Favorite parts for home RF construction projects? - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: December 15, 2018, 04:58:02 am
content: I want to stock up on some cheap parts for projects. What are your favorite parts, particularly capacitors, such s trimmers, and RF capacitors, not for high power, just with good characteristics. For trimmers, good would be able to fit on a PCB trace, having some easy means of changing the value, (screw slot is okay) high Q, relatively high capacitance/size ratio, modern, wont drift in value, tabs in a straight line and low profile. Also what is a brand of cheap but decent ceramic caps that are good for RF?Also, are any of the cheap Chinese RF inductors good, with a high self resonant frequency and Q for their inductance? I'd like to buy a bunch of miscellaneous SMD-ready RF parts for cheap on LCSC to have around and try them out but I have no idea what brands might be good.Also cheap SMD baluns/transformers? (better than the ones I can make myself)

author: cncjerry
author_rank: Unknown
timestamp: December 15, 2018, 05:31:30 am
content: Stock up on variable caps and toroids. Start by building a VFO or two. Go to a surplus electronics store and grab some trimmers, silver mica caps, slug-tuned inductors and build a few tunable filters. Grab a TUF-3 or SBL-1 and make a down converter to take RF down to audio. Buy a tube of SA612 mixers and you can make a slew of DC radios. Find a tunable RF design, better yet, build Bob Heil's Pine Board radio. That looks like fun. If you want something more advanced, build an N2PK VNA, I have 2 of them. -130dB noise floor, good to 60Mhz. Actually if you build this early you'll have an HF RF generator as well. Scour eBay for DDS boards, filter boards, Power meters, cheap VNA's, frequency counters, etc. When you get aggressive, build Scotty's Spectrum Analyzer and the VNA modules that go with it. By the time you get to this sentence, you will be an expert on RF.Jerry

author: coppercone2
author_rank: Super Contributor
timestamp: December 15, 2018, 05:45:34 am
content: your wallet on RF

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 15, 2018, 07:51:42 am
content: BFR92 -- reasonably high fT. Has a complement,for the time being -- purchase a reel now, while you still can!https://www.digikey.com/product-detail/en/nxp-usa-inc/BFT92W115/568-1656-1-ND/763483Possibly the last fast PNP in existence, get it while you can.Everything SMT is fine: chip caps, chip resistors, chip inductors... Get a kit of small value L and C, whatever favorite size you like (0603 to 1206, or 1210 or even 1812 for the larger values, or of course inductors just go up from there, or get into odd shapes like spring inductors do). I'm partial to Coilcraft inductor kits, but anything that specs well is fine of course.Trimmer caps from mainstream distys are basicallygone. You'll have to pick them up (of questionable quality) from China; for mere pennies, at least.Tim

author: Odysseus
author_rank: Regular Contributor
timestamp: December 15, 2018, 09:22:41 am
content: Mouser carries a range Fair-Rite toroids of type 43 (high Mu for transformers, baluns, chokes) and type 61/67 (low mu and low loss for stable, high Q inductors) material. I am particularly fond of the smallest sizes available in the type 43 material (P/N 5943000801 and 5943000101). They are pennies a piece, Qty 100 for only 2-3$, and are perfect for compact, low power RF applications. Size 32 AWG wire works well. Get a pair of hemostats to hold the cores while winding.I like these solid-ground surface-mount protoboards:http://www.busboard.com/surfacemountpcbsI particularly like the 1/32" thin ones for easy scoring/cutting. A line of the 50 mil squares soldered together makes a decent 50 ohm transmission line.I like the PE4140 for making double balanced mixers. I've used them for broadband HF/VHF stuff.

author: CJay
author_rank: Super Contributor
timestamp: December 15, 2018, 10:21:19 am
content: Quote from: Odysseus on December 15, 2018, 09:22:41 amUseful part, but have you had problems with static damage?

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2018, 11:32:12 am
content: Vishay trimmers. Lots of the things. Only ones that are temperature stable I have found.Vishay C0G mono-kap capacitors. And some of their 10nF X7R ones for coupling/decoupling.Amidon toroids. I keep a lot of FT37-43 (coupling/impedance/chokes), T50-2 (LPF/tuned parts), T37-6 (LPF/tuned parts) and some ferrite beads (kill oscillation) in stock and that’s about it.Semiconductors. I am mostly HF so I don’t have a massive requirement for decent transistors. Usually have 2n3904 (GP + RF, not terrible noise figure), 2n3819 (VFO cheap and cheerful), BD139 (driver), BD140 (key/switching), 2n3906 (low current switching, IRF510 (cheap PA - can easily get 20W out at 14MHz with 24v supply for literally no money and quite difficult to blow up). 2n4401/2n4403 for small audio push pull amps.DBMs I make mysellf. I tried a mini circuits SBL-1 in a receiver I built and swapped it out for one with 4x matched 1n4148’s and a couple of FT37-43s and couldn’t tell or measure the difference at 7Mhz.One thing I get through pretty heavily is single sided PCB stock. I ended up buying 50 pieces of 160x100 FR4 from rapid here in the U.K.Edit: I mostly don’t bother with SMD parts for RF things at least at prototype phase and not a lot of stuff gets past that phase or is worth making a PCB for.

