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In band rx IMD

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K8RDD

In band rx IMD

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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Ted Roycraft

Re: In band rx IMD

Why don't you ask the "fellow" Randy?

Randy Downs wrote:

> 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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>

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Geoffrey Mackenzie-Kennedy

Re: In band rx IMD

In reply to this post by K8RDD

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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Guy, K2AV

Re: In band rx IMD

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
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Please help support this email list: http://www.qsl.net/donate.html
>

Geoffrey Mackenzie-Kennedy

Re: In band rx IMD

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. To obtain a clean pair of test
signals, crystal oscillators whose phase noise is suitably low are often
used instead of variable frequency signal generators whose phase noise can
be too high. Also all parts of the test jig, not only the method of
combining the test signals, must be designed and operated to ensure that
receiver IMD measurements are not polluted by test jig generated IMD - which
is, of course, a requirement placed on any IMD test jig.

<snip>

> I for one would like to see some hard lab-grade facts on the existence
> or non-existence of this "problem".

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 includes both the
in-passband and the "out of passband" IMDDR3 stage by stage and overall. A
critical point often missed during receiver design is the level of IMD
generated by a roofing filter, which means that the receiver designer is
flying blind. Filter IMD measurement is one case where in-passband IMD
measurement is very useful.

73,
Geoff
GM4ESD

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Guy, K2AV

Re: In band rx IMD

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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