I agree. Yes, it is some of the best technical dialog that I've seen and
read in quite some time. That's what the reflector is all about.
Thanks guys.
73
Bob, K4TAX
----- Original Message -----
From: "Gary Hoffman" <ghoffman@spacetech.com>
To: <tentec@contesting.com>
Sent: Wednesday, March 05, 2003 10:29 PM
Subject: Re: [TenTec] Re: ARRL Rcvr 3rd and 2nd IPs Test Methods
> I won't speak to the technical points under discussion here, because
> I am not qualified to do so.
>
> However - I will say that this discussion is some of the best stuff I
> have ever seen posted. Informative, based on facts and data, and no
> flames. Excellent !
>
> 73 de Gary, AA2IZ
>
>
> ----- Original Message -----
> From: "Jim Reid" <jimr.reid@verizon.net>
> To: "Jim Reid" <jimr.reid@verizon.net>; "Hare,Ed, W1RFI" <w1rfi@arrl.org>;
> "George, W5YR" <w5yr@att.net>; "Smith, Douglas" <DSmith@arrl.org>;
> <tentec@contesting.com>; <kh7t@arrl.net>
> Cc: "Tracy, Michael, KC1SX" <mtracy@arrl.org>
> Sent: Wednesday, March 05, 2003 8:09 PM
> Subject: [TenTec] Re: ARRL Rcvr 3rd and 2nd IPs Test Methods
>
>
> > Now here again, Ed has responded to my last post. He
> > has also requested that I repost to the reflector, so here
> > goes (this one came here about only 10 minutes ago):
> >
> > "
> > > I am especially pleased that you plan to review, and
> > > probably do some updates to the procedures, Ed. I like the
> > > idea of a standard input signal level for the pair of tones;
> > > the Collins Radio idea of using -109 dBm plus the rcvr noise
> > > figure will be somewhere near a particular radios S5 meter reading I
> > > would bet, hi.
> >
> > Actually, by "Collins" standard, I was referring to the Collins S-meter
> > standard, where S9 is 50 microvolts (-73 dBm at 50 ohms) and each S unit
> is
> > 6 dB. I don't know what levels Collins used/uses for their IP2 and IP3
> > measurements. My guess is that they would have derived their IP3 from
the
> > noise floor and dynamic range measurements. Many of the older radio
> > references *define* IP3 as a relationship between sensitivity and
dynamic
> > range. This is a reasonable assumption for most receivers, although
> subject
> > to all the factors in the sidebar I wrote for Doug's article. Other
texts,
> > especially dealing with high level mixers, where there may NOT be a
noise
> > floor to measure (a passive mixer, for example) use a more generic
> > definition of IP3. Considering the way that the "real" IP3 varies with
> > signal levels in some receivers, a signal level for IP3 measurements
above
> > the noise floor is quite justified -- it just becomes a matter of
> selecting
> > an appropriate signal level. I won't repeat the material in my earlier
> > post, but if you repost it as I had asked, folks can read all about my
> views
> > there. :-) As a quickie here, I will point out that any refinements ARRL
> > makes will NOT make the difference between night and day on the results;
> the
> > measurements as made are reasonable and accurate and are measuring the
> > equipment under test, NOT measuring the test instrumentation. I have
been
> in
> > test engineering for 25 years now, so I know where to draw the lines!
> >
> > > Or maybe just settle on the -97 dBm level for all radios;
> > > haven't quite gotten all the subtleties you have outlined
> > > digested just yet!
> >
> > That could work for me, except that there can be a 20 dB difference in
> > sensitivity between different radio designs. An 80-meter receiver with
> > a -120 dBm noise floor would be QUITE usable on 80 meters, but -97 dBm
> would
> > really be a different level inside the receiver than it would for a
> receiver
> > with a -144 dBm noise floor. And I could imagine an insensitive receiver
> > with a high AGC threshold that might not be showing any AGC action at
all
> > at -97 dBm. It bears more thought and some investigation.
> >
> > W1RFI wrote:
> >
> > >> The only sticking point appears to be dynamic range. Most agree that
> > >> testing IP3 at a level somewhere in the AGC range of the receiver is
> > >>the best test, although I don't think that most hams understand how
> > >>and why IP3 varies in real receivers based on signal levels. If
> > >>nothing else comes of this, understanding that may help hams
> > >>to stop quibbling over a dB or two.
> >
> > >> Those who work with high-level mixers and/or visualize receivers
whose
> > >> non-linearity's follow a classic response tend to think in terms that
> > >> noise floor, dynamic range and IP3 are all precisely related.
