[TenTec] Re: ARRL Rcvr 3rd and 2nd IPs Test Methods

[Jim Reid]

HI again Ed,  And thanks for your note,  in which you wrote,  partly:

> Thanks for the followup. I am still waiting for my tentec at contesting.com
subscription
> to be authorized by the moderator, so my post is actually in limbo.

Ed,  I hope he does not take too long;  a couple of the folks out here had
trouble
being accepted!  One at last got subscribed the other didn't;  too bad,  as
I
am pretty sure he will order an Orion,  but he is not pleased that he can't
read
all the gossip and chatter on the reflector about that rig,  and the other
Ten
Tec info aobut,  hi.

>  I imagine it will show up soon, or I can repost it once I am official.
If this one shows
> up but not the original, I will repost, so everybody can figure out more
about what we
> are talking about. :-)

Ed,  only with your permission, I would be happy to forward your very
thoughtful
comment on to the TT reflector!  Or,  I urge you to do so as soon as you are
accepted
to the list.  Also,  as you have not been reading the reflector,   you could
easily
catch up by going to the Ten Tec Contesting,com archives here:

http://lists.contesting.com/_tentec/

> I am glad we are moving towards a meeting of the minds.  And do feel free
to
> disagree with my conclusions. I have given this matter a LOT of thought,
over
> my entire time at ARRL HQ and think I have the right balance and methods
to
> test what is sometimes a moving target -- real-world receivers.

I am especcially 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.  Or
maybe
just settle on the -97 dBm level for all radios;  haven't quite gotten all
the subtelties
you have outlined digested just yet!

> 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-linearities
> 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.
>
> 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
> of 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 recevier 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
disparte
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 accuratly 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
eliminatioin of parallax,  hi.

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,  0.22 volts,
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 certainlyh performed their IP3 test to produce that curve well up
into "the AGC range of the reciever 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.

> So what DOES it all mean? It means that one needs to evaluate the overall
> performance of a receiver, not necessarily stack them up against each
other
> in a number by number comparison over dBs that are a moving target at
best.
>
> And I do recall you now at dinner; I hadn't associated your call with the
pleasant
> chat we had. It is always nice to put that face to the name, because
having met
> someone is a much better indicator of who they are than words on a screen.
:-)
>
> 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!

Enjoy these discussions,  Ed


>
> -----Original Message-----
> From: Jim Reid [mailto:jimr.reid at verizon.net]
> Sent: Tue 3/4/2003 8:14 PM
> To: Hare,Ed, W1RFI; George, W5YR; Smith, Douglas; tentec at contesting.com
> Cc: Tracy, Michael, KC1SX
> Subject: Re: ARRL Rcvr 3rd and 2nd IPs Test Methods
>
>
>
> Aloha to all following this topic,
>
> Ed Hare has written a very detailed and well presented
> reply to my posts and concerns,  thank you Ed.  And I
> accept your criticism of my "low blow";  was not intended
> as such,  but on re-reading can certainly see your point.
> I apologize for over stepping in my comment.
>
> Comments on only a couple of Ed's comments.  He has
> made an excellent presentation of the facts about the
> ARRL Lab test methods and use,  well worth reading
> by all.
>
> > The article in question is available for download at:
>
> http://www.arrl.org/tis/info/pdf/020708qex046.pdf
>
> Thank you ,  that will be helpful to others.
>
> I am now going to cut out a bunch of Ed's great material,
> and skip on down near to the end.
>
> Ed's concluding paragraph:
>
> > "In this post, I have outlined some of the reasons that ARRL is
> > making the testing choices it is using. I believe them to be the
> > correct choices, offering a reasonable level of standardization
> > in testing and reporting on receivers with a wide range of
> > capabilities and "real-world" receiver performance. There are
> > improvements in the works, but they are not going to make
> > a night and day difference in results, because the test methods
> > used give good results for the test conditions employed, and
> > most improvements I can think of will serve only to tighten up
> > a bit on the test conditions."
>
> Again,  I greatly appreciate the time Ed has taken to prepare this
> thourouh discussion of the ARRL lab methods and the reasons for
> their use.
>
> Now,  I would like to understand why the great difference in IP's
> reported by the Lab for the Ten Tec Argo V from the "claimed"
> IP's for that radio by Ten Tec.
>
> The ARRL lab came out with IP's well below the
> Ten Tec specs.  TT spec is +4 dBm for
> the third order IM intercept point,  at least that is what
> the ARRL lab test reports TT has specified.
>
> At 3.5 MHz, 20 kHz  signal spacing,  the ARRL  Lab
> measured only -4.5 dBm;  and at 14.2 MHz,  only -3.4 dBm.
>
> Those are really significantly lower numbers than the
> Ten Tec claimed spec.  And,  for 5 kHz signal spacing,  the
> deltas are even greater:  3.5 MHz,  ARRL says -30 dBm;
> and for 14.2 MHz,  -29 dBm.  Those are huge differences IF
> TT really specs +4 dBm IP3 for 5 kHz two signal spacing;
> I do not know if Ten Tec specs this spacing for the Argo V.
>
> Also,  TT specs the second order IP to be +66 dBm.
> But the ARRL lab reports only +47 dBm.  Again,  a very large
> difference.
>
> Certainly nothing in the QEX piece,  downloadable as above, is
> there any reason given to explain such large deltas between
> what the engineers at Ten Tec measured, probably several
> times to come up with  "typical" IP2 and IP3 specs for the new
> Argo V and the alarmingly lower numbers reported by ARRL.
>
> These differences between TT claims and the ARRL Lab report
> are what initiated my posts about this topic.  I still do not
> understand why the great deltas,  and worry about the future
> tests on the new Ten Tec Orion!  It seems to me it is imperative
> to identify why the differences in numbers,  and to provide some
> assurance about what we will read next.
>
> Thanks again,  Ed.  And also,  thank you again for your visit
> out here to Hawaii a few years ago. And yes,  I did have an
> opportunity to work the Tuna Tin II you left with the Hilo QRP
> gang.  Had a very good signal up here to Kauai,  some 350
> miles away and through the Mauna Kea Volcano to boot!
> And I enjoyed our across the table visit over dinner at the
> concluding convention event.  You will have to visit us again!
>
> 73,  Jim  KH7M
>
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