[TenTec] FW: Rob Sherwood's official Measurements: OMNI VII

[Rick, NJ0IP / DJ0IP]

I have Rob's written permission to pass this on to the reflector members.

73

Rick, DJ0IP

- - -

 

Test Data on Omni VII, serial number 11C10866
May 2007

Dynamic range tests of the Omni VII using both the 2.5 kHz and 500 Hz
distributed roofing filters.  

 

The 2-kHz dynamic range measured the same with either roofing filter.  This
was expected, since the test tones are spaced 2 and 4 kHz away, and even the
2.5 kHz filter provides very significant rejection of the test tones.  The
500 Hz filter did, however, provide very significant additional rejection of
a test tone or interfering signal 1 kHz from a weak desired signal.  In a
pile up or contest, the 500 Hz distributed roofing filter is highly
recommended. One could also call the 455 kHz filters "DSP protection
filters".  The 300 Hz roofing filter would be useful in very dense signal
environments, such as the ARRL or CQ 160 meter CW contests.  More casual CW
operation may not require the 300 Hz optional filter in addition to the 500
Hz unit.

 

Measured parameters vs. factory specifications:

 

Parameter                                Spec                Measured

DR3 20 kHz                            90                    92 dB

DR3 2 kHz                              78                    80 dB

Sensitivity, preamp off:            0.5                    0.45 uV

Sensitivity, preamp on:          0.18                    0.17 uV

Noise floor, preamp off:                                   -130 dBm

Noise floor, preamp on:                                   -140 dBm

AGC threshold, preamp off:                             0.8 uV

AGC threshold, preamp on:                             0.2 uV

S9                                           50 uV              59 uV

Preamp                                                           12 dB gain

 

S meter reading does not change with preamp or attenuator setting.  While
this may be confusing, it is the correct way to keep the S meter calibration
constant, regardless of preamp or attenuator settings.  Some commercial
receivers keep S meter readings constant regardless of preamp or attenuator
selection, such as the Ten-Tec RX-340.

 

Phase noise measured -124 dBc @ 10 kHz, vs. spec of 125 dBc at 10 kHz,
basically meeting spec. This parameter is the least accurate of my
measurements, as it must be measured indirectly.  IF DSP filters integrate
phase noise differently than classic discrete filters.  A slight change in
the bandwidth compensation for dBc would resolve the 1 dB difference.


The only area where measured numbers are significantly different from spec
is blocking.  

Normally I measure blocking at the onset of AGC, and only at 100 kHz due to
common phase noise limitations.  I don't agree with the ARRL's method of
measuring IP3 and blocking at S5, nominally -93 dBm.  Ten-Tec does not use
either of these methods to specify blocking.  Measuring blocking in a DSP
radio is almost meaningless, due to the way the digital AGC is handled by
the DSP chip.  

 

The following blocking numbers were done using the ARRL method.

 

NF, 500 Hz CW filter: -130 dBm

Blocking at S5 @ 100 kHz 134 dB

Blocking at S5 @ 20 kHz 119 dB

Blocking at S5 @ 2 kHz 118 dB

 

Attempting to measure blocking at the specified level of 135 dB @ 20 kHz, I
fed in a + 5 dBm signal into the Omni VII. Two things were observed: the S
meter went up from S5 to S6, and the audio went down 7 dB.  Blocking is not
a practical limit on the Omni VII.  

 

Rob Sherwood

Sherwood Engineering, Inc.

NC0B