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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.
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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.
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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.
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@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.
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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)
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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
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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.
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On 10/7/21 12:01 PM, msat via groups.io wrote: @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. The Tx and Rx sides of the Nano use different multiples (so that the receiver doesn't "detect" the fundamental or "wrong" harmonics from the Tx side) The code seems to say 5 and 7 for Tx, Rx respectively, but if you're in the fourth zone, it might be 7 & 9 it's in config.harmonic_freq_threshold - the default is 300 MHz (but might be different, it depends on YOUR particular Si5351's range) My copy of the source is pretty old.. in si5351.c ? /* if (freq > config.harmonic_freq_threshold * 5 ) { ??? ??? freq /= 7; ??? ??? ofreq /= 9; ? }else */ ?? if (freq > config.harmonic_freq_threshold * 3) { ??? freq /= 5; ??? ofreq /= 7; ? } else if (freq > config.harmonic_freq_threshold) { ??? freq /= 3; ??? ofreq /= 5; ? } in main.c config_t config = { ? .magic =???????????? CONFIG_MAGIC, #ifdef __DAC__ ? .dac_value =???????? 1922, #endif ? .grid_color =??????? 0x1084, ? .menu_normal_color = 0xffff, ? .menu_active_color = 0x7777, ? .trace_color =?????? { RGBHEX(0xffe31f), RGBHEX(0x00bfe7), RGBHEX(0x1fe300), RGBHEX(0xe7079f) }, ? .touch_cal =???????? { 370, 540, 154, 191 },? //{ 620, 600, 160, 190 }, ? .default_loadcal =?? 0, ? .harmonic_freq_threshold = 300000000, ? .vbat_offset =?????? 480, ? .checksum =????????? 0 };
@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.
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Jim,
In the code, the following lines are commented out
/* if (freq > config.harmonic_freq_threshold * 5 ) {
freq /= 7;
ofreq /= 9;
}else */
Even if it wasn't, it would just mean that if the freq variable was greater than the harmonic threshold variable multiplied by 5 (the 5th harmonic) then it would set the frequency to the appropriate fundamental of the harmonic.
I have no idea what ofreq is, but I recall reading something about some mixer LO frequency voodoo magic the devs did to push some unwanted IFs out of band. Maybe that's what ofreq is?
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I should have said:
Even if it wasn't, it would just mean that if the freq variable was greater than the harmonic threshold variable multiplied by 5 (the 5th harmonic) then it would set the frequency to the appropriate fundamental of the 7th harmonic instead.
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On Thu, Oct 7, 2021 at 12:01 PM, msat wrote: @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.
I worked for a company that sold equipment containing 900 MHz transmitters and my team was responsible for the design, testing and regulatory approval. We sold to may countries in the world and the United States FCC requirements were the most detailed and stringent of all of them. Everything we sold commercially had to be tested by independent labs and the report sent to the FCC for approval and issuance of an FCC ID# prior to sale. The purchaser however was able to use the devices without a license. The only legal way to transmit on this band is: - by purchasing a device which has gone through the approval process above. described in FCC part 15. - to be a manufacturer developing a product using good engineering practices to keep radiation to a minimum. - to construct home-built experimental device defined under 47 CFR 15.23 and constructed with good engineering practice and Part 15 emission limits - to be a licensed amateur radio operator using commercial or home-built equipment operating according to power and out-of-band emission limits. - an approved ISM (industrial, scientific or medical) non-intentional radiator - FCC part 18. The power limits for the band from 902 to 928 MHz. are described in FCC part 15 for devices like key fobs, cordless phones, video links, data links etc. If you use a single carrier for transmission the transmitted power is very low. The regulation is 200 microvolts/meter at 3 meters which is under 1 milliwatt into a small antenna. If frequency hopping or spread spectrum is used the field strength/power level can be much higher. In essence as a home builder you are restricted to 1 mW of CW transmit power for your project if you wish to follow the FCC regulations. The FCC regulations are available online. A very readable condensed version is on the ARRL site. Roger
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On 10/7/21 2:22 PM, msat via groups.io wrote: Jim,
In the code, the following lines are commented out
/* if (freq > config.harmonic_freq_threshold * 5 ) {
freq /= 7;
ofreq /= 9;
}else */
Even if it wasn't, it would just mean that if the freq variable was greater than the harmonic threshold variable multiplied by 5 (the 5th harmonic) then it would set the frequency to the appropriate fundamental of the harmonic. Yes, that's how it decides which harmonics to use.? If it's <threshold, then fundamental on both if >threshold, but < threshold*3 (i.e. 300-900) then source is 3rd harmonic, mixer is 5th - if the frequency were, say, 400 MHz, then the source would be set for 400/3= 133 MHz, mixer LO to 400/5 = 80 MHz If frequency is > threshold*3 (i.e. 900 MHz) then source is 5th harmonic, local oscillator set to 7th,? so for 920 MHz, source would be 920/5 = 184, local oscillator would be set to 920/7 = 131.4 That's where you are running.
