• Subject: Re: [amsat-bb] The "Spreadsheet"
• From: "hasan schiers" <schiers@xxxxxxxxxx>
• Date: Sat, 19 May 2001 22:47:14 -0500

```Or...hmmm...are we mixing apples and oranges? An antenna's gain can be
specified in dBi or dBd, typically. dBd can assume an orientation of
vertical or horizontal. dBi is simply 2.14 dB more than dBd in free space.
Polarization becomes an issue when it needs to be "matched". So, it doesn't
matter whether we specify the gain in dBi or dBd ...polarization is an issue
when the transmitting antenna is in dBc or in this case Right Hand Circular.

I think the problem is we have antennas that are rated at 26 dBi and they
are linearly polarized.

The bird has an antenna that has "x" dB gain and it is circularly polarized.

If there is not a calculation inside the spreadsheet that subtracts 3 dB for
the polarization mismatch, then we have to subtract it when we put the
antenna gain in.

Now...all of this is a bit of a moot point...we are beginning to cut things
way too fine. With or without the 3 dB, we are able to predict whether we
are in the ballpark or not. Passband power sharing is going to make more
than 3 dB difference at any given moment in time in the real world anyway.

The purpose of the spreadsheet is to let us play with variables to see where
we could make the biggest impact in our ability to receive AO-40 Mode S, not
to be overly precise.

Hopefully someone will correct me if my observations are wrong and maybe
Marcus will straighten us all out if he sees the discussion. 73

...hasan
hasan schiers, NØAN
schiers@netins.net

----- Original Message -----
To: <amsat-bb@AMSAT.Org>
Sent: Saturday, May 19, 2001 8:34 PM

> I'm trying to catch up from being at Dayton, but I'm confused about a
> comment that was made about converting dbc to dbi or vice-versa.
>
> The Spreadsheet wants antenna gain in dbi (linear) right?  So, why are you
> converting the BBQ antennas to dbc by subtracting 3 db from them???  The
> 24db is linear on those antennas, they *are* not circular.
>
> Ok, now if you are talking about dbi to dbd.  then it's 2.14 not 3db.
>
> Can someone clear that up for me?
>
> Thanks,
> Alan
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

```

AMSAT Home