From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: rec.radio.shortwave
Subject: Re: New American Made SHORTWAVE available
Date: 12 Nov 92 14:33:25 GMT
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <Sreye-qH3@lopez.marquette.MI.US> flash@lopez.marquette.MI.US (Gary Bourgois,Hamshack) writes:
>I got into a discussion with Bill Grove on the Genie network regarding the
>fact that their whiz bang receiver did not have an RF gain control.  I tried
>to explain as best as I could that the RF GAIN is one of the knobs I use most
>often (And I am sure you DIE HARD SWLS on the net will back me up on this).

I don't know. A properly designed receiver should not require an RF Gain
adjustable by the user. I've been SWL'ing for nearly 20 years and I haven't
seriously fiddled the RF Gain in the last five of them.

>Most NEWBIES just turn their RF gain all the way up so they can hear
>EVERYTHING as loud as possible.  EVERYTHING including NOISE.

This is in fact a good plan. A slightly better one is to fiddle the RF
gain to get the best results and just leave it there permanently, but this
is often the same thing.

>static crashes make the voice uninteligible.  WIth the gain set to just where
the AGC starts working the signals LEAP out from the noise.
>
>Just last week Kristin Kaye told me she used this same method while tuning
>SSB pirates on the NRD 525 and she was amazed at how effective it was, and
>that she would have never thought so.
>

I don't think so yet, and here's why:

When you use a receiver, it adds noise to the incoming signal. There are
lots of stages in the gain structure, and the RF gain is earlier rather than
later, so to speak. Now the radio adds a certain amount of noise regardless
of what the signal is, so the best signal to noise is when the incoming signal
for each stage is as big as possible and the amount of amplification in the
later stages is smaller and smaller, since later stages amplify the signal
plus all the noise of the intermediate stages. The best gain structure is
in practice very much like this - you want to amplify as much as possible
in the early stages without introducing distortion. On a properly designed
receiver, this means setting the RF Gain at a fixed high level.

Now you are describing a situation where the RF Gain interacts with the
AGC - i.e. you are using the RF Gain as a threshold for noise gating the
signal. This is possibly of use in speech signals, but is not such a good
idea for program listening, and what you really want is to vary the threshold
on the AGC, so you don't have to degrade your first stage SNR just to get
the gating effect.

Now in my experience, audio noise gating might do just as well for your
approach to listening. In fact for intelligibility of speech, several
tricks are appropriate, such as using digital delays to produce a false
stereo image, etc.

>that?  OK design innovation I can buy it.  How about then an IF gain control?
>Some means of VARIABLE (Not SWITCHED) Signal gain adjustment to taylor the
>reception to the EXACT conditions of the moment (Which change with Line
>noise, atmospheric conditions and how many computers you are running)...

Actually, controls like this are a pretty good way to introduce noise unless
you implement them in a good (i.e. expensive) way.

>They just kept blowing off my suggestion that a simple one dollar part would
>make the receiver work 1000 times better.

And I suspect they're right. The last thing I want is cheap parts in the early
stages, where any noise or distortion will propagate through the whole unit...

>Does anyone out there think an RF gain control is just a frill?

I might not go that far, but it isn't high up on my list of things to have
in a receiver. I'm willing to consider radios which have them if they've
been done right, but this is not a $1.00 problem.

>Is anyone going to buy the GROVE receiver, or the AMERICAN ELECTROLA?
No Idea.

Later,
Andrew Mullhaupt
Newsgroups: rec.radio.shortwave