[TenTec]General 2nd order questions???

[Steve N4LQ]

Bill etc.
I can make little sense of the ARRL's test. For the VI+, they state the 
signals can be either S9 or S9+40db. Then they show a chart but don't reveal 
which input level they used. They mention 3rd and 5th order IMD but not 2nd 
Order IMD.
Then for the Orion, things are a little more clear. They still don't mention 
2nd order however. Another thing I need help on: They say the input signals 
are spaced 100hz apart then they state that these produce tones of 900hz and 
1100hz. The difference of which is 200hz. This looses me.

The Orion seems to exhibit a huge difference in IMD between fast and slow 
agc. What does agc have to do with steady carriers used in this test? Why 
would agc make any difference at all since the agc voltage should be 
constant as well as the gain of the amplifiers the agc controls?

I think what Clark is hearing is simply the product of 2 carriers within the 
passband. Example: Tune rx to 7100khz. Two carriers present are at 7100.5 
and 7100.7. These produce a 500hz and 700hz tone in the speaker but also 
produce the difference of 200hz and the sum of 1200hz, both can be heard 
with the 1.8mhz filter engaged. So now we have 4 tones all of which 
constitute "2nd order products.

What are the requirement that make a product detector immune to these? Is it 
all based on linearity?
Steve N4LQ
----- Original Message ----- 
From: "Bill Tippett" <btippett at alum.mit.edu>
To: "Clark Savage Turner" <csturner at kcbx.net>; <tentec at contesting.com>
Sent: Monday, January 17, 2005 1:28 PM
Subject: Re: [TenTec] OMNI VI product detector IMD


> 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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