Re: stripline tuning discs?


Chris Ruddy MM0KOS
 

Hi Paul

can you send me your email address for info on how to get precut
discs

Thanks MM0KOS

mm0kos at yahoo dit co dit uk


--- In ukmicrowaves@yahoogroups.com, Chris Bartram <yahoo@...> wrote:

Paul

As for actually tuning the stripline from the Imfets, I guess
the idea
locations are right at the output of the device to the track, or
at
the track positions where the bias DC lines are connected. This
particular PA has a pair of fets in parallel - is there anything
I
need to watch out for when tuning these, like the phasing of the
outputs etc? Or can I tune for maximum RF out and be happy with
that?

The location of the 'snowflakes' can, in principle, be anywhere on
the output
line, and while you are playing they will need to be able to move
over a half
(guided) wavelength along the line.

I suggest you revisit 'impedance matching with stub tuners' in the
Microwave
Handbook before you start playing...

Tuning a PA empirically is always a bit fraught!

You _will_ need to go around a loop. With modern devices, the
impedances are
likely to be reasonably similar from device to device,
particularly within
the design bandwidth. Are you using IMFETs which actually cover
the band? If
you are, you are unlikely to get more than a remarkably few
tenths of a dB
extra output by snowflaking for matching, and you should
concentrate on
getting the phase relationship right.

Were I building a two (or more) amplifier PA at 10GHz, I'd build
two separate
amplifiers, and use external hybrids with an SMA phase adjuster in
one of the
input legs to get the phase right.

If your amplifier uses IMFETs operating outside of their design
band, then I'd
optimise each amplifier individually for best performance wrt
matching, power
output and gain, while trying to keep the matching topology
similar in each
case. Only when you are happy with that should you try to combine
them.

If you do that, you'll save yourself much confused twiddling, and
probably the
cost of several damaged devices!!

I know about these things, and I have a remarkable collection of
undersized
tee-shirts to prove it! I've been there both in a work context,
and in my own
station where I use reasonably 'serious' four-amplifier PAs on
both 144 and
432 (and sometime, when I get time, will have QRO on 1296 by the
same route).

Vy 73

Chris
GW4DGU

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