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#41
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![]() "Cecil Moore" wrote in message ... Reg Edwards wrote: So we need something different from and more sophisticated than the conventional automatic tuner with its relatively simple magnitude and phase-searching abilities. If you remembered what frequency the mag loop had been tuned to last time, would that alleviate the need to know phase? The reason I ask is that is how I auto-tune my screwdriver without knowing phase. -- 73, Cecil http://www.qsl.net/w5dxp ======================================== Cecil, while you are tuning your screwdriver, which is not a magloop, phase and magnitude does not enter your head. Forget all about it! --- Reg |
#42
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![]() "Cecil Moore" wrote in message .. . Reg Edwards wrote: If I can't do it when the transmitter is ON then neither can an automatic ATU. It would have to be more clever than I am. It would be relatively easy to use the SWR meter driving current from an MFJ-259 to control the ATU motor. -- 73, Cecil http://www.qsl.net/w5dxp ================================ Cecil, I keep telling you, there's no such thing as an SWR meter. --- Reg. |
#43
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Reg Edwards wrote:
Cecil, while you are tuning your screwdriver, which is not a magloop, phase and magnitude does not enter your head. Forget all about it! Watching the SWR meter while tuning my screwdriver while driving had always bothered me. I first installed an audio VCO so I wouldn't have to watch the SWR meter. Next I installed a flip-flop so I only had to get the screwdriver started in the right direction and didn't have to hold down the toggle switch. When the SWR starts dropping, an LM-339 shuts off power to the screwdriver motor. And it's all done while my IC-706 is in reduced power tune mode. -- 73, Cecil http://www.qsl.net/w5dxp |
#44
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Reg Edwards wrote:
Cecil, I keep telling you, there's no such thing as an SWR meter. The folks over on sci.physics.electromag disagree. -- 73, Cecil http://www.qsl.net/w5dxp |
#45
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Reg, G4FGQ wrote:
"The transmitter is OFF when I do it manually and I tune for maximum noise in the receiver." As Reg said, reciprocity rules. You can also satisfactotily tune an antenna to resonance by adjusting it for maximum output. When I was in Tierra del Fuego we had Land Rovers and boats equipped rith RCA single-sideband HF radios. The Rovers had whip antennas atop fiberglass boxes containing loading coils and motor-driven tap-changing switches. The coil base-loaded the whip. I routinely tuned the whips by switching my multimeter to the a-c range (it used germanium rectifiers) and tuning for a maximum meter indication. I chose meter-probe positions for a convenient scale indication. The above was accomplished with the transmitter ON and fed with a test tone driving it to put out some power. The whip was mostly non-directional so it made little difference where the r-f sensing antenna was placed. The tuning procedure worked fine even with the multimeter in the near-zone laying on the bonnet (hood) of the Rover. The capacitor tuning a high-Q loop could also be tuned for maximum output because that is your goal. The sampling antenna could be located almost anywhere but probably not in a null of the loop. Best regards, Richard Harrison, KB5WZI |
#46
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Richard Harrison wrote:
The above was accomplished with the transmitter ON and fed with a test tone driving it to put out some power. I don't know much about small loops. Modern transceivers, like my IC-706, have such good protection circuitry that it can be tuned into any load at full power. Is there anything in the design of a small loop that would prevent full power plus foldback tuning? -- 73, Cecil, http://www.qsl.net/w5dxp |
#47
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Reg, G4FGQ wrote:
"Cecil, I keep telling you, there`s no such thing as an SWR meter." Terman says in his 1955 edition, page 99: "The standing-wave ratio S is one means of expressing the magnitude of the reflection coefficient;---." This, Terman illustrates can go either way via formulas. Rho is convertible to SWR and SWR is convertible to Rho. Why should an indication proportional to SWR not be so calibrated and called ? Best regards, Richard Harrison, KB5WZI |
#48
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Cecil, W5DXP wrote:
"Is there anything in the design of a small loop that would prevent full power plus foldback tuning" Maybe off-resonance operation. The small loop is always inductive but its reactance is high and its resistance is low, so it has a high-Q. It has almost uniform current thoughout, so this produces nulls on its axis. Best regards, Richard Harrison, KB5WZI |
#49
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Reg Edwards wrote:
So we need something different from and more sophisticated than the conventional automatic tuner with its relatively simple magnitude and phase-searching abilities. I'll believe it when I see one which works. Reg, I just opened up my 2006 MFJ catalog. They have an "Automatic LoopTuner(TM)", the 300w MFJ-937. It's designed for approximately 1/10WL loops. -- 73, Cecil, http://www.qsl.net/w5dxp |
#50
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On Mon, 10 Oct 2005 11:33:48 +0000 (UTC), "Reg Edwards"
wrote: .... At higher frequencies there's usually enough space to erect a dipole or an inverted-L which will perform at least as well. (Ian, you could perhaps do a useful article on the subject.) .... I wrote an article on the Inverted L with a remote autotuner (designed for end-fed wires) some time ago. The configuration, it is frequency agile, very convenient when integrated with transeiver auto-tune controls, and works a treat. The most significant downside (like most Marconi, Windom, Long Wire etc configs) is from an EMR safety point of view, it has a radiator within reach of people standing on the ground. The article is at http://www.vk1od.net/InvertedL/InvertedL.htm . With the experience of using such a configuration, I reckon that a magloop with an remote autotuner designed specifically for a magloop would be a great option for people with very little space, better than Echolink! Reg, if you have an expression for the loop inductance and resistance as a function of frequency, and we could make the assumption that the coupling coil is a broadband ideal transformer with a fixed z ratio or otherwise characterise the transformation as a function of frequency, I could do a software simulation of an autotuner... be an interesting project. BTW, the tuner values in the article above are found through simulation of an automated L tuner, but the 3 variable binary searching algorithm used for performance would not work for a loop. Owen -- |
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