Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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My Hobby Website:
IM products from HEMT - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: IM products from HEMT Posted: Tue Oct 09,
2007 5:55 pm
Joined: Tue Sep 04, 2007 7:54
i was evaluating
performance of a HEMT device. This device has OIP3 of around 40 dBm.
I am applying tow tones so that the output tone level of each tone is
5 dBm. The third order IM level is around -65 dBm so that OIP3 is 40
dBm. But when I remove DC power from the device the the Tones at the
ouput drops to -17 dBm from +5dBm and the IM tsignals are going up to
-40dBm....Don't understand why the third order IM signals are going
up when DC power is removed from the HEMT. FYI this is a enhancement
hEMT and works on positive bias at gate.
Post subject: Posted: Wed Oct 10, 2007 2:43 pm
Joined: Mon Jun 27, 2005 2:02 pm
When you operate the device under supply voltage, you provide
the right DC operating point for the device. This DC operating point
assure that the device will work in a linear mode (Class A probably)
to avoid distortions.
If you remove the DC supply, then the
only bias is provided through the RF signals which have low voltage,
and therefore can not set a DC operating point.
without supply voltage is in an undefind condition, hence you can expect
abnormal output signals.
Posted: Mon Nov 26, 2007 5:10 am
Mon Nov 26, 2007 4:42 am
all kind of self-biaising effects will occur.