Re: [TenTec] Omni 6 sensitivity

[Ken Brown <ken.d.brown@verizon.net>]

> 2.  The OMNI VI passband tuning (PBT) is set so that you get a lot of 
> "highs" (hiss) from the audio of the receiver.  The carrier setpoints 
> can do the same thing.  The pair of 2.4 stock filters normally produce 
> audio on SSB that my ears don't like and it is very fatiguing to me 
> (so I have slightly wider 2.8 filters from INRAD in there, it mellows 
> the sound just a bit.) 

I do not know whether having the PBT set "wrong" is the cause of your 
Omni's apparent poor sensitivity/high noise. It very well could be. The 
operation of the PBT on my Onmi VI, as well as with most any rig that 
has a narrow filter in the 1st IF, is very much different from PBT on a 
rig with a very wide 1st IF filter.

With my previous rig, a Kenwood TS-440, I could be tuned to a frequency 
in USB and rotate the PBT (I think it is called IF Shift on the Kenwood) 
far counterclockwise, and listen to LSB at the same frequency. This is 
very handy for listening to AM signals which have more QRM on one 
sideband than the other. It also gives the ability to use the narrow CW 
filter and tune the IF Shift so that you can listen to the beat note 
between WWV's carrier and your BFO, without much of WWV's modulation 
interfering with what you want to hear, when you are checking your rig's 
frequency calibration.

I also used the IF Shift control as a sort of "RIT" without an audio 
frequency shift of the CW signals. This way I could listen up and down 
from my TX frequency to hear other stations calling me, and have a more 
direct idea of the offset from my frequency that stations are using. No 
need to look at RIT display numbers, you can hear the different audio 
notes. How far from your TX frequency you can listen using this method 
is limited by the 1st IF filter bandwidth, the audio frequency response 
of the rig and phones, and your ears. I used to make contest QSOs with 
stations probably as much as 7 kHz away from my calling frequency using 
this method. I really liked NOT using the RIT and hearing how all the 
other signals were spread out, without changing my zero beat point of 
reference.

So, moving from the TS-440 to the Omni VI, I lost a lot of what you 
could call receiver "features". I also gained a lot of receiver 
performance, being able to hear the weak ones in the midst of very 
strong signals, that were formerly inside the wide passband of the 1st 
IF filter. There are tradeoffs. General coverage all mode transceivers 
almost have to use wider 1st IF filters, because they generally 
upconvert to a higher frequency IF (say around 45 MHz) where narrow 
filters would be very expensive, and in order to use the same filter for 
FM and AM modes it needs to be pretty wide anyway.

There are ways that a rig with a narrow 1st IF could have the PBT range 
greater than the 1st IF filter bandwidth. This would require offsetting 
the 1st Local Oscillator and the BFO simultaneously by equal amounts. 
This would necessitate a more complicated PLL system, and the cost would 
likely be higher phase noise.

I honestly miss the wider range PBT (IF Shift) functionality of my old 
TS-440, but I am not going back to the poorer overload from strong 
signals that it had. With the Omni VI, I can have a CW  QSO 2 kHz away 
from where my neighbor a mile away and running a kW is also having a 
QSO. I couldn't do that with the TS-440.

DE N6KB

>


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