TenTec
[Top] [All Lists]

[TenTec] K2/Omni VI+ Ip3,Ip2,BDR 5 & 20 kHz

To: <tentec@contesting.com>
Subject: [TenTec] K2/Omni VI+ Ip3,Ip2,BDR 5 & 20 kHz
From: tlogan7@cox.net (tlogan7@cox.net)
Date: Mon Feb 10 15:18:37 2003
Jim - 
You da'man! Thanks! I will of course have to ponder and head scratch over this 
one - if it doesn't all sink in I'll let you know. For myself and others, 
thanks Jim. 73/Tim> 
> From: "Jim Reid" <jimr.reid@verizon.net>
To: <tentec@contesting.com>
> Date: 2003/02/10 Mon PM 02:21:39 EST
> To: <tentec@contesting.com>
> Subject: Re: [TenTec] K2/Omni VI+ Ip3,Ip2,BDR 5 & 20 kHz
> 
> Tim asked:
> 
> > In the real world outside the laboratory what are the following
> > differences truly going to mean to me?
> 
> >.......................Omni VI+.........K2
> > Ip3.................+12dBm......+21.6dBm
> > Ip2.................+58dBm.....,+76dBm
> > BDR 5kHz........86dB...........88dB
> > BDR 20kHz......123dB.........136dB
> >
> > Do these differences truly have significance that can be
> > heard outside the lab? Thanks 73/Tim NZ7C
> 
> Yes, of course,  especially during very busy band conditions,
> such as occur during contest weekends,  or wide open
> DX bands during periods of excellent propagation.  Also,
> the better your antenna system,  the more important such
> numbers become.
> 
> A few weeks ago,  I posted info about the numbers Ten Tec
> is giving for their coming Orion rig.  They can be compared
> with the above,  and you will see the results.  You will also
> have to go back to the Elecraft site to pick up the minimum
> detectable signal numbers for those two rigs;  ARRL measures
> and lists these in all of their rig tests.  Consider:
> 
> Some one had asked:
> 
> "Can you explain IMD in terms of dBm? If I have a
> receiver spec of, say, +20dB IP3, and an IMD3 of 100dB, what
> does that mean in terms of actual signals? Can you explain using
> a real world 160m example. Let's say two S9+60dB signals
> mixing into my passband. How strong would the resulting spurious
> signal be?"
> 
> Wow,  two 9+60 dB signals quite near by; where do you live?
> You must live on the  same block as two other 160 meter
> operators,  hi.
> 
> Here is how to determine the IMD level possible from those two
> signals.
> 
> Step 1.  The 3rd Order IP you specify is +20 dBm.  Your two +60
> dB over S9 signals are at a level of -13 dBm. (S9 = 50 uvolts
> into 50 ohms,  or -73 dBm).
> 
> Step 2.  Third order intercept point theory then says that the
> resulting IMD products from those two gigantic signals will
> be "exactly" twice as far below the power level of the two
> generating signals as those two signals lie below the intercept
> point power level.  Or,  in this case,  the two powerful signals
> lie 33 dB below the IP3 level (the delta in dBm between plus
> 20dBm,  the 3rdIP level and -13dBm the power level of the
> two interacting signals.  Therefore,  the IM products generated
> will have an "in-band" power level 66 dB below -13 dBm,  or
> they will be at a power level of only -79 dBm (25 microvolts)!
> That is an S8 level spurious signal!!  Not good.
> 
> So that would NOT be a good situation in which to be operating, hi.
> 
> Now,  more realistically,  we can determine what is reasonable
> from the IMD3 dynamic range spec.  And,  just for fun,  let's use
> the Ten Tec published typical specs on the Orion as now listed
> on their web site.  In addition to the IP3 and IMD3 numbers,  we
> will also need the MDS,  minimum discernable signal spec.
> 
> For the Orion,  TT gives three bits of pertinent info about the
> MAIN receiver:
> 
> IP3rd:  +24 dBm typical for two signals using an IF bandwidth of
> 500 Hz,  and the Pre amp OFF.
> 
> For the IMD3:  101 dB typical also preamp OFF and for both
> 20 and 5 kHz intermodulating signal spacing.
> 
> But,  no MDS signal level is given for a CW signal in the 500 Hz
> bandwidth with the  preamp ON,  which is what we want to reach
> the MDS level potential of the main rcvr!
> 
> TT gives the following  sensitivity info for SSB signals:
> 
> <0.18 ?V for 10 dB SINAD at 2.4 kHz BW, pre-amp on typical;
> <0.5 ?V for 10 dB SINAD at 2.4 kHz BW, pre-amp off typical.
> 
> 
> OK,  so we are going to have to do a bit of jiggering and estimating,
> will try to be conservative,  hi.  So here goes given the info we
> have to work with.
> 
> We can go straight to a probable MDS number from using
> the IP3 and IMD3 specs given.  However,  we must assume
> that the preamp is turned on to reach the MDS level, and
> since no gain is listed for the preamp,  I will assume it to be
> +10dB.  (Note, however,  that even a 10 dB gain preamp
> only will lower the MDS level 7 or 8 dB because of the
> randomness of the noise level as that minimum signal
> discernment level.)
> 
> Also,  when the preamp in turned ON,  the IP3 level,  for a
