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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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?
--
Bill AA6BD
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Hi, the most likly reason, that the protection diode is not alredy present on the vna, is cost or possible problems against I good measure?
No, cost is very low, jut a few cents. During the design phase ESD strikes were applied directly at the input, it passed the tests. However, after my report of broken units, the designer (Gabriel) tested again, now with at least 50 cm of cable connected and he was able to reproduce the problem. This happened to be my usual setup too. Gabriel concluded that the input voltage protection of the switch is sufficient, but that the current kills it. (current due to discharge of the cable capacitance). He suggested insering a small resistor of 5 Ohm to limit the current to the RF switch's protection diodes. A series resistor probably has some influence on the source impedance. A 0.1 pF protection diode does not. The non-linearity of the diode is a fraction of the 0.1pF. DC levels are zero anyway so you can consider the diode to be of no influence. I did not see any difference with or without diodes.
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Re: backyard antenna ranges
That sounds great Mario! I'd love to see some write-up of what you found worked, and what didn't... anything that would make it easier for us also to get good test antennas.
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Re: NanoVNA RF Demo Kit connection
I couldn't make even the small number of connections suggested with those little connectors. They died before. I put in parallel with each connector a pair of male-male pins used with IC sockets (2.54mm) and another pair of male-female pins at one end of each test lead. They won't be 50 ohms but their length is too small to be very bad at the frequencies involved. And they allow you to connect and disconnect hundreds of times (and are easy to change later).
Regards
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Hi, the most likly reason, that the protection diode is not alredy present on the vna, is cost or possible problems against I good measure?
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OT: Windows software for NWT70 analyzer?
Hello--
Can anyone point me toward a Windows 7 version of the software application
for the NWT70 analyzer?
Thanks in advance, and 73--
Brad? AA1IP
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There are versions of V2 with N and SMA connectors. V2 switches to si5351 for frequencies below 140MHz so that is correct. On Fri, 5 Feb 2021 at 16:05, bruiser419 via groups.io <bruiser419= [email protected]> wrote: Glad I caught this thread. I was thinking of getting a S-A-A-2 but if it
has N connectors that would be problematic short term.
I did hear though that the H4 uses harmonics above 300 Mhz or so, where as
the S-A-A-2 doesn't use harmonics and is a straight measurement. Is that
accurate?
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Glad I caught this thread. I was thinking of getting a S-A-A-2 but if it has N connectors that would be problematic short term.
I did hear though that the H4 uses harmonics above 300 Mhz or so, where as the S-A-A-2 doesn't use harmonics and is a straight measurement. Is that accurate?
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On 2/5/21 6:04 AM, Manfred Mornhinweg wrote: Jim,
Standard 0.405" coax (RG-8, RG-213) is about 40 pF/meter, so a 100 ft/30meter run is 1200pF. You figure is far too low! 100pF per meter comes much closer to reality.
Manfred You're right.. I was looking at the wrong table..
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Roger Need
Gab IU0 OQM