> > >>Ulrich, for example, whose opinion I greatly respect, has stated
> > >>that dynamic range can be calculated from the noise floor
> > >> and an IP3 measurement made at a high level. When you consider that
> > >>the formula ends up assuming that the 1st-order and 3rd-order
> > >>responses are 1:1 and 3:1 sloped and makes a calculation for
> > >>the levels at the noise floor of the receiver, it is, IMHO, more
> > >>accurate to make a measurement at the noise floor because it can
> > >> be done. No one has yet convinced me that making a measurement
> > >>at a higher level and assuming ideal slopes of lines that are
> > >>probably not ideal is a better way to determine dynamic range
> > >>than actually making a measurement that can be made
> > >> accurately.
> >
> > I will clarify that in the above paragraph, I am discussing making IP3
> > measurements at at S5 receiver output level (approximately -109 dBm, if
> > memory serves) and making dynamic range measurements at the noise
> > floor, the very definition of dynamic range.
> >
> > >> Of course, one must always remember that Product Review is
> > >>dealing with a sample of one. IP is really a very nebulous number
> > >>for a number of reasons, and I have just scratched the surface in my
> > >>explanations. When we are dealing wtih receiver intermod with
> > >>receivers that are linear over 90-110 dB, look at how small
> > >> a deviation from perfection a linear range of 100 dB would be.
> > >>Differences of fractions of fractions a percent in the non
> > >>linearity of a mixer can make tens of dB
> > >> of difference in the dynamic range. And if a manufacturer derives
> > >>his IP3 from the measured linearity and the specified receiver
> > >> sensitivity and makes a receiver more sensitive than the spec,
> > >>but whose linearity is as specified, the IP3 calculated from
> > >> the actual measurements is lower than the spec. So if they
> > >>make a better receiver, it doesn't meet spec."
> >
> > > Somewhere, Ed, in your above two paragraphs must lie the
> > > reason for the disparate numbers that Ten Tec is listing for the
> > > IP2 and IP3 numbers of their new Argo V, vs. the numbers your
> > > lab has reported in the April 2003 QST. I went to the
> > > Ten Tec web site this morning, and yes, they do list IP2
> > > of +66 dBm, and they also add that the ARRL Lab test method
> > >was used to determine both it and their listed IP3 number of
> > >+4 dBm, both tested using 20 kHz signal pair spacing.
> > > However, they make no claims about 5 kHz signal spacing.
> > > I thought it was especially interesting that they specifically
> > > mention and list use of your ARRL Lab procedure,
> > > that is they used a power level for the two input signals such
> > > that the S meter on the Argo V read S = 5. And who knows how
> > > accurately that was read by them, or, as you suggest how
> > > accurately the S 5 setting was read by you folks during the test.
> > > The S meter does not have a mirror behind the needle as the old
> > > time Triplett meters did to aid in the elimination of parallax, hi.
> >
> > Parallax is not going to make that much difference. If the reading were
> > S4, S5 or S6, if those lines of first- and higher-order responses were
> > straight, the calculated IP3 would be the same, as long as the parallax
> > error were the same in both cases. If the lines are not ideal, and they
> > probably aren't, the IP3 calculation difference would be different only
by
> > the amount that the first- and higher-order responses deviated from
ideal
> > over that small portion of the curves.
> >
> > To my knowledge, the rig never did make claims wrt 5 kHz spacing. What
you
> > saw on the TT Web site was exactly what we were told the specs were when
> we
> > bought the rig. I think that some may have confused this rig with the
> Orion,
> > which DOES make claims for 5 kHz spacing.
> >
> > I went into the screen room today and set up our Rohde and Schwarz
ESH-2
> > EMC receiver and made some IP2 measurement. I measured the IP2 of
> > the R&S at +86 dBm or so at a number of different levels, indicating
> > that the test-fixture intermod is at least that good. In the past, with
> our
> > older
> > HP8540Bs, we had determined that the IP3 setup was good to at least +33
> dBm
> > and that IP2 measurements could be made to at least +75 dBm. Our newer
> > Marconi generators are even better, and using a separate test fixture
> > donated by Ulrich Rohde, we had verified the IP3 capabilty to at least
+40
> > dBm, and possibly higher. I presume that the IP2 capability is similarly
> > increased between the HPs and the Marconi, and I believe by the way that
> the
> > step attenuators were behaving that I was measuring the ESH-2 directly
> > (every dB of attenuator changed the product by 2 dB for IP2).
> >
> > I may have a bit more to add after I do some testing of the rig again,
> but
> > I want to coordinate this with Ten Tec before adding anything to what
was
> > said in the review. The review process contains checks, balances,
retests
> of
> > anything at all out of line, consultations with multiple engineers in
the
> > ARRL Lab and full communication with manufacturers before it all goes to
> > press. I want to give what I say here about any specific product the
same
> > full consideration. We have, btw, made mistakes in the lab testing, but
> > this system of checks and balances has, to the best of my knowledge,
> caught
> > them all, though a few have been caught by the manufacturers at the 11th
> > hour. :-) And I thank them for it, because manufacturers know their
> products
> > better than the ARRL Lab dudes could.
