50 ohm attenuator "sleeve" for home made inline attenuator? - Page 1
Forum section: electronics / projects

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 23, 2015, 02:53:28 am
content: So I wanted to make some home made attenuators. I can buy them for 10$ each, but I have the BNC male/female connectors, center pin and good quality film resistors (I can even use SMD resistors and solder thick leads to them).I am however missing the sleeve that is shown. Can it be bought (50 ohms impedance) so I can make some home made inline attenuators? I can't find anything on google or ebay.

author: babysitter
author_rank: Frequent Contributor
timestamp: April 23, 2015, 04:43:32 am
content: Not an exact match, but viable option depending on what you want to go for (germany)http://www.box73.de/product_info.php?products_id=1403Just a tin box:http://www.schubert-gehaeuse.de/prod01.htm(German, see "Filtergehäuse")

author: Dago
author_rank: Frequent Contributor
timestamp: April 23, 2015, 04:57:05 am
content: http://www.digikey.com/product-search/en?WT.z_cid=sp_744_0310_buynow&site=us&lang=en&mpart=SMA-KIT-1.5MF

author: ChristofferB
author_rank: Frequent Contributor
timestamp: April 23, 2015, 06:03:56 am
content: At what frequencies should they be usable? - you could maybe press fit (read: hammer) a lenght of copper tube onto the male connector, then thread the other end?--Christoffer

author: TimFox
author_rank: Super Contributor
timestamp: April 23, 2015, 04:56:52 pm
content: You probably want a "box" instead of a "sleeve", since a proper 50 ohm to 50 ohm attenuator requires three resistors (delta or tee connection).

author: edpalmer42
author_rank: Super Contributor
timestamp: April 23, 2015, 06:09:25 pm
content: Is that picture from an HP document? I know that HP produced that as a unit ( I have some ) but I don't know what their part number was. I remember seeing it in an older HP manual. It was intended for making little custom circuits - just like you want to do.They do show up occasionally on ebay.Ed

author: German_EE
author_rank: Super Contributor
timestamp: April 23, 2015, 06:30:58 pm
content: I made disks out of PCB material to fit the end plugs and used 15mm copper pipe for the tube. The result (using lumped lines and SMT resistors) is good to 500 MHz.

author: tggzzz
author_rank: Super Contributor
timestamp: April 23, 2015, 10:09:46 pm
content: Do you actuallyneeda sleeve. In some circumstances an edge (or end) launch connector soldered onto a very small circuit board is sufficient.For 50ohms, just make the track ~2.5mm wide on 1.6mm thick FR4 board, as perhttp://chemandy.com/calculators/coplanar-waveguide-with-ground-calculator.htmAlternatively brass, copper and aluminium tubes are widely available in a range of diameters, for examplehttp://www.technobotsonline.com/materials/model-engineering-materials/round-tubing.html

author: Howardlong
author_rank: Super Contributor
timestamp: April 23, 2015, 11:19:04 pm
content: Right angle BNC plugs for soldered inner cable connections usually have access holes for soldering the inner, they're often a screwed on slug. When you remove the slug to terminate your 50 ohm cable you can get in there and attach a 49.9 ohm SMD resistor, or better still four 200 ohm SMD resistors.Just a suggestion, if you happen to come across these connectors at a reasonable price. I have a few cables I made up like this, they behave better than the commercial inline versions I have. Just take care with the power dissipation.

author: SArepairman
author_rank: Frequent Contributor
timestamp: April 24, 2015, 04:40:43 am
content: Quote from: edpalmer42 on April 23, 2015, 06:09:25 pmyea i had like 300 tabs open though i forgot where i saw it lol

author: hagster
author_rank: Frequent Contributor
timestamp: April 24, 2015, 04:53:26 am
content: As TimFox says you need 3 resistors if you want it to be 50ohm .

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2015, 06:46:38 am
content: Quote from: hagster on April 24, 2015, 04:53:26 amYes, but you can get them in a single package, e.g.http://www.ims-resistors.com/A-series.pdforhttp://www.susumu-usa.com/pdf/products_38.pdf

author: ketil b
author_rank: Regular Contributor
timestamp: April 24, 2015, 11:25:44 am
content: I have found (i think that i may have seen it on the forum somewhere)that thiswill, with a bit of gentle help, will screw intothisthanksketil

author: Howardlong
author_rank: Super Contributor
timestamp: April 24, 2015, 12:20:26 pm
content: Sorry I misread the OP earlier.I have pretty much standardised on SMA for making networks because you can pick up the connectors so cheaply and fabricate the network on a bit of FR4, or, if it's HF or below, on small bits of stripboard.I buy the connectors from a guy I found on ebay a few years ago, but I do use them for production so I buy in the thousands, they come in at about $0.25 each that way. While they're not going to win any prizes at 18GHz, they are fine at 2.5GHz and below, at least according to my old 8753A at any rate.While I realise this doesn't answer your sleeve question directly, hopefully this is food for thought.

