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Yep...He probably bought it from you.
Tracy On Sat, 15 Nov 2003 17:23:50 -0600 (CST), (Bill Turner) wrote: THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T. |
GDOs are sort of dated by now. i build one last year when i was just
getting back into hamming. i found very little use for it over the last 3 months that i have actively been homebrewing. let me explain why ... a gdo is primarily used to check for resonance of a tuned circuit. if you knew the inductance and the capacitance, you could easily compute the resonanating frequency youself. as another poster mentioned, getting a dip is a fight. so, what i do use is a combination of three things: an rf probe with a high impedance voltmeter, a test oscillator and a frequency counter. all these things are in themselves pretty useful. but i seldom go wrong in getting properly tuned circuits. i have a test oscillator (see the schematic http://farhan.net.co.nr/testosc.gif). i plug in a coil with a 330pf capcitance in series between the base of the vfo transistor and the ground. and measure the frequency on the counter. that gives me a pretty accurate (within 1%) measure of the coil's inductance. it involves a bit of calculating, but once i have cast the values, there is seldom need to change them. i tend to do simple maths in my head using 10MHz as starting value for resonance (100pf with 2.5uH). I can now scale up or down without resorting to a calculator. As for peaking a circuit, it is best done by the ear or using an oscilloscope. peaking by the ear is probably the best, if u can manage it. now, i dont mean to be rude, but frankly very few people have the ear to be able to tune for best fidelity rather than loudness. it takes patience and care (i have very little of either). so, i depend upon a scope. it is a little like knowing morse. it is the best mode of communicating, but not all want to use it. a poor man's alternative is using the RF probe. the RF probe will never show distortions. But it can show clear peaks while tuning up a circuit. be sure that you also terminate the output of the tuned stage properly! otherwise you maybe be tuning away from the sweet point. i would rather that you invested into building a simple PIC based counter. It is pretty accurate, you will never need to caliberate it. (I never got around to caliberating mine, it is off by 1.5KHz at 10MHz). That with the test oscillator, you would be completely informed about your coils. An RF probe is a 10 minute project and if you already have a good VOM, you might not need a High impedance voltmeter. I brewed my own voltmeter to keep things completely homebrewed. the counter can always be used with all your projects as a standard read out. The rf probe will the most useful tool in tuning up any transmitter. The voltmeter is indispensable. - farhan |
GDOs are sort of dated by now. i build one last year when i was just
getting back into hamming. i found very little use for it over the last 3 months that i have actively been homebrewing. let me explain why ... a gdo is primarily used to check for resonance of a tuned circuit. if you knew the inductance and the capacitance, you could easily compute the resonanating frequency youself. as another poster mentioned, getting a dip is a fight. so, what i do use is a combination of three things: an rf probe with a high impedance voltmeter, a test oscillator and a frequency counter. all these things are in themselves pretty useful. but i seldom go wrong in getting properly tuned circuits. i have a test oscillator (see the schematic http://farhan.net.co.nr/testosc.gif). i plug in a coil with a 330pf capcitance in series between the base of the vfo transistor and the ground. and measure the frequency on the counter. that gives me a pretty accurate (within 1%) measure of the coil's inductance. it involves a bit of calculating, but once i have cast the values, there is seldom need to change them. i tend to do simple maths in my head using 10MHz as starting value for resonance (100pf with 2.5uH). I can now scale up or down without resorting to a calculator. As for peaking a circuit, it is best done by the ear or using an oscilloscope. peaking by the ear is probably the best, if u can manage it. now, i dont mean to be rude, but frankly very few people have the ear to be able to tune for best fidelity rather than loudness. it takes patience and care (i have very little of either). so, i depend upon a scope. it is a little like knowing morse. it is the best mode of communicating, but not all want to use