It may take a few days but I will try to get the data you need.
Gary
PS: I would focus on a single point failure. It is not likely that you would
have two separate failures so keeping focused on locating a point failure would
be the most efficient way to getting the issue resolved.
73
Gary
> On Jan 25, 2019, at 11:15 PM, Phil Erickson <phil.erickson@gmail.com> wrote:
>
> Hi Gary,
>
> Good tip on the filter bypass.
>
> If not too much trouble, I'd be most grateful if you measured the IF
> filter board "gain". While you are in there, it would also be very helpful
> to check and report the "gain" (sic) of the BPF/front end board thusly:
> what is the difference between the level in at connector 17 (RF) and level
> out at connector 25 (IF)? I was using 14.2 MHz when testing and based on
> the circuit description, it appeared I was missing 6 dB gain there too but
> not sure. A combination of missing front end gain and IF filter board gain
> could explain my apparent insensitivity.
>
> Both of these numbers might also help future troubleshooting efforts.
>
> 73
> Phil W1PJE
>
>
> On Fri, Jan 25, 2019 at 11:56 PM MadScientist <dukeshifi@comcast.net> wrote:
>
>> I have an Omni 6 on the bench now so I can check the “gain” of the 9 MHz
>> board but showing a 7 dB net loss seems a bit high.
>>
>> You can rune out the filter (which I have found to be bad in a few cases)
>> by removing it and putting a wire jumper across the active pins on the
>> board. You loose selectivity but you test the filter loss.
>>
>> The filter can be marginal and not affect TX power much because the TX
>> chain in the Omni 6 has far more than enough gain to produce good output
>> even if the filter is marginal.
>>
>> Gary
>>
>>> On Jan 25, 2019, at 9:19 PM, Phil Erickson <phil.erickson@gmail.com>
>> wrote:
>>>
>>> Hi all,
>>>
>>> [Sending this to the list instead of directly to Gary and Peter, the
>>> usual suspects, in case the results are generally useful.]
>>>
>>> In the process of buttoning up my repaired (mostly) Omni VI+, I noticed
>>> further trouble: the MDS as tested was much worse than expected - at
>> least
>>> 12+ dB less sensitive, not 3 dB or so where I wouldn't care much. It's
>>> hard to ignore that much of a problem on the higher bands where
>> background
>>> noise is lower. Using a spectrum analyzer, I've been tracing first
>> through
>>> the BPF / front end board and then through the 9 MHz crystal filter board
>>> (#81782, surface mount version) to see where the trouble lies.
>>>
>>> Here, I'll stick to the 9 MHz filter board. My tests show that it has
>>> negative gain: the IF signal loses over 7 dB from input (connector 25) to
>>> output (connector 38). In fact, it was even worse at 11 dB overall loss,
>>> but I got 4 dB of that back by adjusting what turned out to be misaligned
>>> tuned circuits (C3 and C4, optimizing impedance match of the 15 kHz Y1
>>> "preselector" filter; C10 and C12, resonating the LC bandpass filter).
>>> These are the only adjustments on this board.
>>>
>>> The 7 dB attenuation is using the always-in-line 2.4 kHz bandpass filter
>>> - i.e. no narrower filters switched in through N-1 or N-2 buttons. The
>> N-1
>>> and N-2 filter positions have gain jumpers to kick in some extra
>>> amplification for those paths, but that doesn't apply here because they
>> are
>>> switched out. 7 dB is not enough loss to make me suspect that some
>> diodes
>>> are blocking the path.
>>>
>>> So anyone know whether is it normal to have this much attenuation
>> through
>>> the board? If not, what to suspect - has the TenTec 2.4 kHz filter gone
>>> too lossy, or is there perhaps something wrong in the Q1 amplifier or one
>>> of the passive stages beyond that?
>>>
>>> [Further datapoint: I know the 2.4 kHz filter is used for TX as well as
>>> RX and I get a full 90 watts out without trouble. Maybe this means the
>>> filter is not excessively lossy? Or perhaps there is some kind of ALC
>>> compensation somewhere that means the filter could still be bad and do
>> OK.
>>> Not sure.]
>>>
>>> Still learning. This much attenuation makes for a cruddy RX noise figure
>>> so I can't imagine this is intended given the expected performance, but I
>>> could be wrong.
>>>
>>> 73
>>> Phil W1PJE
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>
>
> --
> ----
> Phil Erickson
> phil.erickson@gmail.com
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
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