Hi Paul,
Changing the Y2 filter from the stock 2.4 kHz BW filter to 2.1 Khz
BW is not a drastic change. I would expect it to be an improvement in
tough band conditions, but perhaps not as pleasant to listen to when the
band is quiet you have a good solid path to whomever you are in QSO with.
I often use the 6.3 MHz 1.8 kHz filter in difficult conditions to
listen to SSB signals. It is even possible sometimes to use the 500 Hz
6.3 MHz IF filter to listen to and understand an SSB signal. When using
the narrow 6.3 MHz IF filters It is necessary to adjust the the PBT in
order to get the bandpass in the right place to receive the essential
part of the spectrum necessary to understand what the other station is
saying. The PBT adjustment that works may be different for different
people's voice characteristics. With the 9 MHz filters there is no front
panel adjustment to move the filter bandpass with respect to the BFO
frequency, the way you can move the 6.3 MHz IF bandpass using the PBT
control. Putting a really narrow filter, like 1.8 kHz or less in theY2
slot would be a hit or miss proposition as far as letting the important
(for intelligibility) parts of your voice through for transmitting. By
adjusting the BFO (you 'd have to adjust both the USB and LSB BFO
frequencies) you could optimize it for your voice. Maybe you could get
it to work really well for your voice. Then the frequency readout would
be off by a bit, and on receive you might have trouble understanding
people who do not have a vocal range similar to your's.
Also if you were to put a narrower filter in the Y2 position, it
has to have a bandpass that is coincident with any subsequent 9 MHz
filters. For instance if the the Ten-Tec model 218, or Inrad model 761
was put in the Y2 position, and you tried to use the Ten-Tec model 221
filter in one of the N-1, N-2 or the NAR filter slots for CW work, you
would find that very little signal would get through the combination of
those two filters, since they have very little passband frequency range
that coincides.
I agree that experimenting and testing can be beneficial, and it is
a lot of fun.
73 Ken N6KB
veast1 wrote:
Ken,
If you are refering to the Y2 filter in the Omni VI+, i changed mine
from the stock 2.4 khz to an Inrad 2.1 filter. I also have optional
filters in the chain as well as the Inrad SSB roofing filter. The
signal is extremely clean and i have received excellent unsolicited
reports on the audio. I would say that experimenting and testing could
be beneficial for some.
73 Paul (N6MYA)
Ken Brown wrote:
Hi Cal,
There are two common way of generating a SSB signal. There is the
phasing method, and the more common filter method. In the filter method
a double sideband signal is generated by a balanced modulator, and the
unwanted sideband is rejected by a filter, leaving only one sideband.
Almost every SSB transceiver uses the filter method, and shares the
sideband selecting filter used in transmitting with the receive function
in the transceiver. In the Ten-Tec Omni VI radios this filter is 2.4 kHz
bandwidth 8 pole crystal filter with a center frequency of 9.0015 kHz.
The transmit signal for SSB and CW modes goes through this filter, and
in the case of SSB this filter's characteristic determines the opposite
sideband rejection, and along with the audio circuitry and your
microphone, it determines the bandwidth of your transmitted SSB signal.
This filter also determines the maximum bandwidth of your receiver,
because it is always in the receive signal path, regardless of other
optional filters in either the 9 MHz IF or the 6.3 MHz IF. (Please note
that in FM mode this filter in neither in the transmit or receive path)
Normally this "default" filter is never changed, and will always
determine your SSB transmit bandwidth. Optional filters in either the 9
MHz IF or the 6.3 MHz IF only affect receive function, as they are not
in the transmit signal path.
It is possible, but generally not advisable, to change the default
filter. There are two reasons I have heard of for doing this. One is to
produce "High Fidelity" SSB. There are a number of good reasons not to
do this. The most obvious is that it consumes more spectrum in our
crowded bands. Another reason not to use a wider filter in the transmit
signal path is that it can degrade the carrier rejection. The balanced
modulator is not perfect, so some carrier is generated and then
attenuated by the opposite sideband rejecting filter.
A second reason for changing the default filter would almost only
be considered by people, such as myself, who don't operate SSB, or have
another radio to use for SSB. By putting a narrower filter in the
"default" filter position it is possible to improve the receiver
selectivity. Selection of the filter has to be done with care, so that
the bandpass coincides with the bandpass of any other optional filters
in the 9 MHz IF. The SSB transmit bandwidth would become narrower than
normal, making the SSB signal probably not pleasant to listen to. It
could possibly make for a good pile-up busting SSB signal, if the
filter, BFO frequency and operators voice were all matched just right.
All of the above applies to the Omni VI radios. There could be some
differences in the Omni D. I am not familiar with that radio. I am
certain however that as long as you do not change the stock "default"
transmit and receive 9 MHz IF filter, your transmitted signal will not
be changed.
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