Sorta makes me wonder if the front end of that Drake TR-7 is in need or
alignment or repair...
73/Mike K5AWI
-----Original Message-----
From: Jim Reid <jreid@aloha.net>
To: tentec@contesting.com <tentec@contesting.com>; K3BU@aol.com
<K3BU@aol.com>
To: <tentec@contesting.com>
Date: Friday, July 23, 1999 15:15 PM
Subject: Re: [TenTec] Omni VI plus - noise & INRAD filters
>
>Aloha Yuri, You wrote, in part:
>
>> Procedure to verify this is: turn your LP and DSP off, disconnect the
>> antenna, turn your RF gain full up: see if you will hear high pitched
>> hiss/noise from audio.
>
>> On my Omni VI+ this happens when I turn my RF gain past 3 o'clock.
>>
>> Let me know if you get the noise or not.
>
>Yes, Yuri, I do get the noise, whether the antenna input
>terminal to the Omni VI+ is left "open" or terminated in
>50 ohms. BTW, the S-meter reads zero deflection. And,
>yes, perhaps even in the background, below or at the level of
>rigs RF stage internally generated noise, I can hear
>a faint "whine". But read on.
>
>Now, if I connect my 10 meter beam, a dead band this
>morning in KH6 land, the noise level output increases
>quite noticeably, and the S-meter reads 1.5; perhaps due
>to the very high x-rays flux coming from the Sun these past
> hours; actually began some 20 hours or so ago.
>
>In fact, at this moment as I make this measurement, the
>x-ray flux has nearly reached M-class level, at
>1949 UTC, the x-rays are at C9.9 level! Yesterday,
>at this time, about when I was reporting no X band noise
>deflection on my Omni S-meter, the x-ray flux was over
>an order of magnitude lower, in fact about 13 dB lower!!
>
>Not surprising then that I have S-meter noise deflection
>now, hi.
>
>What you are hearing with your RF gain up, and the antenna
>disconnected, is the noise generated in your front end RF
>stages of the Omni. But, so what, as soon as you connect
>to the real world, via your antenna, you hear a much higher
>real world noise environment, which overwhelms your
>RF stages internally generated noise and that very weak
>"whine" tone you hear. It is gone with the antenna bringing
>in all the real "band" noise.
>
>And of course, going to lower bands, the back ground noise
>from any of my other antennas is higher yet: S 2.2 on 21290,
>for example.
>
>BTW, if you repeat these tests, you MUST use an antenna
>resonant at your test frequency. That is it must be very
>close to 50 ohms pure R, or 1.1 or so vswr; otherwise,
>you will not get the solar and galactic noise matched into
>your receiver. That is why a 40 meter antenna used on
>10 meters seems so quiet! It is, because it is coupling
>neither much signal nor noise into the 10 meter tuned
>circuits, hi.
>
>Oops, just made another interesting "discovery". My beam is
>pointed almost exactly to the Sun's present azimuth direction
>from Kauai just now: Sun at 85 degrees azimuth, beam at
>about 60 degrees, toward the US mainland from out here.
>And if I rotate the beam 90 degrees, the S-meter deflection
>drops a unit! So, QED, there is more noise from the Sun today.
>
>I sure would not be concerned in real operation with the Omni
>about the noise level I see coming from the internal circuitry.
>There is a LOT more coming from the antenna operating
>within any of our HF bands.
>
>73, Jim, KH7M
>
>
>
>
>
>--
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