Re: Using Nano VNA as an RF Sniffer
John,
IMSAI guy on YouTube as a video
Gary
W9TD
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Re: Using Nano VNA as an RF Sniffer
By the way, check tinysa.org on the ¡°Where to Buy¡± page.
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Mike, W0IH
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Re: Using Nano VNA as an RF Sniffer
TinySA (spectrum analyzer) is available on R and L (Randal.com) for $50. Be wary of clones on other sites.
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Mike, W0IH
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Re: Using Nano VNA as an RF Sniffer
Gary,
Where can I find info on using the tinySA as an rf sniffer? Looked at the video list and on the home page but it is not addressed there.
Thanks,
John
K?JHL
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Re: Using Nano VNA as an RF Sniffer
Set bandwidth at maximum (4k on H4), connect antenna to CH1 port, and you can get signal strength in 4kHz range for every measure point.
So if measure on 401 point you can measure in span ?401*4k = 1.6MHz (yes can be little higher) If set span more, you can not get signal data (it can be between 2 points and not measured)
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Re: Using Nano VNA as an RF Sniffer
Get a tinySA. Works great for that purpose. You may need shielded loop probe if the interference is caused by current or just the telescoping antenna included and an external LNA to get the best sensitivity. I used it around my house.
Gary
W9TD
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Re: Which analyzer is more accurate?
For what it's worth, I have a similar OFC dipole setup to what you
describe, and the measurements from my nanoVNA-H4 and my MFJ-226 are almost
identical. So what you are describing is not what I experience; maybe
there is a problem with one of your units.
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On Fri, Feb 5, 2021 at 5:11 PM Bill Cromwell <wrcromwell@...> wrote: Hi Bill,
The MFJ seems to be the outlier. Consider that a man with a clock always
knows what time it is. A man with two or three clocks can never be
sure:) Other replies to your post point at other factors so I won't go
over those.
73,
Bill KU8H
t'uther Bill
On 2/5/21 5:34 PM, Bill AA6BD wrote:
I measured my 40M OCF Dipole with my NanoVNA-H4 and it shows that the minimum SWR of 1.68 is at 6.975 MHz. I had the loan of an MFJ-259C, and it
shows the minimum SWR of 1.6 is at 7.14 MHz. I also have an Arduino based
SWR analyzer designed by K6BEZ and it shows the minimum SWR of 1.7 is at
6.92 MHz. The SWR figures align nicely, but the center frequency is not
very close. In the 40M band, this difference represents about half of the
band. I calibrated the NanoVNA, and scanned from 6.5 to 7.5 MHz so
precision of the 101 steps should not be an issue. Which device(s) do I
believe? How can I resolve this difference?
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Has this been implemented for a fix to the issue of protection? I would like to update my unit with the fix.Thank you very much,BillW4MXT
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Re: Which analyzer is more accurate?
On 2/5/2021 6:12 PM, Mel Farrer via groups.io wrote: And then, all 3 have varying degrees of sensitivity to RFI - you're
measuring an antenna that's outdoors. This is definitely something to keep in mind when you are testing an antenna at a tower site, like at a repeater site. Other transmitters at the site can affect the readings. I do antenna testing and certification with an Anritsu Sitemaster analyzer. The Sitemaster has the ability to send a coded signal that it can recognize as a valid test signal. This can eliminate some of the interference (but not always all) at a site during testing. This does affect some testing accuracy. The Sitemaster also has the ability to turn off this coded signal and go into the "CW" mode for greater accuracy. Just something to keep in mind when using the NanoVNA or other device around other live transmitters. Joe
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Using Nano VNA as an RF Sniffer
Has anyone used a Nano VNA as an RF sniffer around the home, a Radio Amateur friend of mine has an annoying RF signal that affects his receivers in his shack, we have been using a small commercial radio to look for this RF Signal. I have an H4 and was wondering if I made a small two-turn loop onto a small Coax cable and attached it to CH1 (S21), I could get the VNA to do a sweep over a band of freqs and see the spikes.
I have some ideas but don't wish to invent the wheel if it has been done before. Thank You.
PS the Setting would be good to know.
Mervyn/G4KLE
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On Fri, Feb 5, 2021 at 03:30 PM, Clifford Heath wrote:
When I redesigned the HackRF antenna protection, I removed the useless TVS, a
bi-directional 15V type (that will only activate after everything in the
HackRF is already dead), and instead used Skyworks Limiter Diodes
SMP1330-085LF.
In the case of the HackRF, I need to protect the LNA from any excursions above
13dBm, but the transmitter and mixer inputs are a bit more robust, so I used
three of these diodes.
