homemade VTX 5.8GHz signal booster - Page 1
Forum section: electronics / rf-microwave

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 11:21:04 am
content: Hi,I have a video transmitter VTX 5.8G 32CH that operates between frequencies 5645 MHz and 5945 MHz. It has 25 mW's power output (mean signal strength). I want to build a circuit that increase the power from 25mW to 500mW, I live inside a valley surrounded by trees and mountains, and the radio signal behave awful.My question is, ¿what approach should i used to achieve the goal of clear visibility? i have two paths in front of me:1- Using a RF amplifier like SST11LP12http://www.farnell.com/datasheets/1669517.pdf2- Using a RF transistor like BFU768Fhttp://www.nxp.com/documents/data_sheet/BFU768F.pdfI have a lots of doubts about db gain, power input, power output, impedance matching... What i am sure is I'll go to 4 layer's PCB, with 50 Ohm traces for RF to match my 50 Ohm VTX otput and 50 Ohm of my Antenna input.Of course i will pay more if the chip makes easy the circuit (KISS principleI'll really appreciate all the help. Thanks a lot!!!PS: ¿Is it possible to simulate this behavior with spice software?

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2016, 11:32:23 am
content: Quote from: mayonesa on March 28, 2016, 11:21:04 amDon't forget to bribe your local law enforcement officers to overlook your transmitter's interference with other users, both in-band and in entirely different bands. Unless you know what you are doing (which you clearly don't), there's a good chance you will stomp over other people.I suggest you join your local radio amateur group and don't think of transmitting until you can answer the question "given my modulation and the IP3 of these components, what is the power spectrum of the output". And even then, you should probably measure the output before connecting it to an antenna.Alternatively, buy equipment that is specifically designed and certified/licenced for your specific requirement.

author: Psi
author_rank: Super Contributor
timestamp: March 28, 2016, 12:04:18 pm
content: Quote from: mayonesa on March 28, 2016, 11:21:04 amYou could buy the parts to make a RF amp for $35Or just buy a new 5.8Ghz 600mW transmitter for $27KISS says you should do that latter

author: energy_hunter
author_rank: Contributor
timestamp: March 28, 2016, 12:15:58 pm
content: I would recommend the RF5616 power amp at 5V for your application along with a 150um thick RF layer. This amplifier has better input and output return losses, comes prematched and the RF caps look like they are integrated on the chip already which will make it easier to use. You may be able to just use the evaluation board out of the box. KISS!http://www.rfmd.com/store/downloads/dl/file/id/27928/rf5616_data_sheet.pdfI agree with the previous poster about transmitting. You need to be careful you're not radiating harmonics and jamming some other application. It looks like harmonics are low for this part but as you increase the transmit power the harmonics will increase and you may be over the allowable limits.

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 01:40:29 pm
content: Quote from: tggzzz on March 28, 2016, 11:32:23 amYes before the brainstorming I made a research and 500 mW is allowed by law in my country. I will study more in order to answer those questionsThank you

author: LaserSteve
author_rank: Super Contributor
timestamp: March 28, 2016, 01:41:22 pm
content: DO us a favor world wide and stay clear of 5760 Mhz please. Also keep in mind that this band is often assigned to military radar and government microwave communications. AT half a watt you'll possibly get noticed, whereas at 25 mw your down in the thermal noise.When this band was assigned to licensed amateur and ISM use, the caveat was transmissions were to be low duty cycle and pulsed, as well as a power/bandwidth product that did not interfere with its main use.I'm willing to bet that your antennas are horribly designed, any one who has worked with microwaves will tell you that antenna "gain" will trump power gain any day of the week. Perhaps consider antennas better suited to your use?Steve

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 01:43:10 pm
content: Quote from: Psi on March 28, 2016, 12:04:18 pm600 mW is not allowed in my countryI will research to make an RF amp that fits the specifications and for fun too

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 01:51:35 pm
content: Quote from: energy_hunter on March 28, 2016, 12:15:58 pmReading the datasheet if my imput power is 25mW (14 dbm aprox) the output at 5805 MHz will be gain+dbm input? or allways 22 dbm (max output) Attached the imgThank you

