[TenTec] More IP3 Stuff

[Bill Miner]

Jim & Ten Tekies,

I think you are the one that started this thread and I have learned a
lot from reading all of the posts as well as being inspired to re-read
the receiver test procedure data that is available on the ARRL web site
and elsewhere.

Here is an observation that may not have been brought up yet and that I
would like to share with the group.  The IP3 numbers from the ARRL
product review of the SGC-2020, a rig that is in the same price class
and similar band coverage, were +12.7 dBm at 3.5 Mhz and +15.5 dBm at 14
Mhz compared to the - 3.4 and -4.5 dBm for the Argonaut V.

If you just look at these numbers you would think that the SGC-2020
receiver is very robust.  My practical experience with the SGC is that
the receiver performance is extremely POOR when exposed to  crowed band
conditions such as you would experience on a big contest week-end.  

I have not yet had a chance to use an Argonaut V but from the remarks
that I have read it worked very well during some recent contests with
good receive performance. 

The point that I take away from all of this is that the test numbers may
vary somewhat from rig to rig and from tester to tester even if the
tests are performed with care.  You can NOT judge how well a rig will
work for YOU from lab test numbers alone.

Ten Tec has a nice 30 day return policy if you find that one of their
rigs does not meet your needs.  If you are considering an Argonaut V
this is a good thing to take advantage of.

MY 2 cents worth!

Thanks & 73,
Bill - K6WLM 

Jim Reid wrote:
> 
> Hi again,
> 
> Am still thinking about the deltas between the ARRL
> IP numbers as they report about the Argo V and the
> Ten Tec claimed typical specs.  Not concerned,  however,
> as TT reports pleasure with the ARRL report.  Also,
> several users of the V during the last contest have
> reported that it did very well in the crowded bands.
> So,  will let that issue be settled.
> 
> I have one of TT's RX-340 rcvrs.  Was going to trade it
> in toward my coming new Orion;  sent the 340 to TT,
> they had it for awhile.  But,  after reading certain info
> which Ulrich Rohde came forth with about the 340, decided
> I did not want to part with it afterall!  Ten Tec folks being good
> guys,  sent it back to me, no problem.  So it is happily
> home on Kauai again!
> 
> Anyway,  if you go to the RX-340 spec page at the TT web site,
> you will find two interesting numbers about the IP of that
> rcvr.  Web site is:
> 
> http://www.tentec.com/rx340.htm
> 
> On down the page a ways,  you find a table of TT's specs
> for IP:
> 
> With the preamp OFF,  TT lists the typical 3rd order IP as
> being -30 dBm;  and since it is a "Mil-Spec" rig,  they must
> also list a guaranteed number,  which they give as -25 dBm,  min. .
> They also show what happens with the preamp ON,  and with
> the attenuator active;  both change the IP's typs and mins.
> 
> Ten Tec does not list either the signal spacing,  nor the
> input power levels used during the test for these numbers.
> 
> Elsewhere on the Ten Tec page,  Dr. Ulrich L. Rohde, KA2WEU,
> is quoted as having written:
> 
> "In testing the RX-340, I find that this is the only affordable,
> totally DSP-based receiver where the digital AGC is as good,
> if not better than analog AGC systems.  The intercept point
> for reasonable spacing is very impressive, better
> than +35 dBm in all cases."
> 
> Again,  no signal levels nor specific signal spacing is given,
> and I have no access to his actual data on the 340.  However,
> Rohde did report specific numbers used in tests on two
> amateur radios:  the FT-890 and the IC-746.
> 
> The powers he used in these test measurements (see
> QEX,  Jan/Feb 2003,  pgs. 30 - 31) were -20 dBm,
> or S9+53 dB (based upon Collins "standard" where
> S9=50 uvolts,  or -73 dBm) for the measure of the
> FT - 890,  but -22 and -10 dBm for two measure runs
> on the IC-746.  Why different input powers for the
> two radios,  he does not say.
> 
> For signal spacings,  he has used  100 kHz when testing
> the FT-890;  and he used both 100 kHz spacing and
> 25 kHz testing the IC-746,  again,  no explanation is given
> for his choice of the two spacings used.
> 
> >From this,  I presume he used both different signal spacings
> and input power levels from what Ten Tec used to generate
> their typical and guaranteed minimum IP2 and IP3 numbers
> for the RX-340 radio.  And,  I am sure that the ARRL Lab
> used different input powers and signal spacings than did
> Ten Tec to come up with the differing numbers they have
> for IP3 and IP2 for the Argo V,  TT says nothing about
> typ IP numbers for 5 kHz spacing in that instance.
> 
> Interesting to me is that TT lists IP3 guaranteed for the 340
> as being at -25 dBm,  and Rohde prints, "The intercept
> point.........is very impressive,  better that +35 dBm in
> all cases."  !!  That's a 10 dB difference, with TT being very
> conservative,  but, of course,  they have to stand behind
> with  a guarantee.
> 
> As Ed Hare of the ARRL has written,  the IP numbers are a
> moving target.  They depend upon where you measure in
> the input power spectrum for a given radio,  what signal
> spacings are used and what gain or attenuation loss is
> used ahead of the first mixer in the radio.  To be meaningful,
> and comparable from one radio to another,  all three
> parameters ought to be specifically listed in any published
> test report.  Only then can we really be comparing an
> apple to another apple;  and not a Pippin apple to
> a Delicious apple either,  hi.
> 
> Ed Hare has said that the ARRL labs choose input powers
> down around -100 or so dBm,  near the S5 meter reading
> level.  Both Ten Tec and Rohde use input powers from
> 80 to 100 dB higher.  That is going to make a significant
> difference in the results depending completely on the
> "real" slopes of the IM curves through out the complete
> input power spectrum response of each radio tested.
> 
> 73,  Jim  KH7M
> 
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