Posted: 12/1/2010 1:21:53 PM EDT
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I had it wrong for over 40 years. I thought a dummy load was for tuning up.
I learned that if you hear a net on 80 meters you are supposed to go to that frequency and tune up there. I'm sorry if I offended people by using the dummy load. 
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Quoted: I had it wrong for over 40 years. I thought a dummy load was for tuning up. I learned that if you hear a net on 80 meters you are supposed to go to that frequency and tune up there. I'm sorry if I offended people by using the dummy load. No kiddin'....some dem folks jus gots no class.... 
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Quoted:
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I had it wrong for over 40 years. I thought a dummy load was for tuning up. I learned that if you hear a net on 80 meters you are supposed to go to that frequency and tune up there. I'm sorry if I offended people by using the dummy load. No kiddin'....some dem folks jus gots no class.... I'm sorry I can't be as classy as other 80 meter ops. What should I do with that big old can with a resistor and oil in it? I even used that to tune up my HW101. I wish someone would have told me I was doing it all wrong. 
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Quoted:
I had it wrong for over 40 years. I thought a dummy load was for tuning up. I learned that if you hear a net on 80 meters you are supposed to go to that frequency and tune up there. I'm sorry if I offended people by using the dummy load. not defending the behavior on 80m, but how do you "tune up" into a dummy load? 
i can see setting plate voltage and bias current on an older tube(*) rig into a dummy load, but how do you match the (real) antenna to the transceiver using a dummy load and a tuner? ar-jedi ps: i have a dummy load. 
pps: note to our foreign readers: "tube" = "valve". note to our younger readers: "tube" = "monstrously large, highly inefficient, notoriously unreliable, very expensive transistor". note to our older readers: "tube" = yeah, yeah, we know, uphill both ways in the snow over to the FCC examiner's office... with bare feet. 
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my frist transmitter was a Heath DX-40
http://www.heathkit-museum.com/ham/hvmdx-40.shtml 
It didn't belong to me. It was loaned to me to use. When he wanted to sell it I couldn't afford it. (High school kid with no money. The receiver took all I had) When my novice license expired I was off the air for nearly 10 years till I got back on. |
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once you have experience with the rig you can finish it in one or 2 seconds. by "it", you mean "tuning up"? again, where does the dummy load come into play here when matching the radio to the antenna? ar-jedi Tuning up the finals in a tube transmitter. |
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once you have experience with the rig you can finish it in one or 2 seconds. by "it", you mean "tuning up"? again, where does the dummy load come into play here when matching the radio to the antenna? Tuning up the finals in a tube transmitter. see blue highlighted text above. ar-jedi |
 since you want me to change from the sarcastic rant mode to something realistic I will try to do that for you.
Several points that hams who have never used tube radios may not understand. * When you tune the finals of a tube rig into a dummy load you are tuning them for a 50 ohm impedance load. If you antenna is reasonably close to 50 ohms no further tuning will be needed. Tube radios are much more tolerant of a slight mismatch than solid state. * With some experience at tuning the finals, like a smart modern auto tuner most of us soon knew about were to set everything without even transmitting a signal to the dummy load or on the air. * If you were using a tuner. (this will also apply to modern radios) use a low power while tuning to cause the least possible interference. Again, with experience you will soon know about where to set your manual tuner for the band and antenna you are using. Write down the settings for your commonly used freqs and start there the next time. * Last point. This was a smart@$$ rant (maybe a bad one at that) making fun of the obviously intentional interference that some like to impose on 80 meters and other bands. I guess my ranting is no better than my ham operating practices. 
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We couldn't tell it was a rant, because there was no cussing in it. I know you aren't supposed to cuss on the radio, but Arfcom ain't the radio.
Now get back on the radio, and slowly, tune up. Make sure you say teeeeeeesssssssst quite a few times, and do it in the middle of someone else's conversation. |
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We couldn't tell it was a rant, because there was no cussing in it. I know you aren't supposed to cuss on the radio, but Arfcom ain't the radio. Now get back on the radio, and slowly, tune up. Make sure you say teeeeeeesssssssst quite a few times, and do it in the middle of someone else's conversation. 