it. a poor man's alternative is using the RF probe. the RF probe will never show distortions. But it can show clear peaks while tuning up a circuit. be sure that you also terminate the output of the tuned stage properly! otherwise you maybe be tuning away from the sweet point. i would rather that you invested into building a simple PIC based counter. It is pretty accurate, you will never need to caliberate it. (I never got around to caliberating mine, it is off by 1.5KHz at 10MHz). That with the test oscillator, you would be completely informed about your coils. An RF probe is a 10 minute project and if you already have a good VOM, you might not need a High impedance voltmeter. I brewed my own voltmeter to keep things completely homebrewed. the counter can always be used with all your projects as a standard read out. The rf probe will the most useful tool in tuning up any transmitter. The voltmeter is indispensable. - farhan |
On Sat, 15 Nov 2003 22:05:45 GMT, "Dale Parfitt"
wrote: | |"Paul Burridge" wrote in message .. . | | Hi gang, | | I've never had a lot of luck with GDMs for some reason. Even with a | decent meter, it seems such a drag tuning across such a vast range | looking for a tiny, easily-missed dip which you have to screw out of | the meter by forcing the sensing coil so far into the circuit | concerned you practically break the circuit board. Am I alone in | finding this potentially invaluable device practically useless in | practice? Is there a more viable alternative? | | p. | -- | | First rule is to get a good dip meter- the stuff made for the amateur |community is very poor- the Eicos, Heath Millen etc. Pick up a Measurments |model 59. With this meter you can take a 1/2 wave wire- say at 2M and hold |the meter a couple inches from the center and see a huge dip. Other meters |don't even respond when held to the wire. Dips on conventional L-C circuits |can easily be full scale. Yep. I have two 59s and they are great. I got rid of two Millens. They are better than anything else but the 59. As to usefulness, a short war story. Another engineer and I were working on an AGC problem in the early Phoenix missile i-f amplifier. Phoenix being a monopulse radar had a three channel receiver with very tight agc tracking requirments (both gain and phase). The agc voltage was fed to each of the three channels via feedthru caps in the walls of a very well shielded and gasketed chassis. Nevertheless, there was obvious crosstalk. The other guy said to me, "Wes, do you have a GDO?" I said, "Sure." A couple of younger engineers who were watching this asked, "What's a GDO?" So we poke the coil of the Model 59 into the chassis and find a nice resonance at the i-f in the agc wiring. The feedthru capacitance and wiring inductance were resonating at i-f. We had millions of dollars worth of test equipment in our lab and I doubt that we could have devised a test for this without heroic efforts. The only problem was keeping the GDO hidden from the metrology guys since they couldn't "calibrate" and service them so they wanted them gone. Wes N7WS |
On Sat, 15 Nov 2003 22:05:45 GMT, "Dale Parfitt"
wrote: | |"Paul Burridge" wrote in message .. . | | Hi gang, | | I've never had a lot of luck with GDMs for some reason. Even with a | decent meter, it seems such a drag tuning across such a vast range | looking for a tiny, easily-missed dip which you have to screw out of | the meter by forcing the sensing coil so far into the circuit | concerned you practically break the circuit board. Am I alone in | finding this potentially invaluable device practically useless in | practice? Is there a more viable alternative? | | p. | -- | | First rule is to get a good dip meter- the stuff made for the amateur |community is very poor- the Eicos, Heath Millen etc. Pick up a Measurments |model 59. With this meter you can take a 1/2 wave wire- say at 2M and hold |the meter a couple inches from the center and see a huge dip. Other meters |don't even respond when held to the wire. Dips on conventional L-C circuits |can easily be full scale. Yep. I have two 59s and they are great. I got rid of two Millens. They are better than anything else but the 59. As to usefulness, a short war story. Another engineer and I were working on an AGC problem in the early Phoenix missile i-f amplifier. Phoenix being a monopulse radar had a three channel receiver with very tight agc tracking requirments (both gain and phase). The agc voltage was fed to each of the three channels via feedthru caps in the walls of a very well shielded and gasketed chassis. Nevertheless, there was obvious crosstalk. The other guy said to me, "Wes, do you have a GDO?" I said, "Sure." A couple of younger engineers who were watching this asked, "What's a GDO?" So we poke the coil of the Model 59 into the chassis and find a nice resonance at the i-f in the agc wiring. The feedthru capacitance and wiring inductance were resonating at i-f. We had millions of dollars worth of test equipment in our lab and I doubt that we could have devised a test for this without heroic efforts. The only problem was keeping the GDO hidden from the metrology guys since they couldn't "calibrate" and service them so they wanted them gone. Wes N7WS |
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i use my GD-meter when building antennas and tuning
antennas and traps to frequency. Although the calibration is quite inexact, it's always possible to listen to the GD-meters frequency on the receiver. "Paul Burridge" On Sat, 15 Nov 2003 17:23:50 -0600 (CST), Turner) wrote: THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T. I'm not using a Millen and this post isn't a troll as someone else suggested. The meter I use started out life as a Tradiper (Japanese) but because it was hopelessly outdated and used old germanium trannies with enough lead inductance to tune a VoA transmitter, I decided to rip its guts out and rebuild from scratch.The actual chassis/meter/facia etc was quite high quality, so it made sense. I got this nice circuit from the UK equivalent of the ARRL Handbook and set about building it. It used 2 SK88 FETs and the output of this oscillator could be adjusted to keep its impedence as high as poss for each test, thereby giving really good dips when even quite heavily loaded low Q circuits were tested *provided* they were physically big enough to shove the sense coil into. The sense coils are about 3/4" in diameter, which although fine for large, out-of-circuit component measurements, is *hopeless* for getting in close on a circuit board with subminature components a fraction of the size. That's the main problem I face with all GDMs, though: they all seem to have relatively huge sense coils relative to today's component sizes :-( |
i use my GD-meter when building antennas and tuning
antennas and traps to frequency. Although the calibration is quite inexact, it's always possible to listen to the GD-meters frequency on the receiver. "Paul Burridge" On Sat, 15 Nov 2003 17:23:50 -0600 (CST), Turner) wrote: THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T. I'm not using a Millen and this post isn't a troll as someone else suggested. The meter I use started out life as a Tradiper (Japanese) but because it was hopelessly outdated and used old germanium trannies with enough lead inductance to tune a VoA transmitter, I decided to rip its guts out and rebuild from scratch.The actual chassis/meter/facia etc was quite high quality, so it made sense. I got this nice circuit from the UK equivalent of the ARRL Handbook and set about building it. It used 2 SK88 FETs and the output of this oscillator could be adjusted to keep its impedence as high as poss for each test, thereby giving really good dips when even quite heavily loaded low Q circuits were tested *provided* they were physically big enough to shove the sense coil into. The sense coils are about 3/4" in diameter, which although fine for large, out-of-circuit component measurements, is *hopeless* for getting in close on a circuit board with subminature components a fraction of the size. That's the main problem I face with all GDMs, though: they all seem to have relatively huge sense coils relative to today's component sizes :-( |
Bill Turner wrote:
On Sat, 15 Nov 2003 23:08:53 -0700, Wes Stewart wrote: snip The only problem was keeping the GDO hidden from the metrology guys since they couldn't "calibrate" and service them so they wanted them gone. __________________________________________________ _______ Great story, Wes. But why couldn't the metrology guys figure out a cal procedure? I suspect the Not Invented Here syndrome, right? -- Bill, W6WRT More likely the results of corporate policy. The last place I worked kept the records on the mainframe, rather than use dedicated software to track the ISO9001 data because, "®That's the way we've always done it!©". That is like some test fixtures have elaborate setup and calibration instructions, wile others are labeled, "Calibration not required" I told the cal lab the label should read, "Calibration not possible". ;-) -- Michael A. Terrell Central Florida |
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