> 10 db gain preamp,  will drop exactly 10 dB,  or from the
> typical +24 dBm level given,  dropping to "only" +14dBm typ.
> (Note:  you can check the impact of preamp on or off on both
> the MDS and IP3 levels by seeing the numbers the ARRL
> lab collected on several rigs in the comparison chart that
> Elecraft has posted,  you will see that my above assumptions
> are about correct.  Again,  check out:
> 
> http://www.elecraft.com/K2_perf.htm  )
> 
> Now,  with the 10 dB gain preamp ON,  our Orion operating IP3
> will be typically around  14dBm.
> 
> Also,  note that the 101 dB typical IMD3 level is given also with
> the preamp OFF.  Looking at the Elecraft chart of typical rig
> numbers,  we see that turning a 10 dB gain preamp ON,  will
> decrease the IMD3 range from 1 to 2 dB or so depending upon
> which rig the ARRL has measured.  Lets say the Orion IMD3
> given number will drop to 99 dB IMD3 with the preamp ON.
> 
> Now we can calculate a "probable" and typical MDS for the
> Orion looking at a CW signal in a 500 Hz bandwidth IF set up.
> 
> We can first estimate the MDS level by fooling around with
> the given info for SSB signals operating using the spec'd
> 2.4 kHz bandwidth above.
> 
> With the preamp ON,  TT gives a sensitivity level of less
> than 0.18 microvolts (-122 dBm) using 2.4 kHz bandwidth IF
> with the SSB signal level +10 dB over the noise level (that
> SINAD stuff).  So,  in the 2.4 kHz bandwidth a CW signal
> could be "just" discerned down at -132 dBm,  probably.
> Now,  we can lower the MDS some by narrowing the
> IF bandwidth;  the noise level will drop 3 dB each time
> we cut the bandwidth in half from the given 2.4 kHz. Or,
> for 1.2 kHz BW,  the MDS will drop to -135 dBm;  and
> for an IF BW of 600 Hz,  it will drop again to -138 dBm,
> and of course a bit lower for the 500 Hz BW of interest,
> maybe to -139 dbm (.03 microvolts). Measurements down at
> these levels are tough and require pretty fancy test gear as
> does the ARRL lab).  Note that the ARRL labs lists several
> of the rigs tested with MDS levels of -139 dbm or so
> operating with 500 Hz IF bandwidth and the preamp ON..
> 
> With this estimated MDS level for the Orion in the given conditions,
> we can now check for the levels of signals which would cause
> spurious response signals at the MDS level.  This defines the
> IMD3 number.  TT says the IMD3 level is 101 dB with the preamp
> OFF,  but we turned it ON,  so we guess the IMD3 will degrade
> just a bit to,  say,  99 dB (seems fair given the data on the other
> rigs tested).  Or the strongest spurious free signal pairs the
> Orion can handle will be at a level of about -139 dBm + 99 dB;
> or at -40 dBm (2236 microvolts)  or about S9 + 33 dBm.
> 
> We can check now using the IP3 number to see if all of these
> numbers and guesstimates "compute",  hi.
> 
> So,  how far below the IP3 number (+14 dBm with the preamp ON)
> is our -40 dBm signal?  Answer:  54 dB.  Therefore,  spurious
> signals generated with this operating IP3 number should lie
> 2 x 54 dB below -40 dBm.  Or,  the spurs should be down at
> -148 dBm..........?
> 
> Something does not compute!  Why?  Our use of the given and
> guessed at numbers gave us an MDS level of -139 dBm or so;
> and the IP3 number,  with the preamp ON says the spurs are
> 9 dB further on down.  So to bring the spurs up to the MDS
> level,  we should be able to increase the strength of the two
> intermodulating signals up 4 or 5 more dB,  or to a level of about
> -35 dBm.  Or the Orion,  per this calculation can handle signals,
> in the 500 Hz BW,  CW mode,  up to S9 + 38 dB based upon
> the Intercept Point numbers and all else we have calculated/
> estimated before intermodulation occurs to clutter the passband.
> 
> Perhpas the Orion IMD3 is even better than the 101dB typical
> number under the conditions just calculated here.  It would
> seem the IMD3 number becomes  the delta between -139
> dBm and -35 dBm,  or 104 dB.....  Recall that using our
> "assumed" degraded IMD3 number with the preamp ON,  we
> used only 99 dB,  which brought the strong signal level up to
> -40 dBm from -139 dBm.
> 
> So,  we find a 5 dB or so delta between our presumed IMD3
> number with the preamp ON,  and what we seem to calculate
> using the MDS we infer and the given typical IP3 number
> with the preamp ON.  That is pretty good agreement using
> our various assumptions and typical only given numbers.
> 
> We will just have to wait to see what the actuals will be
> spec'd by Ten Tec, and what the ARRL labs measure off
> in the future some time.
> 
> Hope this long piece helps , Tim, and anyone else interested
> in what is done with such dynamic range spec numbers;
> 
> 73,  Jim  KH7M
> 
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
> 

<Prev in Thread] Current Thread [Next in Thread>