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Re: LF: Re: Carriers

To: [email protected]
Subject: Re: LF: Re: Carriers
From: "Larry Kayser" <[email protected]>
Date: Tue, 28 Aug 2001 08:29:16 -0400
References: <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>

I am afraid that the dynamic range will be limited by the FM transmitter,
not so much by the FM receiver. For a normal voice link there is no reason
to have a dynamic range at the TX input (mike) in excess of 40dB so I fear
that no constructor will do any efford to increase the dynamic range at
TX input.
and my contention and experience is that the transmitter dynamic range is
adequate for what comes out of the HF/LF receiver.  The FM receiver is
always a fleas flea when it comes to noise contribution in my experience.
I guess if one uses an HF/LF receiver with AGC ON and the RF up and the AF
down then that might be a problem to have good S+N/N performance.  For
myself I got by that issue about day 2 of my work with remote receivers.  I
always run the receiver for maximum dynamic range, ie RF down, AF up and I
do everything possible to get rid of any AGC action in the receiver.

I have in the past used a sound card in the remote PC along with some
software I was experimenting with and the DSP output runs the RF gain
control for maximum S+N/N ratio at a constant peak audio level output,
occasionally the software got it wrong and made things worse but in general
the trick worked reasonably well.  I found however that manual RF gain
control operation on the remote keyboard was more to my liking and works
excellently for me.  My thick and stiff fingers are better at pushing
keyboard keys than they are twisting knobs so I have come to prefer tuning
through the keyboard, very precise oper;ation of the controls, over trying
to make the knobs do what I want with my fingers.

The critical features in the link transmitter and associated receiver are to
ensure that hum and noise is minimized.  The use of low frequency tones for
squelch control I found created additional mixing issues and I have those
automagically turned off when I am using the link with the remote HF/LF
receiver attached.

The key however is that you could not tell if you are looking at an ARGO
.jpg if the file was collected at the remote site or at my home, they look
exactly the same and at the end of the day that for me is what is important.


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