Re: MOSFET as RF on/off switch and how to measure/what to expect
#circuit
On 11/8/22 8:23 AM, Eamon Egan wrote: Miro,
Even if we assume that you can bias the MOSFET properly in the presence of RF and try to use it as a switch, and even if we assume that it behaves pretty well in the ON state given its pretty low Rds, you will need to check what OFF isolation you can achieve given the device's drain to source capacitance.
That will be the challenge - off isolation. (and the usual issues with biasing, just like using diodes as switches) You might look at T/R switch literature - It's a similar problem - slow switching, high RF frequencies. You probably aren't as concerned about the gate capacitance or Miller effect, since you're going to drive it pretty hard. Note this: "PIN diodes are offered by many suppliers of RF components. For example, M/A-COM's MA4AGBLP912 is an AlGaAs PIN diode with just 4 ¦¸ ¡°on¡± resistance, low capacitance, and an extremely fast 5 nsec switching speed (Figure 8). It can be used up to 40 GHz in a shunt configuration, with an operating bias of +10 mA for the low-loss state, and 0 V for the isolation state, using a simple +5 V TTL gate driver." So you have a diode switch 40GHz, but the diode itself is a 50-100 MHz kind of part (5ns switching speed) Figure 13 has S11 and S21 plots, like the ones you're thinking of measuring, eh?
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Re: MOSFET as RF on/off switch and how to measure/what to expect
#circuit
Miro,
Even if we assume that you can bias the MOSFET properly in the presence of RF and try to use it as a switch, and even if we assume that it behaves pretty well in the ON state given its pretty low Rds, you will need to check what OFF isolation you can achieve given the device's drain to source capacitance.
Eamon | VE2EGN or AB1NK
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MOSFET as RF on/off switch and how to measure/what to expect
#circuit
OK, this one is only artificially aligned with this group buy using NanoVNA to actually measure what I expect to be answered in a more "academic" fashion :)
How does MOSFET behaves in the triode region, or BJT transistor in saturation when it comes to the frequency response.
What I'm finding is what to expect in the active regions, but could not find anything when it comes to the "extreme" cases when they are in the "wide open/conductive" state.
Can I use a MOSFET as a replacement for a mechanical relay to switch between my antennas even if MOSFET's max declared small signal frequency is quite lower?
This is not the use case where MOSFET is used for fast switching - I'll turn a MOSFET on or off once a day, and then expect it conducts RF (or not).
Might be different between two - MOSFET is using majority charges, BJT is using both and is acting as fully biased diode.
And, just to justify this topic being asked at this smart group - what would you see if connected to 50ohm dummy load and used NanoVNA to measure S11 :)
Thanks!
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Re: Fixture de-embedding for component measurement
Can someone provide the link to pre compiled version of NanoVNA-App for Windows - link :) -- F1AMM Fran?ois -----Message d'origine----- De la part de Miro, N9LR via Envoy¨¦ : mardi 8 novembre 2022 14:53
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Re: Fixture de-embedding for component measurement
Can someone provide the link to pre compiled version of NanoVNA-App for Windows - link provided here does not work, and github page only offers source so one can compile and mess it up with it if wanted :)
Google search did not reveal much more then that.
Thanks!
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This is a link to a previous discussion in this group about NanoVNA App
/g/nanovna-users/topic/91143866#28096 Thanks The url does not point to a use of the nanoVNA-App software I have "COM9" which is displayed and Connected/Disconnected which switches. If I click "Calibration", [Click to open Calibration Window] I get the message "You need to be connected too your VNA" and then Connected/Disconnected no longer switches (stays on Disconnected). It may come from the fact that my nanaoVNA-F is not compatible with nanaoVNA-App while it is with nanaovna-saver. Software without manuals is not my age (73 years old). It's okay, nanovna-saver works fine. I am quite satisfied: in HF I compare the results produced by EZNEC on the basis of a description of a real antenna with the measurements made with my nanaoVNA-F + nanaovana-saver and it is "in the nails". 73 -- F1AMM (Fran?ois) -----Message d'origine-----
De : [email protected] [mailto:[email protected]] De la part de Roger Need via
Envoy¨¦ : lundi 7 novembre 2022 20:24
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Re: Fixture de-embedding for component measurement
Roger
Thanks for the annotated screen shot. Very helpful. I am a newbie, lying in the weeds observing what is going on. I have made a copy of your post for future reference.
