|
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
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On 10/6/21 3:36 AM, msat via groups.io wrote: Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of? Are you going to be truly fixed frequency, or are you going to sweep within ISM 908-928 range? I'm not sure the NanoVNA-H will actually go that high - The notional range is up to 900, and it kind of depends on whether the Si PLL can get high enough. Note that there are two PLLs and they run at different submultiples (the receiver LO uses a different harmonic than the source LO) Yes, you'll need some sort of filter. How good does it have to be? That depends on your spurious emissions requirements.. You need to look at the rules for your kind of operation - is it a "must be 60dB below desired signal" or is it a "must be below X Volts/meter at Y distance" spec. Some sort of LC would probably work - whether you can get the ultimate rejection you need with a single LC is hard to know, but get yourself a copy of a program like Elsie (Tonne Software, free version) and you can fairly rapidly design a filter.? You'll probably also need a filter on the output of your amplifier, depending on how linear it is.
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On 10/6/21 7:11 AM, Jim Lux wrote: On 10/6/21 3:36 AM, msat via groups.io wrote:
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of? Are you going to be truly fixed frequency, or are you going to sweep within ISM 908-928 range?
I'm not sure the NanoVNA-H will actually go that high - The notional range is up to 900, and it kind of depends on whether the Si PLL can get high enough. Note that there are two PLLs and they run at different submultiples (the receiver LO uses a different harmonic than the source LO)
Yes, you'll need some sort of filter. How good does it have to be? That depends on your spurious emissions requirements.. You need to look at the rules for your kind of operation - is it a "must be 60dB below desired signal" or is it a "must be below X Volts/meter at Y distance" spec.
Some sort of LC would probably work - whether you can get the ultimate rejection you need with a single LC is hard to know, but get yourself a copy of a program like Elsie (Tonne Software, free version) and you can fairly rapidly design a filter.? You'll probably also need a filter on the output of your amplifier, depending on how linear it is. 902-928, misremembered, but otherwise, same.
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Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a carefully regulated and licensed activity, whether for experimentation or any other purpose. Holders of transmitting licences are required to adhere to the local regulations concerning frequency, power, mode of transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and conditions, the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't be legal as, for starters, the 'bare foot' Nano-VNA doesn't have the capability to be modulated and provide your station ID.
I could be wrong, of course.
Regards,
_Norman, G8EYM_
Sent from my GNU-Linux ThinkPad.
toggle quoted message
Show quoted text
On 06/10/2021 11:36, msat via groups.io wrote: Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
|
Hi Norman
On this side of the pond the FCC does recognize the need to radiate signals during testing.
I have an antenna range and commonly transmit on many commercial frequencies.?
I am expected to minimize radiated signals per "Good Engineering Practice" and are responsible for any interference I cause.? ? ? The NanoVNA certainly falls into this category.? ? Just leave it on long enough to get a good reading and you meet FCC guidelines.? ?In the real world you would probably leave it on for a week and no one would notice.? ? ?Kent
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Show quoted text
On Wednesday, October 6, 2021, 09:45:24 AM CDT, Norman_G8EYM <brycek.fs@...> wrote: Good afternoon Mark, In most parts of the world, transmitting a radio frequency signal is a carefully regulated and licensed activity, whether for experimentation or any other purpose. Holders of transmitting licences are required to adhere to the local regulations concerning frequency, power, mode of transmission and harmonic content, to name but a few. Assuming that you can conform to the required standards and conditions, the appropriate filtering methods are well documented. My initial assessment of your planned experiment is that it wouldn't be legal as, for starters, the 'bare foot' Nano-VNA doesn't have the capability to be modulated and provide your station ID. I could be wrong, of course. Regards, _Norman, G8EYM_ Sent from my GNU-Linux ThinkPad. On 06/10/2021 11:36, msat via groups.io wrote: Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
|
On 10/6/21 7:03 AM, Norman_G8EYM wrote: Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a carefully regulated and licensed activity, whether for experimentation or any other purpose. Holders of transmitting licences are required to adhere to the local regulations concerning frequency, power, mode of transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and conditions, the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't be legal as, for starters, the 'bare foot' Nano-VNA doesn't have the capability to be modulated and provide your station ID. Amateur radio transmissions require id, as do broadcasts (both are for the purposes of "communication") but other transmissions generally do not (radars don't ID).? As it happens radars aren't legal for amateur radio in the US - the transmission has to be intended for reception by another station, except for beacons. That's really not an issue here - the OP is talking ISM - Industrial, Scientific, Medical - in the US it's a different set of rules, some in Part 15, some in Part 18. ISM usage (industrial microwave ovens are at 915 MHz for instance) doesn't require transmitting id. It does require compliance to the emission standards (a "field strength at X meters"? kind of measurement, typically) 18.305 has a table that says 25 microvolts/meter at 300 meter distance if your RF power is <500W for "inband" and <10 microvolts/meter at 300 meter distance for "out of band" - that's 2.6E-13 W/square meter. (-126dBW/m2) - spread out over 4pi(300^2) (60 dBsm) - so Max isotropic radiated power is then -66 dBW? or 0.25 microwatt. That is what's going to set your filtering requirement.? if you didn't have an amplifier, and your NanoVNA puts out 1 mW, a 40 dB rejection would probably work, unless you have a gain antenna, in which case it has to be more. If the amplifier is putting out 10 Watts (for example), and there is a 10dBi antenna, then the OP needs 90 dB of rejection - that's quite a lot - a narrow band trap might work, reducing the number of sections required, as opposed to a 915 MHz BPF.? On the other hand, there are probably people selling monolithic 915 MHz filters? - cordless telephones use that band, for instance. Check Johanson, Minicircuits, or Murata - it might take a couple stages, combination of high pass and low pass, and some careful layout.? Eval boards are your friend here, if it's a one off prototype.
|
Hello Kent,
Mark introduced himself as an 'RF newbie' and I was, somewhat clumsily, trying to point out that transmitting RF is not an unregulated activity. I understand that very low power CW transmissions might not be noticed. But adding an RF Amplifier could change the game.
Cheers,
_Norman._
Sent from my GNU-Linux ThinkPad.
toggle quoted message
Show quoted text
On 06/10/2021 16:37, KENT BRITAIN wrote: Hi Norman
On this side of the pond the FCC does recognize the need to radiate signals during testing.
I have an antenna range and commonly transmit on many commercial frequencies.
I am expected to minimize radiated signals per "Good Engineering Practice" and are responsible for any interference I cause.? ? ? The NanoVNA certainly falls into this category.? ? Just leave it on long enough to get a good reading and you meet FCC guidelines.? ?In the real world you would probably leave it on for a week and no one would notice.? ? ?Kent
On Wednesday, October 6, 2021, 09:45:24 AM CDT, Norman_G8EYM <brycek.fs@...> wrote:
Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a
carefully regulated and licensed activity, whether for experimentation
or any other purpose. Holders of transmitting licences are required to
adhere to the local regulations concerning frequency, power, mode of
transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and conditions,
the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't be
legal as, for starters, the 'bare foot' Nano-VNA doesn't have the
capability to be modulated and provide your station ID.
I could be wrong, of course.
Regards,
_Norman, G8EYM_
Sent from my GNU-Linux ThinkPad.
On 06/10/2021 11:36, msat via groups.io wrote:
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
|
FCC Restricted Bands (Part 15.205) is likely to be relevant, where the
requirement is equivalent to -41.2dBm/MHz eirp (assuming a 0dBi antenna),
-41.2dBm/100kHz 960MHz-1GHz, and -49dBm/100kHz at lower frequencies,
although it changes again as you go lower. It rather depends on where the
spurii lie. Notice these are spectral density limits.
