Looking for Klystron alternative 12-18GHz - Page 1
Forum section: electronics / rf-microwave

author: Amper
author_rank: Frequent Contributor
timestamp: January 24, 2019, 09:20:42 pm
content: Hi,Im searching for some source of 12-18GHz RF, preferably vacuum tube or similarly robust and cheap. Modulation is not needed but the frequency should be very stable or controllable and clan. It will be attached to wave guides but if it wont have a flange i could make some coupler. Power of 250mW upwards is fine.A Klystron with wave guide output would be ideal but for some reason i cant find any used ones in this frequency range.Any suggestions for a specific type or alternative?

author: Wolfgang
author_rank: Super Contributor
timestamp: January 24, 2019, 09:55:42 pm
content: What is "cheap" ? A used YIG oscillator could be a way to go.

author: Amper
author_rank: Frequent Contributor
timestamp: January 24, 2019, 10:52:18 pm
content: Its more to the upper limit of what id be willing to spend but its still ok. Sadly the Power is usually in the order of 10db which is a bit to little for what i want to do. Or are there ones with internal amp to lets say 25dbm? Im not an RF guy, i just have a bunch of Ku Band piping laying around and no way to use it. Maybe in the farer future i want to feed a josephson junction with it so im interested in something that i can stabilize using a microwave counter.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 12:31:37 am
content: Not that I know. YIG output is normally just a few dBm. But broadband amps for 25dBm should not be too expensive either.Homebrewing stuff like this is tricky because you would need special RF substrates, milled housings, ...Its not that it cannot be done, but is more mechanics than anything else.

author: daqq
author_rank: Super Contributor
timestamp: January 25, 2019, 10:44:13 am
content: 12-18GHz @ 250mW direct output is a pretty hard. Expect whatever you get to be fairly expensive.As was suggested, some frequency source and a broadband amplifier would probably work better for you.For a 'simple' and cheap way to get the frequency, take a look at this:https://www.st.com/en/wireless-transceivers-mcus-and-modules/stuw81300.htmlhttps://www.analog.com/en/products/adf4371.htmlThere are other 'simple' sources as well :-)As to the amplifier, don't know about that one.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 10:53:39 am
content: ... just found some Mini Circuits part, but not for free:https://ww2.minicircuits.com/pdfs/ZVA-183G+.pdf

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 11:40:13 am
content: Well, The amp is more than 2k$, that arount 20 times as much as i want to spendThats the reason why im looking for vacuum tubes. There are plenty of clystrons delivering powers and frequencies close to what i need, sadly not in the 12-18GHz Ku band fitting my plumbing.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 11:43:12 am
content: What you could try is a used TWT unit.

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 02:56:41 pm
content: I found a few ones labeled as broken on ebay, one for 220€ plus 90€ shipping. If i can fix it and add a yig i could have 10W. Im unsure though if im really willing to spend that much yet...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 25, 2019, 03:04:21 pm
content: YIGs are used when you need very good phasenoise performance. If you don't need that, you can always go with two cheaper, lower frequency PLLs and a mixer, or a PLL and a doubler? (I don't know what is available there in off-the-shelf form)

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 03:13:42 pm
content: yigs in the range i need are below 100€ and will make my ob significantly easier so its not really worth it getting multiple other parts and a sack of really expensive connectors + rigid i guess.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 03:19:32 pm
content: Quote from: Amper on January 25, 2019, 02:56:41 pmFixing a TWT is extremely difficult. First, you can hardly fix a vacuum tube by yourself, and a TWT has a multi-voltage HV supply unit where the startup timing is extremely important (no helix until magnet and anode is stable). Should the supply be broken, the tube alone is almost worthless. IMHO, you need to look for a working one.

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 03:24:50 pm
content: Also i gust noticed taht the cheaper 200$ ones are lower frequency. The only one in question would be this one:https://www.ebay.com/itm/Hughes-1177H04F000-12-4-18-GHz-AY-10W-TWT-Amplifier-3-AMP/263167314212?hash=item3d45fe8924:g:YO0AAOSwqhBZoGMm:rk:4:pf:1&frcectupt=truemy hope would be that "blows fuses" will be a defective part i the HV line like transformer, rectifier or cap but 500+ shipping solves this problem instantly.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 25, 2019, 03:26:34 pm
content: Quote from: Amper on January 24, 2019, 09:20:42 pmIf you are looking for frequency stability, I wouldn't go for a reflex klystron.Back in the day, when they were used as Studio to Transmitter links, (STL) the link receiver local oscillator (another klystron) was fitted with AFC, so it could track the substantial drift in the transmitter frequency.These AFC systems could effectively "lock" to the drifting transmitter, & follow it .On one occasion, we lost power momentarily to the studio end link, the klystron dropped in frequency, captured the competitors STL receiver, then drifted back up to around its correct frequency.Their receiver dutifully followed it most of the way up, before dropping out of lock, so we sent about half a minute of our programme out on their TV transmitter.Needless to say, we picked up the phone which was "ringing off the hook" & were roundly verbally abused by the other Station.

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 03:32:26 pm
content: Ohw, sounds like a lot of funMy original plan was to use my hp5350b for feedback, shouldnt that work if i dont want to broadcast anyways?

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 05:33:35 pm
content: I use a twt at 20w but it not cheap and i have one i need to fix god willing.

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 05:35:59 pm
content: Quote from: Wolfgang on January 25, 2019, 03:19:32 pmYou can fix them... i did one before. Problem is their all so fucking old you need to replace alot of parts and you have no idea how much life it has left.The tube usually has bias ratings.