Thanks again.
Don KC3MPO
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Re: Fixture de-embedding for component measurement
Yes. I agree, R&S has published some very good information. My current questions revolve, very specifically, around fixturing and calibration for measuring "soft" ferrites, of which there is much less information. I may be homing in on though!
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Re: Fixture de-embedding for component measurement
On Sun, Nov 6, 2022 at 09:30 PM, Fran?ois wrote:
NanoVNA App
Roger ** Thanks.
It's pretty but I don't understand this software at all. It runs on my Windows
Seven.
Attached is a description of what all the buttons are used for. You right click on a graph for more options. This is a link to a previous discussion in this group about NanoVNA App /g/nanovna-users/topic/91143866#28096Roger
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Re: Fixture de-embedding for component measurement
Fran?ois, you can easily learn to use NanoVNA App by the good old tried method of clicking on each icon and seeing what it does! The one thing you need to know is to right-click on the graph, to get all the graph options.
It's important to always watch that you are using a correct calibration. The top frame of NanoVNA App tells you which calibration is in use. You can do calibrations, store them with meaningful names, and load them, from the calibration screen, called up from the calibration icon at the top. It's convenient to do complete, detailed, averaged calibrations, with many points, over the whole frequency range, for each of your test jigs, test cables, etc. Then, when using the NanoVNA, you simply call up the correct calibration, instead of re-calibrating every time.
Practice leads to mastery!
Manfred
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Re: Fixture de-embedding for component measurement
NanoVNA App
Roger ** Thanks. It's pretty but I don't understand this software at all. It runs on my Windows Seven. Is there a notice? I'm like a chicken that just found a knife :). I use nanaovana-saver which I think I know how to use. 73 -- F1AMM Fran?ois -----Message d'origine----- De la part de Roger Need via Envoy¨¦ : lundi 7 novembre 2022 02:58
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Re: Fixture de-embedding for component measurement
On Sun, Nov 6, 2022 at 08:03 AM, Fran?ois wrote:
Hello
With which software do you produce these pretty curves?
--
NanoVNA App Roger
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Re: NanoVNA-H4 no longer measures SWR or Smith Chart
My nVNA started giving me garbage results once. The problem went away when I did a "reset calibration" followed by another calibration. I assume a bad cal got it into a divide-by-zero math situation or something like that. It is easy enough to try.
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Re: Fixture de-embedding for component measurement
Hello
With which software do you produce these pretty curves?
--
F1AMM (Fran?ois)
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-----Message d'origine----- De la part de Manfred Mornhinweg dimanche 6 novembre 2022 16:15
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Re: Fixture de-embedding for component measurement
Brent,
I use a small, simple jig for such measurements. I use just one port, and measure directly. No resistors nor any other stuff.
Of course calibration is done at the very spot where the DUT will be connected.
For reference, in case it's useful to you, I'm attaching my complex impedance measurements for several beads. There are small and large ones, and of several different materials.
I find the complex impedance curves far more useful than the simple impedance modulus data published by some manufacturers. Because in many cases it's VERY important whether the impedance at a given frequency is mostly resistive, mostly inductive, or even has a capacitive component!
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Re: NanoVNA-H4 no longer measures SWR or Smith Chart
On Sat, Nov 5, 2022 at 09:46 PM, John Morris wrote:
measure the SWR on a new antenna and the values were crazy and changing all
the time
It looks to me that the antenna is faulty, with a loose connection inside. The symptoms sure seem like those of an erratic connection. -- Doug, K8RFT
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Re: NanoVNA-H4 no longer measures SWR or Smith Chart
I had a similar problem with my NanoVNA.? I would suggest that you change the SA612 that is near the S11 port for a start.? My problem actually was a bad SI5351.? That is harder to change due to the lead spacing but doable.? The fact that it works in the CW mode, probably means the SI5351 is good.