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Now get back on the radio, and slowly, tune up. Make sure you say teeeeeeesssssssst quite a few times, and do it in the middle of someone else's conversation. continue please –– do i do this barefoot or with the big box that says "1.5KW" switched on? ar-jedi 
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Now get back on the radio, and slowly, tune up. Make sure you say teeeeeeesssssssst quite a few times, and do it in the middle of someone else's conversation. continue please –– do i do this barefoot or with the big box that says "1.5KW" switched on? ar-jedi Only 1.5kW? Lightweight 
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Now get back on the radio, and slowly, tune up. Make sure you say teeeeeeesssssssst quite a few times, and do it in the middle of someone else's conversation. continue please –– do i do this barefoot or with the big box that says "1.5KW" switched on? ar-jedi Only 1.5kW? Lightweight i'm a QRP'er...
ar-jedi |
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Serious question.....is there an advantage to tuning at full power vs tuning at say 1/10 W?
I ask because I current use an auto-tuner on a solid state rig. When I hit the tune button on my radio it drops the ampflifier to a fraction of a watt, matches the load, then I am tuned up and can transmit. Im thinking of going to a manual tuner. I planned on manually lowering my power to at least 5W to tune....since I am dealing with solid state electronics, there isnt anything for me to tweak on the radio. Unlike tubes, my radio is what it is....and the amplifier output impedance is (supposedly) fixed at 50 Ohms. Does it make a difference what power I tune at? I would think that an antenna would react differently when different amounts of power are sent into it. Optimally, maybe not....but in the real world, with all kind of reflections and transient variables...is there a 'best practice' for tuning? (besides tuning up on a frequency there is a current QSO on )
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is there an advantage to tuning at full power vs tuning at say 1/10 W? Does it make a difference what power I tune at? it does make a difference, but not because of the antenna. let's stick to the autotuner concept for a second. internal to the autotuner is a device called a directional coupler. it is a novel piece of RF engineering that makes it possible to measure RF power depending on the direction of incidence. http://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers 
the directional coupler is an essential element in an SWR meter, http://en.wikipedia.org/wiki/SWR_meter 
in an autotuner, RF circuitry attached to the directional coupler measures the power reflected back from the antenna (see REV, for reverse, terminal), and compares this to the power applied to the antenna (see FWD, for forward, terminal). a small digital microprocessor then interprets the ratio, and acts as follows... if the antenna is "perfect", there is no/little reflected power (i.e., high return loss) and this indicates that the output impedance of the tuner (nominally 50ohms) is well matched to the antenna. the result in this case is that the tuner doesn't need to try connecting various combinations of discrete L's and C's in an effort to match the antenna. to you, that means the SWR is a nice 1:1. if the antenna is not "perfect", there will be reflected power measured at the directional coupler. the tuner then begins a binary search to find a combination of L and C values to better match the antenna, each time measuring the reflected power again. these components are brought into the fray via RF relays, under the control of the microprocessor. note that most modern autotuners "cheat" by measuring the frequency first, and then using a lookup table to find the values from the last time it matched the antenna at this frequency. this (usually) accelerates finding a solution. in a manual tuner, there is no microprocessor-based measurement and control circuit –– but instead either a pair of needles within one meter, or a single needle meter. adjacent control dials are manipulated by hand to adjust the L and C values while visually monitoring the meter needle(s) for a good SWR. why do you need to know all this? the forward power from the transmitter has to be sufficient for the measurement apparatus (i.e., the meter [manual tuner] or the RF circuit [autotuner]) to provide a valid ratio of the forward and reflected power. said another way, the reflected power HAS to end up slightly above the noise floor of the reflected power measurement circuit. otherwise, the tuner (either person or microprocessor) does not have any feedback to adjust the L and C values. hence, manual or autotuning is not generally practical at very low transmitter output (say around 1W or less). for this reason, most modern autotuners require a minimum of 5 to 10W (CW) for operation. depending on the design (single or cross needle), manual tuners sometimes require slightly more to achieve good matching, generally about 10 to 20W (CW). ar-jedi |