Piotr,
Please, it makes NO SENSE to rebuild the input stage of the radio, if that is
what your last post states, IF you ONLY hear the noise after the volume
control!! Over SEVERAL years on this list, MANY satisfied users say this is
the quietest and most sensitive radio they have, compared to all the Japanese
designs.
The Omni VI is well documented in ARRL tests in QST magazine, and in the
advertising over several years, as having a lower noise floor than Yaecomwood
transceivers. It is therefore more sensitive to RF. It is also INCORRECT
with modern radios, to run all the time with maximum RF gain setting, for as
you correctly state, that would amplify noise as well as signal, and you may
well introduce overloading of early stages and intermodulation products with
excessive gain.
BEFORE you do something to mar the resale value of a very fine designed radio,
like trying redesign a circuit, simply reseat all circuit cards, interboard
jumper cables, and retorque all grounding screw connections to chassis. MANY
times, what appears as noise problems in any receivers of circuit board
construction is a less than tight connection either in interconnect wiring or
grounding jumpers. Make sure ALL ground connections using a screw or solder
tag terminal have a serrated lock washer to break the oxides of the metal
chassis underneath the terminal.
Other noise sources can be a bad contact on the wiper of potentiometers. This
type of noise is heard not just while turning the pot, but after making a
change in the wiper position, the noise will persist. Replacement of the pot
may be necessary in such cases. Statistically, even a brand new pot might be
one of a million in a production lot that was assembled with a weak wiper
spring, and thus prone to noise. Since Ten Tec, like all production
manufacturers, must buy components on the world market, there can be the
occasional bad component. It would be worth your time if simple remedial
measures do not restore noisefree operation, to write a detailed account of
the problem as you saw it, how old the radio is, whether it was bought new or
used, etc., and forward this to the Engineering and Service Dept. of Ten Tec.
They often are very good at troubleshooting their products over the phone, but
given the time zone difference, a letter might be the best way to convey most
details, but you should also included details of your RF environment, (are you
close to MW or SW broadcast towers, a military base with Radar, etc.).
Antenna, and all even seemingly unrelated issues such as earthing of your
station. Many times, in my Radio Frequency Interference professional work, I
have seen noise conducted over the grounds and chassis of equipment to cause
trouble in the circuits as you describe, thus nothing should be overlooked.
Best wishes for finding what probably is a more simple problem than you
believe.
Even the redressing of cabling might move sensitive wiring away from the
computer portions of the radio, (digital circuits), and reduce the noise floor
further. Another detail is whether you hear the noise while using headphones,
or on the speaker or both. The impedance of headphones is also an issue as is
their fidelity. Hi Fi stereo phones do not make the best communications
phones as you want to restrict audio to only the voice or CW bands. Wider
response phones can pick up minute computer noise, and make for very tiring
listening. A very good investment are ex military headsets that are 600 ohm
impedance or higher communications head sets. I was so lucky to find one of
15000 ohms impedance, and it requires very little audio to drive it to full
audio output on signals, and the noise floor is so far down it is quiet
otherwise.
73, Stuart K5KVH
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