Clifford - Just took a look at your schematic. --- I see you reverse biased one of the diodes to Vaa (3V) and the other to ground. Why not both to ground? ---- It look like you used 10 k resistors instead of RF chokes like the Skyworks app note. Any particular reason? ---- How much RF power can you now safely inject without damage using this new circuit. Thanks - Roger
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Re: Which analyzer is more accurate?
Hi Bill,
The MFJ seems to be the outlier. Consider that a man with a clock always knows what time it is. A man with two or three clocks can never be sure:) Other replies to your post point at other factors so I won't go over those.
73,
Bill? KU8H
t'uther Bill
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Show quoted text
On 2/5/21 5:34 PM, Bill AA6BD wrote: I measured my 40M OCF Dipole with my NanoVNA-H4 and it shows that the minimum SWR of 1.68 is at 6.975 MHz. I had the loan of an MFJ-259C, and it shows the minimum SWR of 1.6 is at 7.14 MHz. I also have an Arduino based SWR analyzer designed by K6BEZ and it shows the minimum SWR of 1.7 is at 6.92 MHz. The SWR figures align nicely, but the center frequency is not very close. In the 40M band, this difference represents about half of the band. I calibrated the NanoVNA, and scanned from 6.5 to 7.5 MHz so precision of the 101 steps should not be an issue. Which device(s) do I believe? How can I resolve this difference?
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Re: Which analyzer is more accurate?
On Fri, Feb 5, 2021 at 03:31 PM, Bill AA6BD wrote: I have an older NanoVNA (V1?) and it
gave almost the same measurement as the NanoVNA H4. Since three of four
analyzers yield almost the same values, while the MFJ is off by itself, I
suspect it is the inaccurate one but I will test some more.
Bill, The MFJ analyzers are not that accurate. I own a MFJ-259B and results will vary with battery voltage! There is a calibration procedure for them and I suspect some leave the MFJ facility without proper calibration. I know that sounds unbelievable because MFJ is known for their rigorous quality control but it was the case on my unit. Roger
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Re: Which analyzer is more accurate?
On 2/5/21 3:31 PM, Bill AA6BD wrote: Manfred,
The OCF Dipole has a common mode choke at the feed point. I ran a coax to my shack and connected all three analyzers at the same end of the coax and at the same physical position. The only physical difference is that the MFJ analyzer has a PL259 connector on it, the NanoVNA has a PL259 to SMA adapter, and the K6BEZ analyzer has a PL259 to BNC adapter. I find it hard to believe that this much frequency difference is due to the adapters, and all three were measured at the same operating position. I have an older NanoVNA (V1?) and it gave almost the same measurement as the NanoVNA H4. Since three of four analyzers yield almost the same values, while the MFJ is off by itself, I suspect it is the inaccurate one but I will test some more.
The choke at the feedpoint doesn't mean that the coax is totally decoupled from the antenna - the fields from the antenna will couple to the shield of the coax. A symmetric dipole, with the feedline coming away perpendicular, will be decoupled, but that's a special case. If your OCF feedline has chokes every few meters, then it's not going to "participate" But I'd check the frequency accuracy of the MFJ - There's a 4MHz crystal that sets the frequency of the PIC16C73.
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Re: Which analyzer is more accurate?
Manfred,
The OCF Dipole has a common mode choke at the feed point. I ran a coax to my shack and connected all three analyzers at the same end of the coax and at the same physical position. The only physical difference is that the MFJ analyzer has a PL259 connector on it, the NanoVNA has a PL259 to SMA adapter, and the K6BEZ analyzer has a PL259 to BNC adapter. I find it hard to believe that this much frequency difference is due to the adapters, and all three were measured at the same operating position. I have an older NanoVNA (V1?) and it gave almost the same measurement as the NanoVNA H4. Since three of four analyzers yield almost the same values, while the MFJ is off by itself, I suspect it is the inaccurate one but I will test some more.
--
Bill AA6BD
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When I redesigned the HackRF antenna protection, I removed the useless TVS, a bi-directional 15V type (that will only activate after everything in the HackRF is already dead), and instead used Skyworks Limiter Diodes SMP1330-085LF.
These are low-capacitance PIN diodes, but are designed with an unusual characteristic: after a forward pulse greater than 0.7v has turned them on, they briefly conduct in both directions with between 1 and 2 ohms impedance. The diode itself can absorb up to 30dBm safely, but the impedance discontinuity reflects up to 50dBm back toward the source, which protects the antenna input amplifiers.
In the case of the HackRF, I need to protect the LNA from any excursions above 13dBm, but the transmitter and mixer inputs are a bit more robust, so I used three of these diodes.
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Re: Which analyzer is more accurate?
