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Post subject: module: My Reflection Sucks Posted: Tue
Mar 21, 2006 8:33 pm
Joined: Sun Aug 03, 2003 2:02 pm
NOTICE: I replicated the post of user "module" while moving it to the database on the new server. -
Posted: 21 Mar 2006 06:28 pm Post subject: My Reflection Sucks
have been a good person and tried to design my PA around my load line. Our establishment has this bad habit of
"just dropping transformers in". I would actually like to try to match my input impedance using that stuff called
math. I have calculated my loadline and designed my transformer using UT-34-50 semi rigid coax. Can someone do a
quick check on my equations? I hooked it up to my network analyzer and I get nasty reflection. I am trying to
match the input of a Polyfet SQ721 to a 50Ohm source. I am using Amawave's UT-34-50 50Ohm semi-rigid coax with a
Amidaon BN-61-2402 with an AL=150. My math is here done in Mathcad. Any feedback would be greatly appreciated.
- Kirt Blattenberger
RF Cafe Progenitor & Webmaster
Post subject: ReflectionPosted: Wed Mar 22, 2006 8:53 pm
Joined: Wed Feb 22, 2006 3:51
I guess I'm not clear on what you're doing.
A quick trip to a Smith chart,
matching 50 Ohms to 10-j65 Ohms at 88 MHz, yielded a two-inductor matching solution. One inductor of 45 nH from
the amplifier input to ground, and a 83 nH inductor from the amplifier input to the power FET gate. I'm assuming
the source is grounded.
``` 83 nH
(ignore the ` characters - PHPBB doesn't let me use spaces for ascii art - which I'm not good at
Maybe that's not what you meant. Maybe you meant something like the series 45 nH inductor, with a
shorted stub of about VF*10 inches of 50 Ohm coax in parallel (in place of the 83 nH inductor)?
Or did you
mean a 1:5 transformer, with approximately 517 nH inductor in series with the input winding?
look like I'm "getting it". What configuration is your input matching network? Are we even "on the same page"?