In article <KS*lzNYp@news.chiark.greenend.org.uk>,
Thomas Womack <twomack@chiark.greenend.org.uk> wrote:

I'm slightly surprised that people aren't doing that already; or is
it not reasonable to detect at a couple of parsecs out a signal beamed
with a three-kilowatt signal from an antenna costing $5000 (figures picked

It's not reasonable.  The SETI@Home sensitivity is around 1GW EIRP
at 1 parsec, so you would need an antenna gain of around 60dB.  (Also,
2 parsecs is not reasonable as there are very few stars in that range
and probably no likely ones.)  To get that sort of gain at 23cm, you
will need something of Goldstone to Arecibo size.  (Targetted detection
tactics could reduce the gain needed, but only a little.)

wealthy radio amateur - 3kW is about $3000 a year at the price I pay for
electricity, and I thought radio transmitters were pretty efficient).

The output stage efficiency is unlikely to exceed 67% (class C) and the
power supply efficiency is likely to be rather worse, so I'd suggest that 
3kW input will only give you 1 to 1.5kW of useful output.  Operating at
such powers and 100% duty cycle, you may need to treat the output stage
tubes as consumables, as well.  High power amateur transmitters are 
unlikely to be specified for 100% duty cycle use.

I can't figure out on the Net what kind of directional antenna you get
for $5000.

I'd guess about a 6m dish.  However, you also need to buy the transmitter
and the atomic frequency standard (the detection ranges above assume that
you can mantain frequency to around 1 part in 10^10, at least in the short
term - you might just manage this with a temparature compensated crystal,
but it is not the stuff of off the shelf amateur transmitters).

Or will the FCC shut you down if you try?

It would certainly be illegal because:

- 3kW exceeds the maximum US transmit power for the amateur service, and
  is a lot more than the UK limit;
- it is not a communication with licensed radio amateurs, and there are
  no bi-lateral treaties in place with the ETIs allowing communication
  with non-licensed individuals;
- it is in violation of various international treaties on such activities
  (resulting from concerns about people broadcasting particular political 
  or religious views, and in some quarters, on the fear of attracting a
  pre-emptive attack).

There are stories that some people are doing it, but they have no realistic
chance of success.