[1000mp] MP vs MkV vs K2

[Tom Rohlfing]

Earl,

Thanks for the reply.  So when these tests are run (5 or 20 spacing), do
they then have (for example) one of them tuned into the center of the IF
passband, and the other one 5 or 20 KHz. away (outside the IF filter, but
inside the roofing filter)?  If you are right, then the offending element is
pre-IF, such as the first mixer (70M), or some RF amplifier before the IF
filters.  I guess it's possible.

73,
Tom / W7GT

----- Original Message -----
From: <k6se@juno.com>
To: <1000mp@mailman.qth.net>
Sent: Saturday, June 29, 2002 8:53 PM
Subject: Re: [1000mp] MP vs MkV vs K2


> Tom, W7GT wrote:
>
> "Where are the non-linear products in the MP being generated?  In
> particular, are they in the early stages, prior to the 8.2 and 455 IF
> filters?"
> ----------
> 3rd-order IMD (IMD DR) products are the result of unwanted signals (along
> with the desired signal) getting inside the various filters in a receiver
> and thus producing spurious responses.  In the MP (and most other modern
> receivers), these filters are the "roofing" filter in the early receiver
> stages, the 1st IF xtal filter, and the subsequent IF xtal filter.
> Because the unwanted signals we talk about when we are referring to IMD
> DR and BDR are normally outside of the IF xtal filters (but inside the
> roofing filter), I would say that 3rd-order IMD "birdies" are most often
> generated in the early stages of the receiver.
>
> The ARRL has traditionally tested IMD DR (and BDR) using an unwanted
> signal spaced 20 kHz from the desired signal.  Tom, W8JI finally
> convinced them that 5 kHz spacing would be more meaningful, so now they
> include IMD DR and BDR values for both spacings.
>
> 73, de Earl, K6SE
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