> Not me. While I will agree that higher order products do not necessarily
> track lower order levels, there is usually a pretty good relationship.
> Some products can be generated at audio and some at RF. That is going to
> make a difference in higher level relationships. Other factors may come
> into play also.
>
> But to try and establish a simple means of detecting IM products on a
> signal I think that the low order products are the easiest to detect and
> the most consistent. (especially where there are strong adjacent
> signals) If there are low order products that are strong it is a good
> bet that there are higher order products present with a fairly
> consistent relationship in strength. I am not talking about real
> accurate measurements here but ballpark levels to determine the severity
> of the problems with signals.
High order products have little or nothing to do with low order products.
Some systems go out "forever" in IMD bandwidth while others, with the same
or even higher close-spaced IM levels, roll off quickly with high order
products.
I see this happen all the time.
Another issue, doing a opposite sideband test, would be filter skirts.
Filter skirts (or shape factor) are often not good enough just to do a "flip
sideband" test.
I also hear (and measure) rigs consistently that have non-symmetrical in IM
distribution between upper and lower frequency products. This is
particularly true with voice.
73 Tom
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