> >
> > I will also point out that MOST of the time, though, when a
manufacturer
> > questions a result, the original result has held up. A few manufacturers
> > have even sent their engineers to HQ to work with us on a problem and
when
> > all was said and done, a Feedback in QST was not necessary. :-) I
believe
> > we had to run one Feedback because one of the Lab guys made a
calculation
> > error from raw data. That one broke a 15+ year record of no Feedbacks
due
> to
> > a Lab error, thanks in part to careful cross checking and good
> manufacturer
> > communication. :-)
> >
> > > On the other hand, Ten Tec has listed some outstanding numbers for
IP2,
> > > IP3, and phase noise performance of their soon to be released Orion
> > > rig. BUT, their beautiful IP3 curve of +25 dBm typical for all
signals
> > > spacings down to about 5 kHz spacing, followed by a gradual roll
> > > down to about +21 dBm at 1 kHz spacing was performed using two
> > > input signals of 0 dBm, 1 mW, 0.22volts, or S = 9 plus 73 dB, if
> > > I did my arithmetic correctly, hi. See their Fig. 1 on down this
> > > page about the Orion from the TT web site:
> >
> > > http://www.tentec.com/TT565.htm
> > >
> > > They have certainly performed their IP3 test to produce that curve
well
> > > up into "the AGC range of the receiver as the best test" to quote
> > > from one of your paragraphs above, hi. But that is way above where
> > > the Orion S meter would read S = 5 !! Bet there will be a difference,
> > > based upon your past results, between the IP3 as measured with
> > > 0 dBm signals and when with something like - 97 dBm signals.
> >
> > That is quite a bit higher than the S5ish levels we would use. I don't
> > want to cross that bridge until we come to it, but that is a lot higher
a
> > level than I would use to make the test. I have not measured a lot of
rigs
> > at an S9 level, but one of the rigs we measured for my sidebar showed
> quite
> > an increase in IP3 for S9 level recevier output. The Orion is, however,
a
> > quite robust SDR type rig, where much of the performance is in the DSP
> used
> > for signal generation and detection, so some differences in the way it
is
> > tested -- or even should be tested -- may be in order. Naturally, Mike
> will
> > work closely with Ten Tec. If nothing else, it will be a very
interesting
> > expanded test-result report. :-)
> >
> > For most receivers with final selectivity done at IF with filters, one
> > could possibly not really measure IP3 with 0 dBm signals. Those signals
> > would pin the S meter, so it couldn't be used as an indication of
received
> > signal level. The filtering would not allow the test signals at 5 kHz
> > spacing and the resultant IMD products to all pass through to the
receiver
> > output amplified exactly the same. But with DSP filtering, it may be
> quite
> > possible to gain access to the IF before the final DSP and look at the
> test
> > tones and resultant IMD products. If so, one can use those levels to
> > calculate IP3, at least before the DSP. To know how ARRL would want to
> > apply all this, I really would want to look at the radio, do some
> > preliminary testing and talk to the designers (and possibly a few
> Technical
> > Advisors!).
> >
> > But this DSP/SDR stuff that Ten Tec is doing is personally very exciting
> > to me, so I can't wait to see this radio show up in the Lab. I may kick
> > Mike Tracy out of the screen room, or at least spend a lot of time
hanging
> > over his shoulder. :-)
> >
> > >> Did you get a Certifi-Cat for working the TT2?
> >
> > > No I did not, but probably my fault, as I did not send Dean, KH6B
a
> > > QSL for the contact, so he didn't bother to send something, hi.
> Anyway,
> > > I have too many QSL's in drawers here already as well as a few hundred
> > > hanging on my shack wall!
> >
> > Send me the contact info, including both RSTs, and I will send you a
> > Certif-Cat! Trust me, it is WELL worth asking for it. It is a
> one-of-a-kind
> > sorta' thing. :-)
> >
> > > Enjoy these discussions, Ed
> >
> > As am I. I hope that when all is said and done, folks will realize that
> > the ARRL Lab *is* a world-class test facility. I saw another post on
that
> > subject that is a better place to address that, so I am waiting for my
sub
> > to be approved and my posts to show up.
> >
> > Please post this one to the reflector, too, and we can let people catch
up
> > on where it started later. :-)
> >
> > 73,
> > Ed Hare, W1RFI
> > ARRL Lab "
> >
> >
> >
> >
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
>
>
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