Andy, G4KNO.
toggle quoted message
Show quoted text
On Wed, Oct 6, 2021 at 4:53 PM Jim Lux <jim@...> wrote: On 10/6/21 7:03 AM, Norman_G8EYM wrote:
Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a
carefully regulated and licensed activity, whether for experimentation
or any other purpose. Holders of transmitting licences are required to
adhere to the local regulations concerning frequency, power, mode of
transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and
conditions, the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't
be legal as, for starters, the 'bare foot' Nano-VNA doesn't have the
capability to be modulated and provide your station ID. Amateur radio transmissions require id, as do broadcasts (both are for
the purposes of "communication") but other transmissions generally do
not (radars don't ID). As it happens radars aren't legal for amateur
radio in the US - the transmission has to be intended for reception by
another station, except for beacons.
That's really not an issue here - the OP is talking ISM - Industrial,
Scientific, Medical - in the US it's a different set of rules, some in
Part 15, some in Part 18.
ISM usage (industrial microwave ovens are at 915 MHz for instance)
doesn't require transmitting id. It does require compliance to the
emission standards (a "field strength at X meters" kind of measurement,
typically)
18.305 has a table that says 25 microvolts/meter at 300 meter distance
if your RF power is <500W for "inband" and
<10 microvolts/meter at 300 meter distance for "out of band" - that's
2.6E-13 W/square meter. (-126dBW/m2) - spread out over 4pi(300^2) (60
dBsm) - so
Max isotropic radiated power is then -66 dBW or 0.25 microwatt. That is
what's going to set your filtering requirement. if you didn't have an
amplifier, and your NanoVNA puts out 1 mW, a 40 dB rejection would
probably work, unless you have a gain antenna, in which case it has to
be more.
If the amplifier is putting out 10 Watts (for example), and there is a
10dBi antenna, then the OP needs 90 dB of rejection - that's quite a lot
- a narrow band trap might work, reducing the number of sections
required, as opposed to a 915 MHz BPF. On the other hand, there are
probably people selling monolithic 915 MHz filters - cordless
telephones use that band, for instance.
Check Johanson, Minicircuits, or Murata - it might take a couple stages,
combination of high pass and low pass, and some careful layout. Eval
boards are your friend here, if it's a one off prototype.
|
For filter design and performance, you might try Elsie: <> It's good for lumped element filters. My first knee jerk reaction to your requirements is that you may need to go to a cavity filter to obtain the harmonic and spurious suppression you require to be "legal". Hi-Q helical filters might also get you there. I can't speak for the FCC, but once worked at the very beginning of the RFID craze (right off "The Hill" from Los Alamos) before we went public. RFID was originally developed to track radioactive transport trucks. We had an experimental license from the FCC for the 900 and 2.4 GHz ISM bands. You are likely treading on thin ice with any amount of power, however, even 3 decades ago, FCC (unofficially) considered the 902 to 928 MHz ISM band the new "junk band" (their words). Even in my relatively RF isolated location, I have quite a number of 900 MHz ISM band emissions detectable on the spectrum analyzer with nothing more than a short clip lead as an antenna. Take your chances with unlicensed emissions of any significant amount of power / antenna gain. Dave - W?LEV On Wed, Oct 6, 2021 at 11:43 AM msat via groups.io <msatoria= [email protected]> wrote: Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a
specific experiment I'd like to perform. Without going into the unnecessary
details of the experiment itself, what I'd like to do is use the nano as a
fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an
amp and transmitted via an antenna. A probe on S21 will then be used for
obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating
frequencies are the fundamental and odd order harmonics, along with some
even order and spurious frequencies. I also know that the nano will rely on
the 5th harmonic of some fundamental in order to reach my desired fixed
frequency. Since not only would it be irresponsible to transmit those
various other frequencies, but I also think my experiment would be better
served by having as spectrally pure signal as is reasonably possible. To
avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically
need to be? Would a 1st order LC bandpass do, or do I need something else?
Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Mark,
Since you only want to transmit one of the harmonics from the NanoVNA you will require a bandpass filter for the 900 MHz. band. Here is a link to a good online tool that can design many types of filters with standardized component values.
Once you try it out you will see that the LC component values are small values and PCB layout will be critical.
I suggest you use an off-the-shelf component. You can buy these for a few dollars and most have specs for the PCB layout.
Here is one example...
If you don't want to design and build your own PCB and enclosure you can buy filters that come in a box with appropriate connectors. Google will find quite a few in short order.
Roger
|
Hi Norman
Yes, CE and the FCC would consider that sweeping signal a Transient during any compliance testing.Might even get it declared Spread Spectrum hihi.? ?(That's what Lorawan is doing)? Certainly a Quasi Peak test would take it virtually to zero.? ?Just last week I had to do some patterns on an occupied frequency and had to run +37 dBm vs my usual +13 dBm to get a good plot.? ? Kept the source antenna close the ground and only had it on for a few minutes.??Yes, had some experience with OFCOM.? ?Hold 2E0VAA and G8EMY licenses.? ?I know, an 8, but it is a full license.? Kent
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On Wednesday, October 6, 2021, 11:01:09 AM CDT, Norman_G8EYM <brycek.fs@...> wrote: Hello Kent, Mark introduced himself as an 'RF newbie' and I was, somewhat clumsily, trying to point out that transmitting RF is not an unregulated activity. I understand that very low power CW transmissions might not be noticed. But adding an RF Amplifier could change the game. Cheers, _Norman._ Sent from my GNU-Linux ThinkPad. On 06/10/2021 16:37, KENT BRITAIN wrote: ? Hi Norman
On this side of the pond the FCC does recognize the need to radiate signals during testing.
I have an antenna range and commonly transmit on many commercial frequencies.
I am expected to minimize radiated signals per "Good Engineering Practice" and are responsible for any interference I cause.? ? ? The NanoVNA certainly falls into this category.? ? Just leave it on long enough to get a good reading and you meet FCC guidelines.? ?In the real world you would probably leave it on for a week and no one would notice.? ? ?Kent
? ? ? On Wednesday, October 6, 2021, 09:45:24 AM CDT, Norman_G8EYM <brycek.fs@...> wrote:
?
? Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a
carefully regulated and licensed activity, whether for experimentation
or any other purpose. Holders of transmitting licences are required to
adhere to the local regulations concerning frequency, power, mode of
transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and conditions,
the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't be
legal as, for starters, the 'bare foot' Nano-VNA doesn't have the
capability to be modulated and provide your station ID.
I could be wrong, of course.
Regards,
_Norman, G8EYM_
Sent from my GNU-Linux ThinkPad.
On 06/10/2021 11:36, msat via groups.io wrote:
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
? ?
|
Mark,
as I understand it, your nanoVNA would have to run its synthesizer on one fifth of your operating frequency, and so you would have to use the fifth harmonic. That's because the third-harmonic range of the nanoVNA ends at 900MHz.
To pass the rather weak fifth harmonic while rejecting the much stronger fundamental and the other harmonics, a first order filter will definitely not be good enough.
In that frequency range my best bet for a homemade filter would be a 3-resonator helical filter, made with simple copper wire spirals, on a groundplane, with shields made from copper sheet (or brass, if you can't find copper), tuned by means of brass screws through the top, and coupled through slots cut into the shield walls. There are online calculators that can design such a filter for you. Helical filters can be built without requiring any RF rated component at all, just wire, metal sheet and screws! And they give really good performance.
Using ready-made monolithic filters is probably not a good choice, because they tend to have many spurious responses. They are intended for passing a certain band and rejecting the neighboring bands, but may not have good attenuation on far-away frequencies, such as the fundamental of your square-wave signal. If you use such ready-made filters, be sure to check the specs first and make sure that they actually have good attenuation on all the far-away frequencies you need to attenuate.
