Re: [amsat-bb] cost comparisons

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

>Wayne replies:
>
>I suspect that the combination of an 18-element 70cm CP yagi, 1 meter
>crossboom, and a 54-element 13cm loop yagi is a SMALLER LOAD than the
>average TV antenna.  It is entirely practical to use with cheap TV rotors.

## Ed:  maybe but certainly TV rotors will do if unable to buy ham rotors!

>A 13cm receiving setup consisting of a 3-foot dish (or loop yagi), preamp,
>and surplus downconverter will COST LESS than the big yagi and preamp that
>most people used to receive the 2m downlink from AO10 and AO13.  And that's
>not counting the fact that you can get away with much cheaper rotors.

## Ed:  That was my point, too!  Agreed.

>There seems to be nearly universal agreement that 2m is NOT a good band for
>high-orbit satellites or earth stations.  Antennas are too big, spectrum is
>limited, noise is high, and there is too much legal and illegal interference
>beyond our control.
>
>70cm seems to be the BEST uplink band for the foreseeable future since
>transmitters are widely available, antenna size is reasonable, and cable
>loss is tolerable.

## Ed:  An acceptable change-over compromise for entry-level microwave
operation.  23cm has advantages over 70cm. for uplink.

>
>I'm still not sure if 13 cm is the best downlink band.  Antennas are cheap,
>small, and easy to steer with TV rotors.  Surplus downconverters are cheap.
>Good preamps aren't really very expensive.  But the signal is absorbed by
>trees, which is a problem for a lot of people.  Also, interference from
>unlicensed wireless devices will be a growing problem over the next few
>years.

## Ed:  This is really a shame:  Legally Licensed operations interfered
with by unlicensed equipment...and we will not win this one!
 
>Too band 23cm isn't a permissible downlink band.  It probably would have
>been the great downlink band from the perspective of antenna size and tree
>absorption.  Is 10 GHz less affected by trees than 2.4 GHz?

## Ed:  Sorry, trees increasingly block radiation as you go above 1 GHz.
However, gain of a dish goes up by the square of frequency change, so
dishes can be smaller at 10 GHz depending on the satellite signal
requirements.  The 18 inch DSS dish is almost a standard for microwaver
rovers [gain = 35 dBi].  So easier on your tower tops!

Ed


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