The four transmit filters we have are all low pass filters.
The spur Allison found is below the operating frequency, so those filters don't touch it.
When operating at 28mhz, the spur is at 45mhz - 28mhz = 17mhz
As I understand it, what's happening is the mixer at T1,T2 works as you might expect,?
with the 45mhz IF being converted to 28 mhz by a 45+28 = 73 mhz VFO from clk2.?
But a little bit of that outgoing 28 mhz energy finds its way back into the mixer.
On this second time through it mixes again with the 45mhz IF and we get 45-28 = 17mhz.? ?
There are plenty of other products like this, but this is the only strong one that's low enough
to get through the 30mhz LPF at L1,2,3,4.
This is not a fault in the way the bat54s mixers are built.
It's just the nature of diode ring mixers, and Allison has found that
she gets the same spur when using commercial mixers while?
carefully controlling impedances at all ports.
Jerry
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On Fri, Jun 22, 2018 at 07:52 pm, Ashhar Farhan wrote:
I am not sure if 28 mhz is a problem. I am travelling so I will go back and check. I switched to 4 filters to be fcc compliant from 3.5 mhz to 28 mhz.?
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