A highly selective helical filter, followed by several broadly tuned amplifier stages, should do what you need.
Maybe a better solution is to not use the nanoVNA for this, but use any sort of signal generator that runs directly on the frequency you want.
Manfred
|
Hello Kent,
That sounds like interesting work you do.
Sorry for this off-topic response but, G8EMY. What a coincidence!
_Norman, G8EYM._
Sent from my GNU-Linux ThinkPad.
toggle quoted message
Show quoted text
On 06/10/2021 18:58, KENT BRITAIN wrote: Hi Norman
Yes, CE and the FCC would consider that sweeping signal a Transient during any compliance testing.Might even get it declared Spread Spectrum hihi.? ?(That's what Lorawan is doing)? Certainly a Quasi Peak test would take it virtually to zero.? ?Just last week I had to do some patterns on an occupied frequency and had to run +37 dBm vs my usual +13 dBm to get a good plot.? ? Kept the source antenna close the ground and only had it on for a few minutes.??Yes, had some experience with OFCOM.? ?Hold 2E0VAA and G8EMY licenses.? ?I know, an 8, but it is a full license.? Kent
On Wednesday, October 6, 2021, 11:01:09 AM CDT, Norman_G8EYM <brycek.fs@...> wrote:
Hello Kent,
Mark introduced himself as an 'RF newbie' and I was, somewhat clumsily,
trying to point out that transmitting RF is not an unregulated activity.
I understand that very low power CW transmissions might not be noticed.
But adding an RF Amplifier could change the game.
Cheers,
_Norman._
Sent from my GNU-Linux ThinkPad.
On 06/10/2021 16:37, KENT BRITAIN wrote:
? Hi Norman
On this side of the pond the FCC does recognize the need to radiate signals during testing.
I have an antenna range and commonly transmit on many commercial frequencies.
I am expected to minimize radiated signals per "Good Engineering Practice" and are responsible for any interference I cause.? ? ? The NanoVNA certainly falls into this category.? ? Just leave it on long enough to get a good reading and you meet FCC guidelines.? ?In the real world you would probably leave it on for a week and no one would notice.? ? ?Kent
? ? ? On Wednesday, October 6, 2021, 09:45:24 AM CDT, Norman_G8EYM <brycek.fs@...> wrote:
? Good afternoon Mark,
In most parts of the world, transmitting a radio frequency signal is a
carefully regulated and licensed activity, whether for experimentation
or any other purpose. Holders of transmitting licences are required to
adhere to the local regulations concerning frequency, power, mode of
transmission and harmonic content, to name but a few.
Assuming that you can conform to the required standards and conditions,
the appropriate filtering methods are well documented.
My initial assessment of your planned experiment is that it wouldn't be
legal as, for starters, the 'bare foot' Nano-VNA doesn't have the
capability to be modulated and provide your station ID.
I could be wrong, of course.
Regards,
_Norman, G8EYM_
Sent from my GNU-Linux ThinkPad.
On 06/10/2021 11:36, msat via groups.io wrote:
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a specific experiment I'd like to perform. Without going into the unnecessary details of the experiment itself, what I'd like to do is use the nano as a fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp and transmitted via an antenna. A probe on S21 will then be used for obtaining relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating frequencies are the fundamental and odd order harmonics, along with some even order and spurious frequencies. I also know that the nano will rely on the 5th harmonic of some fundamental in order to reach my desired fixed frequency. Since not only would it be irresponsible to transmit those various other frequencies, but I also think my experiment would be better served by having as spectrally pure signal as is reasonably possible. To avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need to be? Would a 1st order LC bandpass do, or do I need something else? Are there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
|
On 10/6/21 10:09 AM, Roger Need via groups.io wrote: Mark,
Since you only want to transmit one of the harmonics from the NanoVNA you will require a bandpass filter for the 900 MHz. band. Here is a link to a good online tool that can design many types of filters with standardized component values.
