Help with fixing cross talk and some other issues on my board

[psyon]

I would change the IF low pass filter to a diplexer to properly terminate the IF port at LO frequency into 50ohm and avoid LO-IF leakage reflection going back into the mixer and degrading its performance.

I don't think a Bridge Tee will work for what I am doing, so assuming I am understanding things correctly, I just add a high pass filter and terminate to a 50Ohm resistor as shown in my image?

[eb4fbz]

The RF filter design does not look realistic to me. It looks like you assumed the lumped components behave ideally at RF, but they don’t, specially those 560nH inductor.

In what way wouldn't they be behaving idealy?  The filter values are from the design tool on rf-tools.net.  I did initially have issues with the 560nH inductor, because the ones I initially bought had an SRF of only 115Mhz.  It was causing the signal to be attenuated by around 30db or more.  I replaced them with inductors with a SRF of 500Mhz, and the signal strength improved.  What else might I need to be looking at?

Parasitics will ruin the filter response. Those calculators are useless above a few MHz, they are oversimplifying it. Using Kicad without adding the parasitics is equally wrong

You might be OK ignoring PCB parasitics below 200MHz, but inductors are evil. It doesn’t matter if you are working below their SRF, their parasitic capacitance is huge and will ruin the response. Resistive losses will greatly degrade the filter Q. Designing good discrete filters for UHF is an art!

I would change the IF low pass filter to a diplexer to properly terminate the IF port at LO frequency into 50ohm and avoid LO-IF leakage reflection going back into the mixer and degrading its performance.

I don't think a Bridge Tee will work for what I am doing, so assuming I am understanding things correctly, I just add a high pass filter and terminate to a 50Ohm resistor as shown in my image?

Please stop treating inductors as ideal components. That 2.2mH inductor is a capacitor above a few MHz. Your IF is so low you better use LPF+HPF instead of bridged-tee, but I still don’t understand how are you going to achieve any significant image rejection. Not to talk about other mixing spurs.

[psyon]

Your IF is so low you better use LPF+HPF instead of bridged-tee,

Yes?  That's what I said I was doing above?  that's what the last image I posted shows?  I specifically said a bridged-tee won't work, and was double checking that just added the HPF is how to go about it to confirm what I had looked up.

but I still don’t understand how are you going to achieve any significant image rejection.

I apparently don't understand what you think the issue is.  The image frequency is the one the same distance from the LO on the opposite side of it right?  So if I use an LO of 150Mhz, both 149.995 and 150.005 will both result in a 5Khz signal on the output of the mixer.  But, we are using a frequency range that doesn't really have much else, if anything using it, at least not in this area.  The only thing transmitting anything between the 148Mhz and the 152Mhz range that we use for our wlidlife transmitters, is our wildlife transmitters.  I can control what frequencies we use.  So if I want a transmitter that is at 149.995, I just don't also use one that is 150.005.  I can keep them spaced as far apart as I need.  We already have to keep them spaced apart when using our manual receivers.  They use an IF of 10Mhz (I took one apart), and then mix it down again to audio range from there.  If transmitters are too close together we hear multiple beeps at the same time.   Given all the transmitters are within a 1Mhz range in general (most are in 148mhz range, and we have some in 151mhz range), even the bandpass filter on our manual receivers can't filter out individual transmitters, and we do get image frequencies and can even pick up our animals by tuning higher or lower than their transmit frequency.

[eb4fbz]

Yes?  That's what I said I was doing above?  that's what the last image I posted shows?  I specifically said a bridged-tee won't work, and was double checking that just added the HPF is how to go about it to confirm what I had looked up.

Yes, you are right

I apparently don't understand what you think the issue is.  The image frequency is the one the same distance from the LO on the opposite side of it right?  So if I use an LO of 150Mhz, both 149.995 and 150.005 will both result in a 5Khz signal on the output of the mixer.  But, we are using a frequency range that doesn't really have much else, if anything using it, at least not in this area.  The only thing transmitting anything between the 148Mhz and the 152Mhz range that we use for our wlidlife transmitters, is our wildlife transmitters.  I can control what frequencies we use.  So if I want a transmitter that is at 149.995, I just don't also use one that is 150.005.  I can keep them spaced as far apart as I need.  We already have to keep them spaced apart when using our manual receivers.  They use an IF of 10Mhz (I took one apart), and then mix it down again to audio range from there.  If transmitters are too close together we hear multiple beeps at the same time.   Given all the transmitters are within a 1Mhz range in general (most are in 148mhz range, and we have some in 151mhz range), even the bandpass filter on our manual receivers can't filter out individual transmitters, and we do get image frequencies and can even pick up our animals by tuning higher or lower than their transmit frequency.

Even if you think that there will be nothing else on that frequency range, the sensitivity will degrade by 3dB due to the lack of image rejection, because you will have twice the noise at the IF.

[psyon]

Even if you think that there will be nothing else on that frequency range, the sensitivity will degrade by 3dB due to the lack of image rejection, because you will have twice the noise at the IF.

I don't see how using a higher IF would help that if I still need to mix that back down 1Khz.  My initial bandpass filter has to allow through at least between 148Mhz to 152Mhz, so I can tune to every frequency I need in between.  So, even if I use a 10.7Mhz IF (Just picking a standard freq), both 149.995 and 150.005 are coming through, so when I run through a second mixer to get it down to the 5khz range, both will still be present in that.  I am not doing any FM or AM demodulation, just looking at a CW pulse, so I have to get it down somewhere within the range that I can sample it with a low cost ADC.  I guess I am not sure if I am still misunderstanding something here.