Re: RF Gain control


Lee
 

I've done this (throttling the RG gain) for years, and I also teach it to new general licensees who are starting out on low bands. With the low bands, sensitivity is usually not an issue; even a rig with the sensitivity of a drill sergeant will hear signals on 80 and 160. What you need is increased SNR, especially for the CW signals right at or above the noise level. Even a small increase in SNR will often let a signal pop out of the noise. This technique got me DXCC on 160m with a Windom and no separate receive antenna.

For rigs without a RF gain control, a switchable attenuator may be the trick, especially if you run separate transmit/receive................

73 es GL de Lee KX4TT



The idea is a good one and has been for decades. The one question I had was...what do we use with most of the current homebrew and direct conversion rigs that have no separate RF gain controls to allow us to do this magic?

Thank you.

Jim Pruitt
WA7DUY

On 1/29/2019 11:19 PM, Charles W. Powell via Groups.Io wrote:
Bill,

Having said all that, I discovered working last month that what “the
old timers” say about dealing with noise. We are all used to cranking
the AF gain to try to hear signals. That works fine on upper bands,
but on 60, 80, and 160, the adjustment should be primarily through the
RF gain. Why? Let me put it this way: If you have S9 noise and you
turn up the AF gain on the radio, the noise becomes overwhelming. You
know there is a signal that you can hear, but the noise is so loud,
you can’t listen for more than a few minutes before you want to throw
your headphones across the room. If you reduce the RF gain to where
the noise is at a tolerable level, then that signal is suddenly
audible at a reasonable level over the noise. You have optimized your
signal-to-noise ratio by reducing the noise in the mix. You might
ask, “Doesn’t this reduce the sensitivity of the receiver?” Well,
yes, it does. But if your noise is S-whatever, everything below that
level is useless to you. So why amplify the noise and increase your
level of fatigue? The only thing to remember is to turn the RF gain
back up when you change bands. Otherwise you’ll think the front-end
of your radio is blown!

Chas - NK8O

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