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Re: Using AO-40 XLS (AO40_S2.xls)



The NF of virtually all of the multi-mode radios on 2m (or 70cm for that
matter), is pretty poor.  A figure of 15 dB might be a bit harsh, and
chances are a figure of 8 dB is probably too generous.

As it turns out....it doesn't matter much. Once you set the noise figure out
at the antenna where it belongs, the NF of the multi-mode radio doesn't
affect the overall system noise figure to any great extent.

So...use 12 or 15 dB...be conservative...assume your radio is a bit deaf.
By no means, place ANY faith in the idea that the NF of your radio is
somehow going to make up for even minor deficiencies out at the antenna and
preamp side of things. It won't, it can't, so why not assume that 15 dB is
really what it might be for worst case?

To confirm this approach. Set your preamp/converter NF to .8 dB and gain to
25 dB. Set coax loss to 2 dB. Now...set radio NF to 15 dB and read off your
MDS, and other indications of receive quality. Second, change ONLY your
radio NF to 10 dB and see how little things change. Do it again for 5
dB....same results....roughly and believe me, your radio does NOT have
anywhere near a 5 dB NF.

p.s., there are ways to back calculate it from the MDS of the radio, but it
really isn't worth the bother, as you can gather from the info above.

Just in case you might also ask about the effect of Receiver Bandwidth:

It defaults to 2500 hz (ssb). If you would like to hear (or model hearing)
with much more sensitivity, use 250 hz...your MDS will improve by 10 dB! (Of
course, you will be using CW or some other narrow mode at this time, but the
gains are quite real) (You can't do this in practice without a narrow cw
filter.)

73,

...hasan, N0AN
----- Original Message -----
From: "Gerald Payton" <n5gpc@earthlink.net>
To: "AMSAT-BB" <amsat-bb@AMSAT.Org>
Sent: Sunday, June 03, 2001 7:43 PM
Subject: [amsat-bb] Using AO-40 XLS (AO40_S2.xls)


> How does one determine his receiver's NF?  Is the 15dB an average figure?
>
> I have an IC-820H, but the specs. give no NF or bandwidth figures.
>
> Tnx.
>
> Jerry
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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>

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