Once you try it out you will see that the LC component values are small values and PCB layout will be critical.
I suggest you use an off-the-shelf component. You can buy these for a few dollars and most have specs for the PCB layout.
Here is one example...
If you don't want to design and build your own PCB and enclosure you can buy filters that come in a box with appropriate connectors. Google will find quite a few in short order. yes, that's the kind of thing I was thinking of.. 40dB isolation - so you might need 2 or 3 of them, and packaging will be important. There are inexpensive off the shelf boards with a couple SMAs and the solder pads for the filters. If you can't find them, let me know and I'll ask someone who bought them recently.
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These are very useful cheap'ish boards for creating 35MHz to 4.4GHz ..
You can set them to a static carrier or to sweep between two frequencies, up to around 4mW max output.
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Mark,
You might want to consider the TinySA. It has a signal generator function as well as being a spectrum analyzer. It can generate a signal up to 960 MHz as a fundamental. You might need some low-pass filtering to minimize harmonics.
--John Gord
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On Wed, Oct 6, 2021 at 04:43 AM, msat wrote:
Hello everyone!
RF newbie and first time poster here. Recently purchased a NanoVNA-H for a
specific experiment I'd like to perform. Without going into the unnecessary
details of the experiment itself, what I'd like to do is use the nano as a
fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an amp
and transmitted via an antenna. A probe on S21 will then be used for obtaining
relative phase angle measurements.
I know the nano generates a square wave output, thus the dominating
frequencies are the fundamental and odd order harmonics, along with some even
order and spurious frequencies. I also know that the nano will rely on the 5th
harmonic of some fundamental in order to reach my desired fixed frequency.
Since not only would it be irresponsible to transmit those various other
frequencies, but I also think my experiment would be better served by having
as spectrally pure signal as is reasonably possible. To avoid any confusion,
my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna
So my question is this: how sophisticated does the filter realistically need
to be? Would a 1st order LC bandpass do, or do I need something else? Are
there any common "gotchas" that trip up newbs that I should be aware of?
Thanks!
Mark
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First off, thanks to everyone for all the helpful responses! It made me realize just how loaded my question actually was. It also help unjam the gears in my head. That said, there's a lot of stuff here to respond to, so hopefully I don't forget anything I wanted to discuss.
To clarify, I intend to operate at a fixed frequency, no modulation, preferably somewhere in the 900MHz ISM band, driven by an amp operating at less than 5W. Each run of the experiment should only last a few minutes at most.
Probably due to me not knowing any better, I'm leaning towards making my own amp along with bypass filtering. The amp section would be based on modules such as:
@Jim Lux & Andy G4KNO
Your references to the FCC requirements and the given examples are very helpful. It provides a better perspective of what I'm dealing with here. It also shows me how much I still have to learn.
Regarding the monolithic filters in that band, I suspect they're a lot less common than they once were. I see reference to a lot of discontinued items. That said, some can still be found which is plenty for my needs as long as they provide sufficient performance. The datasheets for some of these leave a lot to be desired. I didn't hear of minicircuits until you mentioned it. It looks like they may have a viable solution.
@Roger Need
I actually had both the rf-tools page and that digikey part (along with some others) already opened in a browser tab. I made the mistake of making a really sharp 1st order bandpass without realizing how ridiculously tiny either the capacitor or inductor was. After widening the band enough to allow for more realistic components, the roll off was much more shallow, in turn requiring higher order filters. By that point, I became a bit more concerned regarding the complexity of the filter.
