Join the club on S meter calibration.
Not a single radio I have e ver seen had good S meter linearity until Ten Tec
came up with the multipoint calibration, a process that stores a “graph” of S
meter reading vs input microvolts (assuming 50 Ohm terminations).
I assume that the fully DSP and direct conversion radios do something similar…
Gary
W0DVN
> On Dec 5, 2018, at 6:01 PM, Phil Erickson <phil.erickson@gmail.com> wrote:
>
> Hi all,
>
> Today I had a chance to open the Omni up, desolder the S meter and get
> the face off. Indeed, the needle was good and stuck mechanically against
> the internal spring. Gary W0DVN had the answer: not even a 1/4 turn CCW of
> the tension pot freed everything up and now it's working fine! Thanks to
> all for the suggestions.
>
> While working with a calibrated signal generator, FYI, I discovered that
> even with the S3 and S9 points set correctly with the adjustment pots, the
> S meter scale is definitely not linear (1 S unit = 6 dB) in between those
> marks. Not too surprising - it's not a SDR after all. I've already made
> up a calibration table in case I really need to know.
>
> 73
> Phil W1PJE
>
> On Tue, Nov 20, 2018 at 10:17 AM ROLAND HOWELL via TenTec <
> tentec@contesting.com> wrote:
>
>> Hi PhilUsing a jewellers loupe or similar check to see if there is any
>> crud lodged between the magnets and the meter movement, just a piece of
>> fluff or some such obstruction, even tho' the movement is sealed somehow
>> things work in, I had a 'thrip' that's a very small crawling thing that
>> comes from the corn harvest, they get everywhere and yes into my meter
>> movement.
>> Snowy G0HZE
>>
>> On Tuesday, 20 November 2018, 14:23, Phil Erickson <
>> phil.erickson@gmail.com> wrote:
>>
>>
>> Hi all,
>>
>> Spent a few minutes more with the VI+. I hooked it to a dummy load and
>> keyed the transmitter in TUNE mode. With the knob on FWD power, the meter
>> did move in sync with the power being drawn from the DC supply (15-20 A
>> depending on mode), so the meter movement appears indeed not to be
>> completely dead.
>>
>> However, it's sticky. On the FWD meter setting, when you raise the TX
>> power and then turn it back down, the needle gets stuck midway on the dial
>> and won't go down to zero. Firmly tapping on the front face does
>> eventually get it to zero out, and then you get one pass from zero to max,
>> whereupon it sticks again when the power is turned down.
>>
>> Obviously this is not very useful. Anyone know how to unstick or
>> recondition this kind of movement? Maybe there is some old-time collective
>> wisdom I don't know about. Or am I resigned to finding a new S meter from
>> someone's surplus pile? [If so, who has these kinds of surplus parts now?]
>>
>> Cheers/73
>> Phil W1PJE
>>
>> On Sat, Nov 17, 2018 at 6:17 AM Phil Erickson <phil.erickson@gmail.com>
>> wrote:
>>
>>> Hi Jim,
>>>
>>> Thanks - already checked that part out with the S meter unplugged. I
>>> could adjust R25 through its full range and see the voltage on a DMM go
>> up
>>> and down, so the pot wasn't at a dead spot, but I could certainly see
>> where
>>> this might happen in other cases.
>>>
>>> 73
>>> Phil W1PJE
>>>
>>> On Sat, Nov 17, 2018 at 12:51 AM <w3ka@lycos.com> wrote:
>>>
>>>> Phil OM,
>>>>
>>>> I had similar issues with my TT Omni 6+. S meter readings were there
>>>> but extremely low.
>>>>
>>>> On the IF/AF board, there is an S meter adjust pot, R25 a 1K trimmer
>>>> control. Mine was
>>>>
>>>> sitting on a "dead spot". Gently rock the pot up and down, (not too
>>>> much, just enough to free the dead spot on
>>>>
>>>> the trimmer).. World great on my VI+ and resolved the S meter issues.
>>>> Good luck
>>>>
>>>>
>>>> 73, Jim W3KA
>>>>
>>>>
>>>>
>>>> On 2018-11-17 04:41, Phil Erickson wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I've just acquired an Omni VI+ with all the filters including the Inrad
>>>> roofing filters. It is very sensitive as far as RF goes on all bands
>>>> using
>>>> a HP 8640B signal generator as a calibrated source. However, the S
>> meter
>>>> does not work at all when AGC is enabled (or for that matter, when it
>>>> isn't, although of course AGC should be on to generate a reading).
>>>>
>>>> I pulled the covers off and examined the IF/AF board. According to the
>>>> manual section 4-7, the voltage driving the S meter is at connector 58
>> (a
>>>> 2
>>>> pin one). I pulled the connector off and, using a multimeter, was able
>> to
>>>> verify that a correct voltage was there on the pins in the ~200 to 800
>> mV
>>>> range. I was able to make that voltage go up and down as expected by
>>>> manipulating the RF gain, and also by changing the signal generator's
>>>> amplitude. The R25 and R29 trimmers also made the voltage move up and
>>>> down
>>>> as expected ("full scale" and "offset').
>>>>
>>>> So I think the S meter driving circuitry is working fine in RX mode
>> from
>>>> the IF/AF board..
>>>>
>>>> However, the manual is not clear on how the meter is multiplexed with
>>>> the
>>>> TX section, which I haven't tried yet as I'd like to get the receiver
>>>> going
>>>> first. I tried moving the meter selector knob to a few positions, but
>> of
>>>> course all of those are for when the TX is engaged (FWD, SWR, Ic, PROC)
>> so
>>>> it did not help.
>>>>
>>>> Does anyone have suggestions?
>>>>
>>>> 1) Maybe the meter movement has failed? If so, does anyone have any
>>>> tips
>>>> to isolate the meter and drive it with an appropriate voltage to see if
>>>> the
>>>> needle moves?
>>>>
>>>> 2) Is there any other check to see if the meter is somehow not paying
>>>> attention on RX because it's stuck on one of the TX meter settings?
>>>>
>>>> 3) Are there any other connectors to reseat?
>>>>
>>>> Thanks in advance -
>>>>
>>>> 73
>>>> Phil W1PJE
>>>>
>>>>
>>>>
>>>>
>>>
>>> --
>>> ----
>>> Phil Erickson
>>> phil.erickson@gmail.com
>>>
>>
>>
>> --
>> ----
>> Phil Erickson
>> phil.erickson@gmail.com
>> _______________________________________________
>> 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
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|