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 <[email protected]>
> To: [email protected]
> 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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