80GHz Radio Gigabeam WiFiber Teardown - Page 1
Forum section: electronics / general

author: voltlog
author_rank: Regular Contributor
timestamp: September 28, 2015, 07:16:20 am
content: This is me, doing a teardown of the Gigabeam Wifiber Radio which operates in the 80GHz range.I start from disassembling the die-cast enclosure of the radio, then I continue with presenting the digital section and in the end I open the box where the high frequency RF is generated.I have two of these radio's complete with antenna and one of them is broken showing an error about the "Costas loop".This is a PLL circuit used for carrier phase recovery in this type of millimeter wave radio. So the main reason for the teardown is to have a base for a repair attempt and also to take a look at some cool gear.I hope you will find this interesting:

author: lukier
author_rank: Unknown
timestamp: September 28, 2015, 08:02:44 am
content: Thanks for sharing, very informative teardownThis is some serious RF voodoGood to know you can pass RF signals through a zebra strip

author: voltlog
author_rank: Regular Contributor
timestamp: September 28, 2015, 08:05:09 am
content: I guess that's impedance controlled zebra strip

author: daqq
author_rank: Super Contributor
timestamp: September 28, 2015, 08:26:22 am
content: Thanks for the teardown!Though I think that the middle RF board does not provide the IF frequency, but rather is the local oscillator - the waveguide on its output is far too small for for 4-8 GHz.

author: voltlog
author_rank: Regular Contributor
timestamp: September 28, 2015, 09:03:49 am
content: Quote from: daqq on September 28, 2015, 08:26:22 amGood point! So it must be in the 80GHz range to travel that rather small waveguide.I just couldn't figure out how their multiplying it that high on that board (Silkscreen "P3 SYNTHESIZER")Maybe there is some multiplication happening on the small hybrid board/module right to the input of the waveguide.

author: daqq
author_rank: Super Contributor
timestamp: September 28, 2015, 09:36:41 am
content: QuoteThat is the case most likely. Intermediate frequencies for stuff like this is (as far as I know) generally in the hundreds of MHz regions.Seehttps://youtu.be/TQWKbZo6UCY?t=1419- at the bottom, the relatively low frequency enters, it exits in the really high frequency. The Rx Tx modules are likely "just" mixers and amplifiers.

author: voltlog
author_rank: Regular Contributor
timestamp: September 28, 2015, 10:45:00 am
content: I have added a video annotation, with this observation.Thanks for your insights.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 28, 2015, 02:15:51 pm
content: Hmm, looks like the LO board is ~8GHz, which should be roughly consistent with the size of the filter pattern on the PCB. The converter to ~80GHz must be on the little captive flex board on the housing.Some crazy bits of hardware in there. Can't say I'd like to pay the MSRP on that thing!Tim

author: orion242
author_rank: Unknown
timestamp: September 29, 2015, 02:05:55 am
content: Great vid, thanks for posting.Can't think what the bit of kit costs, nothing I would be ever tearing down. Subscribed and look forward to your posts.

author: voltlog
author_rank: Regular Contributor
timestamp: September 29, 2015, 06:48:19 am
content: I don't own these, I am just the repair guy, that is if I manage to find the faultI believe the MSRP on a pair of these was around 10K USD so totally worth repairing

author: TiN
author_rank: Super Contributor
timestamp: October 04, 2015, 05:54:43 am
content: Nice RF magic there, thanks for video.

author: SNGLinks
author_rank: Regular Contributor
timestamp: October 05, 2015, 09:59:33 am
content: Good video. Only thing missing is a view of the dish feed.

author: voltlog
author_rank: Regular Contributor
timestamp: October 05, 2015, 01:59:38 pm
content: Yes, I kinda skipped that one to avoid making the video too long. I didn't expect to find anything interesting in there.Thanks for the encouragement.

author: GNU_Ninja
author_rank: Regular Contributor
timestamp: October 05, 2015, 02:31:19 pm
content: Bare feet. Check.Black plastic pointer. Check.Windowless lab. Check.Looks like Dave has a competitorNice teardownI've subscribed to your YouTube channel

author: voltlog
author_rank: Regular Contributor
timestamp: October 05, 2015, 02:43:43 pm
content: Quote from: GNU_Ninja on October 05, 2015, 02:31:19 pmThanks! I am constantly trying to improve my english and the video quality.

author: AF6LJ
author_rank: Unknown
timestamp: October 05, 2015, 11:37:28 pm
content: Nice RF Goodness, Thanks.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: December 20, 2015, 06:28:19 pm
content: That was very interesting. Good video work and your English is fine.I think the part you have labelled as a combiner may actually be a duplexer.

author: 1design
author_rank: Regular Contributor
timestamp: December 23, 2015, 08:02:54 pm
content: From the size of the wave guides and topology of the mmW section it might be a sub-harmonic mixer design with the x4 multiplier in the end section of the synthesizer. Old designs used to have a 5GHz IF so they could cover both 71 to 76 and 81 to 86 GHz with the same design just changing the side band they use. This means that the LO would be in the range of 38 and 40.5 GHz. If we divide this by 4 the Synthesizer frequency should be between 8.xx and 10.xx GHz which seems to fit the amplifier range. If they want to fine tune the TX to RX they can do it in the IF section. Most newer designs use a heterodyne or direct conversion architecture. I might be work, just an assumption form what I could catch from the video. The only part that baffles me is the mmW coupler at the RX side. it splits the signal into two branches and thus increasing the noise figure. Any clue why they would decide for such a solution?BR.

author: AF6LJ
author_rank: Unknown
timestamp: December 23, 2015, 08:21:55 pm
content: Quote from: 1design on December 23, 2015, 08:02:54 pmThe only thing I could think of falls in ether of two possibilities.1. two mixers quadrature LO fed to both producing an output that is only the sum or difference frequency, not both.2. That splitter looked more to me like a rat race. (circulator) which would provide protection for the receiver.The view of that section isn't all that good unfortunately.

author: 1design
author_rank: Regular Contributor
timestamp: December 23, 2015, 09:34:19 pm
content: I don't see nay mixer at the input, only 2 LNAs. It would make sense to be a hybrid coupler as they have a hybrid also at the exit of the LNAs. This would suggest the IP3 was too low and they needed to back off the power? It still doesn't make sense why to use this method at the receiver, again you loose on the noise figure. It might be possible that this is a universal board and each of the units cover one band as they are older parts?After taking a better look I noticed all three ICs are the same type of LNA/VGA. This means they are all wide-band and there must be a reason why they decided to use that configuration at the input and it isn't the IP3 as this would affect the second stage even more.I checked the RX IF, it seems to be around 10GHz, so my frequency plan goes out the window. It seems like the TX is directly upconverted and the RX has a heterodyne architecture with the IF being at 10 GHz and all the VGAs are there. The mmW parts are all fixed gain LNA ICs. This also makes sense.

author: voltlog
author_rank: Regular Contributor
timestamp: December 26, 2015, 07:07:42 pm
content: It's nice to read your theories on the architecture that might be used in the microwave section. Myself I know nothing about this stuff and in the end I wasn't able to fix the broken radio. I couldn't find anything wrong in the power section, the cpu/digital section seems to work fine as the OS fully boots and responds to commands but it was showing an error about the "Costas loop".

author: daqq
author_rank: Super Contributor
timestamp: December 26, 2015, 09:48:31 pm
content: Please post the whole message/screenshot, might be interesting.

author: voltlog
author_rank: Regular Contributor
timestamp: December 27, 2015, 11:09:47 am
content: I don't have the radio anymore to get a screenshot from the GUI but it was just an alarm flag "Costas Loop Lock Alarm Flag". Also the RSSI value, shown in the GUI was all over the place for this radio(oscillating), while for the second one it was staying at a constant level.

author: 1design
author_rank: Regular Contributor
timestamp: December 27, 2015, 08:52:36 pm
content: This could mean that something was wrong with one of the ICs in the RX path. Have you checked the spectrum on the receive chain, or the bias/VGA voltages of the chain?BR

author: voltlog
author_rank: Regular Contributor
timestamp: December 27, 2015, 09:43:47 pm
content: I checked every voltage rail that I could find and they were all ok. No signal measurements though since I don't have a spectrum analyzer. That's why I kind off gave up on the repair, I was lacking an important tool and this was a rather complicated radio to start with..

author: Lord of nothing
author_rank: Super Contributor
timestamp: June 12, 2016, 01:24:29 pm
content: Are that hight Freq. not Dangerous for us?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 12, 2016, 03:45:23 pm
content: Quote from: Lord of nothing on June 12, 2016, 01:24:29 pmEM is literally of no danger unless it's intense enough to literally cook you (which you feel, very quickly), or if it causes ionizing damage. This is true from ~MHz (where the voltage drop across flesh becomes enough to dissipate some thermal power), all the way up to blue light. Above blue (UV, x-ray, gamma), ionizing reactions begin.So, this thing is at least 1000 times too low frequency to cause problems.Tim