[TenTec] New radio fever

[Bill Tippett <btippett@alum.mit.edu>]

W6LX wrote:
>Hey, pretty good measurements. A little dirtier than IC-756 PRO but
about as good as MFJ-9020  :^)

>Calm down, I'm only kidding!

        You were?

Model           Band      Noise floor in -dBc/Hz
                (MHz)    5kHz  10kHz  15kHz  20kHz  50kHz

IC7800            14    120.9  131.9  136.1  137.8  142.4
MFJ9020           14    127.3  133.1  135.3  136.6  138.7

Oops...back to "measurements are meaningless" mode!  The $189.95
MFJ-9020 is cleaner than the $13,466.65 "astonishing ultimate
unparalleled Masterpiece" IC-7800 at close spacings (10 kHz and
under).  Oh well...  ;-))

        The following from Figure 5 gives some hints about dynamic
range performance at close spacings:

*******************************************************8
 F         dF      P       noise
  (MHz)     (kHz)  (dBm)    (dBc/Hz)
14.1589       1     -50.6    -105.0
14.1579       2     -37.5    -118.1
14.1569       3     -34.2    -121.4
14.1559       4     -32.7    -122.9
14.1549       5     -35.5    -120.1 (probably typo)
14.1539       6     -28.4    -127.2
14.1529       7     -25.9    -129.7
14.1519       8     -24.2    -131.4
14.1509       9     -22.3    -133.3
14.1499      10     -20.7    -134.9
14.1449      15     -15.5    -140.1
14.1399      20     -12.9    -142.7
14.1349      25     -10.7    -144.9
14.1099      50     -5.0     -150.6

Table 5. Dynamic range of the IC7800 receiver. P is the level of a strong 
signal that reduces S/N of a weak signal by 3 dB. The corresponding LO 
sideband noise level is listed in the last column.
**************************************************************

For a meter calibrated at S9 = 50 uV or -73 dBm,
the 10 kHz spaced interfering signal at S9+53 dB
reduce (i.e. blocks) the weak signal S/N by 3 dB.
For the same measurement at 1 kHz spacing, the
interfering signal only has to be S9+23 dB for the
same effect.  That's a degradation of 30 dB, and
an S9+23 dB signal is certainly not uncommonly
strong.  By way of comparison, Orion's BDR degrades
by 10 dB from 20 kHz to 1 kHz.  SM5BSZ's measurements
are not directly translatable (by me) to absolute BDR
performance which I believe is the effect he is
measuring.  The other issue I see above is how badly
RX phase noise increases near the carrier, if I'm
interpreting the data correctly.  Orion's phase noise is
virtually flat from 20 kHz to 1 kHz as can be seen in
the upper plot on page 22 below:

http://www2.arrl.org/members-only/prodrev/pdf/lab/orion_etrr.pdf

        It's going to be very interesting as more layers
of the "astonishing ultimate unparalleled Masterpiece"
performance are unpeeled by real world measurements,
even if the Icom cult believes they are meaningless.

                                                73,  Bill  W4ZV



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