On 1 mayo, 13:43, _
wrote:
...and if so what can I do about it?

I have a cobbled-together setup that almost works. I coach swimming, and I
have a small video gadget that links to a Tivo and a TV via one of those
video transmitters that you can get from ebay. I think it is a 1.2 gHz
50mw version.

The kids swim and then watch, and having the Tivo means there's a
continuous flow of action. The problem is that the picture quality is bad.
I'm only 20 metres away and there is a direct line-of-sight from
transmitter to reciever - ocassionally with a body or two in the way; but
even without, there is considerable jumping and colour distortion and
generally a bad picture. If I stand still at just about any distance I can
find a place that gets a good picture, but moving - even turning - makes it
change.

The ceiling and the upper half of the inside walls of the pool are panelled
with strips of aluminium sheathing - about 6 inches wide and 20 or more
feet long. These are separated by about a 1-inch gap along the long edges,
and mounted to a framework (which is mounted to concrete) with some sort of
clip arrangement. This is a box about 220 feet long and 25 feet high.

What's the best guess for improving the picture? More power? Different
frequency? Antenna mounting (I could wear a beanie with it sticking up
from the top - that'd be cool)?

Hello,

When the multi path effect only affects received signal strength, you
can find many places with good reception and many with bad reception.

Best thing is to try it in an empty swimming hall. Your environment is
stable in that case. Move slowly 1"/s and see what happens. At 1.2
GHz (WL about 10", 0.25m), the distance between bad reception and good
reception can be as low as some inches.

50mW is more then sufficient power for such an indoor application, so
assuming reasonable receive and transmit antenna, increasing power
will not help. You might switch to another channel or look to the
picture with transmitter off to check for interference from a similar
or other system sharing the same frequency.

In case of severe multi path effects bad and good reception may
alternate within a yard (1m). When in the good places the reception is
noise free, signal will have sufficient strength.

With severe multi path, where path via reflection can be many yards
longer then the direct path, not only signal strength, but also
received signal quality is affected (delay spread). In this case
you will find few places with reasonable reception, even under good
signal strength.

Given your equipment (probably Frequency Modulated system with one
receive antenna), a directional receive antenna may give improvement.
The disadvantage is that you need a second person to have the antenna
aimed at the transmitter (in case of moving setup).

If this all is not possible and it must be wireless, you have to
divert to multi antenna systems (space diversity) in combination with
channel equalization or real wide band systems based on OFDM or other
multi path resistant modulation scheme.

Hope this helps you a bit.

Wim
PA3DJS
www.tetech.nl
please remove abc from the address in case of a direct reply.