Daniel,
Unfortunately, your links did not work this morning.
I recently developed an interest in IMD and bought a copy of:
Intermodulation Distortion in Microwave and Wireless Circuits
J.C. Pedro & N.B. Carvalho
Artech House 2003
That was the only monograph I could find on the topic. I have not spent a lot of time with it, but it looks quite thorough. It's a serious math book, but well illustrated with abundant figures comparing calculated and measured values for a variety of circuit topologies.
Much of the discussion is in terms of Volterra functions which I'd not heard of. But it's a basically a power or Taylor series expansion of ODEs. So to solve an Nth order Volterra series you have to solve N ODEs.
I've attached scans of a few pages which look as if they might be helpful. However, as I don't know the material I can't say if they include enough to be useful. In such matters what you already know is a major factor in what you can understand.
Have Fun!
Reg
NB My current focus is metal casting and similar pursuits, so it will be a while before I dig into this myself. At present I'm trying to set up to melt steel and iron.
On Saturday, January 2, 2021, 07:01:21 AM CST, Daniel Ricardo Perez via groups.io <danyperez1@...> wrote:
Hello group! Happy new year to all!
In PA3CJD's site??there's a good compilation of articles from QEX and QST:
? ?-> Technic -> Electronics -> Radio Tech -> Radio Amateur Magazines
I am specially interested in this:
? ?
Here he makes several IMD tests on a DBM, with matched and mismatched impedances both at the IF and RF ports. I was surprised that RF port matching has an important impact.
After reading this and other similar articles, there's a point that remains unclear for me: what are the specific frequencies that really demand having proper termination? RF+LO if I use RF-LO (or vice versa)? The LO feedthrough? Whatever?
Suppose I want to receive 7.00MHz, and there are strong undesired signals at 7.01 and 7.02. 3rd order IMD within the DBM will fabricate a fake 7.00 IF even with a resistive 50 ohm load.
Now, I place a diplexer after the DBM, and a xtal filter after the diplexer. The diplexer is much wider than the filter, so the DBM will still see a capricious Z at frequencies so close as 10 and 20kHz away from the desired IF, so I thought these ones would reflect back into the DBM, mix again, and worsen the overall IMD. But I must be wrong because if this was true then a diplexer would be useless.
Can anybody explain the IMD worsening mechanism?
Thank you!
Daniel Perez LW1ECP
