how do you think this sphere dipole thing is made? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: October 21, 2019, 02:42:19 am
content: http://www.appliedemtech.com/docs/PSDSSystemBlockDiagram_new.pdfCertainly interesting, could be a good metal working projectprototype with 2 salad bowls and a low power RF amp inside?i wonder what the hell its meant for

author: rs20
author_rank: Super Contributor
timestamp: October 21, 2019, 03:15:22 am
content: Quote from: coppercone2 on October 21, 2019, 02:42:19 amQuote from: http://www.appliedemtech.com/

author: coppercone2
author_rank: Super Contributor
timestamp: October 21, 2019, 03:22:30 am
content: why would they use this thing instead of a normal antenna on a stand?are these some ultra high end EMC chambers? they normally run them at high power levels.. what will a battery powered sphere do ? I mean if you are going into the anechoic chamber, why not just blast it?it runs on AAA batteries. suceptance testing is practically cooking

author: yl3akb
author_rank: Regular Contributor
timestamp: October 21, 2019, 06:35:11 am
content: It has bandwidth of 10 MHz – 2.5 GHz. Good luck getting that with normal antenna

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2019, 09:25:56 am
content: It's the opposite of a useful shape.At best it's equalized or calibrated for some part of that spectrum. The extensions will have to be mighty long to keep any flatness down to 10MHz, more likely it's an electrically short dipole and has a lot of gain inside to account for that (and so a poor noise figure, not that you need much in a lot of cases). May even be tuned, so that they are talking about the tuning range, not the total bandwidth.Tim

author: E Kafeman
author_rank: Regular Contributor
timestamp: October 21, 2019, 03:56:29 pm
content: It is a rather useful tool if you have a measurement range or chamber that needs to be simple and quick verified.It consist of a electrical small antenna (Hertzian dipole) as radiation pattern then can be predicted very well or the opposite, it can be placed in a location to check if expected radiation distortion pattern is same as when chamber or measurement set up was calibrated.A Hertzian dipole in an anechoic chamber can give precise and repetitive radiation pattern, but as anyone that have tried something like this, knows that whole result can be heavily distorted by the needed feeding antenna cable. It is due to cable and turntable reflections causing distortions in chamber planar wave.By hide a battery powered comb generator inside the dipole is distortions in radiation pattern due to a feeding cable avoided.If you want to buy something like this is it sold by many more well known producers of reference antennas and chamber equipment.Here a very similar antenna&CG:http://www.ets-lindgren.com/products/rf-test-sets/10000/100002It is nothing special with the antenna shape, besides that it provides a very predictable radiation field for a wide frequency range.CG frequency linearity is of less interest. It is its repeatability with minimal error sources in measurement setup that is of main interest.If searching can you find several diy versions as it is a common tool if working with EMC/EMI and antenna measurements as well as TEM measurements as these are more complicated to verify or calibrate with conventional reference antennas due to lack of space.I have built a very simple CG version consisting of a 5V 10MHz oscillator from a junk-PCB and two diodes and two transistor. All powered by a 9V battery and with power stage integrated in middle of a short dipole. It radiates well measurable levels from 10MHz to 4-5GHz.I am using it in several other ways as well. As an intentional signal source when searching for EMI related problems is one example.If problem is an metal-box that is leaking RF, causing intermittent EMI, place CG in the box and do a quick search with probe and spectrum analyzer outside of box. A wide frequency range can then quick be searched to get an initial understanding what and how thing are leaking without need to power up actual content in box and waiting for a intermittent problem to happen.If signal source had been a noise generator had it been very hard to identify its signals and signal above noise at spectrum analyzer.More info about CG:https://interferencetechnology.com/harmonic-comb-generators-are-useful-tools/

author: coppercone2
author_rank: Super Contributor
timestamp: October 22, 2019, 02:57:16 am
content: what chips do you think they are using for the fiber transmitter? Is the signal being digitized (i.e. optical USB) or is it a analog laser signal? (hard to imagine making it stable inside of a sphere with peltiers running on AAA's), I assume its digitized..I imagined a high power one powered by a fiber laser too.

author: E Kafeman
author_rank: Regular Contributor
timestamp: October 22, 2019, 08:09:04 am
content: There is no fiber needed at all for this unit. No peltier element either? Ad shows that it is controllable over fiber but there is no good reason for it and no technical data. Adjusting power level at distance,,,maybe, but not likely and there is no need for frequency settings. So what remains to control?Control unit shows something that looks like a voltage control (it is an electrical antenna, no/low current) and two indicator lamps, one for battery voltage and the other is a power indicator. A bit exclusive if reason to use optical fiber mainly is to check if battery level is ok.There is also what looks like a RF pass through for a coaxial connection which not is used as no coaxial cable is intended to be connected to antenna.I think control unit is marketing bull to motivate antenna price tag. It was once sold for $4k without any control unit. It is a bit expensive for something that is very simple to build just as good for a few bucks.Needed amount of emitted power is very low so it is absolutely no need for external power supply. Ad says 8 hours for one battery charge and I am in similar range for my 9V battery.As it is a comb generator, even if signal is extremely weak is it easy to locate its spikes even low below other noise sources as I know where it can be found on each 10MHz multiple and in worst case can some averaging sweeps at SA be done at a narrow bandwidth to digg down at -150dBm. It is in that way much simpler to locate and measure these spikes among other signals compared to a wide band noise generator.Fiber interface is a simple serial port and with no need for long distance transmission (data says 15 meter) why a multimode plastic fiber is good enough. Can be a laser for TX but guess it is a red diode. A such optical interface can be built for less then $10 in low volume. It is basically similar hardware as what you find as optical audio output from most PC's.

author: coppercone2
author_rank: Super Contributor
timestamp: October 22, 2019, 09:26:51 am
content: I thought it said it was also receiving over fiber, its just power NMV