Good luck,
Tom?? W0IVJ
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On 11/5/2022 7:46 PM, John Morris wrote: I bought my nanoVNA-H4 back in 2019 and used it all the time for multiple purposes till early this year. One time i went to measure the SWR on a new antenna and the values were crazy and changing all the time as i looked at the screen. The SWR curve was constantly changing and didn't give a result that meant anything.
I've recalibrated it many many times.
Flashed both Firmware upgrades and downgrades hoping to get it stable with no success.
Before someone says to change the cables, It does however still operate normally as a signal generator and sweep generator using the same cables.
Could it be that the SWR/Smith chart processing is done on a separate chip that has gone bad? If so, can that be replaced. I know I'd probably be better off to just buy a new one but would like the challenge. Can those particular chips be purchased on the open market?
I can't find anything online that tells you what chip does the SWR and related functions.
Thanks to anyone that can point me in the right direction.
73's John / K7RLD
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Re: NanoVNA-H4 no longer measures SWR or Smith Chart
After you've done a calibration, reconnect the open short and load to
port 0, and observe S11. In log mag display the first two should show 0
dB, and the load a negative value less than -20 dB (-40 or more is
nice). With Smith chart display, the open should show a dot at the
right, the short at the left, and the load at the middle of the chart.
If you get something else, the values may help you understand the
problem.
---In fact, especially at low frequency, you don't even have to do a
calibration to get an idea of your VNA's condition. Just connect each
of the three standards and observe S11, as above. If log mag is very
far below zero for a short or load, that says that there is much less
than normal signal. A short or open reflects 100%. Low signal level
indicates that the resistive bridge or the mixer is damaged. A 50 ohm
load will reflect very little power, so the received signal should be
low if the bridge is OK.
--You could use linear display instead of log mag. It might be easier
to understand, though the dynamic range is very much smaller.
The "processing" is all done in software, but the measured data depends
on many parts, both passive and active. Some of these might be damaged
by high voltages that could appear on an antenna and connecting
feedline, especially when they are longer. (So less chance of damage for
a smaller VHF or UHF antenna.) In the nanoVNA H4 the ICs closest to the
SMA connectors are mixers, SA612AD.
Shorting the end of the feedline before connecting it to the VNA may
eliminate such damaging voltages. Use ESD prevention precautions.
73,
Dave WA8YWQ
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Show quoted text
On 2022-11-05 18:46, John Morris wrote: I bought my nanoVNA-H4 back in 2019 and used it all the time for multiple purposes till early this year. One time i went to measure the SWR on a new antenna and the values were crazy and changing all the time as i looked at the screen. The SWR curve was constantly changing and didn't give a result that meant anything.
I've recalibrated it many many times.
Flashed both Firmware upgrades and downgrades hoping to get it stable with no success.
Before someone says to change the cables, It does however still operate normally as a signal generator and sweep generator using the same cables.
Could it be that the SWR/Smith chart processing is done on a separate chip that has gone bad? If so, can that be replaced. I know I'd probably be better off to just buy a new one but would like the challenge. Can those particular chips be purchased on the open market?
I can't find anything online that tells you what chip does the SWR and related functions.
Thanks to anyone that can point me in the right direction.
73's John / K7RLD
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NanoVNA-H4 no longer measures SWR or Smith Chart
I bought my nanoVNA-H4 back in 2019 and used it all the time for multiple purposes till early this year. One time i went to measure the SWR on a new antenna and the values were crazy and changing all the time as i looked at the screen. The SWR curve was constantly changing and didn't give a result that meant anything.
I've recalibrated it many many times.
Flashed both Firmware upgrades and downgrades hoping to get it stable with no success.
Before someone says to change the cables, It does however still operate normally as a signal generator and sweep generator using the same cables.
Could it be that the SWR/Smith chart processing is done on a separate chip that has gone bad? If so, can that be replaced. I know I'd probably be better off to just buy a new one but would like the challenge. Can those particular chips be purchased on the open market?
I can't find anything online that tells you what chip does the SWR and related functions.
Thanks to anyone that can point me in the right direction.
73's John / K7RLD
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I just downloaded and tried NanoVNASaver 0.4.0 and unfortunately got the same outcome.
Thanks to all who are considering this issue!
VE6ATS
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Brent DeWitt
Roger Need
Douglas Butler
