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@Jim Lux

While I'm pretty sure the nano only uses the fundamental as well as the 3rd and 5th harmonic for measurements, your point is taken. You did give me an idea for a potential solution, and that's to feed the nano S11 into a PLL and then multiply the frequency by 5, and low pass filter the output as you state, then go on to the PA stage. The filtering issue would be simplified, and the nano wouldn't know the difference. I think this would work well.


@Roger

I'm in the US. I may very well be wrong, but I don't think operating in the ISM band is as restrictive as you state. I'll certainly look into it more carefully to ensure I'm complying with all applicable laws. Thanks for your concern.

On Thu, Oct 7, 2021 at 09:10 AM, msat wrote:

@Lou W7HV

I understand your concern, but I'll be transmitting on an unlicensed "ISM"
band. I intend to fully comply with the appropriate regulations regarding in
and out of band emissions. That's probably more than could be said for plenty
of consumer electronic products on the market.

The ISM band at 900 MHz. is only "unlicensed" for the user/purchaser of the equipment in most countries (UK, EU, US, Canada, Australia etc.) The manufacturer of this equipment MUST have his product tested to meet the regulations of the country where the product will be sold. Legitimate manufacturers are allowed to test products during the design phase prior to production.

There are two exceptions to the above. Licensed amateur radio operators in many countries are allowed to build and operate equipment in parts of the ISM band if they have a license category that permits home built equipment. Experimenters can build equipment if it has extremely low output power and/or field strength in some countries.

Mark - From what you have posted you don't appear to be an equipment manufacturer or a licensed amateur radio operator so your plan to transmit several watts in this band is not legal and could result in significant fines.

Roger

On Thu, Oct 7, 2021 at 10:30 AM, <friedrich.kairo@...> wrote:

flashed my NanoVNA-H withNanoVNA-H4_20210131.dfu, i think this was wrong.
White screen and usb port is no longer recognized. What should i do?
Friedrich
db6px

You have to reflash with the correct firmware. To get back to DFU mode you have to short the VDD and Boot0 pins inside the NanoVNA.

The procedure is all described in the "Absolute Beginners Guide to the NanoVNA" in the files section of this group. This is also described in this groups Wiki.

Roger

flashed my NanoVNA-H withNanoVNA-H4_20210131.dfu, i think this was wrong.
White screen and usb port is no longer recognized. What should i do?
Friedrich
db6px

On 10/7/21 9:10 AM, msat via groups.io wrote:

@OneOfEleven

I did mention a few times that I intend to transmit at a fixed frequency in the 900MHz ISM band. I haven't decided which frequency specifically, since I'll likely have to base it off my filter options. But unless it ends up being very narrow bandwidth, it probably won't make all that much of a difference.

As far as off-the-shelf power amps go, if I have to build a PCB for the filters anyway, I might as well attempt to add a power amp IC to it.

@Lou W7HV

I understand your concern, but I'll be transmitting on an unlicensed "ISM" band. I intend to fully comply with the appropriate regulations regarding in and out of band emissions. That's probably more than could be said for plenty of consumer electronic products on the market.

@Jim Lux

So far, I only looked on digikey for filters, but the choices there were pretty slim. I'll check with other distributors also. I also came across TOKO which appears to be a subsidiary of Murata. I may have missed it, but Johanson didn't appear to have a suitable part even on their site. Honestly, some of the mini-circuits parts have the best specs I've seen, but they're also by far the most expensive at around $30 a piece. However, they do have fairly high power handling, so I might just splurge and stick one on the PA output.

Digikey isn't a great source for these things.. Usually, a distributor (Avnet) is a better bet. Sometimes you can get samples.


Yes, Toko has all sorts of nice filters including helicals. (and knockoffs of Toko)

Digikey has 915 MHz filters - only 25dB down 100 MHz away, and 2.5dB loss? - $3.65 each

I've considered several ways to build this experiment, but they're all seemingly a lot more complicated (and expensive) while providing little or no added benefit. Honestly, even finding a ~900MHz sine source looks to be pretty much non-existent except for maybe pro gear. Therefore, if I'm going to have to filter anyway, why not just filter the output from the equipment I already have?

Ah, because if you buy a PLL module that puts out 915 MHz, you only need a low pass filter to knock down the harmonics, and that's a *lot* easier than a band pass filter that rejects the subharmonics from the NanoVNA.? Say you're doing 7th harmonic to get 915, that means you need to knock down the 5th (and maybe 6th) harmonic of the 130 MHz base frequency.? So you need a filter that is down >40 dB only a couple hundred MHz away from 915, and that's pretty hard.? A low pass that's down 40dB at 1800 MHz and 2700 MHz is a LOT easier - you don't care where the exact cutoff is (makes component tolerances easier), just that it's "down far enough". And you'd need that on the output of your PA anyway (unless you're spending a lot of money on a nice linear amplifier that you're going to run 20dB below P1dB)

If you don't need good phase noise, just the VCO driven from a pot or DAC might be good enough, and they're not too bad (assuming a harmonic filter)

As far as cascading filters go, I don't think I'll bother trying without amplified inter-stages. RF amps suitable for such a task with minimal required support circuitry (power supply decoupling caps and DC blocking caps) can be had for less than $0.50 a piece in single quantities. I think that's the surer bet.

Well, they're $0.50 for the blob, but then you need a board, and caps, and assembly, etc.? Most of that is available pretty cheap online

That said, I use bucket loads of Minicircuits ZX60-4016E (G:18-20dB, P1dB:+17dBm, NF: 4 dB, 20MHz to 4 GHz) at $100 each at work. (they used to be half that, but, well, COVID, Tariff, chip shortage)

@OneOfEleven

I did mention a few times that I intend to transmit at a fixed frequency in the 900MHz ISM band. I haven't decided which frequency specifically, since I'll likely have to base it off my filter options. But unless it ends up being very narrow bandwidth, it probably won't make all that much of a difference.