@OneOfEleven & John Gord
Thanks for the hardware suggestions (I'm actually considering a TinySA to test filters and amps), but since a critical aspect of my experiment is getting phase angle information, I either have to use the nanoVNA to generate the RF signal, or I don't use the nano at all and instead buy an old so-called "vector voltmeter" along with all the other hardware I'd need. I can't help but to think it should be possible to sufficiently attenuate frequencies outside the nano's 5th harmonic much easier and cheaper than to purchase a bunch of additional equipment.
So one thing that's not clear to me, particularly when it comes to dielectric-type filters, is whether they could be cascaded to increase Q without using amp inter-stages.
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Mark,
You may want to look at the NanoVNA-V2. It can work up to 3GHz (and beyond) using the fundamental.
--John Gord
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Show quoted text
On Wed, Oct 6, 2021 at 10:53 PM, msat wrote:
First off, thanks to everyone for all the helpful responses! It made me
realize just how loaded my question actually was. It also help unjam the gears
in my head. That said, there's a lot of stuff here to respond to, so hopefully
I don't forget anything I wanted to discuss.
To clarify, I intend to operate at a fixed frequency, no modulation,
preferably somewhere in the 900MHz ISM band, driven by an amp operating at
less than 5W. Each run of the experiment should only last a few minutes at
most.
Probably due to me not knowing any better, I'm leaning towards making my own
amp along with bypass filtering. The amp section would be based on modules
such as:
@Jim Lux & Andy G4KNO
Your references to the FCC requirements and the given examples are very
helpful. It provides a better perspective of what I'm dealing with here. It
also shows me how much I still have to learn.
Regarding the monolithic filters in that band, I suspect they're a lot less
common than they once were. I see reference to a lot of discontinued items.
That said, some can still be found which is plenty for my needs as long as
they provide sufficient performance. The datasheets for some of these leave a
lot to be desired. I didn't hear of minicircuits until you mentioned it. It
looks like they may have a viable solution.
@Roger Need
I actually had both the rf-tools page and that digikey part (along with some
others) already opened in a browser tab. I made the mistake of making a really
sharp 1st order bandpass without realizing how ridiculously tiny either the
capacitor or inductor was. After widening the band enough to allow for more
realistic components, the roll off was much more shallow, in turn requiring
higher order filters. By that point, I became a bit more concerned regarding
the complexity of the filter.
@OneOfEleven & John Gord
Thanks for the hardware suggestions (I'm actually considering a TinySA to test
filters and amps), but since a critical aspect of my experiment is getting
phase angle information, I either have to use the nanoVNA to generate the RF
signal, or I don't use the nano at all and instead buy an old so-called
"vector voltmeter" along with all the other hardware I'd need. I can't help
but to think it should be possible to sufficiently attenuate frequencies
outside the nano's 5th harmonic much easier and cheaper than to purchase a
bunch of additional equipment.
So one thing that's not clear to me, particularly when it comes to
dielectric-type filters, is whether they could be cascaded to increase Q
without using amp inter-stages.
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John,
To my knowledge, the V2 outputs a sine wave up to 350MHz, and square wave up to 960MHz. While this would allow me to use the fundamental frequency in the desired ISM band, it would still require filtering. In this case a low-pass. Given that the fundamental is 7dB higher than the 5th harmonic as would be required when using the nano V1, maybe it would be worthwhile. Other than that, I don't know how much it would simplify filter design.
But there is a potential issue with using a V2, and that's the fact that, according to the developer, phase measurements have "significant errors" when used in continuous wave mode. What the dev considers "significant", I don't know. Otherwise, V2 output is not continuous even when set to a fixed frequency. I don't know if that would actually affect my experiment, but I'd rather not base my experiment around the V2 just to find out the hard way that it doesn't work, especially since I don't see the V2 offering any significant benefit in the first place.
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Well, the thing is, if you end up using a band pass filter to select the desired harmonic then if you test at a different frequency inside the ISM the phase of the carrier will change anyway depending on the phase response of the band pass filter. We don't know if you intent to stay at a single fixed frequency or move about it the ISM band.
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Roger Need
