[Elecraft] Digital modes on 144MHz only

[Conrad PA5Y]

Wes is quite right. 

There is a free program called AppCAD that allows system noise figure analysis for up to 7 cascaded stages. It is enlightening and you will understand the significance of each stage in no time just by plugging a few numbers in. Have a try its educational 😊

73

Conrad PA5Y

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of Wes
Sent: 05 July 2019 15:08
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Digital modes on 144MHz only

That isn't quite right either.  The preamp gain must be much higher than the following losses to minimize second stage degradation. (Line loss degrades the NF of the second stage)

Wes  N7WS

On 7/5/2019 5:35 AM, Martin wrote:
>
> That's not quite right. The overall system noise is determined by the 
> preamp noise figure when mounted as close  to the antenna as possible. 
> Cable losses
> (=noise) after the preamp can be neglected, as long as the gain of the 
> preamp is higher than the losses in subsequent components. So the 
> cable AFTER the preamp can be pretty lossy. OTOH, too much gain from 
> the preamp easily overdrives your transceiver's RX. A good balance 
> between gain vs. cable losses is mandatory. The noise figure of the pramp is crucial.
> If you are satisfied with your transverter's noise figure , mount it 
> close to the antenna via a short run low loss cable, if you can. This 
> saves the expenses for a preamp.
>
> This applies to the RX path. I'm not talking cable quality or output 
> power for TX.
>
>
> > Message: 15
> > Date: Thu, 4 Jul 2019 17:11:58 -0500
> > From: Bob McGraw K4TAX <rmcgraw at blomand.net>
> > To: elecraft at mailman.qth.net
> > Subject: Re: [Elecraft] Digital modes on 144MHz only
> >
> > ..... Start with a mast mounted low noise preamp, then low loss 
> > feedline such as 7/8" hard-line, and such. Remember, loss in the 
> > feedline adds to receiver noise.
> > ..........
> >
>
>

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