[amsat-bb] Re: Phase 3
Gordon JC Pearce
gordonjcp at gjcp.net
Sun Sep 22 02:50:32 PDT 2013
On Sat, Sep 21, 2013 at 11:26:08PM -0400, Daniel Schultz wrote:
> That's what Cubesats offer... ability to launch "off the shelf" satellites
> whenever an opportunity comes along, without having to do detailed integration
> with the launch vehicle. If only they were not so damn small...
They don't have to be big. Look at the sort of performance you can pack into a
terrestrial radio these days!
I had a cheapy Chinese HT apart last week for repair (turns out it was extensively
water-damaged, so it was a write-off) from one of the better cheapy Chinese manufacturers.
The whole thing was on two thin boards, with the front panel board populated on both sides
and the RF board mostly only populated on one side, and both boards fit side-by-side in
the palm of my hand. The 1800mAh LiPoly battery was about the size of two Compactflash
cards, and (when they haven't been drowned) run it for a full day of heavy use.
Now the cheapy Chinese radios are often criticised for poor spec, but these have a lovely
clean output spectrum, solid 4W output and a 12dB SINAD down about -120dBm so you can't
really fault them for that - tracking RF filters so the front end is good and tight too -
so they must be doing something right.
The boards weigh about 50 grammes.
You could conceivably rip the RF board out of a UHF and VHF one and couple it with your
own CPU and audio board, and have a ~150 gramme mode V/U transponder on a standard 10x10
cubesat board. You could use a 10m SDR and a wee DSP board like the ones that TI does for
a few beer tokens and build Bob Bruniga's crossband PSK transponder. You could do all
this for the price of the buffet for four and a couple of pints at my local Indian
restaurant, and you could do it in a weekend.
You can cram a lot of radio into a tiny space these days, and with a cubesat you've got a
bit of space about the size and weight of a bag of sugar. You could just about tape two
big old Motorola GP340s together and fit them in a 2U launch. There's no excuse. Yes,
the components are expensive (have you seen the price of a cubesat chassis?) but with
enough people working on it we'll figure out a more affordable way to build a flight-rated
First though, we need to stop bloody moaning about AO40.
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