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

[Jim Reid]

Ok,  folks,  here is a proper format,  I hope,  with
easily read font....and spell checked!   
My continuing note exchange with Ed Hare,  ARRL Lab
Supervisor.


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

> Thanks for the follow-up. 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 about many other topics,  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 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 some
where 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 subtleties 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-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.
>
> 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 with 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 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.

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 spacing 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 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.

> 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.

73,  Jim  KH7M


>
> -----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