[TenTec] Omni-VI+ Phase Nosie and INRAD roofing filter mod?

[Michael Tope]

----- Original Message ----- 
From: "Jerry Volpe" <kg6tt at arrl.net>
To: <tentec at contesting.com>
Sent: Thursday, June 01, 2006 9:32 PM
Subject: [TenTec] Omni-VI+ Phase Nosie and INRAD roofing filter mod?


>I am selecting which of my transceivers to take to Field Day with the
> choices either my Corsair II or my Omni-VI+. You would think this to be
> a slam dunk decision in favor of the newer radio. However, I still have
> a very bad memory from last Field Day when I took a Kenwood TS-940SAT
> which had so much Phase Noise that when transmitting I wiped out the
> other two club stations. I have subsequently deep six'd that
> transceiver. Now not wanting a repeat of that experience I decided to
> make a very simple test.... and got rather disturbing results.
> 
> Test One: Omni-VI+ to a dummy load. 14.005 MHz. Power output varying
> between low and hight power. Keyed with electronic keyer.  Corsair II
> with unterminated receiver (basically on a shorted connector of the same
> switch connecting the Omni-VI+ to the dummy load). As I tuned across
> 20-meters I could not hear the Omni-VI+ transmitting until I was pretty
> much on the transmit frequency +- say 3 kHz. This was satisfactory.
> Changing the Corsair II's XTAL filter to 1.8, 500, or 250 Hz made the
> reception tighter as expected.
> 
> Test Two: Reverse the roles. With the Corsair II transmitting at even
> the least output possible the Omni-VI+ presented 'keying' noise across
> the entire 20-meter band with a few false signals to boot! Inserting
> different first or second IF filters did little to reduce this.
> Eeeaaoooouuucchhhhh! Granted the noise floor alternately raising and
> lowering with the keyed Corsair was maybe an S-3 to S-4 level but having
> that noise constantly present for 24 plus hours..... Hmmmmm.
> 

Jerry,

I'd be careful about how I was doing the testing. I've noticed that 
when testing rigs right next to each other with a common physical 
connection that there are all sorts of common-mode sneak paths 
between the rigs, so what you hear in that kind of configuration isn't 
necessarily representative of what you would hear with two rigs in 
close proximity connected to different antennas. Try for instance 
listening to an HF transciever driving an amplifier on another 
closeby HF receiver with no antenna connected to its input (e.g. 
just listening to the leakage from the trasmitting rig over to the 
receiver). Even though the received signal isn't overwhelmingly 
strong, it will usually sound so bad (clicks, broadband noise, 60 
Hz humm), that it will make your blood curdle, but if you listen to 
that same signal as it goes out over the air, it will sound fine. 

I am not saying that the Omni 6+ should be better than the 
Corsair (I frankly don't know), only that your test might not be 
representative of real world conditions. 

73, Mike W4EF......................