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Spam tool problems
All,
It has come to my attention that some spam tools report received spam to ISPs. The case cited is SpamCop. As I understand it, if you run a spam tool that does this, and the tool auto-reports the spam back to ¡°relevant ISPs¡±, the groups.io owner (not the nanovna-users moderators) will ban you from all groups.io groups. This is because the report can get groups.io marked as a spam source and blacklist it. I will look further into this, but if this happens to you please report it to the nanovna-users owners so that we can fix it once you have disabled the spam tool¡¯s behavior. Thank you. DaveD, co-owner |
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Re: RF Active Probe
KV5R
I got one of those from transverters-store in Ukraine a couple years ago. The design comes from this Elektuur article . The output is about 20dB below the input, and even though its input is high impedance and very low capacitance, it takes a good bit of signal to drive it to a clean signal on the output, which I used with a 'scope. It took over 500mV input to give a nearly clean output at 62mV. At 1V in it put out 132mV. Haven't tried it on the Nano but doubt it'll drive its input port. I was unable to align the oscillators in a radio (IC-751) with it so I dubbed it a "fail."
Right after trying the active probe, I built an inductive probe, (30T #24 3/16th" ID for HF; use way less turns for VHF) and that worked GREAT for sniffing oscillators and stages within an inch or two, with no circuit loading. I use that with an rtl-sdr v.3 in direct sampling mode as an SA, previously calibrated to WWV, to set oscillator freq to +-1Hz and it shows the signal and spectrum around the signal with any spread, spurs, distortion etc. 73, --KV5R 
04-Inductive-RF-Probe-Layout.jpg
07-Inductive-RF-Probe-End-View.jpg
08--Inductive-RF-Probe-With-BNC-Patch-Cable.jpg
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Re: Measure Inductance?
*Clyde K. Spencer* On Thu, Aug 19, 2021 at 10:22 AM Clyde Spencer <cftr01b@...> wrote:
This should be a simpler video on the subject. |
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Re: Measure Inductance?
This should be a simpler video on the subject.
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*Clyde K. Spencer* On Thu, Aug 19, 2021 at 9:44 AM Clyde Spencer <cftr01b@...> wrote:
Try this YouTube video |
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Re: Measure Inductance?
Thanks,
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I also found that.? But while he says what to do, but doesn't show you "HOW" to do what he says to do. Like one part is to set up the smith chart to do "X" and he says "I already did that" well good for you, how do I do it? he gives no clue as to how to do what he said he did, and he does that a LOT in that video. Joe WB9SBD On 8/19/2021 8:44 AM, Clyde Spencer wrote:
Try this YouTube video |
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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* |
Donald S Brant Jr
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