Chris W wrote:

I want to build a 1.2 Ghz antenna for this tiny wireless camera receiver
I have. The antenna on it uses an F connector so I am guessing it is a
75 ohm antenna. I have seen several web pages with a collinear design
using 50 ohm coax cable. If I use some 75 ohm cable TV coax to make the
antenna do I need to do anything else to match the antenna to the 75
ohms of the RX? Also does anyone know what eh velocity factor for the
coax the cable company uses is?


Chris,

If you are talking about "one off" installation, don't worry about the 75 or
50 Ohms coax. As you say, 75 Ohms seems to be the correct guess as it's a F
connector and as the TV world seems to be in love with the 75 Ohms
cables/connectors.

You don't really need to be bothered by matching your 50 to 75 Ohms. Most
cables and connectors deviate so much as +/- 50% on the actual impedance
anyway. The loss tends to be lower in 75 Ohms cables.

If you are concerned over the match, make a Y coax match ( Wilkinson ? ) You
find the recipe for a stup or an Y match in most amateur radio cook books.

The easiest way to make a small aerial for 1.2 GHz ( Weird frequency for a
wireless camera?! ) is to make up a small Yagi aerial on a double sided
PCB. You can also make a nice log periodic on a double sided PCB that works
for both 1.2 and 2.4GHz. --- Unless you want an omnidirectional aerial of
course!


Cheers

Dan / M0DFI