[TenTec] K2/Omni VI+ Ip3,Ip2,BDR 5 & 20 kHz
tlogan7 at cox.net
tlogan7 at cox.net
Mon Feb 10 15:18:31 EST 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 at verizon.net>
> Date: 2003/02/10 Mon PM 02:21:39 EST
> To: <tentec at 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 µV for 10 dB SINAD at 2.4 kHz BW, pre-amp on typical;
> <0.5 µV 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
>
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