The following is resubmitted for benefit of all with questions on the
function of connector 52 and results of some tests I have completed. This
was originally presented to several subscribers, Dale included, directly,
but I feel the number of inquiries justifies the bandwidth.
Here's my original msg and the follow-up results of my experimentation.
> From: Dave Bowker <dbowker@shire.sjv.net>
> To: kg5u@hal-pc.org
> Subject: RE: [TenTec] Omni VI+ Audio
To: <tentec@contesting.com>
> Date: Friday, January 22, 1999 05:01 AM
>
> Dale,
>
The clicks you are hearing in the audio are not going out on the RF
waveform. They are caused by the U7B on the IF/AF Board. U7B is turned
on during key-down to supply sidetone to the speaker/phones at a fixed
level (independent of the front panel AF control) which is set by the
keypad and controlled via connector 52. On XMIT, the sidetone arrives via
connector 54 from the DSP on the Logic Board, and is routed to connector 57
which in turn routes fixed level audio (THAT IS NOT SWITCHED by U7B), to
the rear Audio Out RCA jack.
The reason some OMNI's don't exhibit the clicks has to do with the >
component tolerences of U7B and associated components. Analog switches
are known to exhibit these types of problems.
The cure that some have used is to disconnect connector 52 either at the
IF/AF board (most difficult) or at the Logic Board (easiest). This removes
the clicks, but the sidetone audio is now controlled by the AF gain
control as well as the keypad. This seems to be a minor inconvienence.
I have been experimenting with additional chips to replace U7B (MC14066)
and with associated component values and believe I may have a permanent
cure, but it needs more testing with a few dozen more chips to validate.
I will post to the reflector when the data is in.
Hope this is useful info for you.
> 73, Dave, K1FK
> Fort Kent, ME
---------------------
UPDATE: 18 March 1999
I tried a dozen MC14066 analog switches in the U7 positon and only one
produced a clean audio sig without alteration of any "production"
component values. I then varied with the value of C45 (1 pF) and found
that I could get a few other MC14066's to produce clean audio with values
ranging from 0 pF to 3.3 pF. Basically there seems NOT to be a standard
cure for all OMNI's for this problem, except to remove connector #52 (and
live with the consequences I noted below).
73, Dave, K1FK
Fort Kent, ME
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