[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Satellite Newbee thoughts



For those that may be new to satlelites, here is just something to ponder
if you have listened for SUNSAT and barely heard it in your shack...

You have all seen us say how STRONG the signal is.  This is very true, if
you are Handheld or Mobile, but NOT necessarily true for a well
implemented terrestrial base station.  Here's an example...

I have  been playing with mobile/handheld Packet DIGIPEATING via the
satellites so much for the last 6 months (all from my car and handheld
ourside) that last night for the FIRST time, I got lazy and decided to
just monitor SUNSAT from my den (where I have a 2m radio).

As expected, I began to hear it when it first came up.  But it never got
much better.  But MY HT with rubber duck which I had left on began to hear
it BETTER even through my roof!  Sitting in the den, I could hear it loud
and clear on my HT, but it barely broke squelch on my BASE,

Actually, this is to be expected, and is why I have been pushing this
topic of HANDHELD and MOBILE SAtellite ops so much.  Because an HT and
Mobile have NO CABLE LOSS and NO NEED for antenna height.= when working
satellties.   Here is why it doesnt work well from a terrestrial base
station...

1)  My antenna is at the top of an 85 foot tree with over 100 feet of coax
    (there is at least 4 dB loss).  But I need the 85 foot height...

2)  My antenna is a full 22 foot 6 dB high gain vertical on 2 meters
    It has 6 dB gain (but all of that is focused on the horizon.  It
    mostly cancels everything going up (Throw away maybe 6 dB)

3)  WIth a handheld I can always orient the HT for maximum signal 
   (matching the polarization), but a Fixed vertical base station only
    matches perfect vertical.  Thus, throw in a few more dB loss...

Thus, although the 85 foot height is well worth the 4 dB loss for
terrestrial use, the combined 12 dB total loss is why the HT or the MOBILE
rig will ALWAYS outperform any base station for satllite work (Unless of
cousre you design your external antenns systems specifically for
satellites)...

To do that at the end of a long coax run you have to mess with Rotators,
preamps, power amps, low loss cable, remote controls and az/el indicators.
None of this is needed if you put the antenna right at the radio which you
can do when you are mobile...  And can see the sky...

Just a thought for the satelltie beginner..

de WB4APR, Bob

P.S.  ALso, since SUNSAT is a consistent signal and should see your
atnenna with NO obstructions, if you dont hear it on your base station
antenna, then better check it out.  Its a great way of verifying that yoru
coax and antenna arent deaf...

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



AMSAT Top AMSAT Home