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 05:37:34 pm
content: Quote from: Amper on January 25, 2019, 03:24:50 pmNah it will prob have blown rectifier and power heater resistors. Mine did.Not the easiest thing to fix. I had fried parts all over the place with hughes fixer uppers. I have a feeling the lab does not want to lose these things!! I even had to replace the switch. Complete zombie. They rly meant dead. Also misc parts on the pcb. I have never seen something so thuroughly fucked up other then a SA.The hp twt are all tue based but they also have problems. I had to replace open circuit hv resistors, tubes, pots, etc.Imo not even worth buying the 1w hp units unless you just wanted to play with the tube like i did for special applications which may treat it undecently.Treat all ebay twt purchases as questionable. You also wont like to keep them running based on price and lifetime!!And crikey free up a entire table if you work on this thing. No crowded benches!!! The higher frequency ones kept resetting 34401a i was measuring rails with lol. Despite being in the voltage range. Get the right equipment its not right when you see your multimeter volts mode spark!They are also quite loud the engineers did not care to make them quiet. Typically heavy mesh filters and strong fan... fingers watch outI really appreciated transistors after i delt with these things!!!

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 05:53:58 pm
content: Quote from: Wolfgang on January 25, 2019, 03:19:32 pmI did not really notice the sequencer ... are you sure this is true with the low power units? I never saw timing specs on the tube datasheet either. You sure this is not for kw+devices?I never did full reverse engineering but the supplies in the hughes seemed simple enough other then the absurd voltages and currents. I mean simple in terms of feedback or intelligence

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 06:03:04 pm
content: What I know you can even kill a small tube by applying power in the wrong sequence. Th reason is that the helix inside the tube is *not* meant to digest electron current, even at small rates. All electrons are supposed to fly to the anode, where they hit the electrode and dissipate their considerable kinetic energy as heat. If the anode is off but the helix is on, the energy of the electrons now crashing into the helix will damage the structure and make the tube unusable. When you look on a glass TWT, the helix is a fragile spiral inside the tube deposited inside on the glass wall. To make a TWT happy,- the voltage anode must be right- The magnetic field along the tube must be set (permanent magnets for smaller tubes, electromagnets for large ones)- The beamforming electrodes around the cathode voltages must be right- heater power must be OK- and, last but not least, helix voltage.Again, it can be done, with considerable effort.

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 07:42:02 pm
content: https://literature.cdn.keysight.com/litweb/pdf/00493-90001.pdf?id=1866697I don't recall anything about power sequencing other then inrush control but I will have another look. The old vacuum tube supply was just HV supplies. There was a timing relay to turn it all on after its warmed but IIRC nothing with fields.I don't think anything was done with the hughes models either.edit: I don't see any timing other then the warming current?Also, NONE of the TWT I have seen have any exposed glass. They are just metal boxes. I got seven of them.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 07:53:49 pm
content: ... the glass is *inside* the metal box, as are the magnets.

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 08:05:47 pm
content: i dunno if its hermatically sealed or if it has a glass tube, anyway do you see any reference/indicator of timing circuit? The supplies seemed simple to me. I don't know if I would breach some kind of vacuum if I cut away the metal. There might be a glass liner inside.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 08:28:26 pm
content: Read this:https://en.wikipedia.org/wiki/Traveling-wave_tubebefore cutting anything open.

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 08:34:25 pm
content: never had any intention of opening them up. They are replaceable parts as far as the manufacturers of lab amplifiers are concerned.I don't think any commercial lab amps use power sequencing though, apart from heat. As far as I can tell I can eventually maybe probe the startup behavior of the power rail of one of the hughes units at some later date.

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 08:43:32 pm
content: Depending on the type they may even contain beryllium so better not risk it if in doubt. thats one of the very few materials even im scared of

author: coppercone2
author_rank: Super Contributor
timestamp: January 25, 2019, 08:46:52 pm
content: well most of them actually want the temperature under 40C or so according to the manual because the magnets get effected. I don't know if they would need really high spot temperatures though.Yea but they are typically soldered/brazed shut completely and you would need to get stupid with a dremel to get inside one.I have one free tube that I got real cheap, I don't know the spec but its one of the earliest TWT sylvania made. Can't find spec for it. It has a little radiator Christmas tree on the top to keep it cool (I guess you can direct air flow here).

author: Amper
author_rank: Frequent Contributor
timestamp: January 25, 2019, 08:51:56 pm
content: Beryllium is not needed because of high temp but because its thermal conductivity and electrical insulation is insane, also the rf properties are really good. Next to rf transistors and resistors i even have a power OP (PA03) which inside of the metal can is built on beryllium oxide substrate.

author: OwO
author_rank: Super Contributor
timestamp: January 26, 2019, 04:10:40 am
content: If you can live with lower power I would look into using many small HBT transistors (e.g. bfp640) in a distributed amplifier configuration. The power output of each transistor is 10dBm so you would need ~10 in a chain and possible combine multiple chains to get reasonable power out. The transistors are very cheap ($0.2) so you can experiment with large arrays of them.

author: OwO
author_rank: Super Contributor
timestamp: January 26, 2019, 04:14:23 am
content: At 5.8GHz I used the technique of combining many smaller wifi PA chips. I used 4x SE5004L which cost $0.5 each and can get >6W output total, which at 5.8GHz would normally cost >$50 for the transistor alone. With some clever layout design (minimizing the distance between output of the chip and the combiner) you don't lose any noticeable power on FR4.