is there some bootleg way to make a rf/microwave wireless power sensor? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: October 27, 2018, 07:40:31 pm
content: So I have been interested in CMBR lately and I am wondering if there is some way with simple construction to get rid of the RF-coupling requirements for a broad-band power detector.Typically you would get a dish that focuses into a feedhorn that has a power sensor connected to it. I would imagine the proper way to do this would be to focus a dish onto the input of something like a dual ridged broad band horn antenna and connect a power sensor to the output of the horn. That means alot of expensive hardware.Is there some way to make some kind of apparatus that has a sensor directly on the focal point of the reflector to give a DC output measurement, given that the application is to measure distance sources for general power output and not frequency specific information? Some kind of little integrated module or something?

author: tggzzz
author_rank: Super Contributor
timestamp: October 27, 2018, 07:59:08 pm
content: Frequency? Power? Accuracy? Repeatability?

author: coppercone2
author_rank: Super Contributor
timestamp: October 27, 2018, 08:05:32 pm
content: high microwave/mm wave, cold night sky, not sure, not sure (really depends on cost)i think the CMBR peak is like 160Ghz but there is attenuation.As broad band as possible to make sky maps I guess

author: chris_leyson
author_rank: Super Contributor
timestamp: October 27, 2018, 09:15:03 pm
content: Cosmic backround radiation, you're talking about really really low signal levels, big dish antennas, phased arrays, cryogenically cooled amplifiers and a lot of software to filter out man made interference, short answer is NO.You would have a better chance of picking up a stronger signal in your own back yard, Jupiter for example, quite noisy at 20MHz.

author: coppercone2
author_rank: Super Contributor
timestamp: October 27, 2018, 09:55:45 pm
content: how you do get a directional antenna for 20MHz? It sounds like you need a big phased array installation for that. I don't think reflectors will be practical under like what, 2GHz?For a dish, could you half-shield a RF-Field probe (I am guessing its a tiny bi-cone inside of that ball wand?) and set it up on the focal point for instance? Discounting the noise problems. A bi-cone would be nice because they are really cheap compared to feed horns. And its light and being cheap you don't care if it gets trashed by a storm.I am guessing you need a really really narrow arc to actually pick up the back ground noise without getting a whole bunch of other radiators?I also thought maybe, with something like a tiny bicone, you can mount the diode inside of the horn so you don't have issues bringing out a signal? Not sure how it would work but maybe you could even join it through a diode to make a special antenna?There are youtube videos of electrodeposited copper cones for use with explosives but I suspect you can make an antenna the same way of very tiny size without complicated equipment (i.e. careful work on equipment suitable for wood).I suspect that you can get very precise results in soft materials, I think the electrodeposition might result in cost reduction basically because you can make your base out of soft plastic, then make a lead cast (can be very precise), then electrodeposit the copper. You can then simply melt the lead out.I think if you work from the outside in, with special electrochemical cell, you can get the smooth surface texture you want on the outside. The inside of the cones would be kinda garbled but I don't think it matters that much?Also I think you could get better results by not growing the copper in one layer, instead taking it out of the electrochemical cell and smoothing the surface frequently, so you don't get such large unevenness. For working with cones you might be able to make a custom polishing fixture for the external surface too.I believe that precise metal working equipment is basically expensive because it has a very high stiffness requirement. If you can make your initial part out of plastic I think you could use low quality equipment, so long you measure very frequently while working to get rid of error in your screws.I also think you can get very high quality molds by using ultra-fine sand (specified to a high mesh level where its almost airfloat), using sodium silicate as a binder (good for high temperatures), CO2 as a cure and also maybe vibra-compacting your mold prior to hardening.

author: German_EE
author_rank: Super Contributor
timestamp: October 28, 2018, 11:37:42 am
content: "how you do get a directional antenna for 20MHz? It sounds like you need a big phased array installation for that. I don't think reflectors will be practical under like what, 2GHz?"Sorry, but radio amateurs have had directional antennas as low as 3.5 MHz (yeah, Megahertz) for years. Here's an example of a beam antenna for the 80m amateur band that covers from 3.5 MHz to 3.8 MHzhttps://www.qsl.net/ve6wz/intro.htmJust to show you what this takes, here's one of the antenna loading coilshttps://www.qsl.net/ve6wz/ve6wzcoil.jpgWant to see something totally crazy? A ham up in Finland has built a beam antenna for the 160m band, 1.8-2 MHz, and it's rotatable!, The largest element at the back, that's the reflector.Edit: Better viewhttp://www.vk6ysf.com/Radio_Extremes_image1.jpg

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 28, 2018, 12:40:12 pm
content: Forget about passive detection, the signals you are looking for are several magnitudes below what any passive detector can measure. Like Chris said, you need big antenna's and very quiet preamps to come even close.

author: coppercone2
author_rank: Super Contributor
timestamp: October 28, 2018, 02:19:59 pm
content: Quote from: German_EE on October 28, 2018, 11:37:42 amAll that shit is fuckingmassiveby my standards.

author: German_EE
author_rank: Super Contributor
timestamp: October 28, 2018, 04:06:26 pm
content: Here's what a radio ham in Nigeria decided to build, operating frequency not known:https://dxnews.com/upload/Image/Nigeria_5N7Q_Antenna.jpgNote the size of the crane compared to the antenna, in HF work you sometimes need to 'go large'.Edit 20 dBi gain from 7 MHz to 30 MHz

author: deBug
author_rank: Contributor
timestamp: October 28, 2018, 11:20:30 pm
content: "how you do get a directional antenna for 20MHz? It sounds like you need a big phased array installation for that. I don't think reflectors will be practical under like what, 2GHz?"Yes, an array of several antennas is the way of doing it.In Ukraine they have three locations with HF arrays that they link together to do Radio Astronomy in the HF band.More info here :https://www.ukrinform.net/rubric-society/2535304-kharkiv-scientists-to-study-galaxy-with-europes-largest-radio-telescope.htmlI recently learned from a retired NASA scientist that Jupiter is an active HF transmitter and that it's signal strength is higher when it's moon Io is between Jupiter and Earth.Fascinating stuff, more info here:http://radiosky.com/rjcentral.html//Harry

author: vk6zgo
author_rank: Super Contributor
timestamp: October 29, 2018, 02:09:31 am
content: Quote from: German_EE on October 28, 2018, 04:06:26 pmHe must be that Prince who is always sending me emails!

author: coppercone2
author_rank: Super Contributor
timestamp: October 29, 2018, 02:38:28 am
content: imagine getting a Nigerian scam through ham radio from another continent.