Post subject: Mixer IM3 Problem Posted: Tue Jul
19, 2005 8:06 pm
I´m trying to build a converter
to get my IF signal (143MHz) and convert into TV channels (Yes,
Full Agile). The trouble is the following: When i´m working in I
band and III band, the IM products are about -65dBc but at UHF channels
the IM is < -70dBC. I´d like to know if it (this level of IM)
is normal because i´m new at RF design. below follows the detailed
information about test setup.
Mixer: SYM-25DMHW from MINI-CIRCUITS:
IP3 +26dbm , +9dbm 1dB point
nput Signal: 145,26MHz and 140,76MHz
(-10dBm each tone at mixer input)
LO Signal: +13 dBm (at mixer
All mixer ports have pads to keep de system matched
(LO:-3dB, RF:-3dB, IF:-10dB)
Thanks and sorry about my english!!
Post subject: Posted: Wed Jul 20, 2005
Joined: Mon Jun 27, 2005 2:02
looks OK. You should look at the standard definitions and find out
what is the required IM3 products per your standard.
way, have you checked that the actual power level at the Mixer's
LO port is +13dBm (after the pad)?
If the power level is
lower than it can hurt the linearity of the mixer.
subject: Mixer IM3 ProblemPosted: Wed Jul 20, 2005 6:08 pm
I plugged your numbers (-10 dBm input tone power, -65
dBc IM tone) into the equation for Input Ip3 and I get IIP3 = +22.5
dBm. This assumes a conversion loss of 6.5 dB.
probably increase the input signal power by 6 dB without causing
any noticeable inband distortion for your analog signal. Your power
amplifier will probably create much more distortion than the mixer.
By the way, this mixer has an amazing IIP3 level for +13 dBm
LO drive. Go for it!