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Re: Measure Inductance?
Try this YouTube video
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*Clyde K. Spencer* On Thu, Aug 19, 2021 at 9:14 AM Joe WB9SBD <nss@...> wrote:
Can anyone help me with this? |
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Re: Measure Inductance?
Can anyone help me with this?
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I have the connector(s) but the "Set up The Calibration" I know how to do the calibration for when measuring SWR.? the open, short, Load. This video for when doing SWR is fantastic! Is there one detailed like this step by step for when measuring an inductor? Joe WB9SBD On 8/14/2021 6:29 PM, Bob Albert via groups.io wrote:
First put an adapter on the SMA connector and set up the calibration.? Go to Smith Chart.? Select your frequency range.? Short the test leads and see how much residual inductance there is.? Then connect the unknown.? Move the marker to whatever frequency you like and it will read out directly. |
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Re: danger measuring antenna
High Tension. The plate voltage, or anode voltage in the UK. In old circuit
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diagrams you'll see it labelled HT. Andy. On Wed, 18 Aug 2021, 22:12 Kent Borg, <kentborg-nanovna@...> wrote:
On 8/18/21 10:06 AM, Andy G4KNO wrote:To get to the condition where (in this case) the antenna side of the |
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Re: danger measuring antenna
You beat me to it, Dave.
There seems to be confusion about how capacitors work. Just because you have a DC blocking capacitor present doesn't on its own mean there's zero volts on the other side. To get to the condition where (in this case) the antenna side of the capacitor is at ground potential at the same time as the plate side is at HT potential requires the capacitor to be charged until that condition is achieved. The only way that can happen is if the antenna side has some sort of DC path to ground, to complete the circuit and allow current to charge the capacitor. What limits the peak charging current is the HT source impedance and the resistance of the choke. Peak charging current occurs at t=0 because the plate side of the capacitor starts at ground potential. However, when you first turn on the PA it takes time for the HT voltage to come up, so the peak charging current is lower and doesn't occur at t=0. You'd have to know all the time constants to work out the max, and when it occurs. If the capacitor suddenly goes short-circuit the current is just determined by the HT source impedance and the resistance of the choke. This will be more than for normal switch-on. I would have thought a quick-blow fuse would go before the choke, but the choke would need to be rated for more than the plate current in normal operation. Otherwise you can't come up with a fuse value that doesn't blow in normal operation but does blow before the RF choke melts and goes open-circuit. As a teenager I built a linear using 813s. It didn't have an RF choke on the output, but it did have the DC blocking capacitor. The load variable capacitor used to tick away all the time because it would arc due to the HT on it. The load capacitor doesn't need the same voltage rating as the tune capacitor, so 2.5kV was too much for it. The arc would cause the capacitor to discharge to ground potential again, then it would charge up again. I never understood this at the time, and it's fortunate I never touched the antenna! 73 Andy, G4KNO. On Wed, Aug 18, 2021 at 5:16 PM David Eckhardt <davearea51a@...> wrote: If you look at the typical pi-network configuration of these vintage |
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Re: RF Active Probe
That is 0.75pf in parallel with 10M¦¸ resistor.
Like a scope probe but lower capacitance. Not sure why if you are going to the trouble to build that why you couldn't go with a higher resistance and more gain. ?????????????????????????????????? Mikek On 8/18/2021 1:59 PM, Donald S Brant Jr wrote: That 0.75pF is 4K¦¸ at 50MHz, way down from 10M¦¸....-- This email has been checked for viruses by Avast antivirus software. |
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Re: Will ch1 show an antenna signal?
On 8/18/21 11:51 AM, Mikek wrote:
Can I connect an antenna to ch1 and expect to see any signals?I wouldn't think so. It's *sort* of like a spectrum analyzer - except it's got a few kHz measurement bandwidth, and if you're scanning 200-620, you've got steps every 4 MHz. The odds of you actually landing on a live signal are kind of low. I did a scan, 200MHz to 620MHz of a TV antenna and had no trace.Nope - it's more a "probability of intercept" thing. Aside from VNAs not really being designed for this, it's the bandwidth vs step size problem. This is a difference where people who are used to "sweeper + spectrum analyzer" sorts of measurements get fouled up - the VNA *sort of* does the same thing, but on a sweeper+SA you can set the measurement bandwidth really wide on the SA (and all it does is add noise).? You don't get that sort of choice on a VNA.? They tend to be very narrow band (narrower the better, really). I want to compare two antenna to see frequencies (channels) they are weak on.You want the $50 spectrum analyzer - then you can set the resolution bandwidth really wide, and you'll see the signals.? If you're looking for TV, digital TV is a sort of flat pedestal about 4-5 MHz wide.? So a resolution bandwidth of 5 MHz would be a good choice.? Then it's all about noise figure.? Most spectrum analyzers don't have great NF, but then, neither do TVs. |
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Re: Will ch1 show an antenna signal?
