Posted by
Guy, K2AV on
Jan 14, 2010; 4:53pm
URL: http://elecraft.85.s1.nabble.com/In-band-rx-IMD-tp4374684p4393804.html
This is another one of those subjects that seems to have advanced on
rumor and inuendo. Actually measuring in-band IMD is not as simple as
it looks. Basically (whether included on a single chassis or not) the
apparatus must be able to generate a pair of signals which are
combined in a way that precludes IMD in the test signal to start with.
Then the frequencies must be set so that A, B, 2A-B, and 2B-A are all
inside the passband, (inside the roofing filter for the K3 with dsp
bandwidth set to match) .
Hams without a laboratory grade hamshack are not reliably equipped to
run this, hence the lack of specific reports that such and such ran a
test on K3 serial number, obtaining xxxx results using such and such
equipment, such and such a hookup and such and such procedure.
Note that measuring the outside the bandpass kinds of IMD is now
popularly left to a relatively few reputable labs who have a good deal
at stake maintaining their independent reputations and procedures,
such as Sherwood or ARRL.
There are reasons for handing off this task: the difficulty of the
task, to get measurements free of private agendas and to eliminate
vigilante mob mentality deprecation of commercial products without
hard accurate facts to back up accusations. And unfortunately, there
are those who will author text on the internet just to cause
consternation and get a response (trolls) even if what they are
writing technically is libel.
I for one would like to see some hard lab-grade facts on the existence
or non-existence of this "problem".
73, Guy.
On Thu, Jan 14, 2010 at 4:55 AM, Geoffrey Mackenzie-Kennedy
<
[hidden email]> wrote:
> Randy,
>
> It sounds as though this "fellow" is talking about the *In Passband* IMD
> performance of a receiver, usually expressed in terms of 3rd Order Dynamic
> Range when BOTH test signals are inside the receiver's passband. This
> information can provide, for example, a useful indication of how a receiver
> will cope in a "No Split" pile-up situation with non-stop callers inside the
> passband.
>
> The ARRL does not publish this information in their regular reviews, but
> have in their expanded test results for some receivers - the K2 being one
> example.
>
> 73,
> Geoff
> GM4ESD
>
>
> Randy Downs wrote on Wednesday, January 13, 2010 at 9:25 PM:
>
>
>
>> I'm a bit confused about an email I received. A fellow said "The
>> TS870S is probably still in your shack because of its INBAND IMD
>> performance. The ARRL does not do the inband IMD test anymore. Many of
>> the complaints about the K3's receiver is related to its poor inband
>> IMD performance. However there is various opinions on this."
>> What is he referring too? I'm not aware of this issue.Randy
>> K8RDD
>
>
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