[TenTec] IP3 controversy

[Tommy]

Rick,

I think you did answer the question correctly when you said:

"Altogether, this is what has led me to the point that I take all 
measured
 numbers with a grain of salt and prefer to try all the rigs, 
comparing them
 to several other rigs that I know well - under all kinds of adverse
 conditions.  Then I have a feeling about the performance of the 
rig."

That sum's it up much better than relying on test data from really 
unknown sources. The spec's help sell radios, but it's actually 
trying the radios under conditions as you describe that really tell 
you how well a receiver is designed and how well it's going to 
operate under your own operating conditions.

Great IP specs don't necessiarily make a great radio, it's a 
combination of the design goals and implementation of that complete 
receiver design that makes a great radio receiver.

Tom - W4BQF


> Todd,
>
> It's simple.  You need good IP3 figures to enable a good dynamic 
> range
> figure, but they have to be the result of excellent design and
> implementation.  In order to assure that this is the case, it's 
> better to
> look at both numbers.
>
> It is correct that the IP3 can be improved by placing an 
> attenuator in the
> front end.  It's normally linear.  If you attenuate the front end 
> by 10 dB,
> the IP3 goes up by 10 dB.
>
> The interesting question to be asked is "how much IP3 or dynamic 
> range do we
> need?"
>
> As far as I know, nobody has ever answered this, except to say "as 
> much as
> you can get."  Just as good of an answer would be "it depends."
>
> The problem becomes a diminishing return on your investment.  At 
> some point,
> trying to get another 3 to 6 dB can cost more money than the rest 
> of the
> front end.
>
> And that is all just part of the answer.
>
> The IP3 will also depend on how it is measured.
> If you want to compare numbers on two different rigs, you have to 
> assure
> both numbers were measured exactly the same way.
>
> Altogether, this is what has led me to the point that I take all 
> measured
> numbers with a grain of salt and prefer to try all the rigs, 
> comparing them
> to several other rigs that I know well - under all kinds of 
> adverse
> conditions.  Then I have a feeling about the performance of the 
> rig.
>
> Being a member of one of Europe's largest contest clubs, I get the
> opportunity to eventually try everything that comes on the market 
> with
> excellent antennas at sites which are remote as well as located in 
> an
> industrial city.
>
> I know this wasn't a short, specific answer to your question but I 
> don't
> think there is such an answer.
>
> 73
> Rick
>
> -----Original Message-----
> From: tentec-bounces at contesting.com 
> [mailto:tentec-bounces at contesting.com]
> On Behalf Of KD7EFQ at aol.com
> Sent: Thursday, November 25, 2004 4:46 AM
> To: tentec at contesting.com
> Subject: [TenTec] IP3 controversy
>
> Hello all, I have been reading a few reviews and asking questions 
> about this
>
> "Third order intercept" number that is all the rave these days. I 
> have a
> vague
> understanding of what this is, but some controversy has arisen as 
> to how
> important this really is.
>
> Rob Sherwood of Sherwood Engineering only lists dynamic range 
> numbers on his
>
> Dayton 2004 comparison chart. I ran into him on the air and asked 
> him why he
>
> does not show IP3?
> He responded that anybody can raise there IP3 number simply by 
> turning on
> their attenuator on any rig and so it wasn't that important to 
> him. I just
> read
> the same statement on the latest review of the IC756PROII where 
> the VK
> poster
> said anyone can raise their IP3 by inserting an attenuator in 
> front of the
> receiver.
>
> I vaguely remember reading Doug Smith's Article on receiver 
> performance,
> where he stated that dynamic range numbers alone did not tell the 
> whole
> story on
> receiver performance, and you had to consider IP3 numbers to get 
> an accurate
>
> picture. Since he helped develop Orion, I assume he knows what 
> he's talking
> about.
>
> Bottom line, Who's right, and Just how important is IP3?
>
> 73, Todd - KT0DD - kd7efq at aol.com
> "The race is over...THE RATS WON !"
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