When 5G comes along, I probably won't be able to afford the cost of a professional EMF meter.
Does anyone have any suggestions how I could make a kind of "sniffer" that would display ambient field intensity on an LED bargraph, or even just a audible output with changing pitch?
The range of interest is 25 to 50GHz (millimeter wave) such as would be emitted from small cell antennae, etc.
The meter can be pocket size and have as many wire antenna as necessary to cover this bandwidth.
Kevin Foster
Someone, I think LTC, just announced an RF detector chip that works past 40 GHz.
Yes, here it is:
That would be cool, but it will need some good antenna design.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
That is an excellent chip. But I was hoping for something more like a fractal antenna, plus a few diodes, RF transistors and a VCO driven speaker.
Am I dreaming?
Kevin Foster
Neat. Why is the eval board $450? Is Rogers a verb in this case?
--sp
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
If you mean to amplify the RF pre-detection, past 40 GHz, that would be very difficult. There are some MMIC amps that work out there, but they are expensive and still need careful handling.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
To discourage amateurs, where the revenue to questions ratio is zero? I see all sorts of ridiculously expensive EVM boards out there. Boards that they give to larger companies, by the trunk loads.
And generally have gross gain slopes.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
How ambient? If you could get a fast-enough diode you'd just need an antenna, said diode, a cap and a voltage detector to "see" signals right under the tower.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
A superhet is the way to go.
If the LO was an impulse generator, picket fence in the frequency domain, it would be interesting. It's a sampler. That could be very simple.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yeah, eval boards are often free if you might be a serious user. Distributors are often the best route for them.
But eval boards seem to be designed by the lowest-end junor engineers. And they have so many jumper options that they don't help much.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Nice chip but needs some broadband gain to produce useful output.
Fractal antennas might be useful if you want the largest gain in the smallest package, but are otherwise no better then conventional antennas.
Speaker? 5G is all about high speed data. If you want to actually talk to someone, it's a VoIP channel or service on top of the 5G data. If you managed to demodulate the data, all you'll hear out of speaker is hissing noise.
Nope. Some of my checkered background is in direction finders. I've spent some time working with mechanical rotating antenna DF systems, which work quite nicely. Some of my old rants on Doppler DF. There is a note on the bottom of the first link which explains why I like rotating antenna direction finders:
We don't go to distributors for information. Purchasing buys some components via distributors, mainly because some manufacturers don't want to go direct. The disties are just useless middlemen.
That must depend on the manufacturer. The one's I've used seem to be pretty good. Sometimes we get one that's so complicated that it takes a PC program (and USB) to operate it. Those tend to smoke a lot.
What pisses me off is when the FAE tells me to build like the EVM. Well, if that was all that was on my board, it would make life easy.
Lately, you can't get actual support from a chip manufacturer; they send you to a forum. A distributor's application engineer is often the only path to real support. All the Xilinx help we've got lately is from Avnet, not from Xilinx. TI, ditto.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I don't have that problem. The TI FAE took me out to lunch yesterday and the Atmel/Microchip FAEs had the pleasure Tuesday. ;-) I generally get two invites a week[*] (three this week but likely none next).
[*]Either they bring food in for a "lunch and learn" or take us out. One FAE told us that if he takes us out, the company pays for his lunch, too. Otherwise, he has to pay for it himself. :-)
Most cellular systems rely on reflections, not on LOS (line-of-sight) propagation, Thus, there is not much point of using directional antennas, you should use an omnidirectional (isotropic) antenna to capture the total RF power available in the air volume ("ambient").
A Ka band LNB coupled to more or less omnidirectional antenna feeding a microwave leakage detector might be the simplest approach.
I do not know, how 5G systems are actually going to be implemented, but the nasty problem with microwave dipoles is that the capture area is proportional to the wavelength squared and hence also received power is proportional to the wavelength squared, hence things are quite nasty at 28 - 39 GHz.
One way to avoid this kind of problems is to use phased arrays or MIMO (Multiple input, multiple output) systems.
But apparently the OP is just interested in the total "ambient" power for a signal strength meter, so no MIMO processing needed.
Not being an experienced RF constructor, that is exactly the type of solution I was looking for.
However, standard microwave detectors are calibrated for 2.45GHz. How would it read in the Ka band?
Given that the device needs to be portable, can you point me to a suitable antenna? Cold I just mount the LNB in a stainless steel salad bowl?
Remember, this is just a "sniffer" not a calibrated lab grade instrument.
Kevin Foster
The LNB converts the Ka band signal to something line 950 .. 2xxx MHz. A typical sniffer is usually not that selective, so it should react to
2xxx MHz signals.
The bowl would be too directional. Some simple horn antenna would be sufficient or some other means to connect into the waveguide.
At this time LTE can use reflections in the form of MIMO to boost data performance. It's not a requirement for communications. Since all the MIMO streams are on the same frequency, an RF detector will show the signal coming from two or more sources (one per antenna). However, since the MIMO antennas are all on the same tower or panel, a crude detector will show it coming from a single source (i.e. the top of the tower or panel).
