Questions about simple 10GHz microwave systems - Page 1
Forum section: electronics / rf-microwave

author: Ben321
author_rank: Frequent Contributor
timestamp: February 23, 2017, 01:24:58 am
content: I'm looking to make a simple microwave communicatino link for short distances (like just withing a room, or maybe from one room to an adjacent room). From my understanding, all I need to transmit around 10GHz is a gunn diode, and that a gunn diode's operation is very simple.However, I'm not sure what the simplest method for receiving a 10GHz signal is. Is there a single-component solution like for transmitting (a reception equivalent to the gunn diode)?Also, do I need to operate a gunn diode in a tuned cavity? From what I've been reading online, most setups that involve a gunn diode transmitter, involve placing that diode in a tuned cavity. Is this absolutely esential? Will a gunn diode not oscillate if it's not placed in a cavity? If it does oscillate when it's not placed in a cavity, what frequency will it tend to oscillate at?As for how to power it, are gunn diodes polarity sensitive like other diodes? Also, would I need a current limiting resistor in series with a gunn diode like I would for an LED, to prevent too much current from flowing? What is the typical threshold voltage for a gun diode? Is it usually like 5volts or maybe 12? Or do these specs tend to vary from manufacturer to manufacturer?

author: KE5FX
author_rank: Super Contributor
timestamp: February 23, 2017, 02:21:06 am
content: Lots of good articles here:http://www.n5dux.com/ham/files/pdf/index.phpCtrl-fgunnplexeron that page and you'll find all of the most frequently-cited documents, such as the Gunnplexer Cookbook.

author: Ben321
author_rank: Frequent Contributor
timestamp: February 23, 2017, 07:08:58 am
content: Quote from: KE5FX on February 23, 2017, 02:21:06 amI just was hoping to know whether a gunn diode will operate without a tuned cavity. That is, can it operate in an omnidirectional mode? I don't nececarilly want to focus it in one direction, like a tuned antenna horn/cavity would do. Signal would be weaker that way, but it would mean not having to worry about building something like a cavity or horn which requires very precise tuning, and in my experiment, I don't need the signal to go very far (just a few feet would be quite fine). So is it possible to operate a gunn diode without a tuned cavity? Or will it simply refuse to oscillate if I do that? Or would it even possibly damage the gunn diode?

author: Delta
author_rank: Super Contributor
timestamp: February 23, 2017, 08:27:08 am
content: For Rx use an LNB and the tuner from an old analogue satellite TV receiver (aka SatCan).Modulate the Gunnplexer using a 7805 type regulator, lifting the ground ref voltage to tune and inject your signal here.This is the old school pirate radio studio-transmitter link, and astonishingly good perfermance can be had.

author: mmagin
author_rank: Frequent Contributor
timestamp: February 23, 2017, 05:15:57 pm
content: You can effectively use some dual-band single LNBs with an rtl-sdr dongle and a bias-T (to provide 12V to power it - voltage also selects the polarization) to receive down in the 10 GHz band. Just listen lower than the usual satellite IF frequency. This is not the one I've tried, but it would probably work:http://a.co/gj68qByThis is not the same item provided to US subscribers of paid satelite TV services, as I understand it.These newer LNBs are so cheap because they're vastly simpler than 20 years ago, but it's my impression that they probably perform better, if only because of better transistors. I took one apart and it was basically passives, 3 FETs, a crystal around 27 MHz, and an IC that does everything else (biasing the FETs, LO synthesizer, mixer).As far as I know you'll see a lot less 10 GHz Gunn diode modules of recent manufacture, all of the cheap radar applications (motion sensor) have moved to cheap little DRO oscillators, and the more expensive things (e.g. police speed radar) have moved to higher frequency bands.

author: retrolefty
author_rank: Super Contributor
timestamp: February 23, 2017, 07:18:34 pm
content: QuoteBoth get my vote. Getting anything working correctly at 10gHz is not child's play.

author: rfeecs
author_rank: Frequent Contributor
timestamp: February 23, 2017, 10:10:15 pm
content: Quote from: Ben321 on February 23, 2017, 01:24:58 amThe simplest receiver would be a crystal detector, so a Schottky diode detector.QuoteA gunn diode can oscillate without a resonator. It has a characteristic frequency determined by the transit time. But practical oscillators are going to have a resonator to set the frequency. It doesn't have to be a resonant cavity. It could be a transmission line resonator or dielectric puck resonator for example. But realize that at 10 GHz, any box you put something in becomes a resonant cavity of some sort.QuoteGunn diodes are designed to work in a certain polarity. You bias them with a voltage and don't need a current limiting resistor. The voltage depends on the diode.

author: RadioNerd
author_rank: Regular Contributor
timestamp: March 03, 2017, 11:45:09 pm
content: Do you plan to transmit information or data over the 10 GHz link or do you just wan to play around with a continuous wave?

author: LukeW
author_rank: Frequent Contributor
timestamp: April 25, 2017, 07:26:07 am
content: If you want something extremely cheap and nasty you could always try hacking a couple of those HB100 10GHz automatic-door motion sensor modules.

author: CJay
author_rank: Super Contributor
timestamp: April 25, 2017, 05:53:27 pm
content: Quote from: LukeW on April 25, 2017, 07:26:07 amNo personal experience but they've been discussed recently on a mailing list I subscribe to, they're meant to be rather good, plenty of knowledge out on the web with some astonishing distance contacts being made.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 25, 2017, 07:45:50 pm
content: Please see the following link:http://www.ham-radio.com/sbms/presentations/Walt_Clark/DROplexer.pdfUses world's cheapest IF radio, very nasty, but it works...Also see:https://translate.google.com/translate?sl=auto&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fhome.deds.nl%2F~knol%2FHB100%2F&edit-text=If using them at 10.5 Ghz, no license would be required in most places, provided you did not increase the field strength using an external antenna.If you retune them below 10.5 Ghz, you would need an amateur radio license for operation.SteveSteve