Re: [amsat-bb] Re: HEO naïveté
kd0ar at sbcglobal.net
Sat Feb 7 11:07:40 PST 2009
I usually tend to keep quiet during arguements such as this, but I need to chime in on this one.
I live in a location that frowns upon antennas. I was able to put up a mode V/u as well as S band antenna to get me on AO-51. This antenna has 3 ele on 2m, 6 ele on 70 cm, and the S band antenna is a 18 inch long yagi.
This system is way too small for a GEO or HEO bird. I was on AO-10 + 13 when they were up. My 2M was 22 ele crossed yagi, and a 10 turn 70 cm helix. Very large antennas compared to what I'm using now.
I'm not certain, but I believe I would be able to receive an S band SSB signal with my current S band receive setup from a geo sync orbit.
There is a law of physics that states that if the antenna size remains the same and the frequency increases, the signal strength will also increase. Notice I said antenna SIZE not GAIN, because as the frequency goes up and the antenna remains the same size, the gain will overtake the increased path loss. I understand the reason for having to use microwaves for rideshare birds. Thing is, the microwaves give you a distinct advantage, and that is a stronger signal and less noise. the cost for that? some new equipment.
I recently bought myself a new laptop. It wasnt a very high end unit, about $600. I really didnt NEED it, but the same money would have bought me a new microwave band and had money left over. Reason I didnt get the transverter? lack of activity. If a satellite would have been launched, hey, guess what I would have bought instead? yep, you guessed it... A new DX band!
Lets say 5760 is used on an upcoming bird. Ground station with a 19 inch dish with a simple homebrew feed will have almost 30 dB of gain! thats 100 times more signal than your 2 meter arrow, and the antenna is a lot smaller!
By the way, I hold VUCC on terrestrial 10 GHz, so I think I have some idea as to what I'm talking about.
--- On Sat, 2/7/09, Jeff Davis <ke9vee at gmail.com> wrote:
> From: Jeff Davis <ke9vee at gmail.com>
> Subject: Re: [amsat-bb] Re: HEO naïveté
> To: amsat-bb at amsat.org
> Date: Saturday, February 7, 2009, 11:10 AM
> On Sat, Feb 7, 2009 at 10:50 AM, Gary Joe Mayfield
> <gary_mayfield at hotmail.com> wrote:
> > The microwave thing always gets me though. If the
> antennas are too big how
> > come they can get them on cube sats? I know the
> correct statement is
> > high-gain antennas are too big. The problem is gain
> antennas need some
> > pointing mechanism (complicated and expensive) and
> they need to be pointed
> > no matter what band they are designed for. When using
> omni antennas the
> > lower frequency will yield higher performance due to
> lower path loss....
> CubeSats buzz around 180 miles over your head. At apogee,
> AO-13 was
> 23,000 miles from the ground.
> That's why the gain antennas were needed and when you
> add up the power
> required for a transponder to handle lots of stations at
> the same
> time, then the link budgets and antenna sizes (for more
> gain) at
> higher frequencies begin to make a LOT more sense.
> The tightrope the developers walked was always how to
> performance on frequencies that stubborn members demanded
> always be
> used. The S-mode stuff held much promise with AO-40. James
> G3RUH presented all the superior reasons for S-mode (the
> paper is
> still in the archives) but for a large percentage of
> members it was
> always "2 meters on the downlink or I will withhold
> Just like those who raise a stink now whenever almost
> anything is
> proposed requiring more than a fifteen year old dual band
> handheld and
> an Arrow antenna...
> As has been hinted around this thread, our problems are
> almost 100%
> self-inflicted. We have shot our toes off until we have
> none left to
> shoot. I don't blame the leadership -- this
> "club" contains some of
> the most stubborn individuals in all of hamdom. Perhaps if
> AMSAT can
> stick around long enough, the naysayers will all eventually
> die off
> and we can move forward with reality instead of dreamy-eyed
> reminiscing about days gone by and what might have been.
> Jeff, KE9V
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those
> of the author.
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