No? ?The Nano looks at the amplitude and phase of the signal it generates.
You might see some minor amplitude variations of a strong external signal, but the Nano would nave no idea what frequency it was on.? Wrong tool for that job.? ?Hey, I currently own 7 Spectrum Analyzers and consider that TinySA very cute, and cheap!? And unlike the others, fits in my pocket!? ? Kent On Wednesday, August 18, 2021, 01:51:38 PM CDT, Mikek <amdx@...> wrote: Can I connect an antenna to ch1 and expect to see any signals? I did a scan, 200MHz to 620MHz of a TV antenna and had no? trace. Is the signal just to small? Would a 20 db amp be enough to put it on the screen? I want to compare two antenna to see frequencies (channels) they are weak on. ? It seem like it would show a signal, but probably something I don't understand about the operation, this will help me learn. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Mikek |
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Re: Will ch1 show an antenna signal?
The NANOVNAs are not suited for this application. A spectrum analyzer is.
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Take a visit to the following site: Dave - W?LEV On Wed, Aug 18, 2021 at 6:51 PM Mikek <amdx@...> wrote:
Can I connect an antenna to ch1 and expect to see any signals? --
*Dave - W?LEV* *Just Let Darwin Work* |
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Will ch1 show an antenna signal?
Can I connect an antenna to ch1 and expect to see any signals?
I did a scan, 200MHz to 620MHz of a TV antenna and had no trace. Is the signal just to small? Would a 20 db amp be enough to put it on the screen? I want to compare two antenna to see frequencies (channels) they are weak on. It seem like it would show a signal, but probably something I don't understand about the operation, this will help me learn. Mikek |
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Re: RF Active Probe
The specs say 0.75 pf and 10M¦¸.
On 8/18/2021 6:35 AM, roncraig1@... wrote: This probe is just a capacitor input coupled FET source follower with a voltage regulator to run the FET. Input capacitance loading in in 10-15 pF range.-- This email has been checked for viruses by Avast antivirus software. |
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Re: danger measuring antenna
If you look at the typical pi-network configuration of these vintage
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transmitters, there is nothing for the final plate blocking capacitor to work against. Therefore, it will never charge to the DC potential as a dipole or other balanced antenna is a DC open circuit. Heaven forbid should a bird light across the center insulator of such an antenna fed by such a transmitter. That choke does two things: 1) gives something the plate blocking capacitor can work against to charge so there is no DC potential on the feedline, and 2) serves as a 'fuse' as Jim Lux has described. Of course, the DX-40 has no fuse ! The unit I just received to resurrect - my novice transmitter - has been modified with the addition of a fuse - good work. My original from Heath some 61 years ago did not contain a fuse on the chassis. Oh........., I forgot, it did, but it was a bit dangerous. The AC plug contained cartridge fuses in both sides of the AC plug. They were exposed to contact at the line cord end of the AC plug - open to a rather "awakening" experience. Dave - W?LEV On Wed, Aug 18, 2021 at 3:48 PM Jim Lux <jim@...> wrote:
On 8/18/21 8:25 AM, Victor 4X6GP wrote:Those chokes were rated at 125 ma or 300 ma at the most. If the plateblocking capacitor were to short, they would burn out before the primary --
*Dave - W?LEV* *Just Let Darwin Work* |
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Re: danger measuring antenna
On 8/18/21 8:25 AM, Victor 4X6GP wrote:
Those chokes were rated at 125 ma or 300 ma at the most. If the plate blocking capacitor were to short, they would burn out before the primary fuse blew. Whatever the function is supposed to be, it couldn't protect against a shorted blocking capacitor.I'm not so sure - if you're building a 3kV, 0.5 A supply (1.5 kW DC power) then you'd be putting in something that can suck up half an amp for at least long enough to trigger the overcurrent protection.? A 300mA choke can probably take twice that for a short time.? And remember, it doesn't have to be a very good choke while the fault exists - it can melt the form, it can saturate (if it has an iron core), etc. It just has to last longer than it takes the fuse or breaker to trip. I would think, for instance, that the choke could be comparable to the plate choke from the power supply - both have to be able to potentially stand off the entire HV power supply (if the tube or surroundings arcs to ground). |
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Re: danger measuring antenna
Those chokes were rated at 125 ma or 300 ma at the most. If the plate blocking capacitor were to short, they would burn out before the primary fuse blew. Whatever the function is supposed to be, it couldn't protect against a shorted blocking capacitor.
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73, Victor, 4X6GP Rehovot, Israel CWops #5 Formerly K2VCO On 18/08/2021 2:40, Brian D wrote:
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Donald S Brant Jr
Victor 4X6GP
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