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.
Michael Heim ARS KD0AR Amsat 36924
--- On Sat, 2/7/09, Jeff Davis ke9vee@gmail.com wrote:
From: Jeff Davis ke9vee@gmail.com Subject: Re: [amsat-bb] Re: HEO naïveté To: amsat-bb@amsat.org Date: Saturday, February 7, 2009, 11:10 AM On Sat, Feb 7, 2009 at 10:50 AM, Gary Joe Mayfield gary_mayfield@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 deliver performance on frequencies that stubborn members demanded always be used. The S-mode stuff held much promise with AO-40. James Miller, 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 funding".
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...
Sigh.
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 AMSAT-NA AMSAT-DL _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb