On 2019-04-17 08:33, John Larkin wrote:> On Wed, 17 Apr 2019 07:54:17 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2019-04-13 09:35, John Larkin wrote: >>> On Sat, 13 Apr 2019 09:01:38 -0700 (PDT), sroberts6328@gmail.com >>> wrote: >>> >>>> Jeorg is the one looking for board, I have enough Duroid for a life time of experiments. >>>> >>>> Steve >>> >>> I used to use duroid for prototypes, before I got good at Dremeling >>> FR4. You can score the duroid with an x-acto knife and then peel up >>> strips of copper. But adhesion is poor, so pads tend to lift. >>> >> >> If you do this milling out of FR-4 a lot one of the Carbide 3D routers >> could be really useful: >> >> https://carbide3d.com/shapeoko/ >> >> It would allow you to mill down very close to the top copper and >> maintain a consistently low remaining-layer thickness. > > We have two milling machines, a big old Bridgeport and a fancy n/c > Tormach. We can optionally chuck a high-speed router in either one, so > we could shave out FR4 from below. Chucking a small regular end mill > would probably be good enough. We can do that for you but it will cost > you beer. >I could bring some homebrew as well.> PCB houses have told me that they don't mind routing from below. I > wanted to reduce the capacitance and capacitive tempco of some big > layer 1 pads. FR4 pcb capacitance has a ghastly tempco, like +900 > PPM/K. > > My guys refurbed the ancient Bridgeport and the last step was to paint > it. I wanted to make it purple, but they insisted on old boring grey. >Well, at least make it Giant's orange. With logo. -- Regards, Joerg http://www.analogconsultants.com/
77GHz Radar with FR4 board?
Started by ●April 1, 2019
Reply by ●April 18, 20192019-04-18
Reply by ●April 18, 20192019-04-18
On 2019-04-17 10:21, Lasse Langwadt Christensen wrote:> onsdag den 17. april 2019 kl. 16.54.15 UTC+2 skrev Joerg: >> On 2019-04-13 09:35, John Larkin wrote: >>> On Sat, 13 Apr 2019 09:01:38 -0700 (PDT), sroberts6328@gmail.com >>> wrote: >>> >>>> Jeorg is the one looking for board, I have enough Duroid for a life time of experiments. >>>> >>>> Steve >>> >>> I used to use duroid for prototypes, before I got good at Dremeling >>> FR4. You can score the duroid with an x-acto knife and then peel up >>> strips of copper. But adhesion is poor, so pads tend to lift. >>> >> >> If you do this milling out of FR-4 a lot one of the Carbide 3D routers >> could be really useful: >> >> https://carbide3d.com/shapeoko/ >> >> It would allow you to mill down very close to the top copper and >> maintain a consistently low remaining-layer thickness. > > the shapeoko is beltdrive and a trimrouter, for small and accurate > something like https://carbide3d.com/nomad/ this is more suited >I was concerned about the belts as well but people told me it's accurate enough for such jobs. Similar to the old HP Deskjet printer which was remarkably precise. Until the belt gets old but then you can install a new one. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 18, 20192019-04-18
On Thu, 18 Apr 2019 09:25:20 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-18 08:22, John Larkin wrote: >> On Thu, 18 Apr 2019 07:58:23 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2019-04-17 08:20, John Larkin wrote: > >[...] > > >>>> FR4 would be terrible to use for a high-Q planar filter, and maybe for >>>> a narrowband antenna. >>>> >>> >>> The application would be wideband, several GHz BW, and traces less than >>> 1". Losses are ok, dispersion not so much. >> >> You can get an old 11801 and an SD24 TDR head for a grand or so. It's >> a great tool. >> > >Sure, but now that I am gradually retiring I don't want to increase the >boat anchor clutter in my lab, rather get rid of some of them. Sez >SWMBO. She has got a point there. If we ever want to move it will be a >smaller place with a LOT less yard maintenance. Ideally the yard should >consist of a rock and a cactus. One cactus. > >Also, many of the older gizmos now come in USB pods. My spectrum >analyzer plus tracking generator which can double as a network analyzer >are the size of three cigarette packs each. Plus they go to 4400GHz >while the huge HP3577 can't go past 200MHz (it is better in dynamic >range though). Recently I had a situation where my big old Dolch logic >analyzer didn't have the needed serial decode functions. Bought an >8-channel pod for a little over $10, the size of two matchboxes, does >all the decoding I could ever want, found the bug immediately. > > >> I have hundereds of TDR test photos. We'll sometimes add a couple SMAs >> and a test trace pattern to a production board, to see how we are >> doing. >> >> Here's one. >> >> https://www.dropbox.com/s/qsoqodfdrb80ln0/Z404_PCB.JPG?dl=0 >> >> https://www.dropbox.com/s/cxs5ad7vj2o1d52/Z404_traces.jpg?dl=0 >> >> https://www.dropbox.com/s/qsoqodfdrb80ln0/Z404_PCB.JPG?dl=0 >> >> https://www.dropbox.com/s/unyea2ahjruyvvf/Z404_test_bottom.JPG?dl=0 >> >> https://www.dropbox.com/s/u6yaue3bi3c6nad/Z404_TDR_From_J1.JPG?dl=0 >> >> In that case, I was curious about the behavior of a tight meander >> line, especially preshoot, so I added the test traces to a board we >> were about to order. Preshoot was small and we got all the impedances >> close on all the layers. >> > >That's impressive with such a tight meander. Normally you'd think >capacitive coupling would spoil things. > > >> I should have used edge launch connectors. There's an ugly transition >> when the coax from the scope hits the right-angle SMA on the board. >> > >Or make a slit and ease in coax straight from the side of the board. I >like to avoid connectors where I can.I lately use an SMA edge launch connector for these kinds of PCB tests. I usually get a free "solder sample" bare board to play with TDR or plane capacitances. We buy some nice SMA edge launch connectors for under $2. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 18, 20192019-04-18
On Thu, 18 Apr 2019 09:27:24 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-17 08:33, John Larkin wrote: >> On Wed, 17 Apr 2019 07:54:17 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2019-04-13 09:35, John Larkin wrote: >>>> On Sat, 13 Apr 2019 09:01:38 -0700 (PDT), sroberts6328@gmail.com >>>> wrote: >>>> >>>>> Jeorg is the one looking for board, I have enough Duroid for a life time of experiments. >>>>> >>>>> Steve >>>> >>>> I used to use duroid for prototypes, before I got good at Dremeling >>>> FR4. You can score the duroid with an x-acto knife and then peel up >>>> strips of copper. But adhesion is poor, so pads tend to lift. >>>> >>> >>> If you do this milling out of FR-4 a lot one of the Carbide 3D routers >>> could be really useful: >>> >>> https://carbide3d.com/shapeoko/ >>> >>> It would allow you to mill down very close to the top copper and >>> maintain a consistently low remaining-layer thickness. >> >> We have two milling machines, a big old Bridgeport and a fancy n/c >> Tormach. We can optionally chuck a high-speed router in either one, so >> we could shave out FR4 from below. Chucking a small regular end mill >> would probably be good enough. We can do that for you but it will cost >> you beer. >> > >I could bring some homebrew as well.That might be acceptable if it's not hoppy. I don't like hoppy.> > >> PCB houses have told me that they don't mind routing from below. I >> wanted to reduce the capacitance and capacitive tempco of some big >> layer 1 pads. FR4 pcb capacitance has a ghastly tempco, like +900 >> PPM/K. >> >> My guys refurbed the ancient Bridgeport and the last step was to paint >> it. I wanted to make it purple, but they insisted on old boring grey. >> > >Well, at least make it Giant's orange. With logo.The Giant(s) Milling Machine. We had to move it from the old building into the basement here. I was surprised that it only weighs about 1800 lbs. https://www.dropbox.com/s/7kf8v6j2hzaghyk/DSC00334.JPG?dl=0 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 18, 20192019-04-18
On 19/4/19 2:25 am, Joerg wrote:> Also, many of the older gizmos now come in USB pods. My spectrum > analyzer plus tracking generator which can double as a network analyzer > are the size of three cigarette packs each. Plus they go to 4400GHzWell now, that *is* impressive :)
Reply by ●April 18, 20192019-04-18
Joerg <news@analogconsultants.com> wrote in news:ghrhk4FsmlvU1@mid.individual.net:> On 2019-04-17 08:20, John Larkin wrote: >> On Wed, 17 Apr 2019 07:47:15 -0700, Joerg >> <news@analogconsultants.com> wrote: >> >>> On 2019-04-08 19:42, bill.sloman@ieee.org wrote: > > [...] > > >>>> Not strictly accurate. Joerg just wanted to know if he could >>>> get away with FR4 because it is absolutely the cheapest and >>>> easiest option. >>>> >>>> A more expensive laminate might well be the cheapest option - >>>> looking at the problem as a whole - but Joerg doesn't like >>>> spending any more than he absolutely has to. >>>> >>> >>> I remember the days when people said that under no circumstances >>> could phenolic be used for UHF and higher. I still have examples >>> to the contrary in the garage. In a similar way I have used low >>> cost DC cables for pulse-echo at several GHz and it works well. >>> Lossy, yes, but it's only the echoes we were after. >>> >>> What is key in most such cases isn't to achieve close to ideal >>> RF performance but one that is merely good enough in terms of >>> margins. >> >> I'm using FR4 at 40 ps edges. Just keep the traces short. >> > > The fastest I have used FR-4 for so far was at 100psec and there > it worked well. Nothing was longer than an inch though. No milling > was involved. > > It got interesting when trying to measure resolution, dispersion > and all that. Not having a 20GHz sampling scope required McGyver > style methods such as flattened paperclips on thin transmission > line. Paperclips have almost as many uses as duct tape. > > >> FR4 would be terrible to use for a high-Q planar filter, and >> maybe for a narrowband antenna. >> > > The application would be wideband, several GHz BW, and traces less > than 1". Losses are ok, dispersion not so much. >Quoted: Some circuit materials, such as FR-4 and pure PTFE, can undergo large variations in Dk with changes in temperature and they lack the consistency needed for maintaining constant impedance at millimeter- wave frequencies. Yet another reason FR4 is probably a bad choice.
Reply by ●April 18, 20192019-04-18
Joerg <news@analogconsultants.com> wrote in news:ghrhk4FsmlvU1@mid.individual.net:> The application would be wideband, several GHz BW, and traces less > than 1". Losses are ok, dispersion not so much. ><https://www.microwavejournal.com/blogs/1-rog-blog/post/27798-what- type-of-circuit-material-works-best-for-millimeter-waves>
Reply by ●April 18, 20192019-04-18
On 4/18/19 6:33 PM, Clifford Heath wrote:> On 19/4/19 2:25 am, Joerg wrote: >> Also, many of the older gizmos now come in USB pods. My spectrum >> analyzer plus tracking generator which can double as a network >> analyzer are the size of three cigarette packs each. Plus they go to >> 4400GHz > Well now, that *is* impressive :)Nah, that's 68 um wavelength. My tunnel junction stuff worked at 40 times that frequency. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 19, 20192019-04-19
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in news:1LKdncy8Z61vvyTBnZ2dnUU7-WednZ2d@supernews.com:> On 4/18/19 6:33 PM, Clifford Heath wrote: >> On 19/4/19 2:25 am, Joerg wrote: >>> Also, many of the older gizmos now come in USB pods. My spectrum >>> analyzer plus tracking generator which can double as a network >>> analyzer are the size of three cigarette packs each. Plus they >>> go to 4400GHz >> Well now, that *is* impressive :) > > Nah, that's 68 um wavelength. My tunnel junction stuff worked at > 40 times that frequency. ;) > > Cheers > > Phil Hobbs >There is some 10 bit 51GHz ADC out there. My boss's daughter is a PhD down at Purdue, and she is developing a MEMS clock for it... She gets a Q of 50,000 (=very low noise) using a mere 0.8V @ 120uA in a size of 200nm x 200nm. That's some clock!
Reply by ●April 19, 20192019-04-19
On 2019-04-18 15:33, Clifford Heath wrote:> On 19/4/19 2:25 am, Joerg wrote: >> Also, many of the older gizmos now come in USB pods. My spectrum >> analyzer plus tracking generator which can double as a network >> analyzer are the size of three cigarette packs each. Plus they go to >> 4400GHz > Well now, that *is* impressive :)It's from Signalhound, essentially a glorified SDR with a stepped pre-mixer up front. Does have it's downside such as software-only image rejection which will not work for pulsed signals. They now have a 12GHz version. -- Regards, Joerg http://www.analogconsultants.com/