author: cdev
author_rank: Super Contributor
timestamp: December 15, 2018, 03:12:09 pm
content: Thank you, these are all great tips. You guys know which ones are the keepers and which are not. The great thing about some of these parts is their universal versatility.Recently I got a deal on ebay for an experimenters kit of small fair-rite balun cores and ferrite beads in a bunch of small odd sizes. This has been really a great find. The very small #61 balun cores work well was up into uhf.I wish my hands were smaller for working with these tiny cores and tiny wires. But it is possible to do it. I've got the makings of many small baluns - and materials that I would not have ordinarily bought so I can experiment with different kinds.My mother when she died left me some tools, and some of them are nicer than my previous ones, quite old, for example, several small pliers left me by my mother are ideal for making small air wound coils, such as sharply conical inductors, so now I would like to try that idea out to see if I can make a conical very fine coil good enough for a truly broadband LNA, at least better than I was able to in the past. I was never able to get the shape quite right.And filters. I am going to dedicate another one of my RTLSDRs to direct sampling and see if I can mount a small DIP socket on there (this will be a real challenge!) so I can swap out the input transformer to try out different magnetics and turns ratios. I will probably try to using preheating/hot air and/or chip quik remove all the SMD parts on the tuner side of a dongle (all the tuner-related parts) so I can use that space as a solid anchor for the socket and the antenna input for HF.That should keep me busy for a while. I hope to use this newly HF and hopefully also LF enabled dongle to track down some particularly hard to locate RFI that I have .Thank you for these parts suggestions!

author: cdev
author_rank: Super Contributor
timestamp: December 15, 2018, 03:30:56 pm
content: Quote from: Odysseus on December 15, 2018, 09:22:41 amKitsandparts.com has deals on small toroids in all sizes. I dont know how they compare to the big companies but they seem like the best prices Ive seen.These simple square pad prototype boards also look like a good thing to buy some of. I have some similar old glass epoxy board, quite old in my collection and I have been using chunks of it for all sorts of stuff, including small anchors and transmission lines as you suggest, but I am almost out of it. So this is a great find. A small piece goes a long way. I've been looking for it.Quote

author: cdev
author_rank: Super Contributor
timestamp: December 15, 2018, 03:38:06 pm
content: I like the small purplish colored color coded cube coilcraft inductors, (they really do seem to be the best ones out there) but the experimenters kits are too pricey for me now and I rarely am sure what value I am going to need in the end so I end up often trying to 'roll my own' quite literally.Quote from: T3sl4co1l on December 15, 2018, 07:51:42 amQuote from: T3sl4co1l on December 15, 2018, 07:51:42 amI'd really like to know which of those cheap brands are decent for trimmers. Super cheap would mean I could buy a bunch just to have available. For RF a trimmer is super useful for determining the optimal value.

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2018, 03:42:43 pm
content: Don't try and build anything particularly frequency sensitive like VFOs on any double sided boards however like those SMD boards. The floating pads and ground plane are a rather crappy and unstable low pF capacitor. Been thereI did an extreme demonstration of this here:https://youtu.be/LCUXSaoqUmw

author: chris_leyson
author_rank: Super Contributor
timestamp: December 15, 2018, 03:59:15 pm
content: @Tim, thanks for the heads up on the BFT92. Wow that is scary, I haven't done any real RF design for 20 years but I've used a few BFT92s in some designs. Maybe 30 years ago BFR91 and BFR96 were the parts to use in low power VHF and UHF applications but their getting hard to find. I've got a sick Adret sig gen that needs some BFR96's to fix an active mixer but the whole is full of unobtanium transistors. I can still find NOS BFR91's but not 96's. Would be a shame to scrap a nice sig gen just for the sake of a few transistors.Small twin hole beads are useful for home brewed DBMs and matching transformers and MiniCircuits do them ready wound. Vishay film trimmer caps while you can still get them. Slug tuned coil formers are as rare as hens teeth these days as are helical filters although I found Chinese company still making helical filters.

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2018, 04:14:21 pm
content: I'd kill for a 170MHz-ish very narrow helical filter at the moment - any ideas if that Chinese company sell them?

author: chris_leyson
author_rank: Super Contributor
timestamp: December 15, 2018, 05:59:09 pm
content: @BD139 Sorry I didn't save the link which is somewhat less than helpful. However I found thishttps://www.ebay.co.uk/itm/5-PCS-ELECTROMECHANICAL-FILTER-HELICAL-FILTER-159MHZ-272MT-1007A-272MT1007/273587955497?epid=1418422225&hash=item3fb31ce729:g:qaMAAOSwhnlcAcjt:rk:29:pf:0and thishttp://www.jabdog.com/filters.htmThe insertion loss is quite high on the TOKO CBT 272MT-1007A, 8dB but it is 170MHz and 1MHz BW according to TOKO catalogue. JAB Electronic components is Peter G7JAB, winner winner chicken dinner, lots of lovely RF parts. BookmarkedAnd then there is Temwell who have a webshophttp://www.temwell.com.tw/

author: bd139
author_rank: Super Contributor
timestamp: December 15, 2018, 06:25:27 pm
content: Many thanks for that - much appreciated! May kick a stalled project along a bit that

author: OZ1LQB
author_rank: Regular Contributor
timestamp: December 15, 2018, 06:48:43 pm
content: Chris you can have some brf96s for the repair for free from meOZ1LQB

author: Odysseus
author_rank: Regular Contributor
timestamp: December 16, 2018, 08:55:30 am
content: Quote from: CJay on December 15, 2018, 10:21:19 amI've only assembled a handful, with no casualties so far. That said, I'm sure it's actually quite easy to blow through the gate oxide.I have also tried out one of the surface mount diode arrays that are packaged in a ring configuration. Looks like it was the BAT15-099R. No complaints there, either.

author: radioactive
author_rank: Regular Contributor
timestamp: December 20, 2018, 01:26:12 am
content: Re: PE4140Good to know on that part. I have one in a design that I haven't built yet. I have used their UltraCMOS PE42424 switches in several products. Thousands out the door with no issues yet. Amazing power handling for how small they are. Not the most fun part to solder by hand, but seems to be no issues in manufacturing.