Nobody uses omnidirectional antennas at 30GHz. At best, a sector antenna. What 5G promises is beam steering. This takes a high gain steerable (phased) antenna array, and points it at a specific user for the short period of time that the data needs to be sent. The rest of the time, when nothing is being sent, the antenna beam points to other users. What this means is that if nobody is using the cell site, there's little or no RF being emitted, so there's nothing to detect.
Another problem is automatic power control. The cell site transmit power is automagically adjusted for the lowest possible power that produces a minimum acceptable SNR (signal to noise ratio) at the receiving end. Handsets that are close to the tower get very little RF sent in their direction. Distant stations probably get maximum power. The variable signal levels can make detection a problem if there isn't enough signal to work with.
There are omnidirectional, or rather something like isotropic receivers available for lower frequencies. They're called exposure meters, some of which work to 30GHz and higher: Because of the lack of antenna and RF gain, they are not very sensitive and have limited range.
Agreed. Without the dish, the KA band LNB has about the right amount of gain needed to act as a "detector". The LNB is circular polarized, which will detect both linear (vertical or horizontal) polarizations. However, I do find articles proposing circular polarization for 5G cellular, which may cause difficulties if here is a polarization mismatch.
At 30GHz, one wavelength is about 1cm. A half wave dipole would be
5mm long in free space, and probably 1.5mm long on a ceramic substrate.Phased arrays and MIMO are very different devices. Phased arrays require a fairly large number of dipoles or patches to work. They make plenty of sense on top of a fixed tower or building that doesn't move. They make less sense on a detector that can be aimed in any direction and would not require a directional scanning antenna to function. Methinks a very conventional horn or dish antenna will be just fine for a simple detector.
On the borderline is a phased array on a smartphone or tablet. There's barely enough room for such an antenna, but it would work to keep the handset antenna pointed at the cell tower, or the strongest reflection. However, most of the proposals I've seen have the handset festooned with multiple antennas and switch between antennas for the best signal with no attempt to do beam steering.
MIMO is utilizing reflections to provide additional bandwidth. It does nothing for increasing signal strength. Details if you want them.
Agreed.
The OP didn't bother describing how the detector is to be used. My guess(tm) is a gun like affair, with a small panel, dish, or horn antenna on the front. Or maybe something like a Geiger counter with a cable connected antenna and front end. Or maybe a panel antenna with a black box stuck on the back. My idea would be a mechanically scanning horn antenna with a PPI (plan position indicator) display.
Note that even a small dish at 30GHz is going to have a rather narrow
-3dB beamwidth. A 0.5 meter dish, at 30GHz, will have a whopping 42dBi gain, but with a 0.67 degree beamwidth, will be VERY difficult to aim. If you've ever tried to align a DBS TV satellite dish, you'll understand the problem. Less gain and a wider beamwidth might be better.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
In other words, an RF dosimeter or radiation detector. There are versions of such things all over the internet. Search the RF paranoia web sites for specifics.
I must confess that I've designed a few of these. Here's a free idea if you want to pursue it. It's a brick with several LED's. Each LED represents a cellular band or rather parts of a cellular band. Inside the brick are a collection of cavity bandpass filters, each tuned to one of the cellular bands. Each filter input has a PCB or ceramic antenna for the lower frequencies, and a slot antenna for the higher frequencies. At the output of each filter is a simple diode detector. After the detectors are analog comparators that indicate that there's RF present on that band, which lights up the associated LEDs. The basic idea is that you wave this brick at a cell tower, and it will tell you which bands are active on the tower. Today, cheap spectrum analyzers can all this and more, so it's obsolete except for the possibility of doing it cheap.
It's possible, but you might need to reverse engineer the device in order to generate a schematic. It's difficult to modify such things without knowing how it works.
SMA maxes out at about 25GHz.
No prescaler. A downconverter (mixer) from 30Ghz down to a frequency that the Cornet device can see will work. Building a 30GHz tunable local oscillator will be the tricky part. Again, you should be able to move a Ka band LNB to 30GHz, and use the Cornet device (or any spectrum analyzer) to "see" the signals.
Another possible is a 24Ghz microwave radar gun. I have a really old Kustom Signals 24GHz gun that works nicely for measuring speed. The front end is a Gunnplexer (circulator/oscillator/mixer). Skim through the photos of gunnplexers:
An Introduction to 24 GHz See the section on 24Ghz components.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
What sorts of volume do you buy? Are there many other accounts in your territory?
When I worked in New Orleans, we were practically the only OEM in Louisiana. The TI guys would fly in from Texas to wine and dine us. I was considering using a $7 National part in a new system, so TI quoted us 90 cents.
In San Francisco, our company is relatively small fry. And the big semi companies are backing off on actual support for everyone. It wouldn't be so bad if the data sheets were better.
I am designing in one ADC, the ADC10080. It has an internal bandgap reference that is connected through a resistor to a pin, so you can override it with an external reference. What is the value of that resistor? The data sheet doesn't say, and the support people can't find out.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
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