Posted by
Guy, K2AV on
Jan 14, 2010; 8:55pm
URL: http://elecraft.85.s1.nabble.com/In-band-rx-IMD-tp4374684p4395286.html
On Thu, Jan 14, 2010 at 1:33 PM, Geoffrey Mackenzie-Kennedy
<
[hidden email]> wrote:
> On Thursday, January 14, 2010, at 4:53 PM, Guy Olinger K2AV
> <
[hidden email]> wrote:
>
>
>> 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) .
>
> Hi Guy,
>
> I don't know about the subject being one that has advanced on rumour and
> inuendo, certainly not in "non-amateur" circles, but I agree that measuring
> in-passband IMD is not as simple as it looks.
Rumor and inuendo so far as an in-band "problem" exists on the
K3...not that it does not exist at all on any receiver. I can think of
a few receivers listening to a pile up, both CW and SSB, where the
best way I can describe the audio was "muddled" or "muddied" or
"ground up" or "mixed together", my common world phraseology for what
I impute to in-band IMD. I certainly have listened to receivers that
did NOT have this effect, among them my own K3, Orion II, Collins
S-lines, and my old 75A3.
The first SSB contest I did with my K3 I found that I was greatly
helped by its clarity in pileups. It was a great improvement over my
MP. I am primarily a CW op, and I was in the SSB Sweepstakes to help
with the PVRC club score (sum of both modes). I need every bit of help
I can get in an SSB contest.
>> I for one would like to see some hard lab-grade facts on the existence
>> or non-existence of this "problem".
I should have added "...on the K3", so the sentence could not be
read out of context.
> I can send you direct if you would like some data in the form of a Gain
> Distribution Analysis for a receiver in use here.
This would not be a K3, but different receiver that you own. And as
the direct measurement is a real pain, we would be dealing in what
amounts to a "logical inference" based on "do-able" tests on the
non-K3 receiver you own.
I'll respond to you off-reflector for the details.
> 73,
> Geoff
> GM4ESD
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