As far as off-the-shelf power amps go, if I have to build a PCB for the filters anyway, I might as well attempt to add a power amp IC to it.

@Lou W7HV

I understand your concern, but I'll be transmitting on an unlicensed "ISM" band. I intend to fully comply with the appropriate regulations regarding in and out of band emissions. That's probably more than could be said for plenty of consumer electronic products on the market.

@Jim Lux

So far, I only looked on digikey for filters, but the choices there were pretty slim. I'll check with other distributors also. I also came across TOKO which appears to be a subsidiary of Murata. I may have missed it, but Johanson didn't appear to have a suitable part even on their site. Honestly, some of the mini-circuits parts have the best specs I've seen, but they're also by far the most expensive at around $30 a piece. However, they do have fairly high power handling, so I might just splurge and stick one on the PA output.

I've considered several ways to build this experiment, but they're all seemingly a lot more complicated (and expensive) while providing little or no added benefit. Honestly, even finding a ~900MHz sine source looks to be pretty much non-existent except for maybe pro gear. Therefore, if I'm going to have to filter anyway, why not just filter the output from the equipment I already have?

As far as cascading filters go, I don't think I'll bother trying without amplified inter-stages. RF amps suitable for such a task with minimal required support circuitry (power supply decoupling caps and DC blocking caps) can be had for less than $0.50 a piece in single quantities. I think that's the surer bet.

On 10/6/21 10:53 PM, msat via groups.io 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.

I'd say Murata and Johanson are better bets for filters - a better selection - and then, there's the one posted by someone else. In any case, the filters are cheap.

BTW, it depends on if you have more time or more money, but MiniCircuits also has RF amplifiers. 5W is going to be around $600-1000, depending on how much compression you can tolerate. There are probably also countless surplus sources, but that brings other tradeoffs (time vs money).

@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.

Which is why, if someone makes something like a ceramic filter, that's usually easier.

@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.

Or, if all you need is phase, get yourself a source (a VCO and a pot or DAC to set the frequency), some filters, a PA, and a eval board for an I/Q demodulator to serve as the receiver, then run your I/Q through low pass filter (RC is fine) and digitize with a RPi or an Arduino (I favor the Teensy series, myself).? Use a sample of the transmitted signal as the LO for the demodulator.

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.

Maybe, maybe not - layout is important. They're cheap, try it and see.

I may have missed it but I didn't see if you have an amateur radio license. Transmitting RF is regulated, and licensing is how the regulatory agencies control it. An amateur radio license permits transmitting RF in certain bands using type accepted equipment or equipment designed or built by the amateur. A license is granted after passing a test, the purpose of which is to give at least at start in understanding what the limitations and privileges are, and how to exercise them without straying from the regulations and causing harmful interference.

If you were to settle to a bit less power you can use a ready RF amp something like these cheap ones ..



Don't forget any RF amp you use will also need a low pass filter on the output to reduce the harmonics created by the amp itself down to an acceptable level.

A cheapy band pass filter on the input to the amp could be also be done by cascading 2 or 3 SAW filters with a bit of matching entering in the first SAW's and exiting the last SAW.

Also helical filters as mentioned are nice to use. You can probably find a suitable TEMWELL (ex toko filters) helical filter for the band pass filter.

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.

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.

Mark,
You may want to look at the NanoVNA-V2. It can work up to 3GHz (and beyond) using the fundamental.
--John Gord

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.

Surprised by such a good match with the S11 method.
Considering that DE-5000 measurement uncertainty
is ± 0.023Ω both results are acceptable.
Can you add some common mode chokes and see if
that improves the S21 measurement? Should not make
much of a difference when measuring 1Ω but ...
You can also try to "subtract" the port 2 imperfections with SimSmith.

On Thu, 7 Oct 2021 at 00:50, Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

According to theory the S21 shunt measurement is best for measuring low
impedances. My experience on the NanoVNA-H4 has not been that good with
this method. The CH0 and CH1 impedance should be 50 ohms for an accurate
calculation and this is not the case with the NanoVNA-H and nanoVNA-H4.
Adding attenuators to the test fixture helps improve things but my results
were not as good as a S11 measurement.

Attached are some measurements done with S11 and S21 shunt on a 0805 SMD 1
ohm resistor. It measured 1.003 ohms on a 4 wire Kelvin DE-5000 LCR meter
at 100 kHz.

Roger

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

Demand continues and I will place a third order.
Will order enough that I will have additional spares.

Now have information for International orders.
1 board @ $3.00 CONUS 1 board @ $3.75 International

More info and still adding to the web page


Please reply off list.

Dick K9IVB

According to theory the S21 shunt measurement is best for measuring low impedances. My experience on the NanoVNA-H4 has not been that good with this method. The CH0 and CH1 impedance should be 50 ohms for an accurate calculation and this is not the case with the NanoVNA-H and nanoVNA-H4. Adding attenuators to the test fixture helps improve things but my results were not as good as a S11 measurement.

Attached are some measurements done with S11 and S21 shunt on a 0805 SMD 1 ohm resistor. It measured 1.003 ohms on a 4 wire Kelvin DE-5000 LCR meter at 100 kHz.

Roger

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.

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.

I might leave some feedback on github (did it also in the past). But first
I need to understand what might be the issue. As Chris says, it is all a
little too confusing...
I am still busy untanging it (as I need to get a good workflow for future
NanoVNA measurements...)


Op wo 6 okt. 2021 om 18:34 schreef Roger Need via groups.io <sailtamarack=
[email protected]>: