Re: [TenTec] OMNI VI product detector IMD

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

Hi Clark,

        I'm posting this to the reflector since it may be of
interest to others.  Yes, C6 and R31 were changed to values
Steve mentioned and both R44 and R45 appear to be
eliminated.  I don't know what their purpose was since
they are not on my schematic.

        BTW, In-band IMD tests have been a part of ARRL's
Expanded Test Reports for some time...at least since
November 1997 when the Omni VI+ test was done.

http://www.arrl.org/members-only/prodrev/testroc.pdf

5.15 IN-BAND IMD TEST
5.15.1 The purpose of the In-Band IMD Test is to measure the 
intermodulation-distortion (IMD) products present
in the audio output of the receiver. This test is typically performed on 
units that will undergo the expanded set of
tests. The receiver will be operated in the SSB mode at 14.200 MHz. Two 
input signals, spaced 200 Hz apart, are
applied to the DUT and adjusted for equal output amplitude. (The audio 
tones are approximately 900 and 1100
Hz.) The input signals are adjusted for approximately a single tone n S-9 
level and the audio output is observed on
the Spectrum Analyzer. The tones are set for a 0 dB level for a single tone 
reference. (This is unlike the transmit
two-tone test, where the -6 dB is used for a PEP reference level.) The AGC 
fast option is used for this test.

In-band IMD on pages 26-27 of Omni VI+ ETR:
http://www.arrl.org/members-only/prodrev/pdf/lab/omni-6.pdf

Frequency       AGC     3rd order       5th order
14.020  Fast    -37             -52
14.020  Slow    -39             -57

(Not stated if Fast vs Slow AGC or S9 vs S9+40 signals.)

In-band IMD on pages 22-24 of Orion ETR:
http://www.arrl.org/members-only/prodrev/pdf/lab/orion_etrr.pdf

No tabular data given but graphs for all 4 cases of Fast vs Slow
and S9 vs S9+40.

                                73,  Bill  W4ZV


At 12:05 PM 1/17/05, you wrote:

> Hi Bill -
>
> Good information.  Are the changes exactly what Steve sees?  I have the 
> early OMNI VI and need to make the changes to see if I can eliminate the 
> IMD.  I will try to update the board to the later version of the OMNI VI 
> as N4SU's manual shows, that would appear to be the right thing to try.
>
> Are R44 and 45 taken out of circuit (open?)
>
> Clark
> WA3JPG
>
>
> On Jan 17, 2005, at 8:21 AM, Bill Tippett wrote:
>
> > N4LQ wrote:
> > >I have the manuals for both the VI and VI+ and have compared the IF/AF 
> > board
> > component values fwiw.
> > The only one that stands out it C6. From the VI to VI+, C6 goes from 1,000pf
> > to 2200pf.  R31 from 33k to 100k, R44 eliminated, R45 eliminated.
> >
> >         N4SU's Omni VI manual shows new values, Figure 4-12 (P/N 74229,
> > 6th printing 9/95), so I assume this mod was effective in Omni VI's
> > beginning in 9/95 (possibly earlier).  Dave's unit is S/N 11A10396
> > purchased new in January 1997.
> >
> >                                                 73,  Bill  W4ZV

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