[1000mp] ARRL Lab transmit IMD test-result reporting

Wed, 10 Apr 2002 11:00:17 -0400

> I appreciate your position regarding the presentation of IMD data, as you 
> stated you want to do it the same way it has always been done so it can be

> easily compared to a review from 17 years ago. I respectfully disagree
with this 
> position and maintain my position that I would not present IMD relative to

> PEP output.

Actually, Jeffrey, if making the change would convince manufacturers to make
better rigs, I would be all for it. But the manufacturer's design engineers
understand PEP as a reference just as well as they would understand a single
tone.  The change would mean nothing to those who understand it, and would
break the chain of easy comparison for those that do not, without changing
the performance of the rigs one dB.  There are, IMHO, better ways of
addressing that and, even if ARRL remains stubborn about the PEP reference
level, I will use this discussion as a way of improving the reporting of
poor or marginal IMD performance, possibly through QST (I cannot speak for
the editor) and definately through the ARRL Lab's reports (I can speak for
the Lab Supervisor!).

> and maintain my position that I would not present IMD relative to 
> PEP output. Average power and PEP are usually not the same for SSB and 
> regarding the part 97 rules, I may have been referring to IMD requirements
meant 
> for power amplifiers.

I agree that average power and PEP are not the same for SSB, but a single
tone in a two-tone test is neither.  The reference to PEP is the best tie to
Part 97 regulations, referencing any particular IMD product in the test to
the PEP level of the transmitter.  In general, if one hears splatter on the
band, one is hearing only the upper or lower IMD, so referencing a given IMD
product to the PEP level of the transmitter is also well related to
real-world conditions.  Although if we were starting from scratch today, it
might be a better choice to use a single tone as the reference level, I do
not see enough justification or benefit to changing it, considering the
downside of doing so mentioned above.

I have, btw, been forwarding all of these comments to the Product Review
editor. Fortunately, one of the participants on this list forwarded the
discussion to me, so I joined the list.  If not, the Product Review folks
would have missed out on all of this valuable member input.

73, 
Ed Hare, W1RFI
ARRL Lab
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: [email protected]
Web: http://www.arrl.org/tis

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> -----Original Message-----
> From: Jeffrey Pawlan [mailto:[email protected]]
> Sent: Tuesday, April 09, 2002 11:50 PM
> To: [email protected]
> Subject: Re: [1000mp] ARRL Lab transmit IMD test-result reporting
> 
> 
> Open letter and response to Ed Hare's reply to my posting:
> 
> Dear Ed,
> 
>   Thank you for your comprehensive and thoughtful reply to my 
> posting. I do
> agree that the number of tests run and details presented has 
> grown. I appreciate
> your position regarding the presentation of IMD data, as you 
> stated you want to
> do it the same way it has always been done so it can be 
> easily compared to a
> review from 17 years ago. I respectfully disagree with this 
> position and
> maintain my position that I would not present IMD relative to 
> PEP output.
> Average power and PEP are usually not the same for SSB and 
> regarding the part 97
> rules, I may have been referring to IMD requirements meant 
> for power amplifiers.
> Since today's rigs always contain power amplifiers, unlike 
> some vintage
> equipment that were really low power exciters, I thought that 
> IMD was applicable
> to them. If it does not in a strictly legal interpretation, 
> then you might see
> my point that they should apply as it is OUR bands that are 
> filling up with
> garbage signals since these products are almost always 
> in-band. Similarly, phase
> noise and spurs are going to be amplified by the rig's power 
> amplifier and
> certainly by an external amplifier and also clog OUR bands 
> with noise. This
> problem has been noticed by many hams who happen to live 
> within a mile radius of
> another ham. The effect on receiver performance is not to be 
> ignored either.
>    As you have noticed on your own, the summary or synopsis 
> of the rig in the
> review is always something between "great buy for the 2nd 
> radio" to "fantastic
> new rig well worth its $4000 pricetag."  I only remember 
> seeing one time in 25
> years a very watered down and understated version of "this is 
> garbage  - don't
> waste your time or money".
>    I think the ARRL should hold out for higher standards than 
> barely meeting
> Part 97 rules. I think the ARRL should be our voice and the 
> leader to tell the
> manufacturers in definite and certain terms that we will not 
> tolerate and spend
> our money on equipment that is small and pretty or has 
> glowing color display
> panels and 78 knobs, but is otherwise technically poor in its 
> design and
> mediocre at best in performance.
> 
> 73,
> 
> Jeffrey Pawlan, WA6KBL
> 
> 
> 
> 
> 
> 
> 
> 
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