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Re: [TenTec] Looking for a rig upgrade...

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Looking for a rig upgrade...
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Reply-to: ken.d.brown@hawaiiantel.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 03 Jul 2008 15:14:46 -1000
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
"As for the Inrad mod, I have that on my Omni VI+ and it does broaden the audio 
a bit. It is nice. For me personally, it was not so compelling a change that I 
added it to my Option 3 rigs. If you do want to get in there and make a change, 
that is a good one, and it is not at all expensive. Again, others will have 
different opinions."

There is more than one "Inrad mod" for the Ten-Tec Omni VI. I don't 
claim to know all the details, but I think you might want to be more 
specific about which mod you are talking about.

I believe one "Inrad mod" for the Omni VI changes the 9 MHz filter that 
is used for both receive and SSB transmit. There may be other minor 
component changes in audio stages (perhaps both receive and transmit, I 
don't know) that are part of this package. The intent is to make the SSB 
audio sound better (in both TX and RX I believe).

There is another "Inrad mod" for the Omni VI which allows the insertion 
of a narrower "roofing" filter in the receive only 9 MHz path, before 
the noise blanker.

There may be more Inrad mods that I have not heard of.

I have an Omni VI and don't feel that I need either of those mods. 
Perhaps if I was a SSB operator I'd find something lacking in the SSB 
audio and want to modify it. In the little bit of SSB operation I have 
done with the Omni VI, I have never had a complaint about my TX audio, 
and I have not felt there was anything wrong with the receive audio. I 
have also never experienced any kind of conditions that indicate I need 
better receiver selectivity of the "roofing filter" mod. Perhaps if I 
did not live 2500 miles or more from most of the worlds ham population, 
I would have a different opinion.

One thing I am sure of is that the recently adopted terminology "roofing 
filter" is poorly chosen. A roofing filter was originally a low pass 
filter used in the baseband of analogue multiplexed FM microwave 
systems. It kept unnecessary high frequency noise from the discriminator 
of the receiver out of the baseband, and kept unnecessary high frequency 
noise on the baseband from modulating the FM transmitter in those 
systems. Since it was a low pass filter, the term  "roofing" made some 
sense. Only multiplex channels  below that top "roof" frequency could be 
used in the system. In it's present incorrect usage in ham gear, since 
it is a bandpass filter, it has both a high frequency cut off "roof" and 
a low frequency cut off "floor".

Oh, and by the way, the Omni VI is a great rig. I have no desire for an 
Onion or any other rig with a "display screen". I realize the Omni VI 
uses microprocessors internally to control things, yet externally it 
"feels and smells" like a radio and not a computer, and that is the way 
I like it.


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