I have no idea what ofreq is, but I recall reading something about some mixer LO frequency voodoo magic the devs did to push some unwanted IFs out of band. Maybe that's what ofreq is?
ofreq is the mixer LO frequency, chosen so that it is 5kHz away from the source frequency. (I ignored that in the examples above, but it *is* important)
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On 10/7/21 3:01 PM, Roger Need via groups.io wrote: On Thu, Oct 7, 2021 at 12:01 PM, msat wrote:
@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.
I worked for a company that sold equipment containing 900 MHz transmitters and my team was responsible for the design, testing and regulatory approval. We sold to may countries in the world and the United States FCC requirements were the most detailed and stringent of all of them. Everything we sold commercially had to be tested by independent labs and the report sent to the FCC for approval and issuance of an FCC ID# prior to sale. The purchaser however was able to use the devices without a license.
The only legal way to transmit on this band is:
- by purchasing a device which has gone through the approval process above. described in FCC part 15.
- to be a manufacturer developing a product using good engineering practices to keep radiation to a minimum.
- to construct home-built experimental device defined under 47 CFR 15.23 and constructed with good engineering practice and Part 15 emission limits
- to be a licensed amateur radio operator using commercial or home-built equipment operating according to power and out-of-band emission limits.
- an approved ISM (industrial, scientific or medical) non-intentional radiator - FCC part 18. Part 5 experimental license would be how I suspect most people wanting to do this as an R&D project would do it.? That lets you radiate what you need, at preapproved frequency ranges, with appropriate interference mitigation, and a "stop buzzer" phone number. Part 5 is how a lot of antenna ranges are licensed as well as things like Open Air Test Sites (OATS) who are doing testing of new devices (after all, you don't know, going in, whether it will meet the limits). People developing radars typically use Part 5 as well.? It's not unheard of to use the Part 5 filing (which is public) to reverse engineer a competitor's unit. . . Or, of course, the historical "if your detectable energy is contained within your property lines, and nobody complains" approach.? That's probably pretty common for university and other similar research labs.?? If you're building one of Chauvet's coffee can SARs for instance.
The power limits for the band from 902 to 928 MHz. are described in FCC part 15 for devices like key fobs, cordless phones, video links, data links etc. If you use a single carrier for transmission the transmitted power is very low. The regulation is 200 microvolts/meter at 3 meters which is under 1 milliwatt into a small antenna. If frequency hopping or spread spectrum is used the field strength/power level can be much higher.
In essence as a home builder you are restricted to 1 mW of CW transmit power for your project if you wish to follow the FCC regulations.
The FCC regulations are available online. A very readable condensed version is on the ARRL site.
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Roger,
My experimental setup should fall under part 18. Realistically, this actually is a scientific piece of equipment - it will be used to perform some science experiments not related to communication. Furthermore, it should be eligible for for authorization under an SDoC rather than certification. While it actually is an "intentional radiator", that might not automatically exclude it from part 18 and SDoC eligibility. Looking at the FCC's SDoC's guidance page, section 2 states:
"For equipment that contains both unintentional radiators (e.g., digital logic circuitry) and intentional radiators within an end product (composite system equipment), the unintentional radiator portion generally can be authorized under either SDoC or certification while the intentional radiator (e.g., radio transmitter) contained in the equipment is typically required to be certified."
Notice how it says "typically required" and not "always required". In the unlikely event that the FCC comes knocking and wants me to shut down, then obviously I'll comply.
All that said, I'm building this device which I'll probably power up only a handful of times for maybe a couple minutes at a time. I'd find it unreasonable to not be allowed to do that in a band that was specifically set aside for high powered devices that are capable of generating a large amount of interference.
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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:
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Hello Mark,
The first amplifier you linked above would probably be your best choice. The two Philips modules are designed for the GSM cellular standard, which is pulsed with 12.5% duty cycle. They are not thermally capable of operating at high power with a continuous carrier. The Hitachi module was designed for the long ago obsolete TACS standard which is continuous carrier.
You wouldn't need to use a filter with these amplifiers. They narrowband 3 stage designs; the input, output, and interstage matching networks will have more than enough selectivity. You could verify this by measuring S21 of the amplifier with no filter. Be sure to use sufficient attenuation on the input and/or output to prevent damage to port 2 receiver in the VNA.
Andy - K?AF
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Andy,
I had noticed the duty cycle limitations in the datasheets for the Philips parts, so I figured that if I did use them, then I would limit output power. Perhaps the TACS part is the more sensible choice, as you state.
I was wondering about the attenuation outside of the stated frequency range of these parts. If it reduces external filtering requirements that would be great. I look forwards to testing this.
Thanks for the info!
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Lou W7HV
Roger Need