 40 meters, which is 7 feet off the ground. I'm using fundamental frequency HC6/U crystals for 7110 and 7125 kHz. I've been trying for 2 weeks, at all hours of the day and night, and have had no indication that anyone hears me. I've called CQ, and I've attempted to answer CQ's. Nothing, after about 100 tries. I know it's impossible for any of you to know exactly what's wrong, but I'd like to see what opinions I can glean here. Is there any reason why I should use FT-243 crystals, as specified in the article and on the website? I used HC6/U crystals because they were easy to get. One of the transistors (Q2) is supposed to be heat sinked. I have put a large homemeade heat sink on this, using plenty of heat sink grease, and it gets so hot I can barely touch it. Also, the transmitter chirps a bit at the beginning of each transmission, but settles down after a few strokes of the key. Many thanks for any help you can give. -John Sandin KC0QWE Remove the "T" to respond by e-mail |
The circuit you describe should be delivering approximately the peak
voltage, not RMS, so the formula is more like V X V / 100. At 7 volts peak, that means you're putting out around 1/2 watt. That's a lot below the 3 watt figure you mentioned, so you should track down why it's so much lower. Pay special care to the circuit components in the final transistor output (collector) circuit, and make sure the inductors are built as described and the components are connected correctly. Roy Lewallen, W7EL John Sandin wrote: . . . Voltage is measured across my 50 ohm dummy load and rectified using a .05 mfd ceramic disc cap and a 1N34A diode. Then I'm calculating thusly: Power = (Voltage x Voltage) / 50 I'm taking the author's word that this works for a ballpark estimate. I'm measuring 7 volts across the load, maximum, which works out to 1 watt or less. I've verified that my meter is accurate. . . . |
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