author: TimFox
author_rank: Super Contributor
timestamp: April 24, 2015, 12:43:20 pm
content: If you want to make your own sleeve from a suitable hollow cylinder, the thread on normal BNC connectors is 3/8-32 UNEF, and can be found at mechanical or machinist supply houses: the recommended tap drill is 11/32".http://www.mcmaster.com/#2521a419/=ww2qtc

author: robrenz
author_rank: Super Contributor
timestamp: April 24, 2015, 01:23:39 pm
content: Link to the ones you use please

author: Howardlong
author_rank: Super Contributor
timestamp: April 24, 2015, 02:31:12 pm
content: Quote from: robrenz on April 24, 2015, 01:23:39 pmNot sure of you're referring to my SMAs or something else but this is the guy I use for all my SMA connectorshttp://www.ebay.co.uk/itm/10-SMA-female-PCB-Edge-Mount-RF-Solder-Adapter-0-062-/160518940049?pt=LH_DefaultDomain_0&hash=item255faca591Although not advertised as far as I can see, he does male edge mount as well as the advertised female edge mount, and, in volume, he does a good deal, send him a message via ebay. As I say, I buy them a couple of thousand at a time so I get a reasonable deal. i would imagine if you buy a hundred or so he'll make it worthwhile.Edit: here are the SMA male edge connectors he sellshttp://www.ebay.co.uk/itm/5-SMA-male-PCB-Edge-Mount-Solder-0-062-Connector-/160651476311?pt=LH_DefaultDomain_0&hash=item256792fd57I'm pretty sure he had them made for me at first, because he had to get back to me a few days later to quote me.50pcs SMA female $25 herehttp://www.ebay.co.uk/itm/50pcs-SMA-female-jack-PCB-Edge-Mount-Solder-0-062-Adapter-Connector-/160965031166?pt=LH_DefaultDomain_0&hash=item257a4374feWhen I receive them by the thousand, I count them by weighing them.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 29, 2015, 03:35:38 am
content: Quote from: Howardlong on April 24, 2015, 12:20:26 pmNice collection. I've built a lot of quick assemblies like this as well without any problems in the 1GHz'ish range.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 29, 2015, 06:44:32 am
content: Are there any respectable and cheap prefab SMA cables available? The only reason I'm still using BNC is I got a pile of them off eBay a year ago. They're cumbersome otherwise.

author: KJDS
author_rank: Super Contributor
timestamp: April 29, 2015, 06:52:10 am
content: SMA cables are readily available in many forms. If you want perfection for your 20GHz VNA then Gore will sell you a pair for about £2000.Realistically if you're regularly connecting and disconnecting in a test environment then Suhner, Gore and many others can provide decent cables with a reasonable compromise between flexibility and durability for about £100 each new. In a production environment they always break the outer just behind the connector after a year or two of continual use which can lead to odd results until you work out it's the cable causing the problem.There are plenty more options where continual connecting and disconnecting are not required, such as semi-rigid, semi-flexible and coated semi-flexible. I'll bring a pile of the latter down to the DDRC rally for your perusal.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 29, 2015, 07:03:35 am
content: Thank youI'm not a heavy user by any means but would appreciate the space gain and RA connectors more than anything. I'm working 40m here for the moment and eventually 20m + VHF when I find a cheap scope (stuck at 50MHz at moment)

author: Howardlong
author_rank: Super Contributor
timestamp: April 29, 2015, 09:12:49 am
content: BNC are mostly handy because of their quarter turn. Having to repetitively screw on and off SMA connectors is painful in terms of both time and finger tips health, assuming you don't use an SMA torque spanner for ad hoc connections that isTypically on a single production test run I go up to 1,000 cycles in one go, it's not very exciting work, but doing that level with conventional SMA will give you hand cramp and sore fingers. Doing it with a torque wrench will take you a very long time!Testparts.com do both push fit and ~half turn inline SMA test adapters. I use the approx half turn ones extensively in test jigs, I can tell you from experience they're good for around 6,000 cycles. I use the half turn ones rather than push fit in case the SMA female on the DUT I'm mating it with has a mechanical thread problem, so I am testing both mechanically and electrically. An added benefit is that these act a sacrificial cable savers as you're not cycling the connector on the cable itself. The failure mode is that the centre pin slowly gets thinner due to the abrasive effect of repetitive insertion, and finally it's too thin to make reliable connection to the female inner.