Re: [amsat-bb] 10m on a 20" whip.

["John Stephensen, KD6OZH" <kd6ozh@xxxxxxx>]

Hi Bob,

You are right. I just did some calculations using the efficiency predicted
in my previous email (8%). These assumed a 650 km circular orbit, a low
noise receiving site (18 dB noise level), 0 dBi receiving antenna, 0.5 W
transmitter output, and a 50 Hz receiver bandwidth. At the maximum slant
range the SNR is 23.8 dB. PSK should work if the SNR is above 7 dB so there
is 16.8 dB of margin. Most receiving sites will have significantly higher
noise levels and the transmitting antenna efficiency will probably be lower.

More than 1 user on the transponder will reduce margins. Peak power
requirements in a multitone system are much higher than the sum of the
average power levels of each tone, so not many users can be accomodated. If
there are two users on the transponder they must reduce their individual
power levels by 6 dB to prevent intermodulation. 4 users must reduce the
power per user by 12dB.

73,

John
KD6OZH

----- Original Message -----
From: "Bob Bruninga" <bruninga@usna.edu>
To: "Bruce Bostwick" <lihan@ccwf.cc.utexas.edu>
Cc: <amsat-bb@AMSAT.Org>
Sent: Thursday, 08 March 2001 03:32 UTC
Subject: Re: [amsat-bb] 10m on a 20" whip.


> On Wed, 7 Mar 2001, Bruce Bostwick wrote:
>
> > effects that the calculations don't take into account) but it will be
> > *EXTREMELY* inefficient -- sort of like the helical coil element in a
> > "rubber dummy load" HT antenna.  You may get a good 50 ohm load to
> > the radio, but don't count on much ERP for your PEP .. ;-)
>
> But I think that we have 14 to 20 dB of extra link margin using PSK31 so
> that we can afford the loss.  I dont know how to calculate an "efficiency"
> until we build it and see?
>
> bob
>
>
> ----
> 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