One thing that I did to make sure oranges were oranges and apples were apples.? I constructed a reactive termination for the analyzer.? Based on 10 MHz, I built up a series SMT structure of a 0603 50 ohm and a 0603 -j50 ohm cap to ground.? After all of the SOL calibration I put the reactive load on the analyzer and it better read 50-j50 ohm at 10.000 MHz.? What does this do?? It confirms that the calibration is linear from short to open.? Some of the analyzers have a problem here.? I sleep a lot better at night now.? I have junked a couple of analyzers that did not pass this test.
Mel, K6KBE
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On Friday, February 5, 2021, 02:54:29 PM PST, Jim Lux <jim@...> wrote: On 2/5/21 2:34 PM, Bill AA6BD wrote: I measured my 40M OCF Dipole with my NanoVNA-H4 and it shows that the minimum SWR of 1.68 is at 6.975 MHz.? I had the loan of an MFJ-259C, and it shows the minimum SWR of 1.6 is at 7.14 MHz.? I also have an Arduino based SWR analyzer designed by K6BEZ and it shows the minimum SWR of 1.7 is at 6.92 MHz.? The SWR figures align nicely, but the center frequency is not very close.? In the 40M band, this difference represents about half of the band.? I calibrated the NanoVNA, and scanned from 6.5 to 7.5 MHz so precision of the 101 steps should not be an issue.? Which device(s) do I believe?? How can I resolve this difference? Your question would be "is it a frequency measurement problem" or "is it a impedance measurement problem" - The first one could be answered by measuring a piece of coax that is shorted or open at the far end. It's pretty high Q, and would be unaffected by "fixturing". It's about a 2% frequency different you're observing, which is quite large, considering all three are essentially referenced to a crystal (timebase in the MFJ's counter, PLL ref in the Nano, whatever in the K6BEZ, but almost certainly a crystal). And a 2% error in crystal frequency is enormous. So the next question is "what is the actual R+X being measured" (as opposed to SWR). at resonance, do they give the same numbers? And then, all 3 have varying degrees of sensitivity to RFI - you're measuring an antenna that's outdoors. It's an interesting problem, but I'd rule out frequency errors first
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Re: Which analyzer is more accurate?
Bill,
I would suspect that all three of those meters are right, and that the antenna's behavior is changing according to what you connect to it! It's and OCF dipole, an antenna that is highly unbalanced. You should have a very good common mode choke on that feedline to be able to make any meaningful measurements - and to use it, too. Otherwise not just the antenna will be radiating and receiving signals, but the antenna, the feedline, the ground connection, the radio, the instrumentation, the house wiring, and yourself too!
Manfred
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Re: Which analyzer is more accurate?
On 2/5/21 2:34 PM, Bill AA6BD wrote: I measured my 40M OCF Dipole with my NanoVNA-H4 and it shows that the minimum SWR of 1.68 is at 6.975 MHz. I had the loan of an MFJ-259C, and it shows the minimum SWR of 1.6 is at 7.14 MHz. I also have an Arduino based SWR analyzer designed by K6BEZ and it shows the minimum SWR of 1.7 is at 6.92 MHz. The SWR figures align nicely, but the center frequency is not very close. In the 40M band, this difference represents about half of the band. I calibrated the NanoVNA, and scanned from 6.5 to 7.5 MHz so precision of the 101 steps should not be an issue. Which device(s) do I believe? How can I resolve this difference? Your question would be "is it a frequency measurement problem" or "is it a impedance measurement problem" - The first one could be answered by measuring a piece of coax that is shorted or open at the far end. It's pretty high Q, and would be unaffected by "fixturing". It's about a 2% frequency different you're observing, which is quite large, considering all three are essentially referenced to a crystal (timebase in the MFJ's counter, PLL ref in the Nano, whatever in the K6BEZ, but almost certainly a crystal). And a 2% error in crystal frequency is enormous. So the next question is "what is the actual R+X being measured" (as opposed to SWR). at resonance, do they give the same numbers? And then, all 3 have varying degrees of sensitivity to RFI - you're measuring an antenna that's outdoors. It's an interesting problem, but I'd rule out frequency errors first
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Which analyzer is more accurate?
I measured my 40M OCF Dipole with my NanoVNA-H4 and it shows that the minimum SWR of 1.68 is at 6.975 MHz. I had the loan of an MFJ-259C, and it shows the minimum SWR of 1.6 is at 7.14 MHz. I also have an Arduino based SWR analyzer designed by K6BEZ and it shows the minimum SWR of 1.7 is at 6.92 MHz. The SWR figures align nicely, but the center frequency is not very close. In the 40M band, this difference represents about half of the band. I calibrated the NanoVNA, and scanned from 6.5 to 7.5 MHz so precision of the 101 steps should not be an issue. Which device(s) do I believe? How can I resolve this difference?
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Bill AA6BD
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Gary W9TD
Roger Need