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2016, 03:04:56 pm
content: Quote from: mayonesa on March 28, 2016, 01:40:29 pmNote that answering that question will require a very large amount of study. And even then you will have to verify by measurement. And then there are many many more questions that you will need to be able to answer.For example,is the 500mW RP, IRP or EIRP or what?what are the out-of-band specifications, on the frequencies youwillbe unknowingly be transmitting?I second the suggestion that you investigate high quality antenna installations first.You do have a calibrated spectrum analyser capable of measuring powers at >18GHz, don't you. (18GHz to catch the third harmonic)

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 03:31:46 pm
content: Quote from: tggzzz on March 28, 2016, 03:04:56 pmIt is EIRP (see document attached)http://www.minetur.gob.es/telecomunicaciones/Espectro/CNAF/notasUN2013.pdfNo... I only own and SDR donglebut i will use a lowpass filter to avoid harmonicshttp://www.mouser.com/ds/2/400/e731_multilpf_dea11-8465.pdf

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2016, 04:09:49 pm
content: Quote from: mayonesa on March 28, 2016, 03:31:46 pmAh, someone that is still thinking in terms of discrete components, and that signals stay in wires. At microwave frequencies, they don't. Even thepatternof vias to a ground plane can significantly affect a circuit's performance, as can putting a circuit in a box."It will be OK, because I'll earth the box", I hear you say. Oh, no it won't. Earth is a convenient fiction that has some use in limited situations - microwave most definitely excluded.BTW, what PCB material are you planning on using and why? How will it affect the circuit's operation?Start byunderstandingthe operation of all the circuit elements shown in this teardown:https://www.eevblog.com/forum/other-blog-specific/10ghz-microwave-link-teardown/

author: mayonesa
author_rank: Newbie
timestamp: March 28, 2016, 04:25:43 pm
content: Quote from: tggzzz on March 28, 2016, 04:09:49 pmI want to follow the rules of michael ossman for the PCBhttp://hackaday.com/2016/03/23/michael-ossmann-makes-you-an-rf-design-hero/thanks for the advice, i will watch the link at night

author: LaserSteve
author_rank: Super Contributor
timestamp: March 28, 2016, 04:40:55 pm
content: Ok, lets assume a 25 mW EIRP, and a antenna gain of 4 at the transmitter. So probably some place around -7 dB(m) of output. Which is all of 5 milliwatts, You'll need a ~2-3 dD pad attenuator between your signal source and your new amplifier to insure stability... Now you have 2.5 mW of drive into your 500 mW amplifier. Is that enough? What if its the other way around and your transmitter has a gain of 1.5 antenna and a ~ 15 mW output? How are you going to measure all this?In situation one you would see RF gain, but possibly not use the full gain of your new amplifier, while at the same time it is possibly draining your battery like crazy with quiescent current. In situation two, you may be overdriving your new amplifier and need a bigger attenuator pad. When you overdrive it, the intermodulation distortion on your video plus clipping would probably make your situation worse.This is not that simple, considering you'd need 800 or smaller size SMD resistors to make your attenuator pads..At 500 Mhz and below, you can probably handle RF the way your thinking, but at 5 Ghz, the length and width of traces matter. Small solder blobs can detune your entire system, and you need specialized low loss coaxial cable that does not grow on trees..This very difficult. You need an accurate RF power meter at 5 Ghz to do this well.. Even if it just reads relative, un-calibrated readings. At a minimum, you need a collection of RF pads, a 10 Ghz rated terminator good for 1 watt, and a diode detector to see what is going on.Here is why we keep warning you:In most nations, 5.7 Ghz is used for Government, Military, and TV station Doppler Weather Radar, the storm map on TV. If you radiate too well, and your too close to the local radar, they will come find you... This has happened many times in the US and Canada with 5.8 Ghz wifi operating on booster amplifiers near cities. It shows up as a jamming spike on the Radar display on the TV news.. That gets attention.I would encourage you to get your Amateur Radio license and learn from locals in your area about microwaves and how to play by the rules. It leads to a lifetime of fun and learning.Please find an on-line copy of the RSGB Microwave Handbook and read up on what you are doing...Here is a simple microwave detector:http://www.w1ghz.org/new/portable_powermeter.pdfNote the PCB material and thickness are very critical for its function.Here are some in-expensive patch antennas designed and verified to work at 5.8 Ghz...http://www.wa5vjb.com/products6.htmlLearn to think in dB(m) for RF work, here is a conversion chart:http://www.minicircuits.com/pages/pdfs/dg03-110.pdfYour problem is probably better solved with a dish antenna or patch antenna and low loss cable at the receive site.Steve

author: tggzzz
author_rank: Super Contributor
timestamp: March 28, 2016, 04:55:16 pm
content: Quote from: mayonesa on March 28, 2016, 04:25:43 pmSigh. If only it was that simple.I suggest you find a good technically competent lawyer.

author: orolo
author_rank: Frequent Contributor
timestamp: March 28, 2016, 04:56:45 pm
content: Hola.I think you are wrong about the legality of these 500mW at 5.8GHz. Looking up the document you linked, all I saw was: UN-130 "Dispositivos de corto alcance en 5GHz," with a limit of 25mW. I was curious enough to look around forums, and there are plenty people in our country unlawfully radiating 200, 500 and even 600mW from their drones at 5.8, 2.4 and even 1.3GHz. The rationale being "no one is being caught". This is equivalent, in our country, to going to the forest with your grandpa's uregistered shotgun to blow some cans, funny as hell... until you get caught by the Guardia Civil and get fined to hell or worse. Moreover, the 25mW limit may apply to all of Europe. Checkthis forum, where a manufacturer is quoted:European RTT&E regulations place a limit of 25mW on 5.8GHz video transmitters. The 25mW version of this compact transmitter complies with these regulations but yet retains all the great features and innovative technologies used by our higher powered versions.I'm not a lawyer, however, so I may probably be wrong.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 28, 2016, 05:10:26 pm
content: I just looked at a European weather map. You have beautiful weather today in Spain. There are many well placed, beautiful Doppler Weather Radars, as well. All 14 of them.http://www.aemet.es/en/eltiempo/observacion/radar?w=1We would have to know the characteristics of your antennas to work the Friis Equation and determine just how far you need to be away from the radar... Most likely 20-30 Kilometers for a high power system on a drone.~Perhaps move to 2.45 Ghz where no one cares, and near field propagation is better from drones because of the longer wavelength...Steve

author: hendorog
author_rank: Super Contributor
timestamp: March 29, 2016, 06:20:08 am
content: 5.8GHz at those power levels isn't illegal here, but read up on your on regulations.There are plenty of people who have flown long distances on 25mW, easily several kms. Just google 25mW FPV record and you will find something.The rest has already been said, but it might help to clarify:The secret to FPV is the antennas, not high power. Go to fpvlab.com DIY section and read up on how to build and test them.Long range means you can use a highly directional (high gain) receive antenna - which is perfectly legal. You don't need to adjust its direction much if at all. Long range FPV has its own rules and laws you need to research and abide by of course.If you just want to fly close range reliably but through foliage then 2.4GHz should be better. I've only used 5.8 so would need to ask someone who has direct experience.

author: energy_hunter
author_rank: Contributor
timestamp: March 30, 2016, 09:09:48 pm
content: Quote from: mayonesa on March 28, 2016, 01:51:35 pmThe plot you show is for displaying gain compression of the PA and you can calculate the input power to get 22dBm from the plot. Input Power (dBm)= 22dBm - Power Gain at 22dBm (~29dB) = -7dBm. Please note that at compression you will have more harmonics and worse linearity which may or may not affect you with your signal's modulation. Most WLAN amplifiers are designed to handle 10dB Peak to Average signals so if you have much less then you can use this amp at a higher output power than you can for WLAN. At +14dBm input power you may kill this part so check the datasheet for max input power levels.