Low Cost PCB's Low Cost Components

Author Topic: do vacuum tube devices (microwave) act as parasitic frequency mixers?  (Read 235 times)

0 Members and 1 Guest are viewing this topic.

Offline CopperCone

  • Frequent Contributor
  • **
  • Posts: 343
  • Country: us
Do microwave buffer amplifiers (Traveling wave tubes) act as mixers? (i.e. unwanted signal going into them and being mixed into some other frequency).

Do they act like mixers that make more 3rd harmonic then 2nd harmonic (since they have corrosive metal (do they?) in them) but no PN junctions?

Or does some other effect take place?
 

Offline evb149

  • Super Contributor
  • ***
  • Posts: 1568
  • Country: us
I don't recall them being highly popular for such purposes.
Any amplifier like a tube or transistor is somewhat nonlinear and those nonlinearities produce mixing but I don't recall that such tubes were commonly used in such ways from anything I've read and remember.
Just the nature of the resonant and wave synchronous elements in such tubes tended to mean that they were really optimized to operate over certain bandwidths and usually not more than a couple / few octaves if not much less.
Although if you're interested in 2, 3, 4, 5th harmonic vs the fundamental I guess there are some opportunities even if the device isn't broadband elsewhere.

Crystal (PN / schottky) rectifiers were polularly used from quite early days of radio whereas things like TWTs were more confined to the later decades, 30s maybe a little, 40s & 50s & 60s big time, and less relevant thereafter as solid state and such started to matter.

I guess if you are interested in what was done with 1940s/1950s tube technology then reading through some of their books would give a good overview.  Yeah you run into some examples of multi-stage super-heterodyne radios with more than just RF and baseband but that might be less common with the twt / klystron types of tubes which after all weren't really mainly (1930s-1950s) used for communications (hence caring quite as much about multi stage mixing from baseband to RF)  at first though of course eventually they got used for tv satellites and such applications as well.



 

Offline CopperCone

  • Frequent Contributor
  • **
  • Posts: 343
  • Country: us
well, as far as power devices go they are the only approachable low budget solution for wide band power amplifiers (that tend to operate at 1 or 2 octaves)...

A solid state solution would run like, 20,000$... however with TWT you might only be buying a few minutes or hours of run time from them due to age.
 

Offline CopperCone

  • Frequent Contributor
  • **
  • Posts: 343
  • Country: us
btw, I am interested to know because I want to determine how much isolation (by isolators) is required to prevent harmonic generation for an experiment that I am conducting. I don't want 'crosstalk' between the amplifiers causing harmonic generation, as it is confusing the results of the non linear junction detector experiment.

If the device is known to be a horribly inefficient mixer, perhaps I can ease the isolation requirements (adding 80db of isolation at a high power level to a particular channel is rather pricey).
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf