Hi Merv,
When I first got an OmniVI, I too noticed birdies, with a 50 Ohm
termination and no antenna connected. I compared what I heard on the
Omni VI to my previous "main" rig, a Kenwood TS-440. What I determined
was that the noise level, wherever it was tuned, of the TS-440 was high
enough to cover any birdies of similar magnitude to the ones in the Omni
VI, and that noise would also obscure weak signals that would be
copyable with the Omni VI, provided the signal was not right on a birdie
frequency. With an antenna connected, the noise from elsewhere is almost
always strong enough to make almost every birdie in the Omni VI disappear.
My conclusion, from casual listening comparisons, and which I cannot
back up with laboratory measurements, is that the birdies in my Omni VI
are insignificant compared to the higher overall noise floor of the
TS-440. One of the great advantages of up conversion to a high (40 to
90 MHz ) IF, used in so many general coverage transceivers these days,
is that birdies and image responses can more easily be reduced or
eliminated, or at least moved to where you never hear them. If the LO is
not really clean (all of the LOs), the noise floor will be higher though.
A TS-440 is probably not the best standard for comparison. I'm sure
there are better performing general coverage transceivers, using up
conversion to a high frequency first IF, than the TS-440. Perhaps with
some of those rigs the noise floor is low enough that when connected to
a terminator and not an antenna, the birdies in the Omni VI would be
much stronger than the other rig's noise. Even so, once you connect an
antenna, can you tell the difference?
Ken N6KB
Merv Schweigert wrote:
I have a question, is it common for the Omni 6 to have
so many birdies?
|